Staphylococcus is a genus of gram-positive cocci that commonly causes infections in humans. Staphylococcus aureus is one of the most important pathogenic species, able to produce several toxins and enzymes that contribute to its virulence. These include hemolysins, leukocidins, enterotoxins, toxic shock syndrome toxin, and exfoliative toxins. S. aureus can cause a variety of infections through cutaneous, respiratory, or deep tissue routes. Laboratory identification involves gram stain morphology, culture characteristics such as catalase and coagulase production, and biochemical testing. Methicillin-resistant S. aureus is an important antibiotic resistant variant.

1. Staphylococcus
Dr. Kanwal Deep Singh Lyall
M.D. Microbiology

2. • Staphyle = Bunch of grapes
• Kokos = berry
• GPC in cluseter
• Common cause of suppuration
• Sir Alexander Ogston (1880) – Scottish
surgeon established role in pus formation
• Rosenbach – S. aureus, S. albus
• Passet – S. citrus

3. Staphylococcus
Coagulase
Positive Negative
S. Aureus CoNs
S. Epidermidis
S. Hemolyticus
S. Saprophyticus
S. Intermedius

4. S. Aureus
• GPC in clusters , 1µm , non-motiles, non-
sporing
• Divide in 3 perpendicluar planes – daughter
cells remain in close proximity
• Pigment : golden yellow, non-diffuseble,
carotenoid, best seen at 22 – 25 C, aerobic con
• ↑ed by 1% Glc. Monoacetate, milk
• Grows on BA, MA, NA, MSA (selective)

5. Resistance
• Hardy organisms
• Survives in dried pus x 2 – 3 mnths
• Killed @ 62 C x 30 M
• Tolerates 10% NaCl
• Crystal violet (1:500000)
• Brilliant green (1:10 million)
Lethal

6. Antigenic structure (CPTP)
• Capsule: polysaccharide – virulence
• Peptidoglycan: rigidity, complement
activation, cytokine production
• Teichoic acid: major Ag, adhesions & inhib of
opsonisation
• Protein A: chemotactic, antiphagocytic, anti-
complementary, Cowan – 1 strain, binds IgG,
Used for coaglutination

7. Toxins & Enzymes
• Toxins (HLETEx)
• Hemolysins
• Leucocidens
• Enterotoxins
• TSST
• Exfloiative toxin
• Coagulase
• Clumping factor
• DNAse
• Phosphatase

8. Toxins
• Hemolysins – alpha, beta, gamma, delta
– Alpha lysin – in aerobic cond., protein, inactivates @
60 C, Reactivates @ 80 - 100 C – cytotoxic,
leucotoxic, dermonecrotic
– Beta lysin – lysis activated @ 37, evident on cooling
• Leucocidin – PVL, slow & fast components – damages
PMNs & Macrophages
• Enyterotoxins – A(m/c) BC1,2,3,DEH (8) – food
poisoning, nausea, vomiting, diarrhea with 6 – 8 hrs ,
resist boiling x 30 m, active in minute quantities,
autonomic nervous system

10. • TSST – t , BP, vomitings, diarhoea,, rash,
deaquamation, hyperemia, tampoon users
• Exfoliative toxin: SSSS, Rieter’s disases
– Toxin A : heat stable, chromosome coded
– Toxin B: heat labile, plasmid coded

11. Coagulase
• 8 types (A-H)
• clots human/rabbit
plasma
• Secrerated free
• Heat labile
• Requires CRF
• Dosent clot GP plasma
• Fibrinogen fibrin
• Tube test
• Requires incubation
Clumping factor
• One type
• Clumping of cocci
• Bound to CW
• Heat stable
• Precipitation of fibrin on
cell surface
• Slide test
• Immediate results

12. Pathogenesis
• Cutaneous infections
• Pyogenic infections
• Respiratory infections
• Deep seated infections
• Food poisoning
• Nosocomial infections
• Exfoliative infections
• TSST
• SSSS

13. Lab diagnosis
Sample
Gram stain Culture – BA/GB/BB/MSA
BACTEC
37 C x 18 – 24 hrs
Colonies
GS & Biochemical reactions
Phage typing AST

14. S. aureus S. epidermidis

15. Biochemical reactions
• Catalase + , coagulase +, ferments mannitol,
liquifies gelatin, produces phosphatase,DNAse
• NA + Phen. Pthal. Diphos. Free
phosphatase ammonia vapours Pink
• Urease +, Indole production – ve , MR,VP +
• Nitrate +ve

17. MRSA
• Penicillinase – plasmid coded
• PBP2 – Chromosome coded (mecA gene)
• Resistant to all beta lactams, beta lactam +
beta latamase inhb., monobactams

18. CoNS
• S. epidermidis - Opportunistic infections
• S. saprophyticus – UTI in sexually active females,
resistant to Novobiocin (5µg,< 12mm)
• Micrococci:
 Modified oxidase positive
 In Hugh leefson test – oxidative
 Tetrads
 Larger ( > 1 mm)
 White , small colonies