Tomita Akiko, Shinoda Yoko, Yasuhara Tsutomu, Wakuta Rika, Fukuchi Kunihiko, Gomi Kunihide
Department of Clinical Pathology, Showa University, School of Medicine, Shinagawa-ku, Tokyo.
Rinsho Byori. 2006 Aug;54(8):792-9.
We examined the penicillin and macrolide resistance of 496 strains of Streptococcus pneumoniae (S. pneumoniae) isolated at Showa University Hospital from November 2004 to May 2005. According to the classification established by the Clinical and Laboratory Standards Institute, the ratio of penicillin susceptible S. pneumoniae (PSSP) was 25.8%, penicillin intermediate S. pneumoniae was 35.9% and penicillin resistant S. pneumoniae (PRSP) was 38.3%. The ratios of macrolide resistant S. pneumoniae were 85.3% for erythromycin and 76.2% for clarithromycin. S. pneumoniae strains were isolated mainly from pediatric patients, and the ratios of PRSP were similar between outpatients (39.8%) and inpatients (45.6%). We screened for mutations in pbp1a, pbp2b and pbp2x, and the retention rate of the macrolide resistance genes, ermB and mefA in 90 strains isolated in the same period. Seventy two strains had at least one mutation in the pbp genes. Interestingly, some of the penicillin susceptible strains had one or two pbp mutations, suggesting a progressive genetic acquirement of penicillin resistance. In screening for retention of the macrolide resistance genes, we found that 42 strains(46.7%) had ermB, 19 strains (21.1%) had mefA and 13 strains (14.4%) had both ermB and mefA. The possession of resistance genes and the minimal inhibitory concentration indicate that the resistance to erythromycin and clarithromycin were induced by ermB or mefA, and the resistance to clindamycin was induced only by ermB. Among the 72 strains with pbps mutations, 65 strains (90.3%) had ermB or mefA or both. Together, these results show that the strains with pbp mutations were being selected and, after acquiring the macrolide resistance gene, transform to multidrug resistant S. pneumoniae.
我们检测了2004年11月至2005年5月在昭和大学医院分离出的496株肺炎链球菌的青霉素和大环内酯类耐药性。根据临床和实验室标准协会制定的分类，青霉素敏感肺炎链球菌（PSSP）的比例为25.8%，青霉素中介肺炎链球菌为35.9%，青霉素耐药肺炎链球菌（PRSP）为38.3%。大环内酯类耐药肺炎链球菌对红霉素的耐药率为85.3%，对克拉霉素的耐药率为76.2%。肺炎链球菌菌株主要从儿科患者中分离，门诊患者（39.8%）和住院患者（45.6%）的PRSP比例相似。我们筛选了同一时期分离出的90株菌株中pbp1a、pbp2b和pbp2x的突变情况，以及大环内酯类耐药基因ermB和mefA的保留率。72株菌株在pbp基因中至少有一处突变。有趣的是，一些青霉素敏感菌株有一到两处pbp突变，提示青霉素耐药性的逐步遗传获得。在筛选大环内酯类耐药基因的保留情况时，我们发现42株菌株（46.7%）有ermB，19株菌株（21.1%）有mefAand13株菌株（14.4%）同时有ermB和mefA。耐药基因的拥有情况和最低抑菌浓度表明，对红霉素和克拉霉素的耐药性由ermB或mefA诱导，而对克林霉素的耐药性仅由ermB诱导。在72株有pbps突变的菌株中，65株菌株（90.3%）有ermB或mefA或两者皆有。这些结果共同表明，有pbp突变的菌株正在被选择，并且在获得大环内酯类耐药基因后，转变为多重耐药肺炎链球菌。
