Kempf Allen J, Hulsebus Holly J, Akbar Samina
1 Department of Microbiology and Immunology, Des Moines University , Des Moines, Iowa.
2 College of Osteopathic Medicine, Marian University , Indianapolis, Indiana.
Foodborne Pathog Dis. 2016 Jul;13(7):398-404. doi: 10.1089/fpd.2015.2067. Epub 2016 Apr 12.
Multiple drug resistance (MDR) in bacteria represents a notable problem but if carried on plasmid their spread could become a significant threat to public health. Plasmids in members of the Enterobacteriaceae family and in particular Salmonella and Escherichia coli strains have been implicated in the spread of antibiotic resistance genes. However, the mechanisms involved in the transfer of plasmid-borne resistance genes are not fully understood. Here, we analyzed the ability of Salmonella enterica clinical isolates to transfer plasmid-borne MDR to E. coli. We also determined whether possession of an Inc A/C plasmid by a S. enterica isolate would confer increased fitness compared to an isolate not carrying the plasmid. Sixteen human and animal isolates of S. enterica were screened using a three-panel multiplex PCR assay, and simplex PCR for the blaCMY-2 gene. Using these data we selected a suitable strain as a plasmid donor for the construction of a new Salmonella strain with an Inc A/C plasmid. This allowed us to compare isogenic strains with and without the Inc A/C plasmid in multiple growth, fitness, and invasion assays. The results showed that possession of Inc A/C plasmid confers significant fitness advantage when tested in J774 macrophages as opposed to HEp-2 cells where no significant difference was found. In addition, stress assays performed in vitro showed that the possession of this large plasmid by Salmonella strains tested here does not appear to incur a significant fitness cost. Gaining a better understanding of molecular mechanisms of plasmid transfer between pathogenic bacteria will allow us to characterize the role of MDR in pathogenicity of bacteria and to identify methods to reduce the frequency of dissemination of multiple antibiotic resistance genes.
细菌中的多重耐药性（MDR）是一个显著问题，但如果耐药性由质粒携带，其传播可能会对公众健康构成重大威胁。肠杆菌科成员中的质粒，特别是沙门氏菌和大肠杆菌菌株中的质粒，与抗生素抗性基因的传播有关。然而，质粒携带的抗性基因转移所涉及的机制尚未完全明了。在此，我们分析了肠炎沙门氏菌临床分离株将质粒携带的多重耐药性转移至大肠杆菌的能力。我们还确定了肠炎沙门氏菌分离株携带Inc A/C质粒相比不携带该质粒的分离株是否具有更强的适应性。使用三联多重PCR检测法和blaCMY - 2基因的单重PCR对16株人源和动物源的肠炎沙门氏菌分离株进行筛选。利用这些数据，我们选择了一个合适的菌株作为质粒供体，用于构建携带Inc A/C质粒的新型沙门氏菌菌株。这使我们能够在多种生长、适应性和侵袭试验中比较具有和不具有Inc A/C质粒的同基因菌株。结果表明，在J774巨噬细胞中进行测试时，携带Inc A/C质粒具有显著的适应性优势，而在HEp - 2细胞中测试时未发现显著差异。此外，体外进行的应激试验表明，此处测试的沙门氏菌菌株携带这种大质粒似乎不会产生显著的适应性代价。更好地了解病原菌之间质粒转移的分子机制，将有助于我们阐明多重耐药性在细菌致病性中的作用，并确定降低多重抗生素抗性基因传播频率的方法。
