EPIDEMIOLOGY, ECOLOGY, AND MOLECULAR GENETICS OF ANTIMICROBIAL RESISTANCE IN PATHOGENIC AND COMMENSAL BACTERIA FROM FOOD ANIMALS
Location: Bacterial Epidemiology and Antimicrobial Resistance
Title: Genetic characterization of antimicrobial resistance and virulence genes in “emerging” Salmonella Javiana from humans
Submitted to: American Society for Microbiology Conference
Publication Type: Abstract Only
Publication Acceptance Date: June 8, 2010
Publication Date: June 8, 2010
Citation: Nayak, R., Deck, J., Frye, J.G., Foley, S., Stefanova, R. 2010. Genetic characterization of antimicrobial resistance and virulence genes in “emerging” Salmonella Javiana from humans. American Society for Microbiology Conference. Toronto, Canada. P.36. Poster B-2.
Background: Salmonellosis continues to be a major cause of food borne infections. Over 2,500 Salmonella serovars have been reported worldwide. Among these serovars, the CDC, in 2004, has reported >500% baseline increase in the emergence of Javiana populations in the U.S. Furthermore, this pathogen is the fifth most common serovar submitted to the CDC’s PulseNet database. Exposures to amphibians and consumption of tomatoes have been implicated with S. Javiana outbreaks. There is limited genetic information about this emerging pathogen. Materials and Methods: Clinical S. Javiana isolates (n=409) were analyzed for antimicrobial susceptibility with 15 drugs, plasmid profiles, replicon-typing and virulence genes. Resistant phenotypes with multiple plasmids were further analyzed by a high-density [775 antimicrobial resistance (AMR) genes] microarray to identify the gene profiles that may contribute to drug resistance. Results: <1% of S. Javiana was resistant to the any of the drugs tested. Isolates (n=11) elicited resistance to gentamicin, streptomycin, chloramphenicol, sulfonamides, tetracycline, nalidixic acid, ciprofloxacin or ceftiofur. MDR-phenotypes harbored multiple plasmids (<3 to 165 kb). In general, fluoroquinolone resistant phenotypes harbored low to mid range plasmids (<3 to 68 kb), while aminoglycosides (AG) phenotypes harbored larger plasmids (up to 165 kb). Interestingly, susceptible phenotypes also harbored multiple plasmids (43 to 87 kb). Microarray analysis identified conventional and novel AMR genes for aminoglycosides [aac(3/6), aad(A1/B/E), aph ksg, ntpII, str, yeoO), ß-lactams (ampR, blaIMP-4/PER2, oxa2, pse1, tem), chloramphenicol (cat, flo), efflux system (acrR, corA, emrA/R, marA/B/R, mexR, msrC, ybit), tetracycline (tetA/H/R), trimethoprim (dhf), along with genes encoding for AG phosphate transferase, streptomycin kinase, ABC transporters and several proteins with unknown functions. In addition, these bacteria harbored transfer associated genes (insA, intA, transposase, repE, tnpA1S26), heavy metals (merF/R/T) and disinfectant (qacE'1) genes. The PCR-based replicon typing assay detected 4 (p-1 is proportional to, T, W or I1) of 18 tested plasmid types based on their incompatibility (Inc) replicon types. PCR analysis of 26 virulence genes indicated that these bacteria harbored aceK, cdtB, fimH, hilA, invA/H, iron, orgA, pagC, prgH, sipB, sopB, spiA and tolC. Discussion and Conclusions: Although AMR appears to be limited in S. Javiana, resistant isolates elicit multiple mechanisms of drug resistance, carry multiple plasmids (conventional and replicon), and specialized genes involved in transfer of drug resistance. Furthermore, both resistant and susceptible isolates harbor multiple virulence genes that may exacerbate the disease causing potential of this Salmonella serotype in food and human outbreak scenarios.