Comparison of conventional culture methods and FTA filtration-nested PCR for the detection of Shigella boydii and Shigella sonnei on tomato surfaces.
Detection of Shigella boydii UI02 and Shigella sonnei UI05 artificially inoculated onto tomatoes was evaluated using enrichment protocols of the U.S. Food and Drug Administration's Bacteriological Analytical Manual (BAM) and the American Public Health Association's Compendium of Methods for the Microbiological Examination of Food (CMMEF), enrichment in Enterobacteriaceae enrichment (EE) broth supplemented with 1.0 microg/ml novobiocin and incubated at 42 degrees C, and FTA filtration-nested PCR. To assess the effect of natural tomato microflora on recovery, conventional culture enrichments were repeated using rifampin-adapted inocula and enrichment medium supplemented with 50 microg/ml rifampin. The lowest detection levels for S. boydii UI02 were > 5.3 x 10(5) (BAM, CMMEF, and EE broth) and 6.2 CFU per tomato (FTA filtration-nested PCR). For S. sonnei UI05, the lowest detection levels were 1.9 x 10(1) (BAM), 1.5 x 10(3) (CMMEF), 1.1 x 10(1) (EE broth), and 7.4 CFU per tomato (FTA filtration-nested PCR). Natural tomato microflora had a large impact on recovery of S. sonnei UI05 and completely inhibited recovery of S. boydii UI02. EE broth was inhibitory to S. boydii UI02. FTA filtration-nested PCR provided superior detection (P < 0.05) compared with the conventional culture enrichment protocols.
Department of Food Science and Human Nutrition, University of Florida, 359 FSHN Building, Newell Drive, Gainesville, Florida 32611, USA.
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Warren
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Schneider
D015169:Colony Count, Microbial / Q000379:methods*; D003470:Culture Media / Q000737:chemistry; D005374:Filtration; D005506:Food Contamination / Q000032:analysis*; D005516:Food Microbiology; D018551:Solanum lycopersicum / Q000382:microbiology*; D016133:Polymerase Chain Reaction / Q000379:methods; D012761:Shigella boydii / Q000302:isolation & purification*; D012764:Shigella sonnei / Q000302:isolation & purification*
D003470:Culture Media