Methicillin-resistant S. Aureus (MRSA) in nosocomial infections

Abstract

Since methicillin-resistant S. aureus (MRSA) occupies a prominent position in nosocomial infections, we studied it by coagulase-typing of 214 strains of S. aureus isolated from clinical specimens on the ward from 1983 to 1988 and of 62 strains isolated in the operating room. In the study on the ward strains, highly methicillin-resistant S. aureus strains (H-MRSA, MIC >100 μg/ml) which was not detected in 1983, showed a significant increase in isolation frequency, and accounted for c. 60% of MRSA (MIC12.5 μg/mp) in 1987. Then, with the medical staff's awareness of the prevalence of MRSA on the ward, countermeasures, such as sterilization with chlorhexidine alcohol from 1987 on, significantly decreased the isolation frequency of MRSA and H-MRSA in 1988. In the study on coagulase type, MRSA type IV strains were predominantly isolated until 1984, but after 1986 most MRSA belonged to type II. The characteristics of the current epidermic strain type II were the following. 1. It proved highly resistant to DMPPC and other p-lactam antibiotics. 2. The isolation frequency of highly β-lactamase-producing strains was less than that of the other coagulase types of S. aureus. 3. It was sensitive to MINO and OFLX. 4. GM-sensitive, AMK-resistant strains were circulating from the second half of 1986. In the operating room, all the strains isolated were methicillin-sensitive S. aureus (MSSA), thecurrent epidermic coagulase type there being type VII. We therefore presume that cross-infection with MRSA did not take place in the operating room but on the ward. © 1989, Japanese Society of Chemotherapy. All rights reserved.