Escherichia coli and Salmonella enterica are major pathogens of worldwide importance in the animal industry. Antimicrobial therapy is an important tool in reducing the enormous losses caused by these infectious agents, however, resistance to existing antimicrobials espe- cially quinolones and fluoroquinolones is widespread and of concern to veterinarians. Iranian isolates of E. coli and S. enterica from different species of animals were examined for resistance to quinolones and fluoroquinolones. Thirty-five S. enterica isolates were recovered from different animal origins. Twenty-five E. coli strains were also isolated from poultry with colibacillosis. Eleven strains of E. coli were isolated from cloacal swabs from healthy chicken. All of the E. coli strains were identified by biochemical tests. Gene invA was detected in all of the Salmonella isolates. Serogroups of Salmonella were determined by colored rapid latex test. There was no relationship among serogroups of Salmonella and resistance to quinolones. In vitro antibiotic activities of four antibiotic substances against the isolates were determined by disk diffusion test. Forty percent of S. enterica and 96% of E. coli were found to be resistant to nalidixic acid. Fifty-six percent, 72%, and 36% of E. coli strains were resistant to ciprofloxacin, enrofloxacin, and norfloxacin, respectively. However, 11.42%, 22.85%, and 5.71% of Salmonella strains were resistant to ciprofloxacin, enrofloxacin, and norfloxacin, respectively.

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