This study attempted to correlate quinolone-resistant phenotypes and genetic traits in Enterococcus faecalis from healthy chickens and pigs in Taiwan. The percentage of E. faecalis isolates resistant to ciprofloxacin was 54.0% (162/300) in pigs and 53.5%(107/200) in chickens. Two hundred and sixty-nine ciprofloxacin-resistant E. faecalis isolates showed different levels of resistance to ciprofloxacin (MIC 4 - 512 mg/L), enrofloxacin (MIC 8 - 512 mg/L) and moxifloxacin (MIC 0.5 - 512 mg/L). Two mutations associated with resistance were detected in GyrA at Ser83 (to Arg/Ile) and Glu87 (to Lys/Gly) and one mutation was found in ParC at position 80 (Ser to Ile). In addition, triple-point mutation in DNA gyrase (GyrA) and topoisomerase IV (ParC) of E. faecalis was firstly
reported. Thirty-six isolates with no amino acid substitution in GyrA or ParC showed high levels of ciprofloxacin resistance. In the
presence of reserpine, the levels of resistance to ciprofloxacin for these 36 strains were decreased. The effect of reserpine on ciprofloxacin
resistance was correlated with the level of expression of the emeA gene. Our results demonstrate that not only point mutations in topoisomerase IV and DNA gyrase but also the efflux pump can be used by E. faecalis to generate resistance to quinolones.