Further Characterization of Three Yersinia enterocolitica Strains with a Nalidixic Acid–Resistant Phenotype Isolated from Humans with Diarrhea

Abstract Antimicrobial-resistant bacteria pose a threat to public health. Three Yersinia enterocolitica strains cultured from patients presenting with diarrhea and resistant to nalidixic acid were studied. Target gene mutations in gyrA alone were identified as part of the genetic basis for this phenotype. Efflux activity was also noted, since the presence of the efflux pump inhibitor, phenylalanine-arginine-β-naphthylamide, increased susceptibility to nalidixic acid.