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Guragain M, Schmidt JW, Bagi LK, Paoli GC, Kalchayanand N, Bosilevac JM. Antibiotic Resistance and Disinfectant Resistance Among Escherichia coli Isolated During Red Meat Production. J Food Prot 2024; 87:100288. [PMID: 38697484 DOI: 10.1016/j.jfp.2024.100288] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2023] [Revised: 04/19/2024] [Accepted: 04/25/2024] [Indexed: 05/05/2024]
Abstract
Escherichia coli commonly found in the gastrointestinal tracts of food animals include Shiga toxin-producing E. coli (STEC, stx+, eae-), Enterohemorrhagic E. coli (EHEC, stx+, eae+), Enteropathogenic E. coli (EPEC, stx-, eae+), and "nondiarrheagenic" E. coli (NDEC, stx-, eae-). EHEC, EPEC, and STEC are associated with foodborne disease outbreaks. During meat processing, disinfectants are employed to control various bacteria, including human pathogens. Concerns exist that E. coli resistant to antibiotics are less susceptible to disinfectants used during meat processing. Since EHEC, EPEC, and STEC with reduced susceptibility to disinfectants are potential public health risks, the goal of this study was to evaluate the association of antibiotic resistant (ABR) E. coli with increased tolerance to 4% lactic acid (LA) and 150 ppm quaternary ammonium compounds (QACs). A pool of 3,367 E. coli isolated from beef cattle, veal calves, swine, and sheep at various processing stages was screened to identify ABR E. coli. Resistance to ≥1 of the six antibiotics examined was identified in 27.9%, 36.1%, 54.5%, and 28.7% among the NDEC (n = 579), EHEC (n = 693), EPEC (n = 787), and STEC (n = 1308) isolates evaluated, respectively. Disinfectant tolerance did not differ (P > 0.05) between ABR and antibiotic susceptible EHEC isolates. Comparable frequencies (P > 0.05) of biofilm formation or congo red binding were observed between ABR and antibiotic susceptible strains of E. coli. Understanding the frequencies of ABR and disinfectant tolerance among E. coli present in food-animal is a critically important component of meat safety.
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Affiliation(s)
- Manita Guragain
- Characterization and Interventions for Foodborne Pathogens Research Unit, Eastern Regional Research Center, Agricultural Research Service, US Department of Agriculture, Wyndmoor, PA, USA.
| | - John W Schmidt
- Meat Safety and Quality Research Unit, Meat Animal Research Center, Agricultural Research Service, US Department of Agriculture, Clay Center, NE, USA
| | - Lori K Bagi
- Characterization and Interventions for Foodborne Pathogens Research Unit, Eastern Regional Research Center, Agricultural Research Service, US Department of Agriculture, Wyndmoor, PA, USA
| | - George C Paoli
- Characterization and Interventions for Foodborne Pathogens Research Unit, Eastern Regional Research Center, Agricultural Research Service, US Department of Agriculture, Wyndmoor, PA, USA
| | - Norasak Kalchayanand
- Meat Safety and Quality Research Unit, Meat Animal Research Center, Agricultural Research Service, US Department of Agriculture, Clay Center, NE, USA
| | - Joseph M Bosilevac
- Meat Safety and Quality Research Unit, Meat Animal Research Center, Agricultural Research Service, US Department of Agriculture, Clay Center, NE, USA
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Yang X, Narvaez-Bravo C, Zhang P. Driving forces shaping the microbial ecology in meat packing plants. Front Microbiol 2024; 14:1333696. [PMID: 38322759 PMCID: PMC10844536 DOI: 10.3389/fmicb.2023.1333696] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2023] [Accepted: 12/22/2023] [Indexed: 02/08/2024] Open
Abstract
Meat production is a complex system, continually receiving animals, water, air, and workers, all of which serve as carriers of bacteria. Selective pressures involved in different meat processing stages such as antimicrobial interventions and low temperatures, may promote the accumulation of certain residential microbiota in meat cutting facilities. Bacteria including human pathogens from all these sources can contaminate meat surfaces. While significant advancements have been made in enhancing hygienic standards and pathogen control measures in meat plants, resulting in a notable reduction in STEC recalls and clinical cases, STEC still stands as a predominant contributor to foodborne illnesses associated with beef and occasionally with pork. The second-and third-generation sequencing technology has become popular in microbiota related studies and provided a better image of the microbial community in the meat processing environments. In this article, we reviewed the potential factors influencing the microbial ecology in commercial meat processing facilities and conducted a meta-analysis on the microbiota data published in the last 10 years. In addition, the mechanisms by which bacteria persist in meat production environments have been discussed with a focus on the significant human pathogen E. coli O157:H7 and generic E. coli, an indicator often used for the hygienic condition in food production.
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Affiliation(s)
- Xianqin Yang
- Lacombe Research and Development Centre, Agriculture and Agri-Food Canada, Lacombe, AB, Canada
| | | | - Peipei Zhang
- Lacombe Research and Development Centre, Agriculture and Agri-Food Canada, Lacombe, AB, Canada
- Department of Animal Sciences, Center for Meat Safety and Quality, Colorado State University, Fort Collins, CO, United States
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Kim Y, Ban GH, Hong YW, Jeong KC, Bae D, Kim SA. Bacterial profile of pork from production to retail based on high-throughput sequencing. Food Res Int 2024; 176:113745. [PMID: 38163697 DOI: 10.1016/j.foodres.2023.113745] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2023] [Revised: 11/14/2023] [Accepted: 11/22/2023] [Indexed: 01/03/2024]
Abstract
Pork is a common vehicle for foodborne pathogens, including Salmonella spp. and Yersinia enterocolitica. Cross-contamination can occur at any stage of the pork production chain, from farm to market. In the present study, high-throughput sequencing was used to characterize bacterial profiles and track their changes along the whole supply chain. Tracked meat samples (pig on the farm, carcass in the slaughterhouse, unprocessed carcass and processed meat in the processing plant, and fresh pork at the local retail stores) and their associated environmental samples (e.g., water, floor, feed, feces, and workers' gloves) were collected from sequential stages (n = 96) and subjected to 16S rRNA metataxonomic analyses. At the farm, a total of 652 genera and 146 exclusive genera were identified in animal and environmental samples (pig, drain, floor, fan, and feces). Based on beta diversity analysis, it was demonstrated that the microbial composition of animal samples collected at the same processing step is similar to that of environmental samples (e.g., drain, fan, feces, feed, floor, gloves, knives, tables, and water). All animal and environmental samples from the slaughterhouse were dominated by Acinetobacter (55.37 %). At the processing plant, belly meat and neck meat samples were dominated by Psychrobacter (55.49 %). At the retail level, key bacterial players, which are potential problematic bacteria and important members with a high relative abundance in the samples, included Acinetobacter (8.13 %), Pseudomonas (6.27 %), and Staphylococcus (2.13 %). In addition, the number of confirmed genera varied by more than twice that identified in the processing plant. Source tracking was performed to identify bacterial contamination routes in pork processing. Animal samples, including the processing plant's carcass, the pig from the farm, and the unwashed carcass from the slaughterhouse (77.45 %), along with the processing plant's gloves (5.71 %), were the primary bacterial sources in the final product. The present study provides in-depth knowledge about the bacterial players and contamination points within the pork production chain. Effective control measures are needed to control pathogens and major pollutants at each stage of pork production to improve food safety.
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Affiliation(s)
- Yejin Kim
- Department of Food Science and Biotechnology, Ewha Womans University, Seoul, South Korea
| | - Ga-Hee Ban
- Department of Food Science and Biotechnology, Ewha Womans University, Seoul, South Korea
| | - Ye Won Hong
- Department of Food Science and Biotechnology, Ewha Womans University, Seoul, South Korea
| | | | - Dongryeoul Bae
- Division of Research and Development, TracoWorld Ltd., Gwangmyeong, South Korea
| | - Sun Ae Kim
- Department of Food Science and Biotechnology, Ewha Womans University, Seoul, South Korea.
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Blanco-Lizarazo CM, Sierra-Cadavid A. Prevalence of Escherichia coli generic and pathogenic in pork meat: systematic review and meta-analysis. World J Microbiol Biotechnol 2023; 39:247. [PMID: 37428340 DOI: 10.1007/s11274-023-03687-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2023] [Accepted: 06/24/2023] [Indexed: 07/11/2023]
Abstract
This research aimed to analyze scientific information regarding the prevalence of generic and pathogenic E. coli in the production and supply chain of pork meat, considering different types of samples, places of sampling, and pathotypes using a systematic review and meta-analysis tools. The meta-analysis for the prevalence of generic and pathogenic E. coli was conducted by estimating the effects within subgroups. Data subsets were analyzed using the DerSimonian-Laird method for binary random effects. The average prevalence of generic E. coli in different types of pork meat samples was determined to be 35.6% (95% CI 19.3-51.8), with no significant differences observed between pork meat and carcasses. Conversely, the average prevalence of E. coli pathotypes in samples related to the supply chain of pork meat was found to be 4.7% (95% CI 3.7-5.7). In conclusion, these findings suggest the possibility of establishing an objective threshold for E. coli prevalence as a benchmark for comparison within the meat industry. By utilizing this data, it becomes possible to propose a standardized limit that can serve as a reference point for evaluating and improving processes in the industry.
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Affiliation(s)
- Carla María Blanco-Lizarazo
- Centro de Investigación y Desarrollo Cárnico CI+D, Industria de Alimentos Zenú, Carrera 64 C # 104-03, Medellín, Colombia.
| | - Andrea Sierra-Cadavid
- Centro de Investigación y Desarrollo Cárnico CI+D, Industria de Alimentos Zenú, Carrera 64 C # 104-03, Medellín, Colombia
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Growth behavior of Shiga toxin-producing Escherichia coli, Salmonella, and generic E. coli in raw pork considering background microbiota at 10, 25, and 40 °C. Int J Food Microbiol 2023; 391-393:110134. [PMID: 36812695 DOI: 10.1016/j.ijfoodmicro.2023.110134] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2022] [Revised: 01/24/2023] [Accepted: 02/08/2023] [Indexed: 02/16/2023]
Abstract
Recent epidemiological evidence suggests that pork products may be vehicles for the transmission of Shiga toxin-producing Escherichia coli (STEC) to humans. The severe morbidity associated with STEC infections highlights the need for research to understand the growth behavior of these bacteria in pork products. Classical predictive models can estimate pathogen growth in sterile meat. However, competition models considering background microbiota reflect a more realistic scenario for raw meat products. The objective of this study was to estimate the growth kinetics of clinically significant STEC (O157, non-O157, and O91), Salmonella, and generic E. coli in raw ground pork using competition primary growth models at temperature abuse (10 and 25 °C) and sublethal temperature (40 °C). A competition model incorporating the No lag Buchanan model was validated using the acceptable prediction zone (APZ) method where >92 % (1498/1620) of the residual errors fell within the APZ (pAPZ > 0.70). The background microbiota (mesophilic aerobic plate counts, APC) inhibited the growth of STEC and Salmonella indicating a simple one-directional competitive interaction between pathogens and the mesophilic microbiota of ground pork. The maximum specific growth rate (μmax) of all the bacterial groups was not significantly different (p > 0.05) based on fat content (5 vs 25 %) except for generic E. coli at 10 °C. E. coli O157 and non-O157 behaved similarly in terms of μmax and maximum population density (MPD). Salmonella showed a similar (p > 0.05) μmax to E. coli O157 and non-O157 at 10 and 40 °C but a significantly higher rate (p < 0.05) at 25 °C. STEC were more prone to be inhibited by APC than Salmonella at 10 and 25 °C. The μmax of O91 was lower (p < 0.05) than other STEC and Salmonella at 10 and 25 °C but similar (p > 0.05) at 40 °C. Generic E. coli showed a two- to five-times higher (p < 0.05) μmax (0.028 ± 0.011 log10 CFU/h) than other bacterial groups (0.006 ± 0.004 to 0.012 ± 0.003 log10 CFU/h) at 10 °C making it a potential indicator bacteria for process control. Industry and regulators can use competitive models to develop appropriate risk assessment and mitigation strategies to improve the microbiological safety of raw pork products.
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García-Díez J, Saraiva S, Moura D, Grispoldi L, Cenci-Goga BT, Saraiva C. The Importance of the Slaughterhouse in Surveilling Animal and Public Health: A Systematic Review. Vet Sci 2023; 10:167. [PMID: 36851472 PMCID: PMC9959654 DOI: 10.3390/vetsci10020167] [Citation(s) in RCA: 10] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2022] [Revised: 02/14/2023] [Accepted: 02/14/2023] [Indexed: 02/22/2023] Open
Abstract
From the point of public health, the objective of the slaughterhouse is to guarantee the safety of meat in which meat inspection represent an essential tool to control animal diseases and guarantee the public health. The slaughterhouse can be used as surveillance center for livestock diseases. However, other aspects related with animal and human health, such as epidemiology and disease control in primary production, control of animal welfare on the farm, surveillance of zoonotic agents responsible for food poisoning, as well as surveillance and control of antimicrobial resistance, can be monitored. These controls should not be seen as a last defensive barrier but rather as a complement to the controls carried out on the farm. Regarding the control of diseases in livestock, scientific research is scarce and outdated, not taking advantage of the potential for disease control. Animal welfare in primary production and during transport can be monitored throughout ante-mortem and post-mortem inspection at the slaughterhouse, providing valuable individual data on animal welfare. Surveillance and research regarding antimicrobial resistance (AMR) at slaughterhouses is scarce, mainly in cattle, sheep, and goats. However, most of the zoonotic pathogens are sensitive to the antibiotics studied. Moreover, the prevalence at the slaughterhouse of zoonotic and foodborne agents seems to be low, but a lack of harmonization in terms of control and communication may lead to underestimate its real prevalence.
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Affiliation(s)
- Juan García-Díez
- Veterinary and Animal Research Centre (CECAV), University of Trás-os-Montes e Alto Douro, Quinta de Prados, 5000-801 Vila Real, Portugal
- Associate Laboratory for Animal and Veterinary Sciences (AL4AnimalS), Portugal
| | - Sónia Saraiva
- Veterinary and Animal Research Centre (CECAV), University of Trás-os-Montes e Alto Douro, Quinta de Prados, 5000-801 Vila Real, Portugal
- Associate Laboratory for Animal and Veterinary Sciences (AL4AnimalS), Portugal
| | - Dina Moura
- Divisão de Intervenção de Alimentação e Veterinária de Vila Real e Douro Sul, Direção de Serviços de Alimentação e Veterinária da Região Norte, Direção Geral de Alimentação e Veterinária, Lugar de Codessais, 5000-567 Vila Real, Portugal
| | - Luca Grispoldi
- Dipartimento di Medicina Veterinaria, Università degli Studi di Perugia, 06126 Perugia, Italy
| | - Beniamino Terzo Cenci-Goga
- Dipartimento di Medicina Veterinaria, Università degli Studi di Perugia, 06126 Perugia, Italy
- Faculty of Veterinary Science, Department of Paraclinical Sciences, University of Pretoria, Onderstepoort 0110, South Africa
| | - Cristina Saraiva
- Veterinary and Animal Research Centre (CECAV), University of Trás-os-Montes e Alto Douro, Quinta de Prados, 5000-801 Vila Real, Portugal
- Associate Laboratory for Animal and Veterinary Sciences (AL4AnimalS), Portugal
- Faculty of Veterinary Science, Department of Paraclinical Sciences, University of Pretoria, Onderstepoort 0110, South Africa
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A review of Shiga-toxin producing Escherichia coli (STEC) contamination in the raw pork production chain. Int J Food Microbiol 2022; 377:109832. [PMID: 35834920 DOI: 10.1016/j.ijfoodmicro.2022.109832] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2022] [Revised: 07/02/2022] [Accepted: 07/04/2022] [Indexed: 11/21/2022]
Abstract
Epidemiological evidence of Shiga toxin-producing Escherichia coli (STEC) infections associated with the consumption of contaminated pork highlight the need for increased awareness of STEC as an emerging pathogen in the pork supply chain. The objective of this review is to contribute to our understanding of raw pork products as potential carriers of STEC into the food supply. We summarize and critically analyze primary literature reporting the prevalence of STEC in the raw pork production chain. The reported prevalence rate of stx-positive E. coli isolates in live swine, slaughtered swine, and retail pork samples around the world ranged from 4.4 % (22/500) to 68.3 % (82/120), 22 % (309/1395) to 86.3 % (69/80), and 0.10 % (1/1167) to 80 % (32/40), respectively, depending upon the sample categories, detection methods, and the hygiene condition of the slaughterhouses and retail markets. In retail pork, serogroup O26 was prevalent in the U.S., Europe, and Africa. Serogroup O121 was only reported in the U.S. Furthermore, serogroup O91 was reported in the U.S., Asia, and South American retail pork samples. The most common virulence gene combination in retail pork around the globe were as follows: the U.S.: serogroup O157 + stx, non-O157 + stx, unknown serogroups+stx + eae; Europe: unknown serogroups+(stx + eae, stx2 + eae, or stx1 + stx2 + eae); Asia: O157 + stx1 + stx2 + ehxA, Unknown+stx1 + eaeA + ehxA, or only eae; Africa: O157 + stx2 + eae + ehxA. STEC strains derived from retail pork in the U.S. fall under low to moderate risk categories capable of causing human disease, thus indicating the need for adequate cooking and prevention of cross contamination to minimize infection risk in humans.
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Development and validation of high-resolution melting assays for the detection of potentially virulent strains of Escherichia coli O103 and O121. Food Control 2022. [DOI: 10.1016/j.foodcont.2022.109095] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Wang L, Liu N, Gao Y, Liu J, Huang X, Zhang Q, Li Y, Zhao J, Wang J, Zhao G. Surveillance and Reduction Control of Escherichia coli and Diarrheagenic E. coli During the Pig Slaughtering Process in China. Front Vet Sci 2021; 8:735076. [PMID: 34676255 PMCID: PMC8523888 DOI: 10.3389/fvets.2021.735076] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2021] [Accepted: 09/01/2021] [Indexed: 12/05/2022] Open
Abstract
The microbial contamination of pork during the slaughter process, especially that of the hygiene indicator bacteria, Escherichia coli, is closely related to the safety and quality of the meat. Some diarrheagenic E. coli can cause serious foodborne diseases, and pose a significant threat to human life and health. In order to ascertain the current status of E. coli and diarrheagenic E. coli contamination during the pig slaughter process in China, we conducted thorough monitoring of large-sized slaughterhouses, as well as small- or medium-sized slaughterhouses, in different provinces of China from 2019 to 2020. The overall positive rate of E. coli on the pork surface after slaughter was very high (97.07%). Both the amount of E. coli contamination and the positive ratio of diarrheagenic E. coli in large-sized slaughterhouses (7.50–13.33 CFU/cm2, 3.44%) were lower than those in small- or medium-sized slaughterhouses (74.99–133.35 CFU/cm2, 5.71%). Combined with the current status of sanitary control in slaughterhouses, we determined that pre-cooling treatment significantly reduced E. coli and diarrheagenic E. coli in pork after slaughter, while microbiological testing reduced E. coli. Based on our monitoring data, China urgently needs to establish relevant standards to better control microbial contamination during pig slaughtering progress. This study provided a theoretical basis for the hygiene quality management of the pig slaughter industry in China.
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Affiliation(s)
- Lin Wang
- China Animal Health and Epidemiology Center, Livestock and Poultry Products Quality and Safety Risk Assessment Laboratory of MARA, Qingdao, China
| | - Na Liu
- China Animal Health and Epidemiology Center, Livestock and Poultry Products Quality and Safety Risk Assessment Laboratory of MARA, Qingdao, China
| | - Yubin Gao
- China Animal Health and Epidemiology Center, Livestock and Poultry Products Quality and Safety Risk Assessment Laboratory of MARA, Qingdao, China
| | - Junhui Liu
- China Animal Health and Epidemiology Center, Livestock and Poultry Products Quality and Safety Risk Assessment Laboratory of MARA, Qingdao, China
| | - Xiumei Huang
- China Animal Health and Epidemiology Center, Livestock and Poultry Products Quality and Safety Risk Assessment Laboratory of MARA, Qingdao, China
| | - Qingqing Zhang
- China Animal Health and Epidemiology Center, Livestock and Poultry Products Quality and Safety Risk Assessment Laboratory of MARA, Qingdao, China
| | - Yuehua Li
- China Animal Health and Epidemiology Center, Livestock and Poultry Products Quality and Safety Risk Assessment Laboratory of MARA, Qingdao, China
| | - Jianmei Zhao
- China Animal Health and Epidemiology Center, Livestock and Poultry Products Quality and Safety Risk Assessment Laboratory of MARA, Qingdao, China
| | - Junwei Wang
- China Animal Health and Epidemiology Center, Livestock and Poultry Products Quality and Safety Risk Assessment Laboratory of MARA, Qingdao, China
| | - Ge Zhao
- China Animal Health and Epidemiology Center, Livestock and Poultry Products Quality and Safety Risk Assessment Laboratory of MARA, Qingdao, China
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Velez FJ, Bosilevac JM, Singh P. Validation of high-resolution melting assays for the detection of virulent strains of Escherichia coli O26 and O111 in beef and pork enrichment broths. Food Control 2021. [DOI: 10.1016/j.foodcont.2021.108123] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Locus of Heat Resistance (LHR) in Meat-Borne Escherichia coli: Screening and Genetic Characterization. Appl Environ Microbiol 2021; 87:AEM.02343-20. [PMID: 33483306 DOI: 10.1128/aem.02343-20] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2020] [Accepted: 01/12/2021] [Indexed: 11/20/2022] Open
Abstract
Microbial resistance to processing treatments poses a food safety concern, as treatment tolerant pathogens can emerge. Occasional foodborne outbreaks caused by pathogenic Escherichia coli have led to human and economic losses. Therefore, this study screened for the extreme heat resistance (XHR) phenotype as well as one known genetic marker, the locus of heat resistance (LHR), in 4,123 E. coli isolates from diverse meat animals at different processing stages. The prevalences of XHR and LHR among the meat-borne E. coli were found to be 10.3% and 11.4%, respectively, with 19% agreement between the two. Finished meat products showed the highest LHR prevalence (24.3%) compared to other processing stages (0 to 0.6%). None of the LHR+ E. coli in this study would be considered pathogens based on screening for virulence genes. Four high-quality genomes were generated by whole-genome sequencing of representative LHR+ isolates. Nine horizontally acquired LHRs were identified and characterized, four plasmid-borne and five chromosomal. Nine newly identified LHRs belong to ClpK1 LHR or ClpK2 LHR variants sharing 61 to 68% nucleotide sequence identity, while one LHR appears to be a hybrid. Our observations suggest positive correlation between the number of LHR regions present in isolates and the extent of heat resistance. The isolate exhibiting the highest degree of heat resistance possessed four LHRs belonging to three different variant groups. Maintenance of as many as four LHRs in a single genome emphasizes the benefits of the LHR in bacterial physiology and stress response.IMPORTANCE Currently, a "multiple-hurdle" approach based on a combination of different antimicrobial interventions, including heat, is being utilized during meat processing to control the burden of spoilage and pathogenic bacteria. Our recent study (M. Guragain, G. E. Smith, D. A. King, and J. M. Bosilevac, J Food Prot 83:1438-1443, 2020, https://doi.org/10.4315/JFP-20-103) suggests that U.S. beef cattle harbor Escherichia coli that possess the locus of heat resistance (LHR). LHR seemingly contributes to the global stress tolerance in bacteria and hence poses a food safety concern. Therefore, it is important to understand the distribution of the LHRs among meat-borne bacteria identified at different stages of different meat processing systems. Complete genome sequencing and comparative analysis of selected heat-resistant bacteria provide a clearer understanding of stress and heat resistance mechanisms. Further, sequencing data may offer a platform to gain further insights into the genetic background that provides optimal bacterial tolerance against heat and other processing treatments.
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