Evaluation and Monitoring of Microbial Hazards in Acidic Tropical Fruit Juices

NON-TECHNICAL SUMMARY: E. coli O157:H7, Salmonella, and L. monocytogenes are three serious pathogenic bacteria known to be present on fresh produce and able to survive in certain acidic juices. Little is known about the fate of these pathogenic bacteria in pineapple and guava juices. Moreover, the deadly pathogens may enter a viable-but-nonculturable state in response to stressing acidic conditions. Maintaining virulence and pathogenic potential, stressed cells of the pathogenic bacteria may be underestimated or even escape detection if standard culture methods are solely employed. This project investigates how the pathogenic bacteria survive in pineapple and guava juices. Novel methods will be developed to enhance recovery and detection of stressed bacterial cells in the acidic fruit juices.

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APPROACH: Fresh cultures of E. coli O157:H7, Salmonella and L. monocytogenes will be inoculated respectively into pineapple or guava juices. During incubation of the acidic fruit juices at ambient or refrigeration temperatures, culturability of the pathogenic bacteria will be determined by plating on selective and nonselective agars, whereas viability will be monitored using CTC-DAPI double staining and reverse transcription-polymerase chain reaction (RT-PCR). Moreover, oxygen scavengers and enterobacterial autoinducer will be applied to enhance recovery and culture-based detection of acid-stressed cells of the pathogenic bacteria in the fruit juices. Finally, ethidium monoazide-real time PCR will be employed for selective quantification of viable cells of E. coli O157:H7, Salmonella, and L. monocytogenes in pineapple and guava juices.