Comparison of methods for quantitating Salmonella enterica typhimurium and heidelberg strain attachment to reusable plastic shipping container coupons and preliminary assessment of sanitizer efficacy

Zhaohao Shi, Christopher A. Baker, Sang In Lee, Si Hong Park, Sun Ae Kim, Steven C. Ricke

Research output: Contribution to journalArticlepeer-review

6 Scopus citations

Abstract

Salmonella serovars, one of the leading contributors to foodborne illness and are especially problematic for foods that are not cooked before consumption, such as fresh produce. The shipping containers that are used to transport and store fresh produce may play a role in cross contamination and subsequent illnesses. However, methods for quantitatively attached cells are somewhat variable. The overall goal of this study was to compare conventional plating with molecular methods for quantitating attached representative strains for Salmonella Typhimurium and Heidelberg on reusable plastic containers (RPC) coupons, respectively. We attached Salmonella enterica serovar Typhimurium ATCC 14028 and serovar Heidelberg SL486 (parent and an antibiotic resistant marker strain) to plastic coupons (2.54 cm2) derived from previously used shipping containers by growing for 72 h in tryptic soy broth. The impact of the concentration of sanitizer on log reductions between unsanitized and sanitized coupons was evaluated by exposing attached S. Typhimurium cells to 200 ppm and 200,000 ppm sodium hypochlorite (NaClO). Differences in sanitizer effectiveness between serovars were also evaluated with attached S. Typhimurium compared to attached S. Heidelberg populations after being exposed to 200 ppm peracetic acid (PAA). Treatment with NaClO caused an average of 2.73 ± 0.23 log CFU of S. Typhimurium per coupon removed with treatment at 200 ppm while 3.36 ± 0.54 log CFU were removed at 200,000 ppm. Treatment with PAA caused an average of 2.62 ± 0.15 log CFU removed for S. Typhimurium and 1.41 ± 0.17 log CFU for S. Heidelberg (parent) and 1.61 ± 0.08 log CFU (marker). Lastly, scanning electron microscopy (SEM) was used to visualize cell attachment and coupon surface topography. SEM images showed that remaining attached cell populations were visible even after sanitizer application. Conventional plating and qPCR yielded similar levels of enumerated bacterial populations indicating a high concordance between the two methods. Therefore, qPCR could be used for the rapid quantification of Salmonella attached on RPC.

Original languageEnglish
Pages (from-to)602-608
Number of pages7
JournalJournal of Environmental Science and Health - Part B Pesticides, Food Contaminants, and Agricultural Wastes
Volume51
Issue number9
DOIs
StatePublished - 18 May 2016

Bibliographical note

Funding Information:
We thank the University of Arkansas, Fayetteville, Department of Food Science program for supporting a graduate student assistantship to author Christopher A. Baker and the Michael Johnson Scholarship for author Christopher A. Baker. Author Sun Ae Kim is supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2015R1A6A3A03016811).

Publisher Copyright:
© 2016 Taylor & Francis Group, LLC.

Keywords

  • Attachment
  • Fresh produce
  • Salmonella heidelberg
  • Salmonella typhimurium
  • Sanitization
  • Shipping containers

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