A brief simple description about Staphylococcus, esp S. aureus

1. STAPHYLOCOCCUS

2. STAPHYLOCOCCUS
(Staphyle-bunch of grapes; kokkus- berry)
• Common cause of suppurative lesions
• Very important because it develops resistance to antibiotics in hospital

3. TWO TYPES
1. S. aureus
• pus forming & virulent
• Requires heating at 80 C for 1 hour to kill
2. S. epidermidis
• Non pathogenic & non- virulent
• Present in skin commonly

4. PATHOGENECITY
• Staphylococcus produces 2 types of diseases: Infections &
Intoxications
1. Infections – Gain access through skin, mucosa or tissue sites,
colonise, evade host defence, multiply & tissue damage.
2. Intoxication- caused by the bacterial toxins in infected host or in vitro.

5. INFECTIONS
Following are the main virulence factors of staphylococcus:
I. Cell associated polymers:
1. Peptidoglycan in cell wall gives the structure & rigidity to the
bacterial cell; releases inflammatory cytokines
2.
3.
Teichoic acid facilitates adhesion to host cell wall
Capsular polysaccharide surrounding cellwall inhibits opsonisation

6. II. Cell surface proteins
1.
Protein A – mainly chemotactic and phagocytic in nature; induces
platelet damage & hypersensitivity
2.
Clumping factor-surface protein ‘bound coagulase’ is responsible for
the ‘slide coagulase test’

7. III. Extracellular enzymes:
1.
Coagulase, an enzyme which clots ‘only’ human or rabbit plasma
2.
Lipases (Hyaluronidase & staphylokinase) infects skin and connective
tissues
3.
Nuclease, a heat stable nuclease is a characteristic feature of
staphylococcus aureus
4.
Protein receptors

8. INTOXICATION
• 1. Cytolytic toxins – 4 hemolysins & 1 leucocidin
• α- hemolysin – most important.
-Inactivated at 70 C, but reactivated at 100 C. Because, at 60-70 C, the toxin combines
with a heat labile inhibitor which is denaturated at 100 C, leaving the toxin free.
•
•
•
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β -hemolysin – haemolytic for sheep cells, not for humans or rabbits
γ -hemolysin
δ -hemolysin
Leucocidin

9. 2. Enterotoxin
•
Responsible for staphylococcal food poisoning; nausea, vomiting &
diarrhoea 2-6 hours after consuming the contaminated food.
•
•
Toxin is heat stable, resisting 100 C for 10-40 minutes
•
•
Source of infection is generally food handler (carrier)
Meat and fish or milk or milk products ‘cooked’ & left at room temperature for long
time are the common cause
Recovery in just a day or two

10. • 3. Toxic Shock syndrome Toxin (TSST):
• It is a potentially fatal multisystem disease presenting with fever,
myalgia, hypotension, vomiting, diarrhoea, mucosal hyperaemia and
erythematous rash.

11. 4. Exfoliative (epidemolytic) toxin:
• Also known as ‘exfoliatin’ responsible for ‘staphylococcal Scalded Skin
Syndrome’ (SSSS)

12. STAPHYLOCOCCAL DISEASES
- Most common of bacterial infections ranging from trivial to fatal
- Its localised, unlike streptococcal infections which spreads
1. Skin & soft tissue – folliculitis, furuncle (boils), carbuncle, abscess, wound infection
2. Musculoskeletal – osteomyelitis, arthritis, bursitis
3. Respiratory- tonsillitis, pharyngitis, sinusitis, otitis, emphyema
4. CNS- abscess, meningitis
5. Endovascular- bacteraemia, septicaemia, pyemia, endocarditis
6. Urinary- Uncommon

13. MODE OF TRANSMISSION
• Common source- Human beings
• Patients with superficial & respiratory infection spread a lot
• 10-30% of healthy adults carry it in nose
• Common in umbilical stump of new born
• Shedders in hopsitals- handkerchief, towels & bed linens
• Few bacterias called ‘hospital strains’ develop resistance easily
• Main reason for hospital acquired wound infection and other cross infections

14. • Control measures
- Isolate the infected patients
- Screen hospital staffs during outbreak
- Strict aseptic hospital theatres
Most importantly,
- Wash hands

15. LAB DIAGNOSIS
•
Wound infection
•
Nasal Swab
•
Sputum samples
•
Under microscope, shows cluster of bacteria. Not visible in sputum sample due to contamination
•
Diagnosis easier in culture, as it grows in overnight incubation.
•
If scanty numbers expected, specimen are inoculated in media like ludlam’s or salt-milk agar or Robertson’s cooked meat medium, with 10% NaCl and
coagulase test done with the staph extract.
•
Coagulase test- 2 types
•
1. Tube coagulase: 0.1 ml of agar culture of specimen + 0.5ml of human plasma in a test tube with EDTA or heparin.
- Tube is incubated in water bath for 37 C for 3-6 hours
• 2. Slide coagulase test: The isolate is emulsified in a drop of saline on a slide & a drop of human plasma is added to emulsion & mixed.
Clumping indicates it is positive