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Title: Detection of Salmonella enterica subpopulations by phenotype microarray antibiotic resistance patterns

item Guard, Jean
item Morales, Cesar
item Frye, Jonathan
item Gast, Richard
item Musgrove, Michael

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/26/2007
Publication Date: 12/1/2007
Citation: Bouldin, J.G., Morales, C., Frye, J.G., Gast, R.K., Musgrove, M.T. 2007. Detection of Salmonella enterica subpopulations by phenotype microarray antibiotic resistance patterns. Applied and Environmental Microbiology. 73:7753-7756.

Interpretive Summary: Three strains of Salmonella Enteritidis with characterized genomes and phenotypes were compared to Salmonella Heidelberg, Salmonella Newport and Salmonella Typhimurium for growth in the presence of 240 serially-diluted antibiotics contained within a high throughput phenotype microarray. Monomorphic subpopulations of Salmonella Enteritidis that varied in phenotype and pathotype had significantly different growth patterns in glycine, sorbic acid and sodium selenite and in the '-lactam antibiotics amoxicillin, penicillin G, oxacillin, carbenicillin and phenethicillin. Monomorphic strains of Salmonella Enteritidis PT13a could be differentiated from dimorphic Salmonella Enteritidis PT4, Salmonella Typhimurium, Salmonella Heidelberg and Salmonella Newport by a group of 36 antibiotics. A monomorphic egg-contaminating strain of Salmonella Enteritidis was resistant to '-lactam antibiotics as a class. Resistance to tetracycline antibiotics was not supported by phenotype microarray although conventional assay suggested it was present. In summary, results show that antibiotic compounds included within a high throughput phenotype microarray detect physiological differences in Salmonella Enteritidis that emerge from small scale evolutionary events.

Technical Abstract: Salmonella enterica subspecies I is an important cause of food borne illness. We compared 6 strains of for resistance to 240 antibiotics that were included in a commercially available panel and also compared the strains by a conventional assay that is used to determine clinical resistance. Differences were found between the two assays. The panel of 240 antibiotics, called a phenotype microarray (PM), detected differences in strains that were genetically related and that had less than 0.01% variation in nucleotide sequence (excluding lysogenic bacteriophage). Results suggested that some types of low-level antibiotic resistance emerge from very small scale evolutionary events and that resistance patterns differ somewhat between assays. Additional infection studies in hens suggested that evaluating strains for low-level antibiotic resistance and the ability to disrupt egg production post-infection could be used to rank Salmonella of different serotypes for their potential to make their way into the food supply by contaminating eggs. This research is linked to genomic analysis of Salmonella enterica serovar Enteritidis that reports results through the National Center for Biotechnology Information (NCBI) at website