Epidemiological study of Arbekacin-resistant, methicillin resistant Staphylococcus aureus in Saitama Medical School Hospital]

Arbekacin-resistant, methicillin-resistant Staphylococcus aureus was frequently isolated in Saitama Medical School Hospital during 1996 and 1998. The minimum inhibitory concentration for ABK was 8 micrograms/ml in 14 strains, 16 micrograms/ml in 6 strains, and 32 micrograms/ml in 2 strains. The maximum isolation rate of these resistant strains in one month was 8%. Use of ABK in the hospital did not increase during the same period. The infection control team (ICT) of the hospital recognized the increase of resistant strains and started intervention for the hospital staff. The ICT instructed the staff of each ward to follow standard precautions for the prevention of nosocomial infections and the risk of ABK-resistant MRSA was explained repeatedly. Thereafter, the isolation rate decreased to 3%. An epidemiological study was done using 22 strains of ABK-resistant MRSA that were isolated in this period. The strains originated from different patients and from 10 different wards, which were designated as wards A to J. Eight strains were isolated from surgical ward A, followed by the other wards (ward B: 3, C: 2, D: 2, E: 2, F: 1, G: 1, H: 1, I: 1, J: 1). The specimens from which ABK-resistant MRSA were isolated were as follows,: sputum: 4, wound: 4, decubitus ulcer: 4, urine: 2, pus: 2, blood :1, central venous catheter: 1, drainage tube: 1, tracheal aspirate: 1, skin: 1, stool: 1. Several investigations were done using these strains. Sensitivity tests for ABK, VCM, MINO, LVFX, FOM, IPM were performed by the standard method of the Japan Society for Chemotherapy. Coagulase types were determined. Production of toxic shock syndrome toxin-1 (TSST-1), enterotoxin, and beta-lactamase was assayed. Pulse-field gel electrophoresis (PFGE) using Sma I was also done and differences were compared. Seven of the 8 strains from ward A showed the same drug sensitivity profile and biological phenotype. Two of the 3 strains from ward B and 2 strains from ward C were also identical by these methods. Six of the 8 strains from ward A were also identical by PFGE. These 6 isolates showed the same drug sensitivity pattern, same coagulase type, and same production of TSST-1 and enterotoxin. Two other strains from ward B, one strain from ward F, and one from ward I also showed the same PFGE pattern, drug sensitivity profile, and toxin profile as the 6 strains from ward A. Our data show that the same strains were transmitted around the hospital during the study period, although serious nosocomial infections due to ABK-resistant MRSA were avoided. Thus, intervention by the ICT in each ward was effective. ABK-resistant MRSA should be recognized as an important hospital pathogen and should be surveyed consistently.