title: Pathogenic and commensal Escherichia coli from irrigation water show potential in transmission of extended spectrum and AmpC β-lactamases determinants to isolates from lettuce.
abstract: There are few studies on the presence of extended-spectrum β-lactamases and AmpC β-lactamases (ESBL/AmpC) in bacteria that contaminate vegetables. The role of the production environment in ESBL/AmpC gene transmission is poorly understood. The occurrence of ESBL/AmpC in Escherichia coli (n = 46) from lettuce and irrigation water and the role of irrigation water in the transmission of resistant E. coli were studied. The presence of ESBL/AmpC, genetic similarity and phylogeny were typed using genotypic and phenotypic techniques. The frequency of β-lactamase gene transfer was studied in vitro. ESBLs/AmpC were detected in 35 isolates (76%). Fourteen isolates (30%) produced both ESBLs/AmpC. Prevalence was highest in E. coli from lettuce (90%). Twenty-two isolates (48%) were multi-resistant with between two and five ESBL/AmpC genes. The major ESBL determinant was the CTX-M type (34 isolates). DHA (33% of isolates) were the dominant AmpC β lactamases. There was a high conjugation efficiency among the isolates, ranging from 3.5 × 10(-2) to 1 × 10(-2)  ± 1.4 × 10(-1) transconjugants per recipient. Water isolates showed a significantly higher conjugation frequency than those from lettuce. A high degree of genetic relatedness between E. coli from irrigation water and lettuce indicated possible common ancestry and pathway of transmission.
authors.affiliation: Department of Food Science, University of Pretoria, Lynwood Road, Pretoria, 0002, South Africa.
authors.forename: Patrick M K
authors.initials: PM
authors.lastname: Njage
authors.forename: Elna M
authors.initials: EM
authors.lastname: Buys
mesh_terms: D057914:Agricultural Irrigation; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D016000:Cluster Analysis; D003227:Conjugation, Genetic; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics / Q000302:isolation & purification*; D022761:Gene Transfer, Horizontal; D005838:Genotype; D018545:Lactuca / Q000382:microbiology*; D058889:Molecular Typing; D014871:Water Microbiology; D018440:beta-Lactam Resistance; D001618:beta-Lactamases / Q000235:genetics*; D047090:beta-Lactams / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D047090:beta-Lactams; D001618:beta-Lactamases