[Choice of the NaCl concentration for optimizing the detection of methicillin resistance in Staphylococcus using the gel diffusion method].
The detection of oxacillin resistance is evaluated by the disk diffusion method in a collection of 374 Staphylococcus sp strains. The disk diffusion assay is performed with 5-microgram oxacillin disk and a 10(8) CFU/mL inoculum on Mueller-Hinton agar plates supplemented with 2 or 5% NaCl and incubated at 37 degrees C for 24 h. Strains are considered resistant in accordance to the French recommendations (any growth around the disk is observed). The detection of mecA gene is performed by PCR almost for resistant and discordant strains. Results are concordant for 246 of 256 Staphylococcus aureus strains (182 susceptible and 64 resistant strains) and for 105 of 118 S. epidermidis isolates tested (37 susceptible and 68 resistant strains). Six mecA-negative strains (3 S. aureus and 3 S. epidermidis) give false resistant results on agar with 2 and 5% NaCl. Seventeen isolates are discordant on 5% NaCl: 7 mecA-negative S. aureus strains are susceptible on 2% NaCl agar but resistant at 5% (3% false-positive results), 10 mecA-positive S. epidermidis strains are resistant on 2% NaCl agar but susceptible at 5% NaCl (5% false-negative results). The detection of meticillin resistance is improved on agar supplemented with 2% NaCl.
Bemer-Melchior
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Laboratoire de bactériologie, hôpital Laënnec, CHU Nantes, boulevard J. Monod, 44093 Saint-Herblain cedex 1, Nantes, France. pascale.bemermelchior@chu-nantes.fr
Drugeon
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HB
D000362:Agar; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D004269:DNA, Bacterial / Q000235:genetics; D004058:Diffusion; D004305:Dose-Response Relationship, Drug; D005782:Gels; D006602:Hexosyltransferases; 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; D016133:Polymerase Chain Reaction; D012680:Sensitivity and Specificity; D012965:Sodium Chloride / Q000008:administration & dosage / Q000494:pharmacology*; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D013212:Staphylococcus epidermidis / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism
D001426:Bacterial Proteins; D002352:Carrier Proteins; D004269:DNA, Bacterial; D005782:Gels; D046915:Penicillin-Binding Proteins; D012965:Sodium Chloride; D000362:Agar; D010458:Peptidyl Transferases; D006602:Hexosyltransferases; D002267:Muramoylpentapeptide Carboxypeptidase; D010068:Oxacillin