Abstract:
A total of 355 Escherichia coli isolates from swine were comprising of group I, non Halquinol-exposed E. coli isolates (n=203) and group II, Halquinol-exposed E. coli isolates (n=152). All samples were assayed for usceptibility to Halquinol and 8 antibiotics. Two antibiotic-susceptible E. coli isolates with low Halquinol MIC and E.coli MG1655rifr were used for Halquinol-exposure experiment. Nineteen of the E. coli isolates from group II that exhibited high Halquinol MIC and contained plasmid were assessed for transfer of Haquinol resistance. Most of E. coli in group I (69.1%) exhibited Halquinol MIC of 32-64 ug/ml. The E. coli isolates in group ll formed a large population (86.7%) with Halquinol MIC range 4-64 ug/ml and a frequency peak at MIC of 128 ug/ml (11.8%). The Halquinol MIC90 of E. coli in group I and II were 64 and 128 ug/ml, respectively. Resistance rates to al antibiotics (except trimethoprim) of E. coli in group I were significantly greater than that of E.coli in group II (p<0.05). Most of the E. coli isolates from both groups were multiresistant. Forty-one resistance patterns were defined and the most commnon resistance pattern (16%) wa ampicillin-chloramphenicol-ciprofloxacn-gentamicin-streptomycin-sulfomethoxazole-tetracycline. No spontaneous Halquinol-resistant mutants were obtained and no cross-resistance to antibiotics was observed. Halquinol resistance was not horizontally transferred.
