Mueller-Hinton agar is superior to PDM blood agar for detection of methicillin-resistant Staphylococcus aureus.
The aim of this study was to compare the expression of oxacillin resistance in methicillin-resistant Staphylococcus aureus (MRSA) on Paper Disc Method agar supplemented with 5% defibrinated blood (PDM blood agar) and Mueller-Hinton agar supplemented with 2% NaCl (MH NaCl agar) using different susceptibility tests. Fifty mecA-containing isolates of S. aureus, exhibiting 46 different pulsed-field gel electrophoresis patterns, were comparatively tested using the E test, the single disk diffusion test, and the multipoint inoculation technique, under various culture conditions. The E test incubated at 35 degrees C for 24 h (breakpoint of resistance > or = 2.0 mg/L) detected 94% of the isolates on MH NaCl agar, compared with 28% for PDM blood agar (P < 0.05). The disk diffusion test (breakpoint < 10 mm in diameter) under these incubation conditions detected resistance in 100% of the isolates on MH NaCl agar and in 80% of the isolates on PDM blood agar (P < 0.05). The multipoint technique (breakpoint > or = 1 mg/L), applied at 35 degrees C for 24 h, detected 100% on MH NaCl agar and 46% on PDM blood agar (P < 0.05). Irrespective of the method of susceptibility testing evaluated, MH NaCl agar was superior to PDM blood agar for the detection of oxacillin resistance in mecA-containing S. aureus.
Monsen
T
T
Department of Clinical Bacteriology, University Hospital of Umeå, S 901 85 Umeå, Sweden. tor.monsen@climi.umu.se
Persson
S
S
Edebro
H
H
Granström
S
S
Wiström
J
J
D000362:Agar; D001426:Bacterial Proteins; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D003470:Culture Media / Q000378:metabolism; D006602:Hexosyltransferases; D006801:Humans; D016106:Methicillin Resistance; D008826:Microbial Sensitivity Tests / Q000379:methods*; D002267:Muramoylpentapeptide Carboxypeptidase / Q000235:genetics / Q000378:metabolism; D010068:Oxacillin / Q000494:pharmacology*; D046915:Penicillin-Binding Proteins; D010458:Peptidyl Transferases; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism
D001426:Bacterial Proteins; D002352:Carrier Proteins; D003470:Culture Media; D046915:Penicillin-Binding Proteins; D000362:Agar; D010458:Peptidyl Transferases; D006602:Hexosyltransferases; D002267:Muramoylpentapeptide Carboxypeptidase; D010068:Oxacillin