Specific information concerning taxonomy, pathogenicity and methicillin resistance of staphylococci obtained by a multiplex PCR

Abstract

The use of DNA amplification techniques such as the polymerase chain reaction (PCR) in modern diagnostic microbiology not only allows the sensitive and specific identification of micro-organisms but also the detection of specific antibiotic resistance genes. This study describes a multiplex PCR on bacterial colonies picked directly from agar plates without preceding DNA preparation. Eubacteria and staphylococci were identified by, 16S rRNA specific PCR products. In parallel, specific primers were used for the detection of staphylococcal coa and mecA genes. This 4-h multiplex PCR, consisting of four sets of primers, was evaluated for rapid and specific differential diagnosis of methicillin-resistant and methicillin-susceptible strains of Staphylococcus aureus and coagulase-negative staphylococci. To analyse specificity of the amplification products, 100 non-staphylococcal, eubacterial isolates and 20 Candida albicans strains were tested. In a first step, specificity of all four single sets of primers was evaluated before the co-amplification within the multiplex PCR procedure was performed. The results were compared with those of conventional susceptibility and typing methods. The specific 16S rRNA PCR product for eubacterial isolates (n = 786) and staphylococci (686) was found in all strains tested. The coa gene was detected only in S. aureus (488) strains with a specificity of 100%, and was not detected in any of the coagulase-negative staphylococci (198). The mecA gene was detected in 98% of methicillin-resistant staphylococci (393) and in 2% of all methicillin-susceptible staphylococci (293). The multiplex PCR with co-amplification of different determinants provides rapid reliable information on staphylococcal identification and methicillin susceptibility supporting the diagnosis, treatment and control of staphylococcal infections.