This document defines various microbiological terms related to pathogenicity and infection. It discusses how pathogens can enter the body through mucous membranes, skin, or parenterally. Once inside the host, pathogens use several mechanisms to penetrate defenses, including adherence via adhesins, capsules to avoid phagocytosis, and enzymes that damage host tissues. Toxins, either exotoxins secreted outside bacterial cells or endotoxins in gram-negative cell walls, are also important virulence factors. Vaccines work by using inactivated toxins or toxoids to stimulate antibody production against pathogenic toxins.
Term and Definitions regarding microbiology, Pathogenicity and virulency, acute and chronic infection, primary and secondary infection, opportunistic infection.
host pathogen interaction, Mechanism of pathogenesis rashmi816961
-What is host - pathogen interaction?
-Define terms includes pathogenicity, lethal dose, infection etc.
-Duration of symptom
- Pathogens and steps involved in mechanism of pathogenesis
1. Microbial adherence
2. Invasion
3. Colonization
4. Evasion
5. Damage to host
6. Exiting the host
7. Survival outside the host
8. Transmission
- Host -pathogen interaction in plants and animals
- Defence system in plants and animals
Term and Definitions regarding microbiology, Pathogenicity and virulency, acute and chronic infection, primary and secondary infection, opportunistic infection.
host pathogen interaction, Mechanism of pathogenesis rashmi816961
-What is host - pathogen interaction?
-Define terms includes pathogenicity, lethal dose, infection etc.
-Duration of symptom
- Pathogens and steps involved in mechanism of pathogenesis
1. Microbial adherence
2. Invasion
3. Colonization
4. Evasion
5. Damage to host
6. Exiting the host
7. Survival outside the host
8. Transmission
- Host -pathogen interaction in plants and animals
- Defence system in plants and animals
DR.MRS.BHAVANI.A
NURSING TUTOR, ANNAMALAI UNIVERSITY
INFECTION CONTROL - CHAIN OF INFECTION
INTRODUCTION
A major concern for health practioners is the danger of spreading microorganisms from person to person and from place to place. Microorganisms are naturally present in almost all environments. Some are beneficial; some are not. Some are harmless to most people, and others are harmful to many people. Still others are harmless except in certain circumstances. Prevention of infection is a major focus for nurses. As primary caregivers, nurses are involved in identifying, preventing, controlling, and teaching the patient about infection.
INFECTION
• The word "infection" means something different from "disease," although the two terms sometimes are confused. Disease is a general word that describes any abnormality of the human condition or something that interferes with the normal, healthy functioning of the body.
• Diseases include infections and infestations, among others. Infection is a term that refers specifically to any abnormal condition caused by a microbe, such as a bacterium, virus, or parasite, that has invaded another organism (like a human) and interfered with some aspect of its function. An infestation is similar to an infection. It refers to any abnormal condition caused by an organism larger than a microbe, such as an insect, louse, or worm.
• The phrase "infectious diseases" is used to refer to both infections and infestations, regardless of the severity of the condition. An infection beneath a fingernail and a serious case of hepatitis * C both are considered infectious diseases.
• The hallmark of many infections is inflammation, which is largely a result of the immune system's * response to infection, irritation, or injury.
• The characteristics of inflammation include
• redness,
• warmth,
• swelling, and
• pain.
• Important players in the immune reaction are the white blood cells.
• In response to germs, white cells race to the area of infection to fight off the invader; the word "pus" refers to a thick fluid produced by the body in response to an infection that contains these white cells along with other substances resulting from the reaction.
• Chronic infections are those infections that last a longer time—weeks, months, or even years.
• A chronic infection can develop from an acute infection that does not clear up.
• Some chronic infections continue to have signs and symptoms, causing discomfort and interfering with life for long periods of time.
• Other chronic infections may have few or no signs. People who have a chronic infection may not be aware that they still have an active infection and may still be capable of passing the infectious microbe to others.
• One example is hepatitis C, a disease that can have few symptoms but also can cause cirrhosis, chronic liver disease, or liver cancer. People with hepatitis C may not be aware that they have it without taking an antibody * test that
AS Level Biology - 10/11) Infectious Diseases and ImmunityArm Punyathorn
Finally, to end the AS level syllabus - learn about the diseases that pose threats not only to ourselves but to the community as a whole for being contagious. Also learn about how our body organizes a military section to protect us - discover how the army can be come turncoat and how espionage and information collection can be helpful in secondary responses.
DR.MRS.BHAVANI.A
NURSING TUTOR, ANNAMALAI UNIVERSITY
INFECTION CONTROL - CHAIN OF INFECTION
INTRODUCTION
A major concern for health practioners is the danger of spreading microorganisms from person to person and from place to place. Microorganisms are naturally present in almost all environments. Some are beneficial; some are not. Some are harmless to most people, and others are harmful to many people. Still others are harmless except in certain circumstances. Prevention of infection is a major focus for nurses. As primary caregivers, nurses are involved in identifying, preventing, controlling, and teaching the patient about infection.
INFECTION
• The word "infection" means something different from "disease," although the two terms sometimes are confused. Disease is a general word that describes any abnormality of the human condition or something that interferes with the normal, healthy functioning of the body.
• Diseases include infections and infestations, among others. Infection is a term that refers specifically to any abnormal condition caused by a microbe, such as a bacterium, virus, or parasite, that has invaded another organism (like a human) and interfered with some aspect of its function. An infestation is similar to an infection. It refers to any abnormal condition caused by an organism larger than a microbe, such as an insect, louse, or worm.
• The phrase "infectious diseases" is used to refer to both infections and infestations, regardless of the severity of the condition. An infection beneath a fingernail and a serious case of hepatitis * C both are considered infectious diseases.
• The hallmark of many infections is inflammation, which is largely a result of the immune system's * response to infection, irritation, or injury.
• The characteristics of inflammation include
• redness,
• warmth,
• swelling, and
• pain.
• Important players in the immune reaction are the white blood cells.
• In response to germs, white cells race to the area of infection to fight off the invader; the word "pus" refers to a thick fluid produced by the body in response to an infection that contains these white cells along with other substances resulting from the reaction.
• Chronic infections are those infections that last a longer time—weeks, months, or even years.
• A chronic infection can develop from an acute infection that does not clear up.
• Some chronic infections continue to have signs and symptoms, causing discomfort and interfering with life for long periods of time.
• Other chronic infections may have few or no signs. People who have a chronic infection may not be aware that they still have an active infection and may still be capable of passing the infectious microbe to others.
• One example is hepatitis C, a disease that can have few symptoms but also can cause cirrhosis, chronic liver disease, or liver cancer. People with hepatitis C may not be aware that they have it without taking an antibody * test that
AS Level Biology - 10/11) Infectious Diseases and ImmunityArm Punyathorn
Finally, to end the AS level syllabus - learn about the diseases that pose threats not only to ourselves but to the community as a whole for being contagious. Also learn about how our body organizes a military section to protect us - discover how the army can be come turncoat and how espionage and information collection can be helpful in secondary responses.
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Dear Dr. Kornbluth and Mr. Gorenberg,
The US House of Representatives is deeply concerned by ongoing and pervasive acts of antisemitic
harassment and intimidation at the Massachusetts Institute of Technology (MIT). Failing to act decisively to ensure a safe learning environment for all students would be a grave dereliction of your responsibilities as President of MIT and Chair of the MIT Corporation.
This Congress will not stand idly by and allow an environment hostile to Jewish students to persist. The House believes that your institution is in violation of Title VI of the Civil Rights Act, and the inability or
unwillingness to rectify this violation through action requires accountability.
Postsecondary education is a unique opportunity for students to learn and have their ideas and beliefs challenged. However, universities receiving hundreds of millions of federal funds annually have denied
students that opportunity and have been hijacked to become venues for the promotion of terrorism, antisemitic harassment and intimidation, unlawful encampments, and in some cases, assaults and riots.
The House of Representatives will not countenance the use of federal funds to indoctrinate students into hateful, antisemitic, anti-American supporters of terrorism. Investigations into campus antisemitism by the Committee on Education and the Workforce and the Committee on Ways and Means have been expanded into a Congress-wide probe across all relevant jurisdictions to address this national crisis. The undersigned Committees will conduct oversight into the use of federal funds at MIT and its learning environment under authorities granted to each Committee.
• The Committee on Education and the Workforce has been investigating your institution since December 7, 2023. The Committee has broad jurisdiction over postsecondary education, including its compliance with Title VI of the Civil Rights Act, campus safety concerns over disruptions to the learning environment, and the awarding of federal student aid under the Higher Education Act.
• The Committee on Oversight and Accountability is investigating the sources of funding and other support flowing to groups espousing pro-Hamas propaganda and engaged in antisemitic harassment and intimidation of students. The Committee on Oversight and Accountability is the principal oversight committee of the US House of Representatives and has broad authority to investigate “any matter” at “any time” under House Rule X.
• The Committee on Ways and Means has been investigating several universities since November 15, 2023, when the Committee held a hearing entitled From Ivory Towers to Dark Corners: Investigating the Nexus Between Antisemitism, Tax-Exempt Universities, and Terror Financing. The Committee followed the hearing with letters to those institutions on January 10, 202
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Read| The latest issue of The Challenger is here! We are thrilled to announce that our school paper has qualified for the NATIONAL SCHOOLS PRESS CONFERENCE (NSPC) 2024. Thank you for your unwavering support and trust. Dive into the stories that made us stand out!
2. Infection and Disease
A. Definitions
B. Generalized Stages of Infection
C. Virulence Factors and Toxins
3. A. Definitions
Disease and Infectious Disease
• Disease
• Any deviation from a condition of good
health and well-being
• Infectious Disease
A disease condition caused by the presence
or growth of infectious microorganisms or
parasites
4. A. Definitions
Pathogenicity and Virulence
• Pathogenicity
• The ability of a microbe to cause disease
• This term is often used to describe or compare
species
• Virulence
• The degree of pathogenicity in a microorganism
• This term is often used to describe or compare
strains within a species
5. Definitions
Acute infection vs. chronic infection
• Acute Infection
• An infection characterized by sudden onset,
rapid progression, and often with severe
symptoms
• Chronic Infection
• An infection characterized by delayed onset
and slow progression
6. Definitions
Primary infection vs. secondary infection
• Primary Infection
• An infection that develops in an otherwise
healthy individual
• Secondary Infection
• An infection that develops in an individual
who is already infected with a different
pathogen
7. Definitions
Localized infection vs. systemic infection
• Localized Infection
• An infection that is restricted to a specific
location or region within the body of the host
• Systemic Infection
• An infection that has spread to several
regions or areas in the body of the host
8. Definitions
Clinical infection vs. subclinical infection
• Clinical Infection
• An infection with obvious observable or
detectable symptoms
• Subclinical Infection
• An infection with few or no obvious
symptoms
9. Definitions
Opportunistic infection
• An infection caused by microorganisms that are
commonly found in the host’s environment.
This term is often used to refer to infections
caused by organisms in the normal flora.
10. Definitions
The suffix “-emia”
• A suffix meaning “presence of an infectious agent”
• Bacteremia = Presence of infectious bacteria
• Viremia = Presence of infectious virus
• Fungemia = Presence of infectious fungus
• Septicemia = Presence of an infectious agent in
the bloodstream
11. Definitions
The suffix “-itis”
• A suffix meaning “inflammation of”
• Examples:
–Pharyngitis = Inflammation of the pharynx
–Endocarditis = Inflammation of the heart
chambers
–Gastroenteritis = Inflammation of the
gastointestinal tract
12. Definitions
Epidemiology
• The study of the transmission of disease
Communicable Disease
• A disease that can be transmitted from one
individual to another
Noncommunicable Disease
• A disease that is not transmitted from one
individual to another
13. Definitions
Endemic Disease
• A disease condition that is normally found in a
certain percentage of a population
Epidemic Disease
• A disease condition present in a greater than
usual percentage of a specific population
Pandemic Disease
• An epidemic affecting a large geographical
area; often on a global scale
14. Definitions
Reservoir of Infection
• The source of an infectious agent
Carrier
• An individual who carries an infectious agent
without manifesting symptoms, yet who can
transmit the agent to another individual
Fomites
• Any inanimate object capable of being an
intermediate in the indirect transmission of an
infectious agent
15. Definitions
• Animal Vectors
• An animal (nonhuman) that can transmit an
infectious agent to humans
• Two types: mechanical and biological
• Mechanical animal vectors: The infectious agent is
physically transmitted by the animal vector, but the agent
does not incubate or grow in the animal; e.g, the
transmission of bacteria sticking to the feet of flies
• Biological animal vectors: The infectious agent must
incubate in the animal host as part of the agent’s
developmental cycle; e.g, the transmission of malaria
by infected mosquitoes
16. Definitions
Direct Mechanisms of Disease Transmission
• Directly From Person to Person
• Examples:
Direct Skin Contact
Airborne (Aerosols)
19. Pathogenicity - ability to cause disease
Virulence - degree of pathogenicity
Many properties that determine a microbe’s
pathogenicity or virulence are unclear or
unknown
But, when a microbe overpowers the hosts
defenses, infectious disease results!
20. Molecular Determinants of Pathogenicity
Production
and delivery
of various
factors
Attachment
to host
tissues
Replication
and evasion
of immunity
Damage to
host tissues
23. 1. Mucus Membranes
A. Respiratory Tract
• microbes inhaled into
mouth or nose in
droplets of moisture or
dust particles
• Easiest and most
frequently traveled
portal of entry
24. Common Diseases contracted via
the Respiratory Tract
Common cold
Flu
Tuberculosis
Whooping cough
Pneumonia
Measles
Diphtheria
25. Mucus Membranes
B. Gastrointestinal Tract
• microbes gain entrance thru
contaminated food & water
or fingers & hands
• most microbes that enter the
G.I. Tract are destroyed by
HCL & enzymes of stomach
or bile & enzymes of small
intestine
27. Fecal - Oral Diseases
These pathogens enter the G.I. Tract at one
end and exit at the other end.
Spread by contaminated hands & fingers or
contaminated food & water
Poor personal hygiene.
28. Mucus Membranes of the Genitourinary System - STD’s
Gonorrhea
Neisseria gonorrhoeae
Syphilis
Treponema pallidum
Chlamydia
Chlamydia trachomatis
HIV
Herpes Simplex II
29. Mucus Membranes
D. Conjunctiva –
• mucus membranes that
cover the eyeball and lines
the eyelid
Trachoma
• Chlamydia trachomatis
30. 2nd Portal of Entry: Skin
Skin - the largest organ of the body. When
unbroken is an effective barrier for most
microorganisms.
Some microbes can gain entrance through
openings in the skin: hair follicles and sweat
glands, wound …etc
31.
32. 3rd Portal of Entry: Parentarel
Microorganisms are deposited into the
tissues below the skin or mucus membranes
Punctures and scratches
injections
bites
surgery
33. Preferred Portal of Entry
Just because a pathogen enters your body it
does not mean it’s going to cause disease.
pathogens - preferred portal of entry
34. Preferred Portal of Entry
Streptococcus pneumoniae
• if inhaled can cause pneumonia
• if enters the G.I. Tract, no disease
Salmonella typhi
• if enters the G.I. Tract can cause Typhoid Fever
• if on skin, no disease
35. Number of Invading Microbes
LD50 - Lethal Dose of a microbes toxin that
will kill 50% of experimentally inoculated
test animal
ID50 - infectious dose required to cause
disease in 50% of inoculated test animals
• Example: ID50 for Vibrio cholerea 108 cells
(100,000,000 cells)
• ID50 for Inhalation Anthrax - 5,000 to 10,000
spores ????
36. How do Bacterial Pathogens
penetrate Host Defenses?
1. Adherence - almost
all pathogens have a
means to attach to host
tissue
Binding Sites
adhesins
ligands
37. Some cells use fimbriae to
adhere.
Fimbriae can play
a role in tissue
tropism. Example -
attachment of Candida
to vaginal epithelial
cells
38. Adhesins and ligands are usually
on Fimbriae
Neisseria gonorrhoeae
ETEC
(Entertoxigenic E. coli)
Bordetello pertussis
39. Bacteria typically employ proteins known as Adhesins to
attach to host tissues, which usually are located on ends of
fimbriae.
Alternatively, adhesins can consist of glycocalyx.
42. Cell Wall Components
M protein: Found on cell surface and
fimbriae of Streptococcus pyogenes.
Mediates attachment and helps resist
phagocytosis. M-protein is heat and
acid resistant
Waxes [ Mycolic Acid]: In cell wall
of Mycobacterium tuberculosis helps
resist digestion after phagocytosis and
can multiply inside WBC.
43. 3. Enzymes
Many pathogens secrete enzymes that
contribute to their pathogenicity
45. A. Leukocidins
Attack certain types of WBC’s
1. Kills WBC’s which prevents phagocytosis
2. Releases & ruptures lysosomes
• lysosomes - contain powerful hydrolytic
enzymes which then cause more tissue damage
47. 1. Alpha (α) Hemolytic Streptococci
- secrete hemolysins that cause the incomplete
lysis or RBC’s
Incomplete
Lysis of RBC
48. 2. Beta (β) Hemolytic Streptococci
- secrete hemolysins that cause the complete lysis
of RBC’s
Complete
Lysis of RBC
49. 3. Gamma (γ) Hemolytic Streptococci
- do not secrete any hemolysins
50. C. Coagulase - cause blood to
coagulate
Blood clots protect bacteria from
phagocytosis from WBC’s and other host
defenses
Staphylococcus aureus - are often coagulase
positive
Fibrinogen ----------------- Fibrin ( Clot)
51. D. Kinases - enzymes that dissolve
blood clots
1. Streptokinase - Streptococci
2. Staphylokinase - Staphylococci
Helps to spread bacteria - Bacteremia
Streptokinase - used to dissolve blood clots in the
Heart (Heart Attacks due to obstructed coronary blood
vessels)
52. E. Hyaluronidase
Breaks down Hyaluronic acid (found in
connective tissues)
“Spreading Factor”
mixed with a drug to help spread the drug
through a body tissue
Streptococci, Staphylococci, Clostridia and
pneumococci.
53. F. Collagenase
Breaks down collagen (found in many connective
tissues)
Clostridium perfringens - Gas Gangrene
• uses this to spread through muscle tissue
54. Severe gangrene caused by Clostridium perfringens.
Source: Tropical Medicine and Parasitology, 1997
Tissue Damage Caused by Microbial
Enzymes of Clostridium perfringens
55. G. Necrotizing Factor
- causes death (necrosis) to tissue cells
“Flesh Eating Bacteria”
Necrotizing fasciitis
56. H. Lecithinase
Destroys lecithin ( phosphatidylcholine)
component of plasma membrane.
Allowing pathogen to spread
Clostridium perfringens
57. Summary of How Bacterial
Pathogens Penetrate Host Defenses
1. Adherence
2. Capsule
3. Enzymes
• A. leukocidins B. Hemolysins
• C. Coagulase D. Kinases
• E. Hyaluronidase F. Collagenase
• G. Necrotizing Factor H. Lecithinase
58. 4. Toxins
Poisonous substances produced by
microorganisms
toxins - primary factor - pathogenicity
220 known bacterial toxins
• 40% cause disease by damaging the Eukaryotic
cell membrane
Toxemia
• Toxins in the bloodstream
• Toxigenicity: Capacity of microorganisms to
produce toxins.
59. Two Types of Toxins
1. Exotoxins
• secreted outside the bacterial cell
2. Endotoxins
• part of the outer cell wall of Gram (-) bacteria.
??
62. I- Exotoxins
Mostly seen in Gram (+) Bacteria
Most gene that code for exotoxins are
located on plasmids or phages
63. Three Types of Exotoxins
1. Cytotoxins
• kill cells e.g. Diphtheria toxin
2. Neurotoxins
• interfere with normal nerve impulses.e.g.
Botulinum Toxin
3. Enterotoxins
• effect cells lining the G.I. Tract. e.g. Cholera
toxin or choleragen.
64. Response to Toxins
If exposed to exotoxins: antibodies against the
toxin (antitoxins)
Exotoxins inactivated ( heat, formalin or phenol)
no longer cause disease, but stimulate the
production of antitoxin
• altered exotoxins - Toxoids
Toxoids - modified toxin by heat, chemical,
radiation, that have lost their toxicity. Injected to
stimulate the production of antitoxins and provide
immunity.
67. Most genes that code for exotoxins - plasmids
or phages
Lysogenic convergence
Diphtheria
Cytotoxin inhibits
protein synthesis -
resulting in cell death
Pseudomembrane
• fibrin, dead tissue,
bacterial cells
68. Lysogenic Convergence
Scarlet Fever
Streptococcus pyogenes
• lysogenic convergence
cytotoxin - damages blood capillaries and results in a
skin rash
• Strep Thoat with a rash
69. Rash of Scarlet Fever Caused by Erythrogenic
Toxins of Streptococcus pyogenes
71. Diseases caused by Neurotoxins
Botulism
• Clostridium botulinum
• Gram (+), anaerobic, spore-forming rod, found in
soil
• works at the neuromuscular junction
• prevents impulse from nerve cell to muscle cell
• results in muscle paralysis
72. Tetanus (Lock Jaw)
Clostridium tetani
Gram (+), spore-forming, anaerobic rod
neurotoxin acts on nerves, resulting in the
inhibition of muscle relaxation
tetanospasmin - “spasms” or “Lock Jaw”
73. Neonatal Tetanus (Wrinkled brow and risus sardonicus)
Source: Color Guide to Infectious Diseases, 1992
Muscle Spasms of Tetanus are Caused by
Neurotoxin of Clostridium tetani
75. Cholera toxin
Converts ATP into cAMP
causes cells to excrete Cl- ions and inhibits
absorption of Na+ ions
Electrolyte imbalance
H2O leaves by osmosis
H2O Loss (Diarrhea)
Two polypeptides: A (active) and B (binding).
The A subunit of enterotoxin causes epithelial
cells to discharge large amounts of fluids and
electrolytes.
76. Severe cases, 12 - 20 liters of liquid lost
in a day
Untreated cases - Mortality Rate about 50%
Mortality may be reduced to about 1%
• administering fluids and electrolytes
77. Rice-water stool of cholera. The A subunit of enterotoxin causes
epithelial cells to discharge large amounts of fluids and electrolytes.
Source: Tropical Medicine and Parasitology, 1995
Vibrio Enterotoxin Causes Profuse Watery Diarrhea
78. EHEC (Enterohemorrhagic E. coli)
E. coli (0157:H7)
enterotoxin causes a hemolytic inflammation
of the intestines
results in bloody diarrhea
• Toxin
• alters the 60S ribosomal subunit
• inhibits Protein Synthesis
• Results in cell death
• lining of intestine is “shed”
• Bloody Diarrhea (Dysentary)
80. II- Endotoxins
• Part of outer membrane surrounding gram-negative
bacteria.
• Endotoxin is lipid portion of lipopolysaccharides (LPS),
called lipid A.
• Effect exerted when gram-negative cells die and cell
walls undergo lysis, liberating endotoxin.
• All produce the same signs and symptoms:
• Chills, fever, weakness, general aches, blood clotting
and tissue death, shock, and even death. Can also
induce miscarriage.
• Fever: Pyrogenic response is caused by endotoxins.
83. Endotoxins (Continued)
• Endotoxins do not promote the formation of
effective antibodies.
• Organisms that produce endotoxins include:
• Salmonella typhi
• Proteus spp.
• Pseudomonas spp.
• Neisseria spp.
• Medical equipment that has been sterilized may
still contain endotoxins.
• Limulus amoebocyte assay (LAL) is a test used to
detect tiny amounts of endotoxin.
84. Events leading to fever:
• Gram-negative bacteria are digested by
phagocytes.
• LPS is released by digestion in vacuoles, causing
macrophages to release interleukin-1 (IL-1).
• IL-1 is carried via blood to hypothalamus, which
controls body temperature.
• IL-1 induces hypothalamus to release
prostaglandins, which reset the body’s
thermostat to higher temperature.
86. III. B. The Normal Flora of
Humans
Types of Symbiosis
• Mutualism
• A symbiotic relationship in which both
species benefit
• Commensalism
• A symbiotic relationship in which one
species benefits, and the other species is
neither helped nor harmed
87. III. B. The Normal Flora of
Humans
Types of Symbiosis (cont.)
• Parasitism
• A symbiotic relationship in which one
species benefits, and the other species is
harmed
• Generally, the species that benefits (the
parasite) is much smaller than the species
that is harmed (the host)
88. III. B. The Normal Flora of
Humans
Normal flora is present in
• skin
• upper respiratory tract
• oral cavity
• intestine, especially large intestine
• vaginal tract
Very little normal flora in eyes & stomach
89. III. B. The Normal Flora of
Humans
Notably absent in most all internal organs
• Absent in:
• lower respiratory tract
• muscle tissue
• blood & tissue fluid
• cerebrospinal fluid
• peritoneum
• pericardium
• meninges
90. III. B. The Normal Flora of
Humans
Benefits of the normal flora
• Nutrient production/processing
eg Vitamin K production by E. coli
• Competition with pathogenic microbes
• Normal development of the immune system
Normal flora and opportunistic infections
91. III. C. Generalized Stages of
Infection
1. Entry of Pathogen
• Portal of Entry
2. Colonization
• Usually at the site of entry
3. Incubation Period
• Asymptomatic period
• Between the initial contact with the microbe
and the appearance of the first symptoms
92. III. C. Generalized Stages of
Infection
4. Prodromal Symptoms
• Initial Symptoms
5. Invasive period
• Increasing Severity of Symptoms
• Fever
• Inflammation and Swelling
• Tissue Damage
• Infection May Spread to Other Sites
93. III. C. Generalized Stages of
Infection
6. Decline of Infection
5. Convalescence
94. Course of Infectious Disease
Incubation period is
the interval between
exposure and
illness onset.
Convalescence is
a time of
recuperation and
recovery from
illness.
Depending on various
factors an individual may
still be infectious during
either incubation or
convalescence.