pathogenicity of stap

1. STAPHYLOCOCCUS

2. Staphylococci are :
-Gram positive cocci,
-Occur in grape like clusters,
-They are non motile and non sporing.
-A few strains possess capsules
-Produce pigments

3. Cultural Characteristics:
i) On nutrient agar- The colonies are large,
circular,
convex, smooth, shiny, opaque . Most strains
produce golden yellow pigments.

4. ii) On MacConkey’s agar- The colonies are small
& pink in colour.
iii) On blood agar- Most strains produce β-
haemolytic colonies.

5. CLASSIFICATION:
A) Based on coagulase production:
1. Coagulase positive: Eg- S. aureus
2. Coagulase negative: Eg- S. epidermidis
S. saprophyticus
B) Based on pathogenicity:
1. Common pathogen: Eg- S. aureus
2. Opportunistic pathogens:
Eg- S. epidermidis ,S. saprophyticus
3. Non pathogen: Eg- S. homonis

6. CULTURE:
Media used :-
i) Non selective media: Nutrient agar,
Blood agar,
MacConkey’s agar.
ii) Selective media: Salt-milk agar,

7. Biochemical reactions:
1) Catalase test- Positive.

8. 2) Coagulase test-
i) Slide coagulase test- Positive.
ii) Tube coagulase test- Positive.
SLIDE COAGULASE TEST TUBE COAGULASE TEST

9. 3) Reduces nitrate to nitrite.
4) Ferments mannitol anaerobically with acid
only.
5) Urea hydrolysis test- Positive.
6) Gelatin liquefaction test- Positive.
7) Produces Lipase.
8) Produces Phosphatase.
9) Produces nuclease.

10. PATHOGENICITY:
Source of infection:
A) Exogenous: patients or carriers
B) Endogenous: From colonized site
Mode of transmission:
A) Contact: direct or indirect( through fomites)
B) Inhalation of air borne droplets

11. Virulence factors:
These include
A) Cell associated factors
B) Extracellular factors

12. A) CELL ASSOCIATED FACTORS:
a) Cell associated polymers
b) Cell surface proteins
a) CELL ASSOCIATED POLYMERS
1. Cell wall polysaccharide
2. Teichoic acid
3. Capsular polysaccharide
b) CELL SURFACE PROTEINS:
1. Protein A
2. Clumping factor (bound coagulase)

13. Structure of Staphylococcal cell wall

14. B) EXTRACELLULAR FACTORS
a) Enzymes
b) Toxins

15. a) Enzymes:
1. Free coagulase
2. Catalase
3. Lipase
4. Hyaluronidase
5. DNAase
6. Thermonuclease
7. Staphylokinase (Fibrinolysin)
8. Phosphatase

16. b) Toxins:
1. Cytolytic toxins
i) Haemolysins
Alpha haemolysin
Beta haemolysin
Gamma haemolysin
Delta haemolysin
ii) Leucocidin (Panton-Valentine toxin)
2. Enterotoxin
3. Toxic shock syndrome toxin (TSST)
4. . Exfoliative (epidermolytic toxin)

17. Disease:
Diseases produced by Staphylococcus aureus
is studied under 2 groups:
A) Infections
B) Intoxications

18. A) INFECTIONS:
Mechanism of pathogenesis:
Cocci gain access to damaged skin, mucosal or
tissue site
Colonize by adhering to cells or extracellular
matrix
Evade the host defense mechanisms and
multiply
Cause tissue damage

19. Common Staphylococcal infections are:
1) Skin and soft tissue: Folliculitis, furuncle (boil),
carbuncle, styes, abscess, wound infections,
impetigo, and less often cellulitis.
Folliculitis
Folliculitis

20. Furuncle (boil)
Carbuncle

21. Styes Abscess

22. Impetigo Paronychia
Cellulitis
Mal_Perforans_Infected_Callous-001_002
Wound infection

23. 2) Musculoskeletal: Osteomyelitis, arthritis.
3) Respiratory: Tonsillitis, pharyngitis, sinusitis,
otitis, bronchopneumonia, lung abscess, rarely
pneumonia.

24. 4) Central nervous system: Abscess, meningitis,.
5) Endovascular: Bacteremia, septicemia, pyemia,
endocarditis,
6) Urinary: Urinary tract infection.

25. B) INTOXICATIOINS:
The disease is caused by the bacterial exotoxins,
which are produced either in the infected host
or preformed in vitro.
There are 3 types-
Food poisoning
Toxic shock syndrome
Staphylococcal scalded skin syndrome

26. 1) Food poisoning:

Enterotoxin is responsible for manifestations
of staphylococcal food poisoning.

Eight types of enterotoxin are currently
known, named A, B, C1-3, D, E, and H.

It usually occurs when preformed toxin is
ingested with contaminated food.

The toxin acts directly on the autonomic
nervous system to cause the illness, rather
than gut mucosa.

27. 
The common food items responsible are - milk
and milk products, meat, fish and ice cream.

Source of infection- food handler who is a
carrier.

Incubation period- 2 to 6 hours.

Clinical symptoms- nausea, vomiting and
diarrhoea.

The illness is usually self limited, with recovery in
a day or so.

28. 2) Staphylococcal Toxic shock syndrome (STSS):

STSS is associated with infection of mucosal or
sequestered sites by TSST( formerly known as
enterotoxin type F) producing S.aureus.

It is fatal multisystem disease presenting with
fever, hypotension, myalgia, vomiting, diarrhoea,
mucosal hyperemia and erythematous rash which
desquamates subsequently.

30. 3) Staphylococcal scalded skin
syndrome (SSSS):

Exfoliative toxin produced by S.aureus is
responsible for this.

It is a skin disease in which outer layer of
epidermis gets separated from the underlying
tissues.

31. LAB DIAGNOSIS:
Specimens collected: Depends on the type of
infection.
Suppurative lesion- Pus,
Respiratory infection- Sputum,
Bacteremia & septicemia- Blood,
Food poisoning- Feces, vomit & the remains of
suspected food,
For the detection of carriers- Nasal swab.

32. I) Direct microscopy:
Direct microscopy with
Gram stained smear
is useful in case of
pus, where cocci in
clusters are seen.
Methods of examination:

33. c) Gram staining:
Smears are examined
from the culture plate
and reveals Gram
positive cocci(1μm in
diameter) arranged in
grape like clusters.
II) Culture:
a) Media used:
b) Cultural Characteristics:

34. d) Biochemical reactions:
III) Antibiotic sensitivity tests done as a guide to
treatment.
IV) Bacteriophage typing is done for
epidemiological purposes.
V) Serological tests are not useful.

35. TREATMENT:
Drug resistance is common.
Benzyl penicillin is the most effective antibiotic, if
the strain is sensitive.
Cloxacillin or Methicillin is used against
beta-lactamase producing strains.
Methicillin Resistant Staphylococcus aureus
(MRSA) strains have become common.
Vancomycin is used in treatment of infections
with MRSA strains.

36. EPIDEMIOLOGY:
Staphylococci are primary parasites of human
beings and animals.
Hospital infections caused by staphylococci
deserve special attention because of their
frequency & they are caused by strains resistant
to various antibiotics.
Staphylococci are the common cause of
postoperative wound infection and other hospital
cross infections.

37. PREVENTION:
Isolation & treatment of MRSA patients.
Detection of carriers among hospital staff, their
isolation & treatment.
Avoid indiscriminate usage of antibiotics.

38. Coagulase Negative Staphylococci( CoNS ):
Two species of coagulase negative
Staphylococci can cause human infections-
1. Staphylococcus epidermidis
2. Staphylococcus saprophyticus

39. S. Epidermidis:
It is a common cause of stitch abscesses.
It has predilection for growth on implanted
foreign bodies such as artificial valves, shunts,
intravascular catheters and prosthetic
appliances leading to bacteraemia.
In persons with structural abnormalities of
urinary tract, it can cause cystitis.
Endocarditis may be caused, particularly in drug
addicts.

40. S.saprophyticus:
It causes urinary tract infections, mostly in
sexually active young women.
The infection is symptomatic and may involve the
upper urinary tract also.
Men are infected much less often.
It is one of the few frequently isolated CoNS that is
resistant to Novobiocin.

41. Novobiocin sensitivity test

42. THANK YOU