There are few studies on the presence of extendedspectrum
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.