Resistance mechanisms and farm-level distribution of fecal Escherichia coli isolates resistant to extended-spectrum cephalosporins in pigs in Spain.
BACKGROUND
Fecal Escherichia coli isolates showing a phenotype of reduced susceptibility or resistance to extended-spectrum cephalosporins are common among pigs in Spain. The aim of this study was to describe the main beta-lactam resistance mechanisms carried by these strains and their distribution at farm-level.


METHODS
Twenty-nine E. coli isolates showing reduced susceptibility or resistance to extended-spectrum cephalosporins were collected from a sampling frame of 80 pig farms distributed over 13 Spanish provinces. The survey was carried out at the slaughterhouse level in 2004.


RESULTS
Of the 29 isolates, 21 (72%) met the criteria for a positive phenotypic confirmatory test for extended-spectrum beta-lactamases (ESBL). The following ESBLs were detected: SHV-12 (12 isolates, 41%), CTX-M-1 (three isolates, 10%), CTX-M-9 (three isolates, 10%), and CTX-M-14 (three isolates, 10%). The remaining eight isolates (28%) were phenotypically non-ESBL, with seven of them (24%) showing mutations on the chromosomal ampC gene promoter at positions -42 (C-->T), -18 (G-->A), -1 (C-->T), and +58 (C-->T). A multiplex PCR for detection of plasmidic class C beta-lactamases was negative for all isolates.


CONCLUSIONS
Different ESBLs and other mechanisms linked to extended-spectrum cephalosporin resistance are widely distributed among fecal E. coli from slaughter pigs in Spain.
Escudero
E
E
Centro de Vigilancia Sanitaria Veterinaria, Universidad Complutense, Madrid, Spain.
Vinué
L
L
Teshager
T
T
Torres
C
C
Moreno
M A
MA
D000822:Animal Husbandry; D000818:Animals; D018550:Cephalosporin Resistance; D004927:Escherichia coli Infections / Q000188:drug therapy / Q000453:epidemiology / Q000635:transmission / Q000662:veterinary*; D005243:Feces / Q000382:microbiology; D010641:Phenotype; D016133:Polymerase Chain Reaction; D013030:Spain / Q000453:epidemiology; D013552:Swine / Q000382:microbiology; D013553:Swine Diseases / Q000188:drug therapy* / Q000453:epidemiology / Q000635:transmission; D001618:beta-Lactamases / Q000235:genetics
D001618:beta-Lactamases