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Title: Characterization of Salmonella isolates from retail foods based on serotyping, pulse field gel electrophoresis, antibiotic resistance and other phenotypic properties

Author
item XIA, XIADONG - UM, COLLEGE PK, MD
item ZHAO, SHAOHUA - FDA, LAUREL, MD
item Smith, Allen
item McEvoy, James
item JIANGHONG, MENG - UM, COLLEGE PK, MD
item Bhagwat, Arvind

Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/2/2008
Publication Date: 1/1/2009
Citation: Xia, X., Zhao, S., Smith, A.D., Mcevoy, J.L., Jianghong, M., Bhagwat, A.A. 2009. Characterization of Salmonella isolates from retail foods based on serotyping, pulse field gel electrophoresis, antibiotic resistance and other phenotypic properties. International Journal of Food Microbiology. 129:93-98.

Interpretive Summary: Salmonella enterica serovar strains are important food-borne pathogens and the ability of the pathogen to survive environmental stress conditions plays a crucial role in the spread of salmonelosis. The severity of the illness also varies among various strains of this pathogen. Only limited information exists related to growth, biochemical and genetic characteristics of S. enterica serovar strains isolated from retail foods. We used DNA-based analysis in combination with antibiotic resistance profiles to classify different Salmonella isolates obtained from retail foods. The characterization of Salmonella isolates with the proposed scheme enabled us to determine the potential risk associated with individual strains. Both the food-preparation industry and consumers will benefit from the results of this research.

Technical Abstract: Sixteen Salmonella strains isolated from a variety of foods during 2000 and 2003, by the Florida State Department of Agriculture, were characterized by various genotypic and phenotypic tests. Among 16 isolates, 15 different serotypes were identified. Pulse-Field Gel Electrophoresis (PFGE) fingerprinting profiles obtained using restriction endonucleases XbaI and BlnI revealed that 16 Salmonella isolates were genetically diverse with 16 unique PFGE patterns. The PFGE pattern of eight isolates matched with the CDC/FDA data base of previous outbreak and clinical isolates indicating their potential to cause disease. With the exception of isolates obtained from alligator meat (tetracycline resistant) and orange juice (chloramphenicol and sulfisoxazole resistant), the remainder of the isolates were susceptible to the panel of 15 antimicrobials tested. The induced acid tolerance level of the isolate obtained from orange juice was not significantly different from the laboratory reference strain S. enterica serovar Typhimurium SL1344. Six isolates exhibited very low levels of constitutive acid-tolerance, of which four isolates failed to infect differentiated Caco-2 cells. Only one isolate was defective in constitutive and inducible acid-tolerance pathways and failed to infect Caco-2 cells. We also determined the biofilm formation ability of all 16 isolates. Although all isolates formed biofilms, there was no clear relation between the ability to form biofilms, infect differentiated Caco-2 cells and induce acid-tolerance. This study indicated that different serotypes of Salmonella were present in a variety of retail foods and exhibited diverse phenotypic characteristics.