Evaluation of Screening and Commercial Methods for Detection of Methicillin Resistance in Coagulase-Negative Staphylococci

Abstract

The National Committee for Clinical Laboratory Standards recommends 48 h of incubation by the oxacillin salt agar screen (OSAS) method for the detection of methicillin-resistant coagulase-negative staphylococci (CoNS). An earlier identification of methicillin resistance is desirable. The time to detection of the mecAgene by PCR was compared with the times to detection by OSAS, by the oxacillin disk diffusion (ODD) method, and with MicroScan Gram Positive Combo type 6 panels (MicroScan Inc. Sacramento, Calif.) and Vitek GPS-SA cards (bioMérieux Vitek Inc., Hazelwood, Mo.). The combination of the Vitek card and the ODD method detected 92 of 99 methicillin-resistant strains of CoNS at 24 h; however, 6mecA-positive strains were phenotypically methicillin susceptible. We conclude that most methicillin-resistant CoNS can be detected and the results can be reported after overnight incubation by a combination of methods.

Evaluation of phenotypic methods for methicillin resistance characterization in coagulase-negative staphylococci (CNS)

“…Even though researchers have shown that an agar screening test containing 6 ìg oxacillin ml À1 is not efficient towards CNS (Tenover et al, 1999), and it is no longer recommended for CNS (NCCLS, 1999), comparative studies to assess the agar screening test and disc-diffusion have pointed out that agar screening is more sensitive for identifying methicillinresistant strains (York et al, 1996;Hussain et al, 1998;Frebourg et al, 1998;Kohner et al, 1999). For the agar screening test we used Mueller-Hinton agar plates supplemented with 4 % NaCl and incubated for 48 h because, under these conditions, methicillin resistance coded by the mecA gene is easily characterized (York et al, 1996).…”

Differentiation BetweenStaphylococcus AureusandCoagulase-Negative StaphylococcusSpecies by Real-Time PCR Including Detection of Methicillin Resistants in Comparison to Conventional Microbiology Testing

“…Polymerase chain reaction (PCR) to detect the mecA gene as a rapid method for the identification of MRSA has been amply demonstrated (11,(20)(21)(22)(23)(24)(25)(26)(27). Some even consider PCR to be the method of choice for identifying MRSA and other methicillinresistant staphylococci (8,(28)(29)(30)(31)(32)(33)(34).…”

Clinical validation for oxacillin susceptibility testing of coagulase negative staphylococci

“…In order to encourage appropriate use of β lactam antibiotics for CNS infections, several approaches have been proposed to improve in vitro susceptibility testing performance. [5][6][7][8][9] These techniques aim to show heteroresistance by phenotyping or finding resistance genes by molecular techniques. In this report, we illustrate the application of one such technique to the successful treatment of six patients with invasive CNS infections.…”