Affiliation:
1. Department of Food and Environmental Safety, Veterinary Laboratories Agency, Addlestone, Surrey KT153NB
2. Laboratory for Enteric Pathogens, Health Protection Agency, London NW95HT, United Kingdom
Abstract
ABSTRACT
Extended-spectrum β-lactamase (ESBL)-mediated resistance is of considerable importance in human medicine. Recently, such enzymes have been reported in bacteria from animals. We describe a longitudinal study of a dairy farm suffering calf scour with high mortality rates. In November 2004, two
Escherichia coli
isolates with resistance to a wide range of β-lactams (including amoxicillin-clavulanate and cefotaxime) were isolated from scouring calves. Testing by PCR and sequence analysis confirmed the isolates as being both
bla
CTX-M14/17
and
bla
TEM-35
(IRT-4)
positive. They had indistinguishable plasmid and pulsed-field gel electrophoresis (PFGE) profiles. Transferability studies demonstrated that
bla
CTX-M
was located on a conjugative 65-MDa IncK plasmid. Following a farm visit in December 2004, 31/48 calves and 2/60 cows were positive for
E. coli
with
bla
CTX-M
. Also, 5/48 calf and 28/60 cow samples yielded
bla
CTX
- and
bla
TEM
-negative
E. coli
isolates that were resistant to cefotaxime, and sequence analysis confirmed that these presented mutations in the promoter region of the chromosomal
ampC
gene. Fingerprinting showed 11 different PFGE types (seven in
bla
CTX-M
-positive isolates). Six different PFGE clones conjugated the same
bla
CTX-M
-positive IncK plasmid. One clone carried a different-sized,
bla
CTX-M
-positive, transformable plasmid. This is the first report of
bla
CTX-M
from livestock in the United Kingdom, and this report demonstrates the complexity of ESBL epidemiology. Results indicate that horizontal plasmid transfer between strains as well as horizontal gene transfer between plasmids have contributed to the spread of resistance. We have also shown that some clones can persist for months, suggesting that clonal spread also contributes to the perpetuation of resistance.
Publisher
American Society for Microbiology
Cited by
110 articles.
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