EPIDEMIOLOGICAL STUDY OF NOSOCOMIAL MRSA INFECTION BY PLASMID DNA AND ANTIBIOTIC SUSCEPTIBILITY ANALYSES

为进行医院感染流行病学调查，对1991年旭川医科大学附属医院住院患者分离的87株耐甲氧西林金黄色葡萄球菌（MRSA）进行了质粒谱和药物敏感性调查。质粒谱分为7个谱（A ~ G），21株无质粒。47株（54%）属于A型，10株属于B型，其余为C型至G型。只有米诺环素（MINO）的敏感性模式被清楚地分为两种模式，敏感（最小抑制浓度，MIC为0.5或1 μ g/ml）或耐药（MIC为4或8 μ g/ml）。MINO敏感菌株47株，耐药菌株40株。因此，质粒图谱结合MINO敏感性用于流行病学调查。其中一个外科病房患者分离的菌株以质粒谱A和MINO敏感为主，而另一个外科病房、神经外科病房和泌尿外科病房患者分离的菌株以质粒谱A和MINO耐药为主。谱型C菌株仅在耳鼻喉科病房中鉴定，我们进一步检查了1991年以后分离的一些菌株的质粒谱型，发现谱型B而不是谱型A成为优势菌株。结果表明，它们与Asahikawa菌株的质粒谱不同，我们还开始研究MRSA的基因组谱通过脉冲场凝胶电泳（PFGE）对菌株进行鉴定。23株质粒谱均为A型的菌株，PFGE可分为10个谱，因此PFGE比质粒谱更有鉴别力，甚至可以结合药敏谱作为流行病学工具。将对库存的400余株MRSA菌株进行该方法的调查，以进一步开展MRSA医院感染的流行病学调查。

Plasmid profile and antibiotic susceptibility of 87 strains of methicillin-resistant staphylococcus aureus (MRSA) isolated from inpatients in Asahikawa Medical College Hospital in 1991 were investigated for epidemiologic survey of nosocomial infection. Plasmid profile was classified into 7 profiles (profile A to G) and 21 strains had no plasmids. Forty-seven strains (54%) belonged to profile A,10 to profile B and the rest to profile C to G.Nine antibiotics were tested. Only the susceptibility pattern of minocycline (MINO) was clearly divided into two patterns, sensitive (minimal inhibitory concentration, MIC is 0.5 or 1 mug/ml) or resistant (MIC is 4 or 8 mug/ml). Forty-seven strains were MINO sensitive and 40 were resistant. Thus plasmid profile combined with MINO susceptibility was used for epidemiologic investigation. Most strains isolated from patients in one of the two surgery wards had plasmid profile A and MINO sensitive, whereas in another surgery ward, neurosurgery ward and urology word, profile A and MINO resistant strains were predominant. Profile C strains were identified just in otolaryngology ward.We further examined plasmid profiles of some of the strains isolated after 1991 and found that profile B became dominant rather than profile A.The strains isolated in Kagoshima University Hospital, which is located far from Asahikawa, were also investigated and they had the different plasmid profiles from those of Asahikawa strains.We also started to examine genomic profile of MRSA strains by pulsed field gel electrophoresis (PFGE). Twenty-three strains which had all plasmid profile A were classified into 10 profiles by PFGE.Thus PFGE is more discriminant than plasmid profiling, even combined antibiotic susceptibility pattern as epidemiological tool. More than 400 MRSA strains stocked will be investigated by this method for further epidemiological investigation of nosocomial MRSA infection.