Evaluation of a polymerase chain reaction-based system for detection of Salmonella enteritidis, Escherichia coli O157 : H7, Listeria spp., and Listeria monocytogenes on fresh fruits and vegetables

A polymerase chain reaction (PCR)-based detection system, BAX, was evaluate d for its sensitivity in detecting Salmonella Enteritidis, Escherichia coil O157:H7, Listeria sp., and Listeria monocytogenes on fresh produce. Fiftee n different types of produce (alfalfa sprouts, green peppers, parsley, whit e cabbage, radishes, onions, carrots, mushrooms, leaf lettuce, tomatoes, st rawberries, cantaloupe, mango, apples, and oranges) were inoculated, in sep arate studies, with Salmonella Enteritidis, E. coli O157:H7, and L. monocyt ogenes down to the predicted level of 1 CFU per 25-g sample. Detection by B AX was compared to recovery of the inoculated bacteria by culture methods a ccording to the Food and Drug Administration's (FDA) Bacteriological Analyt ical Manual (BAM). BAX was essentially as sensitive as the culture-based me thod in detecting Salmonella Enteritidis and L. monocytogenes and more sens itive than the culture-based method for the detection of E, coli O157:H7 on green pepper, carrot, radish, and sprout samples. Detection of the pathoge nic bacteria in samples spiked with a predicted number of less than 10 CFU was possible for most produce samples, but both methods failed to detect L. monocytogenes on carrot samples and one of two mushroom and onion samples spiked with less than 100 CFU. Both BAX and the culture method were also un able to consistently recover low numbers of E. coli O157:H7 from alfalfa sp routs. The PCR method allowed detection of Salmonella Enteritidis, E. coli O157:1-17, and L. monocytogenes at least 2 days earlier than the convention al culture methods.