Comparison of chromogenic Shigella spp. plating medium with standard media for the recovery of Shigella boydii and Shigella sonnei from tomato surfaces

• Published in: Journal of food protection 2005-03, Vol.68 (3), p.621-624
• Main Authors: Warren, B.R, Parish, M.E, Schneider, K.R
• Format: Article
• Language: English
• Subjects: Bacteriological Techniques; Biological and medical sciences; Colony Count, Microbial; culture media; Culture Media - chemistry; food contamination; Food Contamination - analysis; Food industries; Food Microbiology; food pathogens; Fruit and vegetable industries; Fundamental and applied biological sciences. Psychology; General aspects; isolation; Methods of analysis, processing and quality control, regulation, standards; plate count; serotypes; Shigella - growth & development; Shigella - isolation & purification; Shigella boydii; Shigella boydii - growth & development; Shigella boydii - isolation & purification; Shigella sonnei; Shigella sonnei - growth & development; Shigella sonnei - isolation & purification; Solanum lycopersicum - microbiology; Species Specificity; surface area; taxonomy; tomatoes
• ISSN: 0362-028X; 1944-9097
• DOI: 10.4315/0362-028X-68.3.621

Isolation of Shigella spp. from food is difficult because of a lack of appropriate selective media and the presence of low numbers of shigellae relative to competitive microorganisms. Chromogenic Shigella spp. plating medium (CSPM) was evaluated for use with the U.S. Food and Drug Administration Bacteriological Analytical Manual (BAM) enrichment procedure for isolation of artificially contaminated Shigella boydii UI02 and Shigella sonnei UI05 from tomato surfaces. Tomatoes were inoculated with various concentrations of S. boydii UI02 or S. sonnei UI05 and rinsed using a shake-rub-shake procedure. Tomato rinses were enriched overnight according to the BAM procedure and streaked for isolation on CSPM, Salmonella-Shigella agar (SSA), and MacConkey agar (MAC). To access the isolation of S. boydii UI02 and S. sonnei UI05 without competition from natural tomato microflora, experiments were repeated using rifampin-adapted inocula and enrichments supplemented with 50 microg/ml rifampin. Isolation of S. boydii UI02 and S. sonnei UI05 with or without natural tomato microflora was not significantly different (P > 0.05) on CSPM, MAC, or SSA. Colony color enhancements created by CSPM may ease differentiation of Shigella colonies from those of closely related competitors.