ZO 211 Week 4 lecture

©McGraw-Hill Education
Week 4 Lecture
(Chapter 9, 10 & 11)

Physical and Chemical Control
of Microbes

Concepts in Antimicrobial Control
Term Definition Key Points Examples of Agents
Sterilization Process that destroys or
removes all viable
microorganisms (including
viruses)
The term sterile should be used only in the
strictest sense to refer to materials that have
been subjected to the process of sterilization
(there is no such thing as slightly sterile)
Generally reserved for inanimate objects as
it would be impractical or dangerous to
sterilize parts of the human body
Common uses: surgical instruments,
syringes, commercially packaged food
Heat (autoclave)
Sterilants (chemical
agents capable of
destroying endospores)
Disinfection Physical process or a
chemical agent to destroy
vegetative pathogens but not
bacterial endospores
Removes harmful products
of microorganisms (toxins)
from material
Normally used on inanimate objects because
the concentration of disinfectants required
to be effective is harmful to human tissue
Common uses: boiling food utensils,
applying 5% bleach solution to an examining
table, immersing thermometers in an iodine
solution between uses
Decontamination/
Sanitization
Cleansing technique that
mechanically removes
microorganisms as well as
other debris to reduce
contamination to safe levels
Important to restaurants, dairies, breweries,
and other commercial entities that handle
large numbers of soiled utensils/containers
Common uses: Cooking utensils, dishes,
bottles, and cans must be sanitized for reuse
Antisepsis/
Degermation
Reduces the number of
microbes on the human skin
A form of decontamination
but on living tissues
Involves scrubbing the skin (mechanical
friction) or immersing it in chemicals (or
both)
Alcohol
Surgical hand scrubs

Microbial Control Methods
Jump to long description

Relative Resistance of Different Microbial
Types to Microbial Control Agents

Comparative Resistance of Bacterial Endospores
and Vegetative Cells to Control Agents
Method
Required to
Destroy
Endospores
Required to
Destroy
Vegetative Forms
Endospores Are
_____ x More
Resistant
Heat (moist) 120°C 80°C 1.5
Radiation (X-ray)
dosage
4,000 Grays 1,000 Grays 4
Sterilizing gas
(ethylene oxide)
1,200 mg/L 700 mg/L 1.7
Sporicidal liquid
(2% glutaraldehyde)
3 h 10 min 18

Agents versus Processes(1)
Sterilization and disinfection: processes
Agents used in the process
• Bactericide: chemical that destroys bacteria except for
those in the endospore stage
• Fungicide: chemical that can kill fungal spores, hyphae,
yeasts
• Virucide: chemical known to inactivate viruses,
especially on living tissue
• Sporicide: an agent capable of destroying bacterial
endospores
• Germicide/microbicide: chemical agents that kill
microorganisms

Sepsis: the growth of microorganisms in the
blood and other tissues
Asepsis:
• Any practice that prevents the entry of infectious
agents into sterile tissues and thus prevents
infection
• Aseptic techniques: practiced in health care; range
from sterile methods to antisepsis

Antiseptics: chemical agents applied directly to
exposed body surfaces (skin and mucous
membranes), wounds, and surgical incisions to
prevent vegetative pathogens
• Preparing the skin before surgical incisions with
iodine compounds
• Swabbing an open root canal with hydrogen
peroxide
• Ordinary hand washing with a germicidal soap

Stasis and static mean “to stand still”
Bacteristatic: chemical agents that prevent the
growth of bacteria on tissues or on objects in the
environment
Fungistatic: chemicals that inhibit fungal growth
Antiseptics and drugs often have microbistatic
effects because microbicidal compounds can be
toxic to human cells
Even a -cidal agent does not necessarily result in
sterilization, depending on how it is used

Microbial Control on Medical Devices
Critical medical devices:
• Expected to come into contact with sterile tissues
• Must be sterilized before use
Semicritical devices:
• Come into contact with mucosal membranes
• Must receive high-level disinfection, preferably sterilized
Noncritical devices:
• Do not touch the patient or only touch intact skin
• Require only low-level disinfection unless they become
contaminated with blood or body fluids

What Is Microbial Death?
Death: permanent termination of an organism’s
vital processes
Microbes have no conspicuous vital processes;
therefore, death is difficult to determine
Permanent loss of reproductive capability, even
under optimum growth conditions, has become the
accepted microbiological definition of death

Factors Affecting Death Rate
Death of the whole population is not
instantaneous:
• Begins when a certain threshold of microbicidal
agent is met
• Death continues in a logarithmic manner as the time
or concentration is increased
• Active cells tend to die more quickly than less
metabolically active cells
• Eventually, a point is reached at which survival of
any cells is highly unlikely; this point is equivalent to
sterilization

Factors That Influence the Action of
Antimicrobial Agents(1)
The number of microbes:
• Higher load of contaminants takes longer to destroy
The nature of the microorganisms in the
population:
• Target population is usually a mixture of bacteria,
fungi, spores, and viruses with broad spectrum of
resistance
Temperature and pH of the environment

Factors That Influence the Action of
Antimicrobial Agents(2)
The concentration (dose, intensity) of the agent:
• UV radiation is most effective at 260 nm
• Most disinfectants are more active at higher
concentrations
The mode of action of the agent:
• How does it kill or inhibit the microorganism?
The presence of solvents, interfering organic
matter, and inhibitors:
• Saliva, blood, and feces can inhibit the actions of
disinfectants and even of heat

Actions of Various Physical and
Chemical Agents upon the Cell
Cellular Target Effects of Agents Examples of Agents
Used
Cell wall Chemical agents can damage the cell wall by
• blocking its synthesis, or
• digesting it
Chemicals
Detergents
Alcohol
Cytoplasmic
membrane
Agents physically bind to lipid layer of the cytoplasmic
membrane. This opens up the cytoplasmic membrane
and allows damaging chemicals to enter the cell and
important ions to exit the cell.
Detergents
Cellular synthesis Agents can interrupt the synthesis of proteins via the
ribosomes, inhibiting proteins needed for growth and
metabolism and preventing multiplication.
Agents can change genetic codes (mutation).
Formaldehyde
Radiation
Ethylene oxide
Proteins Some agents are capable of denaturing proteins
(breaking of protein bonds, which results in
breakdown of the protein structure).
Agents may attach to the active site of a protein,
preventing it from interacting with its chemical
substrate.
Moist heat
Alcohol
Phenolics

Methods of Physical Control: Heat
Elevated temperatures are microbicidal
Lower temperatures are microbistatic
Moist heat: hot water, boiling water, or steam
between 60°C and 135°C
Dry heat: hot air or an open flame, which ranges
from 160°C to several thousand degrees C

Action of Heat and Chemicals on
Proteins

Comparison of Times and Temperatures to
Achieve Sterilization with Moist and Dry Heat
Temperature (°C) Time to Sterilize (Min)
Moist heat 121 15
125 10
134 3
Dry heat 121 600
140 180
160 120
170 60

Heat Resistance and Thermal Death:
Endospores and Vegetative Cells
Bacterial endospores:
• Exhibit greatest resistance
• Destruction of spores usually requires temperatures
above boiling
Vegetative cells:
• Vary in sensitivity to heat
• Death times vary from 50°C for 3 minutes to 60°C
for 60 minutes

Thermal Death Measurements
Thermal death time (TDT): shortest length of
time required to kill all test microbes at a
specified temperature
Thermal death point (TDP): the lowest
temperature required to kill all microbes in a
sample in 10 minutes
Heat treatment of perishable substances must
render the product free of agents of spoilage or
disease without affecting the speed and cost of
processing

Moist Heat Methods(1)
Boiling Water:
Disinfection
Pasteurization:
Disinfection of Beverages
Top left: ©McGraw-Hill Education/Charles D. Winters, photographer; Bottom left: ©James King-Holmes/Science Source Top right: ©John A. Rizzo/Getty Images

Moist Heat Methods(2)
©DenGuy/Getty Images

Dry Heath Methods
Incineration Hot Air Oven
Top: ©UIG via Getty Images; Bottom: ©RayArt Graphics/Alamy Stock Photo

The Effects of Desiccation and
Lyophilization
Desiccation:
• Vegetative cells directly exposed to normal room
temperature gradually become dehydrated
• Some microbes are killed by desiccation; many others are
not killed and some are even preserved
Lyophilization:
• Combination of freezing and drying
• Method of preserving microorganisms in a viable state for
many years
• Pure cultures are frozen instantaneously and exposed to a
vacuum that removes water, avoiding the formation of ice
crystals

Radiation
Energy emitted from
atomic activities and
dispersed at high
velocity through
matter or space:
• Gamma rays
• X rays
• Ultraviolet radiation

Formation of Pyrimidine Dimers by
the Action of UV Radiation

Filtration
Effective method to remove microbes from air and
liquids:
• Fluid is strained through a filter with openings large
enough for the fluid to pass, but too small for microbes
• Also used are thin membranes of cellulose acetate,
polycarbonate, and plastics whose pore size is carefully
controlled
• Charcoal, diatomaceous earth, or unglazed porcelain are
also used
• Pore sizes can be controlled to permit true sterilization
by trapping viruses or large proteins

Uses of Filtration
Used to prepare liquids that cannot withstand heat
such as serum, blood products, vaccines, drugs, IV
fluids, enzymes, and media
Alternative method for decontaminating milk and
beer without altering their flavor
Important step in water purification
Unable to remove soluble molecules (toxins) that
can cause disease
High-efficiency particulate air (HEPA) filters are used
in hospital rooms and sterile rooms

Membrane Filtration
Source: CDC/Dr. Ray Butler; Janice Carr (b)

Osmotic Pressure
Adding large amounts of salt or sugar to foods
creates a hypertonic environment for bacteria,
causing plasmolysis
Pickling, smoking, and drying foods have been
used for centuries to preserve foods
Osmotic pressure is never a sterilizing technique

Chemical Agents in Microbial Control
Occur in the liquid, gaseous, or solid state
Range from disinfectants and antiseptics to
sterilants and preservatives
Aqueous: chemicals dissolved in pure water as
the solvent
Tinctures: chemicals dissolved in pure alcohol or
water-alcohol mixtures

Desirable Qualities in a Germicide
Rapid action, even in low concentrations
Solubility in water or alcohol and long-term stability
Broad-spectrum microbicidal action without being toxic to
human and animal tissues
Penetration of inanimate surfaces to sustain a cumulative or
persistent action
Resistance to becoming inactivated by organic matter
Not corrosive and nonstaining
Sanitizing and deodorizing properties
Affordability and availability

High-, Intermediate-, and Low-Level
Germicides
Germicides are evaluated in terms of their
effectiveness in destroying microbes in medical
and dental settings:
• High-level germicides kill endospores and can be
used as sterilants
• Intermediate-level germicides kill fungal, but not
bacterial, spores, resistant pathogens, and viruses
• Low-level germicides eliminate only vegetative
bacteria, vegetative fungal cells, and some viruses

Factors Affecting the Germicidal
Activity of Chemicals
Nature of the microorganisms being treated
Nature of the material being treated
Degree of contamination
Time of exposure
Strength and chemical action of the germicide

Required Concentrations and Times for
Chemical Destruction of Selected Microbes
Organism Concentration Time
Agent: Chlorine
Mycobacterium tuberculosis 50 ppm 50 sec
Entamoeba cysts (protozoa) 0.1 ppm 150 min
Hepatitis A virus 3 ppm 30 min
Agent: Ethyl Alcohol
Staphylococcus aureus 70% 10 min
Escherichia coli 70% 2 min
Poliovirus 70% 10 min
Agent: Hydrogen Peroxide
Staphylococcus aureus 3% 12.5 sec
Neisseria gonorrhoeae 3% 0.3 sec
Herpes simplex virus 3% 12.8
Agent: Quaternary Ammonium Compound
Staphylococcus aureus 450 ppm 10 min
Salmonella typhi 300 ppm 10 min
Agent: Ethylene Oxide Gas
Streptococcus faecalis 500 mg/L 2 to 4 min
Influenza virus 10,000 mg/L 25 h

Germicidal Categories According to
Chemical Group(1)
Agent Target
Microbes
Form(s) Mode of Action Indicators for Use Limitations
Halogens:
chlorine
Can kill
endospores
(slowly); all
other microbes
Liquid/gaseous
chlorine (Cl2),
hypochlorites
(OCl),
chloramines
(NH2Cl)
In solution, these
compounds
combine with
water and release
hypochlorous
acid (HOCl);
denature
enzymes
permanently and
suspend
metabolic
reactions
Chlorine kills bacteria, endospores,
fungi, and viruses; gaseous/liquid
chlorine: used to disinfect drinking
water, sewage and waste water;
hypochlorites: used in health care
to treat wounds, disinfect bedding
and instruments, sanitize food
equipment and in restaurants,
pools, and spas; chloramines:
alternative to pure chlorine in
treating drinking water; also used
to treat wounds and skin surfaces
Less effective
if exposed to
light, alkaline
pH, and excess
organic matter
Halogens:
iodine
Can kill
endospores
(slowly); all
other microbes
Free iodine in
solution (I2);
Iodophors
(complexes of
iodine and
alcohol)
Penetrates cells
of
microorganisms
where it
interferes with a
variety of
metabolic
functions;
interferes with
the hydrogen and
disulfide bonding
of proteins
2% iodine, 2.4% sodium iodide
(aqueous iodine) used as a topical
antiseptic; 5% iodine, 10%
potassium iodide used as a
disinfectant for plastic and rubber
instruments, cutting blades, etc.;
Iodophor products contain 2% to
10% of available iodine, which is
released slowly; used to prepare
skin for surgery, in surgical scrubs,
to treat burns, and as a
disinfectant
Can be
extremely
irritating to
the skin and is
toxic when
absorbed;
many
iodophors
banned in
consumer
products in
2017.

Chemical Group(2)
Agent Target
Microbes
Oxidizing
agents
Kill
endospor
es and all
other
microbes
Hydrogen
peroxide,
peracetic acid
Oxygen forms free
radicals (–OH),
which are highly
toxic and reactive to
cells
As an antiseptic, 3% hydrogen
peroxide used for skin and wound
cleansing, mouth washing,
bedsore care; used to treat
infections caused by anaerobic
bacteria; 35% hydrogen peroxide
used in low temperature
sterilizing cabinets for delicate
instruments
Sporicidal only
in high
concentrations
Aldehydes Kill
endospor
es and all
other
microbes
Organic
substances
bearing a
–CHO
functional
group on the
terminal
carbon
Glutaraldehyde can
irreversibly disrupt
the activity of
enzymes and other
proteins within the
cell; ortho-
phthalaldehyde
Glutaraldehyde kills rapidly and is
broad-spectrum; used to sterilize
respiratory equipment, scopes,
kidney dialysis machines, dental
instruments; ortho-
phthalaldehyde is safer than
glutaraldehyde and just as
effective
Glutaraldehyd
e is somewhat
unstable,
especially with
increased pH
and temp;
ortho-
phthalaldehyd
e is much
more
expensive than
glutaraldehyde

Chemical Group(3)
Agent Target
Microbes
Gaseous
sterilants/
disinfectan
ts
Ethylene
oxide kills
endospore
; other
gases less
effective
Ethylene
oxide is a
colorless
substance
that exists as
a gas at room
temperature
Ethylene oxide
reacts vigorously
with functional
groups of DNA
and proteins,
blocking both
DNA replication
and enzymatic
actions; chlorine
dioxide is a
strong alkylating
agent
Ethylene oxide is used to
disinfect plastic materials and
delicate instruments; can also
be used to sterilize syringes,
surgical supplies, and medical
devices that are prepackaged
Ethylene oxide is
explosive—it must be
combined with a high
percentage of carbon
dioxide or
fluorocarbon; it can
damage lungs, eyes,
and mucous
membranes if
contacted directly;
ethylene oxide is rated
as a carcinogen by the
government
Phenol
(carbolic
acid)
Some
bacteria,
viruses,
fungi
Derived from
the distillation
of coal tar;
phenols
consist of one
or more
aromatic
carbon rings
with added
functional
groups
In high
concentrations,
they are cellular
poisons,
disrupting cell
walls and
membranes,
proteins; in
lower
concentrations,
they inactivate
certain critical
enzyme systems
Phenol remains one standard
against which other (less
toxic) phenolic disinfectants
are rated; the phenol
coefficient quantitatively
compares a chemical’s
antimicrobial properties to
those of phenol; phenol is
now used only in certain
limited cases, such as in
drains, cesspools, and animal
quarters
Toxicity of many
phenolics makes them
dangerous to use as
antiseptics; many
phenols banned in
consumer products in
2017, including
triclosan and
triclocarban.

Chemical Group(4)
Agent Target
Microbes
Chlorhexidine Most
bacteria,
viruses,
fungi
Complex organic
base containing
chlorine and two
phenolic rings
Targets bacterial
membranes, where
selective permeability
is lost, bacterial cell
walls, and proteins,
resulting in
denaturation
Mildness, low toxicity
and rapid action make
chlorhexidine a popular
choice of agents; used
in hand scrubs,
prepping skin for
surgery, as an obstetric
antiseptic, as a mucous
membrane irrigant, etc.
Effects on
viruses and
fungi are
variable
Alcohol Most
bacteria,
viruses,
fungi
Colorless
hydrocarbons with
one or more –OH
functional groups;
ethyl and isopropyl
alcohol are suitable
for antimicrobial
control
Concentrations of 50%
and higher dissolve
membrane lipids,
disrupt cell surface
tension, and
compromise
membrane integrity
Germicidal,
nonirritating, and
inexpensive; routinely
used as skin degerming
agents (70% to 95%
solutions)
Rate of
evaporation
decreases
effectiveness;
inhalation of
vapors can
affect the
nervous system

Chemical Group(5)
Agent Target
Microbes
Detergents Some
bacteria,
viruses,
fungi
Polar molecules
that act as
surfactants;
anionic
detergents have
limited
microbial
power; cationic
detergents, such
as quaternary
ammonium
compounds
(“quats”), are
much more
effective
antimicrobials
Positively charged end
of the molecule binds
well with the
predominantly
negatively charged
bacterial surface
proteins; long,
uncharged hydrocarbon
chain allows the
detergent to disrupt
the cytoplasmic
membrane;
cytoplasmic membrane
loses selective
permeability, causing
cell death
Effective against
viruses, algae, fungi,
and gram-positive
bacteria; rated only
for low-level
disinfection in the
clinical setting; used
to clean restaurant
utensils, dairy
equipment,
equipment surfaces,
restrooms
Ineffective against
tuberculosis bacterium,
hepatitis virus, Pseudomonas,
and endospores; activity is
greatly reduced in presence
of organic matter; detergents
function best in alkaline
solutions; some quats banned
in consumer products in
2017.
Heavy
metal
compounds
Some
bacteria,
viruses,
fungi
Heavy metal
germicides
contain either
an inorganic or
an organic
metallic salt;
may come in
tinctures, soaps,
ointment, or
aqueous
solution
Mercury, silver, and
other metals exert
microbial effects by
binding onto functional
groups of proteins and
inactivating them
Organic mercury
tinctures are fairly
effective antiseptics;
organic mercurials
serve as
preservatives in
cosmetics,
ophthalmic
solutions, and other
substances; silver
nitrate solutions are
used for topical
germicides and
ointments
Microbes can develop
resistance to metals; not
effective against endospores;
can be toxic if inhaled,
ingested, or absorbed; may
cause allergic reactions in
susceptible individuals

Active Ingredients of Various
Commercial Antimicrobial Products(1)
Product Specific Chemical Agent
Antimicrobial
Category
Lysol® Sanitizing Wipes Dimethyl benzyl ammonium chloride Detergent (quat)
Clorox® Disinfecting Wipes Dimethyl benzyl ammonium chloride Detergent (quat)
Tilex® Mildew Remover Sodium hypochlorites Halogen
Lysol® Mildew Remover Sodium hypochlorites Halogen
Ajax® Antibacterial Hand Soap Triclosan; banned beginning in fall 2017 Phenolic
Dawn® Antibacterial Hand
Soap
Triclosan; banned beginning in fall 2017 Phenolic
Dial® Antibacterial Hand Soap Triclosan; banned beginning in fall 2017 Phenolic
Lysol® Disinfecting Spray Alkyl dimethyl benzyl ammonium
saccharinate/ethanol
Detergent (quats)/
alcohol

Active Ingredients of Various
Commercial Antimicrobial Products(2)
Product Specific Chemical Agent
Antimicrobial
Category
ReNu® Contact Lens Solution Polyaminopropyl biguanide Chlorhexidine
Wet Ones® Antibacterial Moist
Towelettes
Benzethonium chloride Detergents (quat)
Noxema® Triple Clean Triclosan; banned beginning in fall
2017
Phenolic
Scope® Mouthwash Ethanol Alcohol
Purell® Instant Hand Sanitizer Ethanol Alcohol
Pine-Sol® Phenolics and surfactant Mixed
Allergan® Eye Drops Sodium chlorite Halogen

Antimicrobial Treatment

Principles of
Antimicrobial Therapy
The introduction of modern drugs to control
infections was a medical revolution in the 1940s
Antimicrobial drugs have reduced the incidence
of certain infections, but they have not
eradicated infectious diseases and probably
never will
Today, doctors are worried that we are
dangerously close to a postantibiotic era, where
the drugs we have are no longer effective

Antimicrobial Chemotherapy
Goal of antimicrobial chemotherapy:
• Administer a drug to an infected person that
destroys the infective agent without harming the
host’s cells
A drug must be able to:
• Be easy to administer and able to reach the
infectious agent anywhere in the body
• Be absolutely toxic to the infectious agent and
absolutely nontoxic to the host
• Remain active in the body as long as needed and be
safely and easily broken down and excreted

Characteristics of the Ideal
Antimicrobial Drug
• Toxic to the microbe but nontoxic to host cells
• Microbiocidal rather than microbiostatic
• Relatively soluble; functions even when highly diluted in body
fluids
• Remains potent long enough to act and is not broken down or
excreted prematurely
• Does not lead to the development of antimicrobial resistance
• Complements or assists the activities of the host’s defenses
• Remains active in tissues and body fluids
• Readily delivered to the site of infection
• Reasonably priced

Terminology of Antimicrobials
Prophylaxis Use of a drug to prevent infection of a person at risk
Antimicrobial Chemotherapy The use of drugs to control infection
Antimicrobials All-inclusive term for any antimicrobial drug,
regardless of its origin
Antibiotics Substances produced by the natural metabolic
processes of some microorganisms that can inhibit or
destroy other microorganisms; generally, the term is
used for drugs targeting bacteria and not other types
of microbes
Semisynthetic Drugs Drugs that are chemically modified in the laboratory
after being isolated from natural sources
Synthetic Drugs Drugs produced entirely by chemical reactions
Narrow-Spectrum (Limited Spectrum) Antimicrobials effective against a limited array of
microbial types—for example, a drug effective mainly
against gram-positive bacteria
Broad-Spectrum (Extended Spectrum) Antimicrobials effective against a wide variety of
microbial types—for example, a drug effective against
both gram-positive and gram-negative bacteria

Origins of Antimicrobial Drugs
Antibiotics are natural metabolic products of
bacteria and fungi:
• Produced to inhibit the growth of competing microbes
in the same habitat (antagonism)
Greatest numbers derived from:
• Bacteria in the genera Streptomyces and Bacillus
• Molds in the genera Penicillium and Cephalosporium

Kirby-Bauer Technique
Surface of an agar plate is spread with test
bacterium
Small discs containing a prepared amount of
antibiotic are placed on the plate
Zone of inhibition surrounding the discs is
measured and compared with a standard for
each drug
Antibiogram provides data for drug selection
This method is less effective for anaerobic,
highly fastidious, or slow-growing bacteria

Results of a Sample Kirby-Bauer Test
Drug
Zone Size (mm)
Required for
Susceptibility (S)
Zone Size (mm)
Required for
Resistance (R)
Example Results for
Staphylococcus
aureus Evaluation
Bacitracin >13 <8 15 Sensitive
Chloramphenicol >18 <12 20 Sensitive
Erythromycin >18 <13 15 Intermediate
Gentamicin >13 <12 16 Sensitive
Kanamycin >18 <13 20 Sensitive
Neomycin >17 <12 12 Resistant
Penicillin G >29 <20 10 Resistant
Polymyxin B >12 <8 10 Intermediate
Streptomycin >15 <11 11 Resistant
Vancomycin >12 <9 15 Sensitive
Tetracycline >19 <14 25 Sensitive

Disc Diffusion Tests
(a) ©McGraw-Hill Education/Don Rubbelke, photographer

Alternative to the Kirby-Bauer
Procedure
CDC/Dr. Richard Facklam

Tube Dilution Test(1)
More sensitive and quantitative than the Kirby-Bauer
test
Antimicrobial is diluted serially in tubes of broth
Each tube is inoculated with a small uniform sample
of pure culture, incubated, and examined
Minimum inhibitory concentration (MIC): the
smallest concentration (highest dilution) of drug that
visibly inhibits growth
• Useful in determining the smallest effective dosage and
providing a comparative index against other antimicrobials

Tube Dilution Test(2)

Therapeutic Index
The ratio of the dose of the drug that is toxic to
humans as compared to its minimum effective
(therapeutic) dose:
• The smaller the ratio, the greater the potential for
toxic drug reactions
• TI = 1.1 is a risky choice
• TI = 10 is a safer choice
• The drug with the highest therapeutic index has the
widest margin of safety

Before Prescribing an Antibiotic
The physician must take a careful history before
prescribing an antibiotic:
• Preexisting conditions that might influence the activity of the
drug or the response of the patient
• History of allergy to a certain class of drugs
• Underlying liver or kidney disease
• Infants, the elderly, and pregnant women require special
precautions
• Intake of other drugs can result in increased toxicity or failure of
one or more drugs
• Some drug combinations have synergistic effects, may allow for
reduced dosages

Goal of Antimicrobial Drugs
Disrupt cell processes or structures of bacteria,
fungi, or protozoa
Inhibit virus replication
Interfere with the function of enzymes required to
synthesize or assemble macromolecules
Destroy structures already formed in the cell
Selectively toxic: kill or inhibit microbial cells
without damaging host tissues

Interactions Between
Drug and Microbe
Drugs with excellent selective toxicity block the
synthesis of the bacterial cell wall (penicillins):
• Human cells lack the chemical peptidoglycan and are
unaffected by the drug
Drugs most toxic to humans:
• Drugs that act upon a structure common to both the
infective agent and the host cell (cytoplasmic
membrane)
• As characteristics of the infectious agent are more and
more similar to the host cell, selective toxicity
becomes more difficult to achieve

Mechanisms of Drug Action
Goals of chemotherapy: disrupt the structure or
function of an organism to the point where it can
no longer survive
Antimicrobial drug categories:
• Inhibition of cell wall synthesis
• Inhibition of nucleic acid structure and function
• Inhibition of protein synthesis
• Interference with cytoplasmic membrane structure
and function
• Inhibition of folic acid synthesis

Drugs That Target the Cell Wall
Penicillins
• Penicillins G and V
• Ampicillin, carbenicillin,
amoxicillin
• Nafcillin, cloxacillin
• Clavulanic acid
Cephalosporins
• Cefazolin
• Cefaclor
• Cephalexin, cefotaxime
• Ceftriaxone
• Cefepime
• Cegtaroline
Carbapenems
• Doripenem, imipenem
• Aztreonam
Miscellaneous drugs that
target the cell wall
• Bacitracin
• Isoniazid
• Vancomycin
• Fosfomycin tromethamine

Drugs That Target Protein Synthesis
Aminoglycosides: insert on
sites on the 30S subunit and
cause the misreading of the
mRNA, leading to abnormal
proteins
• Streptomycin
Tetracyclines: block the
attachment of tRNA on the A
acceptor site and stop further
protein synthesis
• Tetracycline
Glycylcyclines
• Tigecycline
Macrolides: inhibit
translocation of the subunit
during translation
(erythromycin)
• Erythromycin, clarithromycin,
azithromycin
Miscellaneous drugs that
target protein synthesis
• Clindamycin
• Quinupristin + dalfopristin
(Synercid)
• Linezolid

Drugs That Target Folic Acid Synthesis
Sulfonamides: interfere with folate metabolism
by blocking enzymes required for the synthesis
of tetrahydrofolate, which is needed by the cells
for folic acid synthesis and eventual production
of DNA, RNA, and amino acids
• Sulfamethoxazole
• Silver sulfadiazine
• Trimethoprim

Drugs That Target DNA or RNA
Sulfonamides: interfere with folate metabolism
by blocking enzymes required for the synthesis
of tetrahydrofolate, which is needed by the cells
for folic acid synthesis and eventual production
of DNA, RNA, and amino acids
• Sulfamethoxazole
• Silver sulfadiazine
• Trimethoprim

Drugs That Target Cytoplasmic or Cell
Membranes
Polymyxins (colistins): interact with membrane
phospholipids; distort the cell surface and cause
leakage of protein and nitrogen bases,
particularly in gram-negative bacteria
• Polymyxin B
• Daptomycin

Spectrum of Activity for Antibiotics
Jump to long decription

Characteristics of Selected Penicillin
Drugs
Name
Spectrum
of Action Uses, Advantages Disadvantages
Penicillin G Narrow Best drug of choice
when bacteria are
sensitive; low cost;
low toxicity
Can be hydrolyzed
by penicillinase;
allergies occur;
requires injection
Penicillin V Narrow Good absorption
from intestine;
otherwise, similar to
Penicillin G
Hydrolysis by
penicillinase;
allergies
Methicillin,
nafcillin
Narrow Not usually
susceptible to
penicillinase
Poor absorption;
allergies; growing
Resistance
Ampicillin Broad Works on gram-
negative bacilli
Can be hydrolyzed
by penicillinase;
allergies; only fair
absorption
Amoxicillin Broad Gram-negative
infections; good
absorption
Hydrolysis by
penicillinase;
allergies
Azlocillin,
mezlocillin,
ticarcillin
Very broad Effective against
Pseudomonas
species; low toxicity
compared with
aminoglycosides
Allergies;
susceptible to many
beta-lactamases
Jump to long decription

Bacteria in Biofilms
Bacteria in biofilms behave differently than
when they are free-living:
• Often unaffected by antimicrobials
• Antibiotics often cannot penetrate the sticky
extracellular material surrounding biofilms
• Bacteria in biofilms express a different phenotype
and have different antibiotic susceptibility profiles
than free-living bacteria

Antibiotics and Biofilms
Biofilm treatment strategies:
• Interrupting quorum sensing pathways
• Daptomycin: shown success
• Adding DNAse to antibiotics aids penetration
through extracellular debris
• Impregnating devices with antibiotics prior to
implantation
Some antibiotics cause biofilms to form at a
higher rate than they normally would

Agents Used to Treat Fungal Infections
Drug Group Drug Examples Action
Macrolide
polyenes
Amphotericin B Bind to fungal membranes, causing loss of selective
permeability; extremely versatile
Can be used to treat skin, mucous membrane lesions
caused by Candida albicans
Injectable form of the drug can be used to treat
histoplasmosis and Cryptococcus meningitis
Azoles Ketoconazole,
fluconazole, miconazole,
and clotrimazole
Interfere with sterol synthesis in fungi
Ketoconazole—cutaneous mycoses, vaginal and oral
candidiasis, systemic mycoses
Fluconazole—AIDS-related mycoses (aspergillosis,
Cryptococcus meningitis)
Clotrimazole and miconazole—used to treat
infections in the skin, mouth, and vagina
Echinocandins Micafungin, caspofungin Inhibit fungal cell wall synthesis
Used against Candida strains and aspergillosis
Allylamines Terbinafine, naftifine Inhibit enzyme critical for ergosterol synthesis
Used to treat ringworm and other cutaneous mycoses

Antimalarial Drugs
Quinine:
• Principal treatment of malaria for hundreds of years
• Has been replaced by less toxic synthesized quinolones,
chloroquine and primaquine
• Several species of Plasmodium and many stages in its life
cycle mean that no single drug is universally effective
Artemisinin:
• Has become the staple for malaria treatment in most parts of
the world
• Artemisinin combination therapy (ACT): artemisinin with
quinine derivatives or other drugs

Chemotherapy for Other
Protozoal Infections
Metronidazole: widely used amoebicide:
• Treats intestinal infections and hepatic disease
caused by Entamoeba histolytica
• Also treats Giardia lamblia and Trichomonas
vaginalis
Other drugs with antiprotozoal activities:
• Quinacrine
• Sulfonamides
• Tetracyclines

Agents to Treat
Helminthic Infections
Mebendazole and albendazole inhibit
microtubules of worms, eggs, and larvae
Pyrantel paralyzes the muscles of intestinal
roundworms
Praziquantel:
• Tapeworm and fluke infections
Ivermectin:
• Veterinary drug used for strongyloidiasis and
oncocerosis in humans

Antimicrobial Resistance
Drug resistance:
• An adaptive response in which microorganisms
begin to tolerate an amount of drug that would
normally be inhibitory
• Due to the genetic versatility and adaptability of
microbial populations
• Can be intrinsic as well as acquired

How Does
Drug Resistance Develop?
In the 1980s and 1990s scientists began to
observe treatment failures on a large scale
Microbes become newly resistant to a drug after
one of the following occurs:
• Spontaneous mutations in critical chromosomal genes
• Acquisition of entire new genes or sets of genes via
horizontal transfer from another species

Development of Drug Resistance

Resistance Through Horizontal
Transfer
Resistance (R) factors: plasmids containing antibiotic
resistance genes
Can be transferred through conjugation,
transformation, or transduction
Plasmids encoded with drug resistance are naturally
present in microbes before they have been exposed to
an antibiotic
Transposons also duplicate and insert genes for drug
resistance into plasmids
Sharing of resistance genes accounts for the rapid
proliferation of drug-resistant species

Mechanisms of Drug Resistance

Threats
Urgent threats:
• Clostridium difficile (C. diff)
• Carbapenem-resistant Enterobacteriaceae (CRE)
• Drug-resistant Neisseria gonorrhoeae
Serious threats:
• Multidrug-resistant Acinetobacter
• Drug-resistant Campylobacter
• Fluconazole-resistant Candida
• Many more
Concerning threats:
• Vancomycin-resistant Staphylococcus aureus (VRSA)
• Erythromycin-resistant Group A Streptococcus
• Clindamycin-resistant Group B Streptococcus

Examples of Superinfection
Urinary tract infection caused by E. coli treated with
antibiotics:
• Lactobacilli in the female vagina are killed by the broad-
spectrum cephalosporin used to treat the UTI
• Overgrowth of Candida albicans occurs, causing a vaginal
yeast infection or oral thrush
Antibiotic-associated colitis:
• Oral therapy with tetracyclines, clindamycin, and broad-
spectrum penicillins kills off normal biota of the colon
• Overgrowth of Clostridium difficile invades the intestinal lining
and releases toxins that cause diarrhea, fever, and abdominal
pain

Role of Antimicrobials in Disrupting
Microbial Biota and Causing Superinfections
Jump to long descriptiona

Interactions Between Microbes
and Humans

The Human Microbiome(1)
Humans and other mammals have the form and
physiology that they have due to having been
formed in intimate contact with their microbes
Human microbiome:
• The sum total of all microbes found on and in a
normal human
• Critically important to the health and functioning of
its host organism

Colonization, Infection, Disease
For the most part, our resident microbiota
colonize us for the long term and do not cause
disease
Infection: microbes get past host defenses,
enter tissues, and multiply
Disease: deviation from health; pathologic state
that results when cumulative effects of infection
damage or disrupt tissues and organs
Infectious disease: a pathogenic state caused
directly by microorganisms or their products

Colonization of the Fetus
Until recently, the uterus and its contents were
thought to be sterile during embryonic and fetal
development:
• Analysis of newborns’ stools sampled before their first
meal show a diversity of bacteria
• This indicates that their intestines are colonized in
utero

Colonization of the Newborn
Important source of microbiota for a newborn is
its trip through the vagina:
• Lactobacillus provides the baby with the necessary
enzymes to digest milk
• Other species protect the baby from skin disorders
and other conditions
Human milk contains around 600 species of
bacteria, and sugars that are digested by healthy
gut bacteria

Where Babies Get a Microbiome
©Jim Connely (ultrasound); ©Adam Gault/SPL/Getty Images (birth); ©Jose Luis Pelaez Inc/Blend Images LLC (breast feeding); ©Pixtal/SuperStock (bottle);
©Marc Romanelli/Blend Images (family) ©Kwame Zikomo/ Purestock/SuperStock (with dog); ©alexmak72427/iStock/Getty Images (scar)Jump to long description

Virulence
Virulence:
• Relative severity of a disease caused by a particular microbe
• Degree of pathogenicity
Virulence of a microbe is determined by its ability to:
• Establish itself in a host
• Cause damage
Virulence factor: any characteristic or structure of the
microbe that contributes to its ability to establish itself
in the host and cause damage

Portal of Entry Organism/Disease How Access Is Gained
Skin Staphylococcus aureus, Streptococcus pyogenes,
Clostridium tetani
Via nicks, abrasions, punctures, areas of
broken skin
Skin Herpes simplex (type 1) Via mucous membranes of the lips
Skin Helminth worms Burrow through the skin
Skin Viruses, rickettsias, protozoa (i.e., malaria, West
Nile virus)
Via insect bites
Skin Haemophilus aegyptius, Chlamydia trachomatis,
Neisseria gonorrhoeae
Via the conjunctiva of the eye
Gastrointestinal
tract
Salmonella, Shigella, Vibrio, Escherichia coli,
poliovirus, hepatitis A, echovirus, rotavirus,
enteric protozoans (Giardia lamblia, Entamoeba
histolytica)
Through eating/drinking contaminated
foods and fluids
Via fomites (inanimate objects
contaminated with the infectious
organism)
Respiratory tract Bacteria causing meningitis, influenza, measles,
mumps, rubella, chickenpox, common cold,
Streptococcus pneumoniae, Klebsiella,
Mycoplasma, Cryptococcus, Pneumocystis,
Mycobacterium tuberculosis, Histoplasma
Via inhalation of offending organism
Urogenital tract HIV, Trichomonas, hepatitis B, syphilis, Treponema
pallidum, Neisseria gonorrhoeae, Chlamydia
trachomatis, herpes, genital warts
Enter through the skin/mucosa of penis,
external genitalia, vagina/cervix, urethra;
may enter through an unbroken surface
or through a cut or abrasion

Quantity of Microbes in the
Inoculating Dose
Infectious dose (ID):
• The minimum number of microbes necessary to cause
an infection to proceed
• Microorganisms with smaller infectious doses have
greater virulence
• ID for Q fever is a single cell
• ID for tuberculosis, giardiasis, and coccidioidomycosis
is about 10 cells
• ID for gonorrhea is 1,000 cells
• ID for typhoid fever is 10,000 cells
• ID for cholera is 1,000,000,000 cells

Adhesion Mechanisms
Bacterial, fungal, and protozoal pathogens
attach by:
• Fimbriae (pili)
• Surface proteins
• Adhesive slimes or capsules
Viruses attach by specialized receptors
Parasitic worms fastened by suckers, hooks, and
barbs

Step Three: Becoming Established—
Surviving Host Defenses
Phagocytes: cells that engulf and destroy host pathogens
by means of enzymes and antimicrobial chemicals
Antiphagocytic factors:
• Virulence factors used by some pathogens to avoid phagocytes
• Leukocidins: kill phagocytes outright
• Extracellular surface layer (slime or capsule) makes it difficult
for the phagocyte to engulf the pathogen
• Some bacteria survive inside the phagocyte

Step Four: Causing Disease
Virulence factors are simply adaptations a
microbe uses to establish itself in a host
Three ways that microorganisms cause damage
to their host:
• Directly through the action of enzymes or toxins
(both endotoxins and exotoxins)
• Indirectly by inducing the host’s defenses to
respond excessively or inappropriately
• Epigenetic changes made to host cells by microbes

Exotoxins
Hemolysins: class of
bacterial exotoxin
that disrupts the cell
membrane of red
blood cells
• Cause the RBC to
hemolyze, to burst
and release
hemoglobin pigment
©McGraw-Hill Education/Lisa Burgess, photographer

Endotoxin
Lipopolysaccharide (LPS), part of the outer
membrane of gram-negative cell walls
Has a variety of systemic effects on tissues and
organs
Causes fever, inflammation, hemorrhage, and
diarrhea
Blood infections by Salmonella, Shigella, Neisseria
meningitidis, and Escherichia coli are particularly
dangerous and can lead to shock

Definitions of Infection Types
Type of Infection Definition Example
Localized infection Microbes enter the body, remain confined to a
specific tissue
Boils, warts, fungal skin
infections
Systemic infection Infection spreads to several sites and tissue
fluids—usually via the bloodstream—but may
travel by other means such as nerves (rabies) and
cerebrospinal fluid (meningitis)
Mumps, rubella, chickenpox,
AIDS, anthrax, typhoid,
syphilis
Focal infection Infectious agent spreads from a local site and is
carried to other tissues
Tuberculosis, streptococcal
pharyngitis
Mixed infection
(polymicrobial infection)
Several agents establish themselves
simultaneously at the infection site
Human bite infections, wound
infections, gas gangrene
Primary infection The initial infection Can be any infection
Secondary infection A second infection caused by a different microbe,
which complicates a primary infection; often a
result of lowered host immune defenses
Influenza complicated by
pneumonia, common cold
complicated by bacterial otitis
media
Acute infection Infection comes on rapidly, with severe but short-
lived effects
Influenza
Chronic infection Infection that progresses and persists over a long
period of time
HIV

Warning Signals of Disease
Sign: objective evidence of disease as noted by
an observer
Symptom: subjective evidence of disease as
sensed by the patient
Syndrome: a disease identified by a certain
complex of signs and symptoms

Infections That Go Unnoticed
No noticeable symptoms are produced
Microbe is active in host tissues
Host does not seek medical attention
These infections are known as asymptomatic, or
subclinical (inapparent)

Steps Involved When a Microbe
Causes Disease in a Host

Long-Term Infections and
Long-Term Effects
Latency: a dormant state of microbes in certain chronic
infectious diseases
• Viral latency: herpes simplex, herpes zoster, hepatitis B, AIDS,
Epstein-Barr
• Bacterial/protozoan latency: syphilis, typhoid fever,
tuberculosis, malaria
Sequelae: long-term or permanent damage to tissues
or organs caused by infectious disease
• Meningitis: deafness
• Strep throat: rheumatic heart disease
• Lyme disease: arthritis
• Polio: paralysis

Stages in the Course of
Infection and Disease

Reservoirs:
Where Pathogens Come From
Reservoir:
• Primary habitat in the natural world from which a
pathogen originates
• Often a human or animal carrier
• Also soil, water, and plants
Transmitter: individual or object from which an
infection is acquired
• Syphilis: reservoir and transmitter are the same
• Hepatitis A: reservoir is a human, transmitter is food

Zoonosis
Zoonosis: an infection indigenous to animals but
naturally transmissible to humans
• Humans are essentially dead-end hosts that do not
contribute to the natural persistence of the microbe
• Some zoonotic infections have multihost involvement
• Some have complex life cycles in the wild
• Zoonotic spread of disease is promoted by close
associations between humans and animals
• Make up a full 70% of all new emerging diseases worldwide
• Impossible to eradicate without also eradicating the animal
reservoir

Nonliving Reservoirs
Microorganisms have adapted to nearly every habitat in the
biosphere:
• Thrive in soil, water, air
• Surfaces in homes, offices, and other structures in the “built
environment”
Most are saprobic and cause little harm and considerable
benefit
Some are opportunists
A few are regular pathogens
Because humans are in regular contact with environmental
sources, acquisition of pathogens from nonliving reservoirs
is always a possibility

Most Common
Healthcare-Associated Infections

Control of HAIs
Infection control officer: implements proper practices
and procedures, tracks potential outbreaks, identifies
breaches in asepsis, and trains health care workers in
aseptic techniques
Training for nurses and caregivers - regularly exposed to
needlesticks, infectious secretions, blood, and physical
contact with patients; they need to be especially aware
of infection control
Most hospitals have adopted universal precautions that
recognize that all secretions from all persons in the
clinical setting are potentially infectious and that
transmission can occur in either direction

Which Agent Is the Cause?
Using Koch’s Postulates
Etiologic/causative agent: the cause of infection
and disease
Koch’s postulates:
• A series of proofs that became the standard for
determining causation of infectious disease
• Continue to play an essential role in modern
epidemiology
• Reliable for many diseases, but cannot be
completely fulfilled in certain situations

Koch’s Postulates

Exceptions to Using Koch’s Postulates
Some infectious agents cannot be readily isolated
or grown in the laboratory
Some infections cannot be elicited in animals;
viruses have a limited host range, human viruses
will only cause disease in humans, etc.
Not possible to determine causation in
polymicrobial diseases

Epidemiology:
The Study of Disease in Populations
Epidemiology:
• Study of frequency and distribution of disease and
other health-related factors in defined populations
• Involves many disciplines: microbiology, anatomy,
physiology, immunology, medicine, psychology,
sociology, ecology, and statistics
• Considers all forms of disease: heart disease, cancer,
drug addiction, and mental illness

Tracking Disease in the Population
Reportable or notifiable diseases:
• Certain diseases must be reported to authorities
• Other diseases are reported on a voluntary basis
A network of individuals and agencies at the local,
district, state, national, and international levels
keeps track of infectious diseases

Epidemiological Statistics(1)
Prevalence: total number of existing cases in a given
population; snapshot
• Total number of cases in population ÷ total number of persons
in population × 100 = %
• Example: The prevalence of smoking among adults in the U.S. is 17%
currently
Incidence: the number of new cases over a certain time
period
• Number of new cases in a designated time period÷ total
number of susceptible persons (usually reported per 100,000
persons):
• Example: The incidence of new Lyme disease cases in the U.S. in 2014
was 8.6 per 100,000

Epidemiological Statistics(2)
Statistics of concern to the epidemiologist are
rates of disease with regard to sex, race, or
geographic region
Mortality rate:
• Measures the total number of deaths in a population
due to a certain disease
• Overall death rate from infectious diseases has
dropped, although the number of persons afflicted
with infectious rates (morbidity rate) has remained
high

Epidemics
Common-source epidemic: results from common
exposure to a single source of infection over a
period of time
Propagated epidemic: results from an infectious
agent that is communicable from person to person
and is sustained over time in a population
Point-source epidemic: infectious agent came
from a single source, and all of its “victims” were
infected at once

Additional Epidemiology Terms
Index case: may not be the first case of the disease, but it is
the first case that brought the epidemic to the attention of
officials
Endemic: an infectious disease that exhibits a relatively steady
frequency over a long time period in a particular geographic
locale
Sporadic: occasional cases are reported at irregular intervals
at random locales
Epidemic: when statistics indicate that the prevalence of an
endemic or sporadic disease is increasing beyond what is
expected for a population
Pandemic: spread of an epidemic across continents

ZO 211 Week 4 lecture

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to ZO 211 Week 4 lecture

Similar to ZO 211 Week 4 lecture (20)

More from BHUOnlineDepartment

More from BHUOnlineDepartment (20)

Recently uploaded

Recently uploaded (20)

ZO 211 Week 4 lecture