This document discusses bacterial pathogenesis and laboratory diagnosis of bacterial infections. It describes how bacteria can cause disease by penetrating host defenses through various mechanisms, including adherence, capsules, and enzymes. It also discusses the different types of toxins bacteria can produce, including exotoxins and endotoxins. The document provides an overview of the general procedures used for collecting and processing specimens for bacterial culture and identification, including selecting appropriate specimens, avoiding contamination, and transporting samples promptly to the laboratory for microbiological examination.

1. Bacterial pathogenesis
&
Laboratory diagnosis
By Walter Waswa,BSC.MLS,
MSC.PUBLIC HEALTH
WALTER WAKHUNGU WASWA

2. Pathogenesis
• The word comes from the Greek pathos, "disease",
and genesis, creation.
• The term pathogenesis means step by step
development of a disease.
• The chain of events leading to that disease due to a
series of changes in the structure and /or function
of a cell/tissue/organ.
• Caused by a microbial, chemical or physical agent.
WALTER WAKHUNGU WASWA

3. 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, disease results!
WALTER WAKHUNGU WASWA

4. Portals of Entry
• 1. Mucus Membranes
• 2. Skin
• 3. Parenteral
WALTER WAKHUNGU WASWA

5. 1. Mucus Membranes
• A. Respiratory Tract
• Sticky mucous secretion
• Muco polysachharides
• Cough reflex
• Phagocytic cells
WALTER WAKHUNGU WASWA

6. Common Diseases contracted via the
Respiratory Tract
• Common cold
• Flu
• Tuberculosis
• Whooping cough
• Pneumonia
• Measles
• Strep Throat
• Diphtheria
WALTER WAKHUNGU WASWA

7. 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.
WALTER WAKHUNGU WASWA

8. Common diseases contracted via the G.I. Tract
• Salmonellosis
– Salmonella sp.
• Shigellosis
– Shigella sp.
• Cholera
– Vibrio cholorea
• Ulcers
– Helicobacter pylori
• Botulism
– Clostridium botulinum
WALTER WAKHUNGU WASWA

9. 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.
WALTER WAKHUNGU WASWA

10. Mucus Membranes of the Genitourinary System
Acidic urine
Vaginal secretion- Acidic due to fermentation of glycogen by
lactobacillus
Gonorrhea
Neisseria gonorrhoeae
Syphilis
Treponema pallidum
Chlamydia
Chlamydia trachomatis
HIV
Herpes Simplex II
WALTER WAKHUNGU WASWA

11. Mucus Membranes
• D. Conjunctiva –
Lacrymal secretion
• Lysozyme
• Trachoma
– Chlamydia
trachomatis
WALTER WAKHUNGU WASWA

12. 2. Skin
• Skin - the largest organ of the body.
• Sebaceous secretion-containing fatty acids
• Resident flora
• When unbroken is an effective barrier for most
microorganisms.
• Some microbes can gain entrance thru openings in
the skin: hair follicles and sweat glands
WALTER WAKHUNGU WASWA

13. 3. Parentarel
• Microorganisms are deposited into the tissues
below the skin or mucus membranes
• Punctures
• injections
• bites
• scratches
• surgery
• splitting of skin due to swelling or dryness
WALTER WAKHUNGU WASWA

14. 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
WALTER WAKHUNGU WASWA

15. How do Bacterial Pathogens
penetrate Host Defenses?
1. Adherence - almost all pathogens
have a means to attach to host tissue
Binding Sites
adhesins
ligands
WALTER WAKHUNGU WASWA

16. 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 FactorWALTER WAKHUNGU WASWA

17. Adhesins and ligands are usually on
Fimbriae
• Neisseria
gonorrhoeae
• ETEC
(Entertoxigenic E. coli)
• Bordetella pertussis
WALTER WAKHUNGU WASWA

18. 2. Capsules
• Prevent phagocytosis
• Attachment
• Streptococcus
pneumoniae
• Klebsiella pneumoniae
• Haemophilus
influenzae
• Bacillus anthracis
• Streptococcus mutans
• Yersinia pestis
K. pneumoniae WALTER WAKHUNGU WASWA

19. 3. Enzymes
• Many pathogens secrete enzymes that
contribute to their pathogenicity
WALTER WAKHUNGU WASWA

20. 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
WALTER WAKHUNGU WASWA

21. B. Hemolysins - cause the lysis of RBC’s
Streptococci
WALTER WAKHUNGU WASWA

22. 1. Alpha Hemolytic Streptococci
- secrete hemolysins that cause the
incomplete lysis or RBC’s
WALTER WAKHUNGU WASWA

23. 2. Beta Hemolytic Streptococci
- Secrete hemolysins that cause the complete lysis of RBC’s
WALTER WAKHUNGU WASWA

24. C. Coagulase - cause blood to coagulate
• Blood clots protect bacteria from phagocytosis
from WBC’s and other host defenses
• Staphylococci - are often coagulase positive
– boils
– abscesses
WALTER WAKHUNGU WASWA

25. 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)
WALTER WAKHUNGU WASWA

26. 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
WALTER WAKHUNGU WASWA

27. F. Collagenase
• Breaks down collagen (found in many connective
tissues)
• Clostridium perfringens - Gas Gangrene
– uses this to spread thru muscle tissue
WALTER WAKHUNGU WASWA

28. G. Necrotizing Factor
- Causes death (necrosis) to tissue cells
“Flesh Eating Bacteria”
WALTER WAKHUNGU WASWA

29. Bacterial 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
WALTER WAKHUNGU WASWA

30. Types of Toxins
• 1. Exotoxins
– Exotoxins are generated by the bacteria and actively
secreted
– Secreted outside the bacterial cell
• 2. Endotoxins
– Part of the outer cell wall of Gram (-) bacteria
– The body's response to endotoxin can involve severe
inflammation.
WALTER WAKHUNGU WASWA

31. Exotoxins
• Mostly seen in Gram (+) Bacteria
• Heat labile, can be inactivated by heating at 60-80
۠ C.
• Excreted [ secreted] from the microbial cells into
the surrounding ie culture media or circulatory
system
• Don’t require bacterial death or cell lysis for their
release.
WALTER WAKHUNGU WASWA

32. Types of Exotoxins
• 1. Cytotoxins
– Kill cells- shigella, vibrio
• 2. Neurotoxins
– Interfere with normal nerve impulses
– Clostridium botulinum
– Clostridium tetani
• 3. Enterotoxins
– Effect cells lining the G.I. Tract
– E. coli
– Salmonella WALTER WAKHUNGU WASWA

33. 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 - injected to stimulate the production of
antitoxins and provide immunity
WALTER WAKHUNGU WASWA

34. Endotoxins
• Part of the Gram (-) Bacterial cell wall.
• Biological activity or toxicity of endotoxin is largely
due to lipid A.
• Relatively heat stable can withstand heat over 60 ۠
C for many hours.
• Released upon cell lysis or death.
• Less potent than exotoxins, active in large doses
only.
• Pyrogenic often produce fever in hosts.
• Salmonella, Shigella, Escherichia, Neisseria.
WALTER WAKHUNGU WASWA

35. Bacteriocin
• Bacteriocins were first discovered by A. Gratia in 1925.
• He called his first discovery a colicine because it killed E.
coli.
• Bacteriocins are proteinaceous toxins produced by
bacteria to inhibit the growth of similar or closely
related bacterial strain(s).
• They are typically considered to be narrow spectrum
antibiotics, though this has been debated.
WALTER WAKHUNGU WASWA

36. • Medical significance
• Bacteriocins are of interest in medicine because
they are made by non-pathogenic bacteria that
normally colonize the human body.
• Loss of these harmless bacteria following antibiotic
use may allow opportunistic pathogenic bacteria to
invade the human body.
WALTER WAKHUNGU WASWA

37. • Manifestations of Infection: Signs and symptoms vary
according to the site and severity of infection. Diagnosis
requires a composite of information, including history,
physical examination, radiographic findings, and laboratory
data.
• Microbial Causes of Infection: Infections may be caused by
bacteria, viruses, fungi, and parasites. The pathogen may be
exogenous (acquired from environmental or animal sources or
from other persons) or endogenous (from the normal flora).
WALTER WAKHUNGU WASWA

38. Specimen Selection, Collection, and Processing
• The quantity material must be adequate
• Specimens are selected on the basis of signs and
symptoms, should be representative of the disease
process
• Contamination of the specimen must be avoided by
using only sterile equipment and aseptic
precautions
• The specimen must be taken to the laboratory and
examined promptly. Special transport media may
be helpful.
• Meaningful specimens to diagnose bacterial
infections must be secured before antimicrobial
drugs are administered.WALTER WAKHUNGU WASWA

39. Microbiologic Examination
• Culture:Isolation of infectious agents frequently requires specialized media.
Nonselective (noninhibitory) media permit the growth of many microorganisms.
Selective media contain inhibitory substances that permit the isolation of specific
types of microorganisms.
• Microbial Identification: Colony and cellular morphology may permit preliminary
identification. Growth characteristics under various conditions, utilization of
carbohydrates and other substrates, enzymatic activity, immunoassays, and genetic
probes are also used.
• Antimicrobial Susceptibility: Microorganisms, particularly bacteria, are tested in
vitro to determine whether they are susceptible to antimicrobial agents.
• Serodiagnosis:A high or rising titer of specific IgG antibodies or the presence of
specific IgM antibodies may suggest or confirm a diagnosis.
• Direct Examination and Techniques: Direct examination of specimens reveals
gross pathology. Microscopy may identify microorganisms. Immunofluorescence,
immuno-peroxidase staining, and other immunoassays may detect specific
microbial antigens. Genetic probes identify genus- or species-specific DNA or RNA
sequences.
WALTER WAKHUNGU WASWA

40. WALTER WAKHUNGU WASWA

41. General procedure for collecting and processing specimens for
aerobic and/or anaerobic bacterial culture
WALTER WAKHUNGU WASWA

42. Agglutination test in which inert particles (latex beads or heat-killed S aureus Cowan
1 strain with protein A) are coated with antibody to any of a variety of antigens and
then used to detect the antigen in specimens or in isolated bacteria.WALTER WAKHUNGU WASWA

43. The end
Questions ?
WALTER WAKHUNGU WASWA