Location: Meat Safety and QualityTitle: Screening and characterization of genetic locus of heat resistance (LHR) in meat-borne Escherchia coli
Submitted to: American Society for Microbiology Conference
Publication Type: Abstract Only
Publication Acceptance Date: 6/22/2020
Publication Date: 6/22/2020
Citation: Guragain, M., Kalchayanand, N., Wang, R., Bosilevac, J.M. 2020. Screening and characterization of genetic locus of heat resistance (LHR) in meat-borne Escherchia coli [abstract]. American Society for Microbiology Microbe Conference. Available: https://www.abstractsonline.com/pp8/#!/9103/presentation/7252.
Technical Abstract: Prevalence of extreme heat resistant (XHR) bacteria in meat may pose a serious public health threat as thermal interventions are routinely used in meat processing to control contamination. The genetic basis of XHR in gram negative bacteria has been attributed to a locus of heat resistance (LHR). Despite the original report of XHR E. coli from a ground beef processing plant, there has been no study to assess XHR E. coli in meat processing environments in US. Therefore, this study aimed to screen for the LHR and XHR in previously collected E. coli isolates from various steps during animal harvest in meat processing environments (skins/hides, pre-intervention carcasses, final carcasses, and finished meat products). Isolates surviving 80°C for 20min were judged XHR. LHR was screened by a multiplex PCR that covered its 5’-, 3’-, and two internal regions. Prevalences were compared using Fisher’s exact test. E. coli isolated from beef (n=1054), veal (n=994), pork (n=517), and lamb (n=511) showed low overall prevalence (1%) of the LHR. The LHR+ isolates were most prevalent in beef (2%; P<0.05), and absent in pork. Two hundred and nine isolates tested positive for XHR phenotype, with the highest prevalence among veal (9%) and pork (8%), and lowest among lamb (2%; P<0.05). Only 9 XHR isolates were LHR+. Prevalence of XHR isolates was highest amongst skin (10%; p<0.05) and lowest amongst final carcasses (2%; p<0.05). While no LHR was observed among skins/hide isolates, finished meat products showed the highest prevalence of LHR (2%; P<0.05). Whole genome sequencing of four LHR+ XHR isolates (Beef 873, Sheep 2273, Beef 97, and Beef 730) by SMRT sequencing using v3.0 chemistry on PacBIO Sequel revealed that numbers and locations of the LHR varied among isolates. LHR sequence identities among the isolates ranged from 99% to 22%. Chromosomal LHR of 3 (Beef 873, Sheep 2273, and Beef 97) and plasmid LHR of 2 (Beef 873, and Beef 730) XHR isolates group together closely based on the nucleotide sequences. The most heat resistant isolate Beef 873 and the following isolate Sheep 2273 carry three homologs of LHR, the highest number per isolate reported to date. Two LHRs in Beef 873 and one in Sheep 2273 are plasmid borne. This study showed the distribution of LHR and XHR among meat-borne E. coli in the US. It further established a foundation to investigate the genetic background that allows optimal expression of heat resistance imparted by the LHR. Additionally, findings here strongly suggest a novel mechanism of heat resistance in the majority of XHR E.coli.