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Lab diagnosis of staphylococcal infections deepa babin

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Lab diagnosis of staphylococcal infections deepa babin

  1. 1. Lab Diagnosis InStaphylococcal Infections Deepa Babin
  2. 2. Diseases Caused by Staphylococcus Infections aureus  Localised pyogenic infections  Intoxications  Folliculitis, furuncle,  carbuncle Abscesses (e.g. Breast  Food  abscess) Umbilical sepsis poisoning Wound infections  Staphylococc   Respiratory infections  Upper respiratory tract infections al scalded   Sinusitis, otitis media Lower respiratory tract skin infections  Lung abscess, empyema, syndrome  bronchopneumonia Musculoskeletal (SSSS) Osteomyelitis  Toxic shock   Systemic   Septicaemia, Endocarditis UTI (Caused by Staphylococcus syndrome saprophyticus) Deepa Babin at TMC Kollam 2
  3. 3. Specimens Collected Depends on type of lesion / disease  Pus (aspirates or swabs)  Sputum (in respiratory infections)  Blood (in endocarditis, septicaemia)  Pleural fluid (in empyema)  Nasal swab (detection of MRSA carriage) Deepa Babin at TMC Kollam 3
  4. 4. Direct Microscopy Pus cells Gram stain of pus  Pus cells with Gram positive cocci (GPC) in groups GPC in groups Deepa Babin at TMC Kollam 4
  5. 5. Culturing of Staphylococcus Media used:  Blood agar, chocolate agar, MacConkey agar  Mannitol salt agar (Selective / Differential medium)  Liquid media: Glucose broth, brain-heart infusion broth Colony characteristics  On blood agar: Golden yellow, opaque, β-lytic colonies  On mannitol salt agar: yellow colonies (mannitol fermenting) Deepa Babin at TMC Kollam 5
  6. 6. Identification of Isolate Gram smear examination Positive catalase test (to distinguish from Tube Coagulase Test streptococci) Positive coagulase test (to distinguish Staphylococcus aureus from other staphylococci)  Slide coagulase test  For detection of bound coagulase  Make a saline suspension of the + organism on a clear glass slide; add a drop of human plasma  Immediate clumping indicates a positive reaction  Tube coagulase test 0.1ml of overnight broth culture of  organism is mixed with 0.5ml of citrated / – oxalated / heparinised human plasma in a test tube  Tube is incubated at 37ºC for 3–6 hours in a water bath  A plasma clot indicates the presence of free coagulase  Positive DNase test (to distinguish Staphylococcus aureus from other staphylococci) Deepa Babin at TMC Kollam 6
  7. 7. Antibiotic Sensitivity Testing I line  II line  Penicillin (Ampicillin in urinary isolates)  Vancomycin  Gentamicin  Erythromycin (not used in  Rifampicin urinary isolates)  Clindamycin  Cephalothin (I generation cephalosporin)  Linezolid  Amoxicillin-Clavulanate  Oxacillin (or  Netilmicin Cloxacillin,cefoxitin)  Amikacin  Tetracycline  Nitrofurantoin (only in urinary isolates) Deepa Babin at TMC Kollam 7
  8. 8. Treatment If Penicillin is sensitive:  Penicillin is the drug of choice If not sensitive  Oxacillin / Cloxacillin + an Aminiglycoside For MRSA  Vancomycin or Linezolid  Chlorhexidine or Mupirocin for local application Treatment of abscesses  Drainage is essential + antibiotics In severe, life-threatening infections (septicaemia, endocarditis, pneumonia,osteomylitis)  Oxacillin / Cloxacillin + an aminiglycoside Deepa Babin at TMC Kollam 8
  9. 9. Coagulase Negative Staphylococci Staphylococcus epidermidis  Stitch abscess  Infection associated with artificial implants and prosthetics, such as:  Central venous line  Intra ocular lens  Ventriculo-peritoneal shunt  Artificial heart valves (endocarditis)  Artificial joints Staphylococcus saprophyticus  Causes UTI in young adult females  Resistant to Novobiocin (as opposed to Staphylococcus epidermidis, which is sensitive) Deepa Babin at TMC Kollam 9

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