COAGULASE GENE POLYMORPHISM IN STAPHYLOCO CCUS-AUREUS - A NEW EPIDEMIOLOGIC MARKER

Nosocomial infections with Staphylococcus aureus necessitate the promp t recognition of the infectious chain as well as a rapid investigation and exclusion of infectious sources. Conventional typification proced ures (e.g. phage typing) and genotyping methods with pulsed-field gel electrophoresis (PFGE) are labor-intensive and time-consuming and can be performed only in a few laboratories. A new attractive typing techn ique for S.aureus utilizes the polymorphism of the coagulase (coal gen e as an epidemiological marker. This typing method is performed with p rimers, homologous to a conserved region within the coa gene, in order to amplify the sequences encoding the C-terminal region of this molec ule. Since the number of repetitive sequences varies within the coa ge ne, the resulting PCR products of individual strains can be of differe nt lengths. We have assessed the coa gene length polymorphism in 150 s trains of S.aureus. By the sizes of the PCR products these strains cou ld be categorized into 10 subgroups. AluI restriction analysis of the PCR products resulted in a significantly higher degree of discriminati on. Since the repeated sequences, consisting of 81 base pairs, possess a high variability of the nucleotides, a characteristic restriction f ragment length polymorphism (con-RFLP) pattern is yielded. Overall, we could distinguish 64% of the clinical isolates by RFLP analysis; in s trains sharing identical antibiograms, 56% could be distinguished. 46% oxacillin-resistant strains, some of which originated from epidemic o utbreaks, could be discriminated by their RFLP pattern. Comparing thes e results with those obtained from the PFGE method, isolates which dif fered by their coagulase gene RFLP also differed by their PFGE pattern s. However, not all isolates with an identical coa-RFLP had an identic al PFGE pattern. To assess clonality in S.aureus strains with identica l con-RFLP it is, therefore, recommended to either perform sequence an alysis of the PCR products or to carry out PFGE to further discriminat e between strains. The stability of the coagulase gene sequences was i nvestigated. Following subcultivation every 2 weeks over a 6-month-per iod, the con gene sequence was found either not to change or to only v ary in one nucleotide. As demonstrated in this study, the structure ch aracteristic of the con gene allows us to use con gene typing as an ep idemiological tool for analysing nosocomial S.aureus outbreaks.