Submitted to: Applied and Environmental Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/30/2010
Publication Date: 7/30/2010
Citation: Chen, C., Lindsey, R.L., Strobaugh Jr, T.P., Meinersmann, R.J., Frye, J.G. 2010. Prevalence of ColE1-like plasmids and kanamycin resistance genes in Salmonella enterica serotypes. Applied and Environmental Microbiology. doi:10.1186/1471-2180-10-207. Interpretive Summary: Salmonella is a major bacterial food-borne pathogen that causes salmonellesis resulting in significant economic losses annually in US and worldwide. Many Salmonella strains are resistant to multiple antibiotics posing serious public and animal health concerns. Molecular methods employing PCR (polymerase chain reaction) were developed to detect the presence of a plasmid and a specific gene encoding the kanamycin (antibiotic) resistance gene found on this plasmid in Salmonella strains. The differences in the kanamycin resistance genes were compared to gain insight into the prevalence and distribution of these genes in various strains isolated from sick animals. Three groups of the small plasmids carrying these resistance genes were identified in this study. This study provides tools for characterization of Salmonella strains and increases our understanding of antibiotic resistance gene transmission, thus enabling the design of effective strategies to prevent or minimize the dissemination of the resistance genes.
Technical Abstract: Multi-antibiotic resistant Salmonella enterica serotypes are increasing in prevalence and concern in human and animal health. Many strains carry resistance determinants on plasmids; current practices focus heavily on large plasmids, and the role that small plasmids play in resistance gene transfer is largely unknown. Our previous studies showed that some isolates harbor ColE1-like plasmids carrying the aph gene responsible for kanamycin-resistance (KANR) phenotypes. One hundred and two KANR Salmonella isolates collected through the National Antimicrobial Resistance Monitoring System (NARMS) in 2005 were screened by PCR using ColE1 typing primer sets. Thirty isolates were found to be positive for ColE1. DNA from 27 isolates was able to transform into E. coli DH5alpha. Plasmids from the E. coli clones were propagated and subjected to further characterization. Restriction mapping revealed three major plasmid groups found in 3 or more isolates, and each group also consisted of 1 or 2 variants. The aph genes from the Salmonella isolates were amplified using PCR and sequenced. Nucleotide sequence results showed 4 different aph(3')-I genes, three of which were identical to entries in the NCBI GenBank database. The distribution of the ColE1 plasmid groups in association with the aph gene, Salmonella serotype, and isolate source was analyzed. Due to their high copy number and mobility, the ColE1-like plasmids may play a critical role in transmission of antibiotic resistance genes among enteric pathogens and these findings warrant a close monitoring of this plasmid incompatibility group.