Abstract
The wide usage of antibiotics contributes to the increase in the prevalence of antibiotic-resistant Salmonella. Plasmids play a critical role in horizontal transfer of antibiotic resistance markers in Salmonella. This study aimed to screen and characterize plasmid profiles responsible for antibiotic resistance in Salmonella and ultimately to clarify the molecular mechanism of transferable plasmid-mediated antibiotic resistance. A total of 226 Salmonella isolates were examined for antimicrobial susceptibility by a disk diffusion method. Thirty-two isolates (14.2%) were resistant to at least one antibiotic. The presence of plasmid-mediated quinolone resistance (PMQR) genes and β-lactamase genes were established by PCR amplification. PCR-based replicon typing revealed that these 32 isolates represented seven plasmid incompatibility groups (IncP, HI2, A/C, FIIs, FIA, FIB, and I1), and the IncHI2 (59.4%) was predominant. Antibiotic resistance markers located on plasmids were identified through plasmid curing. Fifteen phenotypic variants were obtained with the curing efficiency of 46.9% (15/32). The cured plasmids mainly belong to the HI2 incompatibility group. The elimination of IncHI2 plasmids correlated with the loss of β-lactamase genes (blaOXA-1 and blaTEM-1) and PMQR genes (qnrA and aac(6′)-Ib-cr). Both IncHI2 and IncI1 plasmids in a S. enterica serovar Indiana isolate SJTUF 10584 were lost by curing. The blaCMY -2-carrying plasmid pS10584 from SJTUF 10584 was fully sequenced. Sequence analysis revealed that it possessed a plasmid scaffold typical for IncI1 plasmids with the unique genetic arrangement of IS1294-ΔISEcp1-blaCMY -2-blc-sugE-ΔecnR inserted into the colicin gene cia. These data suggested that IncHI2 was the major plasmid lineage contributing to the dissemination of antibiotic resistance in Salmonella and the activity of multiple mobile genetic elements may contribute to antibiotic resistance evolution and dissemination between different plasmid replicons.
Highlights
Salmonella is recognized as the predominant pathogen implicated in bacterial foodborne diseases worldwide (Yang et al, 2016)
Further active surveillance is needed to minimize the spread of particular plasmids such as IncHI2 group to control the dissemination of antibiotic resistance
We screened and characterized antibiotic resistance plasmids from clinical and food Salmonella isolates in this study and discovered that IncHI2 was the major plasmid lineage contributing to the dissemination of antibiotic resistance in Salmonella
Summary
Salmonella is recognized as the predominant pathogen implicated in bacterial foodborne diseases worldwide (Yang et al, 2016). The emergence of multidrug-resistant (MDR) Salmonella strains due to the prolonged and extensive usage of antibiotics has become a public health issue. Such resistance toward medically significant antimicrobial agents including fluoroquinolones and Antibiotic resistance plasmids in Salmonella extended-spectrum cephalosporins (ESCs) that are regarded as primary treatment options for bacterial infections will make it difficult for antibiotic therapy due to the reduced efficiency of empirical strategies as well as limited choice of treatment (Wong et al, 2014; Folster et al, 2015). It has been reported that plasmids with IncA/C, B/O, HI1, HI2, I1, N, F, and P replicons are often associated with MDR in Salmonella, while many of them are found to be co-resident in some MDR Salmonella strains (Poole et al, 2009; Glenn et al, 2013)
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