Molecular characterization of extended-spectrum cephalosporin and fluoroquinolone resistance genes in Salmonella and Shigella isolated from clinical specimens in Thailand.

Antimicrobial resistance of and has become a major clinical and public health problem. The incident of co-resistance to third generation cephalosporins and fluoroquinolone is a serious therapeutic issue in Thailand. The present study aimed to investigate the antimicrobial resistance and molecular character of clinical and isolates. A total of 33 and 53 cefotaxime-resistant isolates were collected from human clinical cases in Thailand during the period from 2011-2018. The antimicrobial susceptibility of and was determined by the disk diffusion method, and extended-spectrum beta-lactamase (ESBL) production was characterized by the double-disk synergy test. Genotype characterization was performed by PCR and DNA sequencing. Thirty-two (97.0%) and fifty-two (98.1%) isolates of cefotaxime-resistant and , respectively, were identified as ESBL producers. (4 isolates), serovar 4,5,12:i:- (6 isolates), serovar Agona (2 isolates) and serovar Rissen (2 isolates) showed co-resistance to ciprofloxacin and cefotaxime or ceftriaxone. The combination of plus other ESBL and/or AmpC β-lactamase genes was the most dominant of the genotype patterns in ESBL-producing isolates. The plasmid harbouring the gene and mutations of (S83F, D87Y or D87G) and (T57S) genes was found in 2 ESBL-producing isolates. Three isolates harboured mutations in (S83L, D87Y or D87G), and only one phase I isolate showed mutations in both (S83L and D87G) and (S80I) genes. Among these clinical isolates, determinants were identified. Production of ESBLs is an important mechanism for resistance to extended-spectrum cephalosporins in and . The emergence of a decreased susceptibility to extended-spectrum cephalosporins and fluoroquinolone in ESBL-producing isolates has important clinical and therapeutic implications.