Epidemiological studies on drug-resistance patterns, coagulase types, and MRSA-phage types of MRSA isolates during 1990-1994

We examined drug-resistance patterns, coagulase types, and MRSA-phage types of 125 MRSA strains isolated from clinical specimens during the period of January 1990 and December 1994. No vancomycin-resistant strain was isolated. Twenty one antibiotics were divided into three classes, low-intermediate- and high-isolation-frequency class, based on isolation frequencies of resistant strains. Minocycline, chloramphenicol, streptomycin, and imipenem were found to be included in low-isolation-frequency class (16.8-40%). In intermediate-isolation-frequency class (45.6-62.9%), cefmetazole, amikacin, gentamicin, and tetracycline were included. Oxacillin, ampicillin, piperacillin, ceftizoxime, cefoperazone, cefazolin, erythromycin, oleandomycin, kitasamycin, clindamycin, kanamycin, tobramycin, and ofloxacin belonged to high-isolation-frequency class (97.6-100%). MIC90s of vancomycin and minocycline (1.56 and 25 micrograms/ml) were lower than that of other 13 drugs. Comparing medical ward with dental ward, imipenem-, gentamicin-, and minocycline-resistant strains at medical ward, chloramphenicol- and streptomycin-resistant strains at dental ward were isolated dominantly on each ward, MRSA isolates were classified to 39 types by drug-resistance patterns. The isolation frequencies of coagulase type II and type IV strains were 65.6% and 29.6%, respectively. At dental ward, the isolation frequency of coagulase type IV strains was higher than that of coagulase type II strains during 1990-1992. However, coagulase type II strains were isolated considerably more than type IV strains during 1993-1994. By MRSA-phage typing, MRSA isolates were grouped into 18 MRSA-phage types. One hundred and twenty five MRSA isolates were divided into 56 types by using drug-resistance patterns, coagulase typing, and MRSA-phage typing. It was considered that such classification in combination of three methods is useful to make decision of epidemic by the same MRSA strain.