Staphylococcus aureus の Arbekacin 耐性遺伝子
(aacA/aphD)は in vitro 継代培養中に脱落する

陳　　　戈　林*1　福　地　邦　彦*2　和久田　梨　香*3　久　保　定　徳*4
安　原　　　努*5　高　木　　　康*6　五　味　邦　英*7　　　　　　　　　
　　　　　　　　　　　　　　　　　　　　　　
Arbekacin Resistant Gene, aacA/aphD, in Staphylococcus aureus is
Lost during in vitro Passage

Gelin CHEN, MD*1, Kunihiko FUKUCHI, MD*2, Rika WAKUTA*3, Sadanori KUBO, MD*4,
Tsutomu YASUHARA, MD*5, Yasushi TAKAGI, MD*6 and Kunihide GOMI, MD*7

We analyzed for the presence of the aacA/aphD gene in arbekacin resistant-Staphylococcus aureus. Tested strains were 50 clinically isolated Staphylococcus aureus that had an MIC of more than 2 mg/ml for arbekacin. Among the primary cultures, aacA/aphD genes were detected in 42 of 50 strains(84%) overall, including 34 of 41 Methicillin resistant Staphylococcus aureus(MRSA) strains, and 8 of 9 strains of Methicillin sensitive Staphylococcus aureus(MSSA). After 10 or 20 passages, the aacA/aphD gene was lost in 5 strains of MRSA and 2 strains of MSSA. In the strains that lost the gene, the MIC of arbekacin was reduced remarkably in 3 strains of MRSA and 2 strains of MSSA. Further, MICs of arbekacin decreased along with passages even in the strains that did not loose the aacA/aphD gene, as well as in the strains that did not possess the aacA/aphD gene originally. The fact that MIC values are easily reduced with in vitro passage is important to consider when performing the arbekacin-resistance test for Staphylococcus aureus.
[Rinsho Byori 50 : 79〜84, 2002]

*1Department of Clinical Pathology, Showa University, School of Medicine, Shinagawa-ku, Tokyo 142-8666

受付2001年9月25日・受理2001年11月15日
*1〜7昭和大学医学部臨床病理学教室(〒142-8666 東京都品川区旗の台1-5-8)

E-mail :gelin@med.showa-u.ac.jp