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Angie Pinto, John Merlino, CO2-dependent methicillin-resistant Staphylococcus aureus, Journal of Antimicrobial Chemotherapy, Volume 66, Issue 3, March 2011, Pages 676–677, https://doi.org/10.1093/jac/dkq510
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Sir,
A female patient in her 20s presented with a right thigh abscess. There was local swelling and erythema. There was no indication for surgical drainage and the patient was commenced on intravenous flucloxacillin with clinical improvement. This was changed to oral flucloxacillin and the patient self-discharged and was lost to follow-up.
A wound swab of the thigh abscess was sent to the laboratory. Gram staining revealed polymorphs and Gram-positive cocci. The specimen was incubated on horse blood agar with 5% CO2 and on MacConkey agar aerobically. Growth of Gram-positive cocci, which were slide coagulase positive (Remel), was noted within 24 h on horse blood agar, but not on MacConkey agar. Susceptibility testing was attempted using Vitek2, but growth in the control well was not achieved, and therefore the attempt was terminated. The organism did not grow under aerobic conditions on a purity plate.
Disc susceptibility was performed on Mueller–Hinton agar and the isolate was subcultured on MRSASelect (Bio-Rad, Australia). Both were incubated in 5% CO2 as well as O2. Growth was observed only in the presence of CO2. CLSI disc diffusion susceptibility testing was performed and the cefoxitin (30 μg) zone diameter was 12 mm.1 RT–PCR for femA and mecA genes was positive.2,3 The isolate was confirmed to be methicillin-resistant Staphylococcus aureus (MRSA). In addition, molecular testing for the Panton–Valentine leucocidin (PVL) gene by SYBR green RT–PCR assay was performed and was positive.4 The isolate was sent for typing at the Department of Microbiology and Infectious Diseases, Path West Laboratory Medicine, Nedlands, WA, Australia, and was sequence type 30 (ST30).
