STAPHYLOCOCCI, DIAGNOSIS, PREVENTION & TREATMENT

MODE OF TRANSMISSION:
  • Person with lesions
  • Airborne droplets
  • Asymptomatic carrier
  • Cross-infection
PREVENTION:
  • Wash your hands
  • Keep wounds covered
  • Reduce tampon risks
  • Avoid sharing personal care items 
  • Cooking and storing food properly
LAB DIAGNOSIS:
  • Haematological Investigation:
  1. TLC (Total leukocyte count):
  • Normal: 4000-10000 cells/mm³
  • In case of infection: > 10000 cells/mm³
  1. DLC (Differential leukocyte count):
  • Normal neutrophil : 80%
  • In case of infection: > 80%
  1. Bacteriological Investigation:
  • Specimens:
  1. Pus: from wound or abscess or burns]
  2. Nasal Swab: from suspected carrier
  3. Food: to diagnose staphylococcal intoxication
  4. Blood: to diagnose endocarditis and bacteremia
  5. Sputum: to diagnose lower respiratory tract infection
  • Culture and isolation:
  1. Specimens are cultured on BA plate and are incubated @ 37 °C for 24 hours
  2. After incubation, BA plate is observed for significant bacterial growth (> 2mm in diameter)
  3. Then, Gram-staining is performed of the isolated organisms
  4. Then, subcultured on NA plate for further biochemical tests
  • Tube coagulase test:
  1. Mix 0.5ml of human plasma with 0.1ml of an overnight broth culture of S.aures
  2. Incubate the mix in a water bath @ 37°C for 3-6 hours
  3. Result: plasma clots and doesn’t flow if the tube is inverted
MRSA:
  • Most strains of S.aureus, even those acquired in community, are penicillin resistantv Resistance is attributable to beta-lactamase production due to genes located on extrachromosomal plasmids.
  1. Some are resistant to the newer beta-lactamase resistant semisynthetic penicillins, such as methicillin, oxacillin, nafcillin.
  • Resistance is due to presence of unusual penicillin-binding protein(PBP)in the cellwall of resistant strains
  1. Infection with MRSA is likely to be more severe and require longer hospitalization, with incumbent increased costs than infection with a methicillin susceptible strain.
CONS:
  • Coagulase Negative Staphylococci(CONS) that are commonly implicated as pathogens include
  • Staphylococcus epidermidis: causes infection of native heart valves and intravascular protheses.
  • Staphylococcus saprophyticus: causes urinary tract infections, mainly in sexually active women.
  • CONS that are less commonly implicated as pathogens include: S.hominis, S.haemolyticus, S.cohnii, s.lugdunensis, S.saccharolyticus, S.schleiferi, S.simulans and S. warneri
TREATMENT:
  • Antibiotic therapy
  1. Broad-spectrum penicillins
  2. Oxacillin is the drug of choice for penicillinase resistant staphylococcus
  3. Transfer of drug resistance in staphylococcus is by Transduction & Conjugation
  4. MRSA are susceptible to Vancomycin, Teicoplanin and Linezolid
  5. Drug of choice for Methicillin resistant staphylococcus aureus is (MRSA) is vancomycin (glycopeptide)
  • Wound drainage
  • Device removal
  • Removal of dead tissue
Exam Question
  • Oxacillin is the drug of choice for penicillinase resistant staphylococcus
  • MRSA are susceptible to Vancomycin, Teicoplanin and Linezolid
  • Resistance in MRSA is attributable to beta-lactamase production due to genes located on extrachromosomal plasmids.
  • Transfer of drug resistance in staphylococcus is by Transduction & Conjugation
  • Drug of choice for Methicillin resistant staphylococcus aureus is (MRSA) is vancomycin(glycopeptide)

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