The evaluation of a typing scheme for coagulase-negative staphylococci suitable for epidemiological studies

A typing scheme was devised for an epidemiological study of infection with coagulase-negative staphylococci in patients undergoing continuous ambulatory peritoneal dialysis (CAPD). The scheme was constructed in four stages suitable for the screening of large numbers of isolates: antibiogram, biotype, phage type, and plasmid profile. The discrimination and reproducibility of the scheme was established by the examination of 50 isolates from 33 consecutive episodes of peritonitis affecting 18 patients. The discrimination of the scheme was 76%, with a reproducibility of 86%. Indistinguishable strains occurred in individual patients only, demonstrating that no cross-infection between patients occurred during the 10-month period of collection of strains, and suggesting that the discriminating power of the scheme was, in fact, much higher. The antibiogram, selected as the first stage of the scheme because it was the simplest and cheapest test, proved to be the most discriminatory stage, providing 60% of the final discriminatory power.