Abstract: Objective: In this study, the prevalence, antimicrobial susceptibility, antibiotic resistance associated genes and horizontal transfer of the IncI1 and IncN plasmid positive Salmonella recovered from retail foods, clinical patients and food animals in Beijing, Shanghai, Henan, Sichuan, Guangdong, Guangxi, Shaanxi and Xinjiang province, respectively, were investigated. Methods: The incompatible plasmids IncI1 and IncN in Salmonella were screened by PCR replicon typing method, the antimicrobial susceptibility was tested via agar dilution method, antibiotic resistance associated genes were detected using PCR; the horizontal transfer of IncI1 and IncN plasmid were conducted via conjugation. Results: Forty-two IncI1 positive isolates (4.39%) and 3 IncN positive isolates (0.31%) were identified among the 956 Salmonella. Of 26 IncI1 and/or IncN plasmid positive Salmonella representatives, antibiotic resistance was commonly found to ceftiofur (100.0%), nalidixic acid (92.3%), ampicillin (92.3%), cefoperazone (88.5%), tetracycline (84.6%), ceftriaxone (80.8%), and sulfamethoxazole/trimethoprim (76.9%), streptomycin (76.9%) and chloramphenicol (61.5%); and followed by kanamycin (26.9%), gentamicin (23.1%), polymyxin B (23.1), ciprofloxacin (19.2%), amoxicillin-clavulanic acid (15.4%), cefoxitin (11.5%) and amikacin (3.8%). IncI1 plasmid positive Salmonella exhibited broader antibiotic-resistance profiles and higher resistance ability to cephalosporins than that of IncN plasmid positive ones, whereas IncN plasmid positive isolates were more resistant to aminoglycoside antibiotics. blaTEM and blaCTX-M were more frequently detected from IncI1 positive Salmonella; however, qnrA, qnrB and qnrS were more prevalent in IncN positive isolates. The IncI1 and/or IncN plasmid in the donor strains could transfer to the recipient Salmonella at conjugation frequency ranging from 3.2×10-5 to 2.0×10-3 transconjugant per recipient cell, while to E. coli at 8.7×10-7 to 9.6×10-5. Antibiotic resistance encoding genes qnrB, acc (6’)-Ib, blaTEM and blaCTX-M could be transferred from donors to the recipient Salmonella and Escherichia coli during conjugation. The recipients acquired antibiotic resistance phenotypes to kanamycin, ceftiofur, ceftriaxone, ampicillin, streptomycin, and gentamicin after conjugation. Conclusion: The prevalence of IncI1 and IncN plasmid positive Salmonella was relatively low, the antibiotic resistance phenotypes of the hosts were found associating with the types of plasmids they carried to some extent. Antibiotic resistance encoding genes in the plasmid could transfer from the donor to the recipient by horizontal gene flow among different species, which conferred resistance to the recipient.

Key words: Salmonella, IncN plasmid, IncI1 plasmid, antibiotic resistant genes, conjugative transfer