Molecular characterization and antibiotic resistance of Salmonella enterica serovar 1,4,[5],12:i:- environmental isolates from poultry farms

Salmonella enterica serovar 1,4,[5],12:i:- (S. 1,4,[5],12:i:-) has been recognized as an emerging foodborne pathogen in recent years. It can cause human salmonellosis predominated by the contamination of animal-derived foods such as raw poultry and pork. This study aimed to characterize the genetic diversity, plasmid replicon types, and antibiotic resistance of 15 S. 1,4,[5],12:i:- environmental isolates collected from two poultry farms using pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST), polymerase chain reaction-based replicon typing, and minimum inhibitory concentration approach. Ten different PFGE genotypes were detected, indicating a high diversity among these S. 1,4,[5],12:i:- isolates. Three sequence types (ST19, ST1544, ST34) were identified by MLST. Among them, ST1544 was first detected in S. 1,4,[5],12:i:- environmental isolates from poultry farms. All isolates were resistant to cefazolin, cefotetan, tobramycin, amikacin, and gentamicin, but susceptible to piperacillin-tazobactam, aztreonam, ceftazidime, cefepime, and ertapenem. Five incompatibility groups (Inc) of plasmids were identified, including IncFIIs (66.7%), IncHI2 (20%), IncI1 (6.7%), IncN (6.7%), and IncQ (6.7%). Among these, 80% of isolates carried at least one plasmid replicon type, and 20% of isolates carried multiple plasmid replicon types. Interestingly, the multidrug-resistant isolate 263 carried numerous resistance genes (i.e., qnrS, aac(6’)-Ib-cr, blaTEM, blaCTX-M-9, blaOXA-1, sul1, sul2, sul3, floR, and mcr-1) and class I integronase gene intI1, which possessed both IncHI2 and IncQ plasmids, suggesting that resistance genes may be horizontally transferred by the combination of IncHI2 and IncQ plasmids. Collectively, antibiotic-resistant S.1,4,[5],12:i:- isolates were first found in poultry farm environments in China, and its surveillance should be strengthened to prevent its further spread from poultry farms to foods.