Urase laboratory web site

Antibiotic-Resistant Bacteria

Characterization of Extended Spectrum β-lactamase-producing Escherichia coli in the Environment Isolated with Different Concentrations of Cefotaxime

ABSTRACT; Hirofumi Tsutsui, Taro Urase. J. of Water and Environment Technology, Vol. 17, No. 4, pp.262-271, 2019. DOI: 10.2965/jwet.18-091

Wastewater treatment plays an important role in controlling the release of antimicrobial resistant bacteria to the environment. We characterized extended spectrum β-lactamase (ESBL)-producing Escherichia coli strains isolated from the environment by cefotaxime (CTX)-containing agar plates in this study. The results on the samples under the influence of treated wastewater showed that 1.2% to 5.3% of the total E. coli population formed colonies on the ECC medium containing 4 µg/mL CTX and all of them were ESBL-producing strains. Addition of 4 µg/mL CTX to the ECC medium imposed a selection pressure equivalent to MIC higher than 64 µg/mL (MIC breakpoint in the previous Clinical and Laboratory Standards Institute [CLSI] criteria) because the medium containing CTX not only inhibited the growth of the strains with lower MICs than the concentration in the medium but also suppressed the formation of colonies of the strains with higher MICs. Adding 64 µg/mL CTX in the ECC medium selected only clinically important strains with an intensively resistant spectrum covering cephalosporins (including ceftazidime) and fluoroquinolones. Some isolates harbored multiple ESBL-producing genes. The dominant genes encoding ESBL were blaCTX-M group 1, blaCTX-M group 9, and blaTEM group.

Quantitative monitoring of resistance in Escherichia coli to clinically important antimicrobials in an urban watershed

ABSTRACT; Taro URASE, Takaya SATO. J. of Water and Environment Technology, Vol. 14, No. 5, pp.341-349, 2016. DOI: 10.2965/jwet.16-002

The resistance in Escherichia coli to clinically important antimicrobial agents including fluoroquinolones and third-generation cephalosporins was investigated in the Tama river watershed to obtain the regional prevalence of the resistance to the newer antimicrobials. Among a total of 3629 isolates, 78 strains (2.1%) were resistant to cefotaxime (probable extended-spectrum beta-lactamases producers) and 76 isolates were resistant to levofloxacin, although no carbapenem-resistant strains were found. A high occurrence of the multiple resistant bacteria to different classes of newer antimicrobials was seen. The gap in the resistant ratio on the boundary between the mountainous area and urbanized area suggests that the antimicrobial resistance is a more sensitive indicator for fecal contamination than the density of E. coli. The resistant ratios of the environmental samples taken even at the middle to downstream in the watershed were lower than those of clinical isolates reported in a nationwide monitoring.

Keywords; antimicrobial resistance, Escherichia coli, third-generation cephalosporins, fluoroquinolones.

Profile of antibiotic resistance of Escherichia coli isolated from different water environments

ABSTRACT; Syo TERADA, Hidemi MIYAKE, and Taro URASE. J. of Japan Society on Water Environment, 35, 5, 73-80, 2012.

The incidence and the profile of resistance to antibiotics were examined for Escherichia coli isolated from different water environments. Strains of the bacterium isolated from a stream in a mountain area showed relatively simple profiles of resistance to only one antibiotic. Those isolated from treated wastewater showed a profile of simultaneous resistance to various antibiotics including cephalosporins of latter generation, new quinolones, and aminoglycosides, which are intensively used in human therapy. Strains isolated from the Tama River on clear days showed similar characteristics to those isolated from treated wastewater, while a considerable number of those isolated on rainy days were resistant to tetracycline, possibly linked to the effect of livestock farming. The incidence of resistances to cephalosporins of different generation was dependent on origin of the samples.

Keywords; antibiotic resistance; water environments; Escherichia coli; treated wastewater.

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