16S rRNA Methylase–producing, Gram-Negative Pathogens, Japan

To investigate the exact isolation frequency of 16S rRNA methylase–producing, gram-negative pathogenic bacteria, we tested 87,626 clinical isolates from 169 hospitals. Twenty-six strains from 16 hospitals harbored 16S rRNA methylase genes, which suggests sparse but diffuse spread of pan-aminoglycoside–resistant microbes in Japan

Vertical distribution and bacterial cell size and biomass in Lake Vanda, an Antarctic lake

Vertical distribution of bacteria in Lake Vanda in the Dry Valleys region of the Antarctic was examined by the acridine orange direct count (AODC) method in December 1984 and the results were compared with those of January 1984 (S. TAKII et al. : Hydrobiologia, 135,15,1986). Bacterial numbers, cell sizes, and biomass in the water showed an almost identical pattern of vertical distribution at the two sampling times. Total bacteria by the AODC method were in the order of 10^4cells/ml in the water at the depth of 55m and above, and increased markedly to 5.0×10^6cells/ml in the bottom water (69m depth). Bacteria from the water between 5 and 60m depths were dominated by rods of 1.0-2.0μm length, and, particularly, filamentous bacteria more than 10μm long occurred a relatively high frequency in the water above the depth of 55m. On the other hand, most bacteria from the water at depths below 65m were coccoidal or short rods less than 1.0μm long. Bacterial biomass estimated from cell volumes ranged from 0.0026 to 0.079mgC/l

New Plasmid-Mediated Fluoroquinolone Efflux Pump, QepA, Found in an Escherichia coli Clinical Isolate▿

Plasmid-mediated Qnr and AAC(6′)-Ib-cr have been recognized as new molecular mechanisms affecting fluoroquinolone (FQ) resistance. C316, an Escherichia coli strain demonstrating resistance to various FQs, was isolated in Japan. Resistance to FQs was augmented in an E. coli CSH2 transconjugant, but PCR failed to detect qnr genes, suggesting the presence of novel plasmid-mediated FQ resistance mechanisms. Susceptibility tests, DNA manipulation, and analyses of the gene and its product were performed to characterize the genetic determinant. A novel FQ-resistant gene, qepA, was identified in a plasmid, pHPA, of E. coli C316, and both qepA and rmtB genes were mediated by a probable transposable element flanked by two copies of IS26. Levels of resistance to norfloxacin, ciprofloxacin, and enrofloxacin were significantly elevated in E. coli transformants harboring qepA under AcrB-TolC-deficient conditions. QepA showed considerable similarities to transporters belonging to the 14-transmembrane-segment family of environmental actinomycetes. The effect of carbonyl cyanide m-chlorophenylhydrazone (CCCP) on accumulation of norfloxacin was assayed in a qepA-harboring E. coli transformant. The intracellular accumulation of norfloxacin was decreased in a qepA-expressing E. coli transformant, but this phenomenon was canceled by CCCP. The augmented FQ resistance level acquired by the probable intergeneric transfer of a gene encoding a major facilitator superfamily-type efflux pump from some environmental microbes to E. coli was first identified. Surveillance of the qepA-harboring clinical isolates should be encouraged to minimize further dissemination of the kind of plasmid-dependent FQ resistance determinants among pathogenic microbes

PCR Classification of CTX-M-Type β-Lactamase Genes Identified in Clinically Isolated Gram-Negative Bacilli in Japan

Of 1,456 strains isolated from 2001 to 2003 demonstrating resistance to either oxyimino-cephalosporin, 317 strains, isolated in 57 of 132 clinical facilities, were found to harbor bla(CTX-M) genes by PCR. Fifty-seven, 161, and 99 strains harbored bla(CTX-M) genes belonging to the bla(CTX-M-1), bla(CTX-M-2), and bla(CTX-M-9) clusters, respectively

ナンキョク バンダ コ ニ オケル サイキン ノ サイボウ サイズ ト ゲンゾン リョウ ノ スイチョク ブンプ

南極ドライバレー地域のバンダ湖における細菌の垂直分布について, 1984年12月にアクリジンオレンジ染色による直接計数(AODC)法を用いて調べた結果を, 1984年1月の調査結果(S.TAKII et al. : Hydrobiologia, 135,15,1986)と比較した。湖水中の細菌数・細胞サイズ・現存量の垂直分布パターンは, 両調査時期でよく類似していた。すなわち, 全菌数(AODC)は, 水深55m以浅では(10)^4cells/mlのオーダーであったが, それ以深で急激に増加して, 底層水(69m)では5.0×10^6cells/mlに達した。細菌の細胞サイズについてみると, 5m層から60m層までは長さ1.0-2.0μmの桿菌が最も多く, 特に水深55m以浅では長さ10μm以上の糸状細菌も比較的多く出現したが, 水深65m以深では長さ1.0μm以下の球桿菌や短桿菌がほとんどであった。細菌体積量から炭素量に換算した細菌現存量は, 0.0026-0.079mgC/lの範囲であった。Vertical distribution of bacteria in Lake Vanda in the Dry Valleys region of the Antarctic was examined by the acridine orange direct count (AODC) method in December 1984 and the results were compared with those of January 1984 (S. TAKII et al. : Hydrobiologia, 135,15,1986). Bacterial numbers, cell sizes, and biomass in the water showed an almost identical pattern of vertical distribution at the two sampling times. Total bacteria by the AODC method were in the order of 10^4cells/ml in the water at the depth of 55m and above, and increased markedly to 5.0×10^6cells/ml in the bottom water (69m depth). Bacteria from the water between 5 and 60m depths were dominated by rods of 1.0-2.0μm length, and, particularly, filamentous bacteria more than 10μm long occurred a relatively high frequency in the water above the depth of 55m. On the other hand, most bacteria from the water at depths below 65m were coccoidal or short rods less than 1.0μm long. Bacterial biomass estimated from cell volumes ranged from 0.0026 to 0.079mgC/l

SMB-1, a Novel Subclass B3 Metallo-β-Lactamase, Associated with ISCR1 and a Class 1 Integron, from a Carbapenem-Resistant Serratia marcescens Clinical Isolate▿

A carbapenem-resistant Serratia marcescens strain, 10mdr148, was identified in a Japanese hospital in 2010. The carbapenem resistance of this strain was attributed to the production of a novel metallo-β-lactamase (MBL), named SMB-1 (Serratia metallo-β-lactamase). SMB-1 possessed a zinc binding motif, H(Q)XHXDH (residues 116 to 121), H196, and H263 and was categorized as a member of subclass B3 MBL. SMB-1 has 75% amino acid identity with the most closely related MBL, AMO1, of uncultured bacterium, recently identified through the metagenomic analysis of apple orchard soil. The introduction of blaSMB-1 into Escherichia coli conferred resistance to a variety of β-lactam antibiotics, penicillins, cephalosporins, and carbapenems, but not aztreonam, a resistance pattern consistent with those of other MBLs. SMB-1 demonstrated high kcat values of >500 s−1 for carbapenems, resulting in the highest hydrolyzing efficiency (kcat/Km) among the agents tested. The hydrolyzing activity of SMB-1 was well inhibited by chelating agents. The blaSMB-1 gene was located on the chromosome of S. marcescens strain 10mdr148 and at the 3′ end of the ISCR1 element in complex with a typical class 1 integron carrying aac(6′)-Ib and catB3 gene cassettes. Downstream of blaSMB-1, the second copy of the 3′conserved segment and ISCR1 were found. To our knowledge, this is the first subclass B3 MBL gene associated with an ISCR1 element identified in an Enterobacteriaceae clinical isolate. A variety of antibiotic resistance genes embedded with ISCR1 have been widely spread among Enterobacteriaceae clinical isolates, thus the further dissemination of blaSMB-1 mediated by ISCR1 transposition activity may become a future concern