Effect of Enrichment Medium on Real-Time Detection of Salmonella enterica from Lettuce and Tomato Enrichment Cultures

• Published in: Journal of food protection 2010-06, Vol.73 (6), p.1047-1056
• Main Authors: GORSKI, Lisa, LIANG, Anita S
• Format: Article
• Language: English
• Subjects: Bacteria; Biological and medical sciences; Colony Count, Microbial - methods; Culture Media - chemistry; Dairy products; Disease Outbreaks - prevention & control; Enrichment; Fluorescent Dyes; Food contamination & poisoning; Food Contamination - analysis; Food industries; Food Microbiology; Food safety; Food science; Fundamental and applied biological sciences. Psychology; Gene expression; General aspects; Genes; Genomes; Humans; Immunology; Immunomagnetic Separation; Lactuca - microbiology; Lettuce; Lycopersicon esculentum; Methods of analysis, processing and quality control, regulation, standards; Microbiota; Peptones; Polymerase Chain Reaction; Salmonella; Salmonella enterica; Salmonella enterica - isolation & purification; Salmonella Food Poisoning - prevention & control; Solanum lycopersicum - microbiology; Species Specificity; Tomatoes; Vegetables
• ISSN: 0362-028X; 1944-9097
• DOI: 10.4315/0362-028X-73.6.1047

Three enrichment broths commonly used for detection of Salmonella (buffered peptone water [BPW], tryptic soy broth [TSB], and universal preenrichment broth [UPB]) were compared for use in real-time SYBR Green PCR detection of Salmonella introduced into enrichment cultures made from store-bought lettuce and tomatoes. The produce served as a source of normal plant microbiota to measure how well DNA-based detection methods for Salmonella work in a suspension of plant-associated bacteria that may be closely related to Salmonella. A qualitative assessment of the background microbiota that grew in the three enrichment broths cultures from tomato and lettuce samples revealed that different bacteria predominated in the different broths. Results obtained with five produce-related outbreak Salmonella strains and PCR primers directed toward three different Salmonella genes suggest that the ability to detect Salmonella from these enrichment cultures by real-time PCR was 10 to 1,000 times better with TSB enrichment cultures. Detection levels were similar between the different enrichment media when an immunomagnetic separation method was used; however, the immunological technique did not enhance detection from TSB enrichment cultures. Detection could be affected by the medium and by the background microbiota. An immunomagnetic separation method may be useful in BPW and UPB enrichment cultures but not in TSB enrichment cultures.