Vol.55 No.5 September 2007

Ratio of mecA gene in oxacillin-insusceptible and susceptible Staphylococcus aureus

Akiko Wada^{1, 2)}, Tetsuro Muratani^{2, 3)}, Tomoko Kobayashi²⁾, Ryoko Gotoh²⁾, Naonori Kido²⁾, Kazumasa Koga²⁾ and Tetsuro Matsumoto³⁾

¹⁾Kokura Medical Association in Kitakyushu City, 1-19-17 Nakashima, Kokurakita-ku, Kitakyushu, Fukuoka, Japan
²⁾Hibiki Research Group for Clinical Microbiology
³⁾Department of Urology, School of Medicine, University of Occupational and Environmental Health

Abstract

In northern Kyushu and Yamaguchi, 323 Staphylococcus aureus isolates which MIC of oxacillin was less than 4 μg/mL by broth microdilution method were collected in 2005. The susceptibility of isolates was examined using Kirby Bauer disk diffusion test of cefoxitin and MIC determination by agar dilution method. The MIC range of oxacillin against all 323 isolates was ≤0.25-2 μg/mL. mecA was detected from 9 (2.8%) of all isolates. In this 9, the inhibitory zone diameter of cefoxitin ranged from 18 to 22 mm. According to Clinical and Laboratory Standards Institute M100-S17, if the zone diameter of the cefoxitin disk is less than 21 mm, the isolate is judged as methicillin-resistant S. aureus (MRSA). Eight of the 9 isolates were judged as MRSA by the cefoxitin disk diffusion test. Among specimens, isolates from skin had mecA most frequently at a ratio of 23.5% (4/17). Regarding patient age, isolates having mecA from patients who were less than 5 years old accounted for 12.2% (5/41) among patients in the corresponding age group. Seven of the 9 isolates that were mecA-positive and oxacillin-susceptible were outpatients. Since these 7 isolates were divided into 4 groups by Sma I-digested DNA pattern, the result suggested that some clone of mecA-positive and oxacillin-resistant S. aureus may have spread in this area.
Though mecA-positive and oxacillin-susceptible (MIC ≤2 μg/mL) isolates were detected 2.8% of all isolates, the ratio was reduced by using cefoxitin disk diffusion test until 0.3%. The frequency of mecA-positive, oxacillin-susceptible, and cefoxitin-susceptible S. aureus isolates is yet very low, but it is important to continue studying its ratio.

Key word

MRSA, mecA, Staphylococcus aureus, cefoxitin

Received

March 19, 2007

Accepted

June 19, 2007

Jpn. J. Chemother. 55 (5): 374-377, 2007