Variations in the Produce-Associated Microbiota and the Occurrence Frequency of Extended-Spectrum Beta-Lactamase Gram-Negative Bacteria Result in Different Level of Ingestion Risks

  • Osama Bokhari

Student thesis: Master's Thesis


A monitoring effort that spanned across one and a half years was conducted to examine three types of produce-associated microbiota. Produce type was determined to be the predominant factor affecting the microbial communities. Other significant factors that resulted in differences in the microbial populations were the origin and sampling date. Specifically, produce-associated microbiota among lettuce and tomatoes clustered based on the sampling period. Through molecular and cultivation-based approaches, sporadic presence of extended spectrum beta-lactamase (ESBL)-positive Klebsiella pneumoniae and Acinetobacter baumannii was detected on lettuce and cucumbers during certain periods of sampling. Quantitative microbial risk assessment denoted varying levels of ingestion risks associated with different types of produce. In particular, the risks arising from ESBL-positive K. pneumoniae in the lettuce were higher than the acceptable annual risk of 10-4. Commonly used approaches to clean and wash the produce were insufficient in removing majority of the produce-associated microbiota. More invasive cleaning approaches or thorough cooking of the produce would be required to mitigate the associated risks. Most of the current reports of ESBL-positive bacterial isolates were identified in nosocomial environment. However, the carriage of such drug-resistant bacteria in food that is consumed daily
Date of AwardApr 2016
Original languageEnglish (US)
Awarding Institution
  • Biological, Environmental Sciences and Engineering
SupervisorPeiying Hong (Supervisor)


  • Produce
  • Isolates
  • Type
  • Microbiota
  • Ingestion
  • Risk assessment

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