Emergence and Diversity of Salmonella enterica Serovar Indiana Isolates with Concurrent Resistance to Ciprofloxacin and Cefotaxime from Patients and Food-Producing Animals in China

Abstract

Salmonellosis is a major global foodborne infection, and strains that are resistant to a great variety of antibiotics have become a major public health concern. The aim of this study was to identify genes conferring resistance to fluoroquinolones and extended-spectrum β-lactams in nontyphoidal Salmonella (NTS) from patients and food-producing animals in China. In total, 133 and 21 NTS isolates from animals and humans, respectively, exhibiting concurrent resistance to ciprofloxacin and cefotaxime were cultured independently from 2009 to ∼2013. All of the isolates were identified, serotyped, and subjected to antimicrobial susceptibility testing. Importantly, the isolates with concurrent resistance to ciprofloxacin and cefotaxime all were confirmed as S. enterica serovar Indiana. The presence of fluoroquinolone resistance genes and extended-spectrum β-lactamases (ESBLs) was established by PCR and DNA sequencing. The occurrence and diversity of different genes conferring fluoroquinolone resistance [qepA, oqxAB, and aac(6')-Ib-cr] with mutations in topoisomerase-encoding genes (gyrA and parC) and several ESBLs (including CTX-M-65, CTX-M-27, CTX-M-15, CTX-M-14, and CTX-M-14/CTX-M-15) were noteworthy. Genes located on mobile genetic elements were identified by conjugation and transformation. Pulsed-field gel electrophoresis, used to determine the genetic relationships between these isolates, generated 91 pulsotypes from 133 chicken isolates and 17 pulsotypes from the 21 clinical isolates that showed considerable diversity. Analysis of the pulsotypes obtained with the isolates showed some clones appeared to have existed for several years and had been disseminating between humans and food-producing animals. This study highlights the emergence of ciprofloxacin- and cefotaxime-resistant S. enterica serovar Indiana, posing a threat to public health.

FIG 1

Plasmid profiles of representative S. enterica serovar Indiana isolates and transconjugants determined by S1-PFGE. Transmissible plasmids from S. enterica serovar Indiana and transconjugants (T) are highlighted. Lanes 1, 6, 11, and 14, marker H9812 with different bands labeled (used as a molecular size marker); lane 2, isolate P9; lane 3, isolate P9-(T); lane 4, isolate P10; lane 5, isolate P10-(T); lane 7, isolate D25; lane 8, isolate D25-(T); lane 9, isolate D26; lane 10, isolate D26-(T); lane 12, isolate D169; lane 13, isolate D169-(T).

FIG 2

Dendrogram of 21 clinical and 12 poultry S. enterica serovar Indiana isolates that were resistant to both ciprofloxacin and cefotaxime, constructed based on PFGE with XbaI on patient samples. The isolate identity, source, pulsotype, year of isolation, antimicrobial resistance profile, ESBL genes, mutations in QRDRs, and PMQR determinants were identified. D in strain names indicates isolates from poultry, and P indicates isolates from patients. DF, Dengfeng; JY, Jiyuan; HB, Hebi; KF, Kaifeng; LH, Luohe; SQ, Shangqiu; ZK, Zhoukou; ZZ, Zhengzhou; NT, an isolate whose plasmid replicon typing was nontypeable.