|Bosilevac, Joseph - Mick|
Submitted to: Frontiers in Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/15/2015
Publication Date: 9/23/2015
Publication URL: https://handle.nal.usda.gov/10113/61716
Citation: Luedtke, B.E., Bosilevac, J.M. 2015. Comparison of methods for the enumeration of enterohemorrhagic Escherichia coli from veal hides and carcasses. Front Microbiol. 6:1062. doi:10.3389/frmicb.2015.01062.
Interpretive Summary: Food safety is a continual concern during the processing of beef from farm to fork. Different types of E. coli can vary from causing severe disease to not harming humans. Recently, veal calves have been identified as a source of disease-causing pathogenic E. coli bacteria. During animal harvesting, fecal matter on hides is a potential source of contamination of the carcass with pathogenic E. coli. However, no current molecular assays have been developed to detect and enumerate pathogenic E. coli from veal hides and carcasses. In addition, current tests do not cover all the types of pathogenic E. coli and the protocols require 2 to 3 days for results. To address these problems, we compared three molecular assays that can rapidly detect and enumerate all types of pathogenic E. coli directly from veal hides and carcasses, even at low levels. The significance of this work is that it provides assays that are economical and can provide results in 1 to 2 days and are able to identify veal that are carrying any type of pathogenic E. coli so that focused antimicrobial interventions can be used to decrease the risk of meat contamination.
Technical Abstract: The increased association of enterohemorrhagic Escherichia coli (EHEC) with veal calves has led the United States Department of Agriculture Food Safety and Inspection Service to report results of veal meat contaminated with the Top 7 serogroups separately from beef cattle. However, detection methods that can also provide concentration for determining the prevalence and abundance of EHEC associated with veal are lacking. Here we compared the ability of qPCR and a molecular based most probable number assay (MPN) to detect and enumerate EHEC from veal hides at the abattoir and the resulting pre-intervention carcasses. In addition, digital PCR (dPCR) was used to analyze select samples. The qPCR assay was able to enumerate total EHEC in 32% of the hide samples with a range of approximately 34 to 91,412 CFUs/100 cm2 (95% CI 4-113,460 CFUs/100 cm2). Using the MPN assay, total EHEC was enumerable in 48% of the hide samples and ranged from approximately 1 to greater than 17,022 CFUs/100 cm2 (95% CI 0.4-72,000 CFUs/100 cm2). The carcass samples had lower amounts of EHEC with a range of approximately 4 to 275 CFUs/100 cm2 (95% CI 3-953 CFUs/100 cm2) from 17% of samples with an enumerable amount of EHEC by qPCR. For the MPN assay, the carcass samples ranged from 0.1 to 1 CFUs/100 cm2 (95% CI 0.02-4 CFUs/100 cm2) from 29% of the samples. The correlation coefficient between the qPCR and MPN enumeration methods indicated a moderate relation (R2=0.39) for the hide samples while the carcass samples had no relation (R2=0.002), which was likely due to most samples having an amount of total EHEC below the reliable limit of quantification for qPCR. Interestingly, after enrichment, 81% of the hide samples and 94% of the carcass samples had a detectable amount of total EHEC by qPCR. From our analysis, the MPN assay provided a higher percentage of enumerable hide and carcass samples, however determining an appropriate dilution range and the limited throughput offers additional challenges.