Characterization Of Clinical Shigella Isolates Producing Both Of The Extended-spectrum And AmpC Beta-lactamases

Objective To determine the phenotypes and genotypes of extended-spectrum β-lactamases (ESBLs) and AmpC β-lactamases as well as the virulence features of certain cefoxitin-resistant Shigella isolates.Methods K-B diffusion method was used to screen cefoxitin-resistant strains from356Shigella isolates and serotypes of the cefoxitin-resistant strains were subsequently determined. The phenotypes of ESBLs and AmpC beta-lactamases of the cefoxitin-resistant strains were detected by ESBLs confirmatory test and AmpC-three-dimensional test, respectively. Genotypes of while the ESBLs and AmpC were determined by PCR and sequence analysis. Moreover, the virulence genes (virA, ial, iapH, setlA, set1B and sen) in the cefoxitin-resistant strains were screened by PCR.Results Eight cefoxitin-resistant strains were identified from the356Shigella isolates. Six of the eight strains were identified as S. fleaneri (four F2a, one F2B and one F2c), and two were identified as S.sonnei. In the eight cefoxitin-resistant strains, five strains were positive for ESBLs confirmatory test and two strains positive for AmpC-three-dimensional test. Seven of the eight strains harbor ESBLs genes (CTX-M-14,15,57and/or OXA-30), in which two strains were positive for AmpC genes (DHA-1and CMY-2). Five of the eight cefoxitin-resistant strains carried all the six tested virulence genes while the other three strains possessed four virulence genes except for setlA and setlB. The two strains that produced both of the ESBLs and AmpC beta-lactamases were only susceptible to imipenem.Conclusion Most of the cefoxitin-resistant Shigella isolates produce ESBLs with high virulence potential, while some of them also produce AmpC P-lactamases, in which DHA-1type AmpC beta-lactamase is reported in Shigella for the first time in China.