In contrast to the results with S. aureus, when 52 strains of CoNS were examined for the presence of the femA gene by pentaplex PCR, all were negative. The femA gene in the pentaplex PCR assay was able to rule out non-S. aureus staphylococci, as reported by Francois et al. [25]. The mecA gene is unique to methicillin-resistant staphylococci [26]. The DNA sequences of the mecA genes found in S. aureus and CoNS are >99% identical [27]. Thus, the mecA gene represents a useful molecular component for rapid identification of MRSA and methicillin-resistant CoNS by PCR. One of the 147 MSSA isolates was shown to be mecA-positive by

pentaplex PCR. Although genotypically the mecA gene was detected and confirmed by PCR, it is possible that P505-15 the mecA gene is non-functional (non-PBP-2a producing) and is not expressed phenotypically or due to the presence of pseudogene [28]. Clinically, it is important to buy Quisinostat differentiate between classical type mecA-positive MRSA strains among other borderline-resistant S. aureus strains

that result from hyperproduction of β-lactamases [11]. The mecA-positive isolates were either heterogeneous or homogeneous in their expression of resistance. When heterogeneous isolates are tested by standard conventional methods, some cells appear susceptible buy GS-1101 and others resistant, while almost all homogeneous isolates express resistance when tested by standard methods [29]. Production of PBP-2a may be stimulated during chemotherapy with β-lactam antibiotics, which converts heterogeneous isolates into oxacillin-resistant strains, therefore, the identification of methicillin-resistant staphylococci in the laboratory is

complicated by the heterogeneous nature of the resistance, and by the variables that influence its expression (i.e., medium, inoculum size, pH, temperature, and salt concentration) [30]. For these reasons, detection of mecA gene is crucial for precise discrimination of methicillin resistance among staphylococci. Almost 100% of CA-MRSA strains contain the lukS gene, compared to <5% of HA-MRSA. The PVL-encoding gene allows the production of a necrotizing cytotoxin, which may be responsible for staphylococcal invasiveness and virulence [4, 31]. We included this gene in the pentaplex PCR assay to Megestrol Acetate categorize our isolates and accurately discriminate CA-MRSA and HA-MRSA. None of the MRSA, MSSA and CoNS isolates harbor the PVL-encoding lukS gene. With regard to MRSA, this is not surprising because all MRSA isolates in our study were nosocomial organisms. A high prevalence of lukS gene among MSSA has been reported in the neighboring countries of Singapore and Indonesia, with none and low prevalence of lukS gene among MRSA [32, 33]. The low prevalence in Malaysia is ascribed to restrictive antibiotic usage and a strict policy of national surveillance for MRSA.