Wednesday, 22 January 2014

Staph

STAPHYLOCOCCUS
G+, aerobic n faculative anaerobe
spherical cells arranged in irregular clusters.
Grows readily on mosy media.  Grow most rapidly at 37°C.
Pigment producer,  most rapidly at 20 -25°C.
▪S aureus-deep golden yellow colonies.
▪S epidermidis-grey to white.
▪No pigment production anaerobically.
MC route of infection-Skin.
MC source of infection- patients'own colonizing strains.
CULTURE
⛔ Oilpaint appearance on nutrient agar.
⛔ beta hemolysia on rabbit or sheep blood.
⛔ Mannitol fermenter anaerobically only by S aureus.
⛔ Prompt phosphatase rxn.

Most constant association of virulence is wid Coagulase.
A heat stable nuclease is characteristic of S aureus.
◼ TOXINS
➰ Beta hemolysin-  Hot cold phenomenon.
➰ delta- detergent effect.
➰ Synergohymenotropic toxin- bicomponent as Leucocidin n gamma hemolysin.
➰ Leucocidin is imp virulent factor in MRSA infection.
➰ Enterotoxin-  causes food poisoning within 6h as its preformed n acts directly on ANS(vagal stimulation ) n vomiting center.
➰ TSST 1 n Enterotoxin F =pyrogenic exotoxin C responsible for TSS.
➰ Exfoliative toxin causes SSSS has serine protease activity.
🔵 DIAGNOSIS.
🔷 Coagulase test is d standard criteria for its identification.
🔹Slide coagulase test detects clumping factor.
🔹Tube coagulase detects Coagulase.  Its more specific.
🔷 Typing is based on bacteriophage susceptibility.  Phage typing done by pattern method.
⚫ Infections caused by Staph are
➖Folliculitis
➖Faruncles (boils)
➖Carbuncle
➖Ac Paronychia
➖Bullous impetigo
➖Ecthyma
➖Cellulitis
➖Hidradenitis suppurativa
➖Sycosis barbae
➖Botryomycosis.
⚫ MC cause of
 Ac endocarditis
 Spinal epidural abscess.
 Septic intracranial thrombophlebitis
 Skin n ST infection
 Ac osteomyelitis
 Nosocomiap pneumonia
 Paronychia
 Surgical wound infection.

⚫Coagulase negative Staph are MC source of infection on any exogenous implant.
⚫ Staph epidermidis is common source of stitch abscess becos of its ability to produce slime.
⚫ Staph saprophyticus causes UTI in sexually active women.

◼ TREATMENT
✔ Penicillin sensitivity- Penicillin G
✔ Penicillinase producer but methicillin sensitivity- Nafcillin or Oxacillin
✔MRSA- Vancomycin
✔ VRSA- Quinopristin dalfopristin n linezolid.
✔ Empirical th- Vancomycin
〰 Special cases
▪TSS- Clindamycin,  reduces toxin synthesis
▪Food poisoning- No antibiotic.
⬜ Additional important points.
🔘Anterior nares is d most common site of colonisation.
🔘TSST 1 epidermolytic toxins n Enterotoxins are superantigens.
🔘Methicillin resistance located in a chromosome region called staphylococcal cassette chromosome.
🔘Tropical myositis is caused by S aureus.
🔘Pyomyositis is caused by S aureus.
🔘 Primary myositis is usually caused by Strepto.
🔘 MC mechanism of drug resistance in Staph is Transduction
🔘Staph remains on skin for long due to hyaluronidase.
🔘Selective media-  Ludlam' s or salt milk agar or Robertson cooked meat media containing 10% NaCl

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