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MICROBIAL MECHANISMS OF
PATHOGENECITY AND PRINCIPILES OF
DISEASE AND EPIDEMIOLOGY
MICROBIAL MECHANISMS OF PATHOGENECITY
 Pathogenecity
 Virulence
PORTALS OF ENTRY
1
...
Skin
3
...
Respiratory Tract
2
...
Skin
4
...
Genitourinary Tract
ADEHERENCE
- Adhesins/Ligands binds to receptors on host
cells:
 Glycocalyx – Streptococcus mutans
 Fimbriae – Escherichia coli
 M protein – Streptococcus pyogenes
 Opa protein – Neisseria gonorrhea
 Tapered end – Treponema pallidum
Capsules and organs of locomotion also contribute to
microbial pathogenicity
...
TYPE I TOXINS
- Cause intense immune response due to release
of cytokines from host cells
- SUPERANTIGENS
2
...
TYPE III TOXINS
- With active and binding components
- Alters cell function by inhibiting protein
synthesis
- AB toxins (cholera toxin, diphtheria toxin)
HOW PROSTAGLANDINS ARE PRODUCED
1
...
The bacterium is degraded in a vacuole,
releasing endotoxins that incase the
macrophage to produce Interleukin 1 (IL-1)
3
...

4
...

PROSTAGLANDINS
- Causes fever

SOURCE
METABOLIC
PRODUCT
CHEMISTRY
FEVER
NEUTRALIZED
BY ANTITOXIN

ENDOTOXINS
Gram Present in LPS of
outer membrane
Lipis
Yes
No

EXOTOXINS
Gram +
By-products of
growing cell
Protein
No
Yes

PRINCIPLES OF DISEASE
PATHOLOGY
- Study of disease
ETIOLOGY
- Study of cause of disease
PATHOGENESIS
- Development of disease
INFECTION
- Colonization of bacteria of body
DISEASE
- An abnormal state in which the body is not
normally functioning
SYMPTOMS
- Change in body function felt by patient
SIGN
-

A change that can be measured or observed as
a result of a disease

SYNDROME
- Group of signs that accompany a disease

4
...
SEPTICEMIA
- Bacterial growth in blood
6
...
PRIMARY INFECTION
- Acute infection that causes the initial illness
8
...
SUBCLINICAL DSE
- No noticeable S/S
SEVERITY OR DURATION OF DISEASE
1
...
CHRONIC DISEASE
- Disease develops slowly
3
...
NONCOMMUNICABLE
- A disease that is not transmitted from one host
to another
3
...
LOCAL INFECTION
- Pathogens limited to an area of the body

4
...
(Sickness/Illness rate)



Prevalence- is the number of cases of disease in
existence at any given time in that population



CLASSIFYING INFECTIOUS DISEASES
1
...

(death rate)



Sporadic- a disease that occurs occasionally in a
community or population of a particular
geographic area
...


2
...
FOCAL INFECTION
- Systemic infection that began as a local
infection



Epidemic- a disease that attacks a larger
number of persons in a community within a
relatively short period of time
...




Zoonotic- Infectious diseases that humans
acquire from animal sources
...
CONTACT
 Direct: close association with inspected host
 Indirect: spread by fomites
 Droplet: via airborne droplets
B
...
experiences the
typical symptoms associated with the particular
disease
...
VECTORS – arthropods (fleas, ticks, mosquitos)
 Mechanical: arthropod carries pathogen on feet
 Biological: pathogen reproduces in vector

NORMAL MICROBIOTA
- Bacteria was once classified as plants
MICROBIOTA
1
...
NORMAL
3
...
Commensalism
2
...
Mutualism
BENEFICIAL FACTORS OF THE NORMAL MICROBIOTA
- Prevent growth of pathogens by occupying
niches that pathogens might occupy
- Produce growth factors such as folic acid
- Probiotics
PROBIOTICS
- Live microbes applied/ingested into the body
MICROBIAL ANTAGONISM
- Normal microbiota preventing pathogens from
causing disease

GRAM POSITIVE COCCI
Staphylococcus and Streptococcus

STAPHYLOCOCCI
FAMILY MICROCOCCUS
1
...
Micrococcus – free living saprophyte
3
...
Staphylococcus
and mammals

ENZYMES
3 SPECIES OF CLINICAL IMPORTANCE:
1
...
Staphylococcus epidermidis
3
...
COAGULASE
- Binds to prothrombin causing fibrin
polymerization
- Prevents opsonization and phagocytosis

GENERAL CHARACTERISTICS
 Most important genus in the family
Micrococcaceae
 Gram + spherical cells in grape-like clusters
 Non motile, non-encapsulated, non
sporeforming
 Aerobic or microphilic
 Strongly catalase (+) GAS Effervescence
 Pyogenic (pus forming)

2
...
PEPTIDOGLYCAN
- Elicits production of IL-1 and opsonic abs by
monocytes
- Chemoattractant for PMNs
- Have endotoxin-like activity
- Activates complement
- Have endotoxin-like activit
1
...
CLUMPING FACTOR
- Binds to fibrinogen and fibrin causing bacterial
aggregation
3
...

-

STAPHYLOKINASE
Fibrinolysin
Dissolves fibrin clots
Responsible for spread of infection

4
...
HYALURONIDASE
- Hydrolyzes hyaluronic acid
6
...
HEMOLYSIN
- A-exotoxin, cytolytic toxin
- g = Panton Valentine Leukocidin (lyse
neutrophils/macrophage)
2
...
ENTEROTOXIN
- Heat-labile, resistant to GIT enzymes

4
...
TOXIC SHOCK SYNDROME TOXIN-1
- Prototype superAG
- TSS: fever, shock, desquamative rash,
multisystem involvement
- Enterotoxin F
MODES OF TRANSMISSION
1
...
INGESTION OF CONTAMINATED FOOD
- Food poisoning
3
...
PHENYLETHYL ALCHOHOL
- Inhibits Gram neg
2
...
Local Abscesses
2
...
Disease caused by toxin elaboration
LOCAL ABSCESSES
1
...
Furuncles
3
...
Osteomyelitis
2
...
Meningitis
4
...
Endocarditis
6
...
Skin infections (impetigo, pyoderma)

STREPTOCOCCI
EXOTOXIN ELABORATION
1
...
aureus (on food)
 Toxin ingested
 Interacts with mucosa
 Vomiting
 Diarrhea
2
...
aureus (on tampons)
 TSST-1
 Enters the bloodstream
 Fever
 Rash
 Hypotension
3
...
Streptococcus
- Major cause of human infection
2
...

4
...

6
...
Gemella
- Rare isolate of upper Respiratory tract infection

BERGEY’S/ACADEMIC CLASSIFICATION
(THERMAL REQUIREMENT)

GROUP CHARACTERISTICS
 Gram-positive cocci in chains
 Catalase (-)
 Nutritionally fastidious
 Hemolytic a-, B-, or none
 Some are encapsulated
 Facultative anaerobes
 Requires enriched medium and 10% CO2

PYOGENIC
STREPTOCOCCI

CLINICALLY SIGNIFICANT PATHOGENS
 Group A – Streptococcus pyogenes
 Group B – Streptococcus pneumoniae
 Group D
 Streptococcus pneumoniae
 Viridans Group

ENTEROCOCCUS Grows at 45° and
GROUP
10°C
LACTIC GROUP
Grows at 10°C

CLASSIFICATION OF STREPTOCOCCI
1
...
BERGEYS’S/ACADEMIC CLASSIFICATION
- Based on the physiologic divisions of
Streptococcus or thermal requirement
3
...
pneumoniae
S
...
pyogenes
S
...
faecalis

VIRIDANS
STREPTOCOCCI

Neither 45°C nor
10°C
Produce pus
Mostly B-hemolytic
Grows at 45°C
Normal mouth flora

S
...
salivarius
S
...
mitis
S
...

sanguinosus
S
...
cremoris
S

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