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Abstract
Antimicrobial susceptibility testing was performed on a total of 581 clinical Escherichia
coli isolates from diarrhea and edema disease in pigs, from acute mastitis in dairy
cattle, from urinary tract infections in dogs and cats, and from septicemia in laying
hens collected in Switzerland between 1999 and 2001. Among the 16 antimicrobial agents
tested, resistance was most frequent for sulfonamides, tetracycline, and streptomycin.
Isolates from swine presented significantly more resistance than those from the other
animal species. The distribution of the resistance determinants for sulfonamides,
tetracycline, and streptomycin was assessed by hybridization and PCR in resistant
isolates. Significant differences in the distribution of resistance determinants for
tetracycline (tetA, tetB) and sulfonamides (sulII) were observed between the isolates
from swine and those from the other species. Resistance to sulfonamides could not
be explained by known resistance mechanisms in more than a quarter of the sulfonamide-resistant
and sulfonamide-intermediate isolates from swine, dogs and cats. This finding suggests
that one or several new resistance mechanisms for sulfonamides may be widespread among
E. coli isolates from these animal species. The integrase gene (intI) from class I
integrons was detected in a large proportion of resistant isolates in association
with the sulI and aadA genes, thus demonstrating the importance of integrons in the
epidemiology of resistance in clinical E. coli isolates from animals.