Aggregative swab sampling method for romaine lettuce show similar quality indicators and microbial profiles compared to composite tissue samples in a pilot study

Gathman, Rachel Jade

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https://hdl.handle.net/2142/115962 Copy

Description

Title

Aggregative swab sampling method for romaine lettuce show similar quality indicators and microbial profiles compared to composite tissue samples in a pilot study

Author(s)

Gathman, Rachel Jade

Issue Date

2022-07-22

Director of Research (if dissertation) or Advisor (if thesis)

Stasiewicz, Matthew J

Committee Member(s)

• Miller, Michael J
• Feng, Hao

Department of Study

Food Science & Human Nutrition

Discipline

Food Science & Human Nutrition

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• preharvest produce safety
• leafy greens
• microbial community
• food safety sampling

Abstract

The practice of collecting preharvest leafy greens composite tissue samples produces few positive pathogen results. Aggregative sampling is potentially more representative. The purpose of this pilot study was to determine aggregative swabs’ ability to pick up quality indicators, to detect Escherichia coli, and determine if microbial profiles of swabs and tissues were similar. Aggregative swabs (n=12) and composite tissues (n=14) were collected from a one-acre commercial romaine lettuce field in Salinas, CA. Some field portions were inoculated with a rifampicin resistant E. coli cocktail. Aerobic plate counts (APC), coliform counts, and generic E. coli presence were determined using culture-based methods. Further identification of bacteria, their abundances, and microbial diversity of the samples were determined from microbial community profiling using full-length 16S rRNA sequencing. Recovery of APCs were 9.17±0.43 and 9.21±0.42 log(CFU/g) for tissues and swabs, respectively. Means and variance differences between sample types were insignificant (p=0.38 and p=0.92, respectively). Coliform recoveries were 3.80±0.76 and 4.19±1.15 log(CFU/g) for tissues and swabs, respectively. Means and variance differences between sample types were insignificant (p=0.30 and p=0.16, respectively). Presence of generic E. coli showed that swabs could detect E. coli more often than tissues with 8/12 swabs detecting E. coli compared to 3/14 tissues. Microbial profiling revealed that swabs and tissues have similar alpha diversities (p=0.75) and the most prevalent bacterial taxa in similar abundances. These data suggest aggregative swabs perform similar, if not better, than tissue samples in recovering quality and food safety indicators.

Graduation Semester

2022-08

Type of Resource

Thesis

Copyright and License Information

Copyright 2022 Rachel Gathman

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