Epidemiologic Typing of Methicillin-Resistant Staphylococcus aureus in Neonate Intensive Care Units Using Pulsed-Field Gel Electrophoresis

To elucidate the mode of dissemination of methicillin-resistant Staphylococcus aureus (MRSA) in neonate intensive care units (NICUs), a total of 223 isolates from 3 separate hospitals were investigated between 1994 and 1996 by a DNA fingerprinting technique with pulsed-field gel electrophoresis (PFGE). Exoprotein profiles of some strains were also examined using SDS-polyacrylamide gel-electrophoresis (SDS-PAGE) and the assessment of enzyme/toxin production such as coagulase, enterotoxin and TSST-1. Judging from the strain typing data from PFGE results and the epidemiological data, 2 different types of PFGE patterns (A and B) and their subtypes (A', A" and B') were identified. The A type including A' and A" (comprising approximately 95% of the isolates) was markedly dominant. Only 5% of the isolates belonged to type B and subtype B'. On the other hand, MRSA isolated from adult patients admitted to the same hospital showed many different PFGE patterns. The results strongly suggested that some strain(s) with specific PFGE pattern(s) is prevalent in NICUs. Furthermore, isolates which expressed the same PFGE pattern did not always express the same SDS-PAGE pattern. There were some isolates with different abilities to produce coagulase, enterotoxin C and toxic-shock syndrome toxin (TSST)-1, and the abilities had no relation with a particular type of PFGE pattern. Therefore, a combination of PFGE analysis and biochemical analyses of coagulase, enterotoxin C and TSST-1 may provide us with more detailed information for the epidemiological study of MRSA in NICUs.