Molecular typing of CTX-M-producing escherichia coli isolates from environmental water, swine feces, specimens from healthy humans, and human patients

Abstract

CTX-M-producing Escherichia coli is the predominant type of extended-spectrum β-lactamase (ESBL)-producing E. coli worldwide. In this study, molecular typing was conducted for 139 CTX-M-producing E. coli isolates, phenotypically positive for ESBLs, isolated from environmental water, swine, healthy humans, and hospitalized patients in Hangzhou, China. The antibiotic resistance profiles of the isolates for the cephalosporins and fluoroquinolones were determined. The isolates showed 100% resistance to cefotaxime and ceftriaxone while maintaining relatively high susceptibility to cefoxitin, cefepime, and ceftazidime. A total of 61.9% (86/139) of the isolates, regardless of origin, showed high resistance to fluoroquinolones. PCRs and DNA sequencing indicated that blaCTX-M-14 was the most prevalent CTX-M-9 group gene and that blaCTX-M-15 and blaCTX-M-55 were the dominant CTX-M-1 group genes. Isolates from all sources with CTX-M types belonging to the CTX-M-1 or CTX-M-9 group were most frequently associated with epidemics. Molecular homology analysis of the isolates, conducted by phylogenetic grouping, pulsed-field gel electrophoresis (PFGE), and multilocus sequence typing (MLST), demonstrated that the dominant clones belonged to B2-ST131, D-ST648, D-ST38, or A-CC10. These four sequence types (STs) were discovered in E. coli isolates both from humans and from environmental water, suggesting frequent and continuous intercompartment transmission between humans and the aquatic environment. Seven novel sequence types were identified in the current study. In conclusion, this study is the first to report the molecular homology analysis of CTX-M-producing E. coli isolates collected from water, swine, and healthy and hospitalized humans, suggesting that pathogens in the environment might originate both from humans and from animals.

Fig 1

Proportions of bacteria from each source belonging to phylogenetic groups A, B1, B2, and D. HP, hospitalized patients; HH, healthy humans. Pie charts 1, 2, 3, and 4 represent the distributions of isolates from hospitalized patients, healthy humans, pigs, and water, respectively. Pie chart 5 displays the proportion of all 139 CTX-M-producing E. coli strains in each phylogenetic group.

Fig 2

PFGE of XbaI-digested DNA from 19 A-CC10 E. coli isolates. An UPGMA dendrogram based on Dice similarity coefficients was generated using UVI-Band software (Bio-Rad). Eighty percent similarity was used as the cutoff point.

Fig 3

PFGE of XbaI-digested DNA from 16 D-ST38 E. coli isolates. An UPGMA dendrogram based on Dice similarity coefficients was generated using UVI-Band software (Bio-Rad). Eighty percent similarity was used as the cutoff point.

Fig 4

PFGE of XbaI-digested DNA from 20 B2-ST131 E. coli isolates. An UPGMA dendrogram based on Dice similarity coefficients was generated using UVI-Band software (Bio-Rad). Eighty percent similarity was used as the cutoff point.

Fig 5

PFGE of XbaI-digested DNA from 19 D-ST648 E. coli isolates. An UPGMA dendrogram based on Dice similarity coefficients was generated using UVI-Band software (Bio-Rad). Eighty percent similarity was used as the cutoff point.