1. Lab Diagnosis In
Staphylococcal
Infections
Deepa Babin

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. 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. 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. 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. 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. 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. 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. 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