Submitted to: American Society for Microbiology Annual Meeting
Publication Type: Abstract only
Publication Acceptance Date: 2/16/2007
Publication Date: 5/21/2007
Citation: Killinger-Mann, K.M., Dowd, S.E., Fralick, J.A., Brashears, M.M. 2007. Changes in expression of virulence mechanisms in three related Salmonella Typhimurium mutants with increasing multi-drug resistance properties, as determined by microarray analysis [abstract]. American Society for Microbiology 107th General Meeting, May 21-25, 2007, Toronto, Canada. Abstract No. K-101. Interpretive Summary:
Technical Abstract: Salmonella Typhimurium is a common cause of Salmonellosis and has been associated with multi-drug resistance. Previously, the wild-type strain (Salmonella Typhimurium ATCC 14028) was exposed to increasing concentrations of nalidixic acid to derive naturally occurring drug resistant isolates. Three derivatives were chosen to determine how changes in drug resistance profiles affect virulence gene expression. When tested for multi-drug resistance, 26A was sensitive to all drugs examined as was the wild-type. 1A was resistant to nalidixic acid and chloramphenicol, and 2A was resistant to 5 drugs: nalidixic acid, chloramphenicol, cefoxitin, sulfisoxazole and tetracycline. RNA was isolated, converted to labeled cDNA, and subjected to microarray analyses. Three biological replications were used to identify significantly (FDR<0.05) upregulated or downregulated genes validated with quantitative RT-PCR. Among the mutants, 46 genes were had the lowest level of expression in 26A, intermediate expression in 1A and the highest expression in the multidrug resistant 2A. For 27 genes, the highest expression was exhibited in 26A, with slightly lower expression in 1A and a dramatic decrease in expression for 2A. Finally, 121 genes had the highest expression in 26A, a significant decrease in 1A and a slightly lower level of expression in 2A. When comparing all 3 mutants to the wild-type strain, the following were upregulated in each of the mutants: acrA, acrB, and tolC, suggesting a mechanism for antibiotic resistance. As resistance increases, however, there are changes in expression of key virulence mechanisms including a repression of flagellar expression and changes in LPS and key pathogenicity islands including SPI1, SPI2, and SPI5. Motility, serotyping, and additional antibiotic resistance studies further confirm the results of the microarrays. Results suggest that these mutants may not be as pathogenic as the parent strain.