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.

Fig 1

Illustrative multiplex PCR III for ACC (ACC-1 and ACC-2), FOX (FOX-1 to FOX-5), MOX (MOX-1, MOX-2, CMY-1, CMY-8 to CMY-11 and CMY-19), DHA (DHA-1 and DHA-2) and CIT (LAT-1 to LAT-3, BIL-1, CMY-2 to CMY-7, CMY-12 to CMY-18 and CMY-21 to CMY-23). Lanes L, DNA ladder; 1, RNAse free sterile water; 2, E. coli W1.8; 3, E. coli W1.9; 4, E. coli W 1.11; 5, E. coli L1; 6, E. coli W2.6; 7, E. coli W1.3; 8, E. coli W2.8; 9, E. coli W1.15; 10, E. coli W1.4; 11, E. coli L7; 12, E. coli W2.1; 13, E. coli W2.2; 14, E. coli W2.3; 15, E. coli W2.10; 16, E. coli W2.7; 17, E. coli W1.1; 18, E. coli W2.9; L, Quick-load, 100 bp DNA ladder (Biolabs New England). Expected amplicon sizes were 162 bp (FOX), 346 bp (ACC), 538 bp (CIT), 895 bp (MOX) and 997 bp (DHA).

Fig 2

The frequency of conjugative ESBL/AmpC β-lactamase resistance gene transfer among E. coli from lettuce and irrigation water. Vertical bars represent standard deviations.

Fig 3

Dendrogram for REP-PCR fingerprints of E. coli isolates obtained from irrigation water and lettuce and their ESBL/AmpC β-lactamase resistance profiles^a. Calculations were based on the Jaccard similarity coefficient using an unweighted pair group method with arithmetic average dendrogram type, 1.30% position tolerance and 2.00% optimization. ^aVariants explained in Table 1 footnote. Clusters defined at ≥ 85% similarity.