GENETIC-VARIATION IN STAPHYLOCOCCUS-AUREUS COAGULASE GENES - POTENTIAL AND LIMITS FOR USE AS EPIDEMIOLOGIC MARKER

To perform coagulase gene typing, the repeated units encoding hypervar iable regions of the Staphylococcus aureus coagulase gene were amplifi ed by the PCR technique; this was followed by AluI restriction enzyme digestion and analysis of restriction fragment length polymorphism (RF LP) patterns. In order to assess the discriminatory power of this typi ng method, 30 epidemiologically unrelated S. aureus strains which diff ered by their pulsed-field gel electrophoresis patterns were examined. Although 18 of the 30 strains had unique and unshared AluI RFLP patte rns, there were only four observed patterns in the remaining 12 strain s. This finding indicated that unrelated strains may share identical A luI RFLP patterns. To elucidate the degree of genetic variation in the C-terminus-encoding loci within the coagulase genes, the PCR products of these 12 strains were subjected to Tag polymerase-mediated sequenc ing. Sequence analysis confirmed the AluI recognition sites in each of the four RFLP groups and demonstrated that AluI appears to yield the highest RFLP in restriction enzyme analysis. By their DNA sequences th e majority of strains sharing common AluI groups could be clearly diff erentiated from each other and revealed between 93.2 and 98.5% homolog y. When we determined the nucleotide sequences of two strains after si x subcultivations no significant alterations were observed. Because th e discriminatory power of the current coagulase gene typing method is not great enough to be used as the sole method to type S. aureus, addi tional techniques are necessary. Sequence analysis of the repeated uni t-encoding region for the typing of S. aureus may be potentially usefu l as an alternative to other current molecular typing techniques.