A combined molecular approach to screen for mec gene variants from methicillin-resistant Staphylococcus aureus

Molecular diagnostics of clinically important staphylococci

Bacterial species of the genus Staphylococcus known as important human and animal pathogens are the cause of a number of severe infectious diseases. Apart from the major pathogen Staphylococcus aureus, other species until recently considered to be nonpathogenic may also be involved in serious infections. Rapid and accurate identification of the disease-causing agent is therefore prerequisite for disease control and epidemiological surveillance. Modern methods for identification and typing of bacterial species are based on genome analysis and have many advantages compared to phenotypic methods. The genotypic methods currently used in molecular diagnostics of staphylococcal species, particularly of S. aureus, are reviewed. Attention is also paid to new molecular methods with the highest discriminatory power. Efforts made to achieve interlaboratory reproducibility of diagnostic methods are presented.

Direct mecA detection from blood culture bottles by branched-DNA signal amplification

A branched-DNA (bDNA) signal amplification method was used to detect the mecA gene directly from blood culture broth growing staphylococci. BACTEC blood culture bottles with positive growth indices and containing staphylococcus-like organisms as shown by Gram stain were tested for the presence of the mecA gene. Comparison of test results was done among 225 patients (one blood culture from each patient). Compared with PCR, the sensitivity and specificity of the bDNA method are 100 and 99%, respectively. The bDNA test is carried out in a 96-well format and requires approximately 6 h to perform. Our preliminary results suggest that direct detection of the mecA gene by bDNA signal amplification is (i) sensitive enough to detect mecA directly from blood culture bottles without the requirement for subculture and (ii) as sensitive and specific as the PCR-based method.