Assessing the impact of heat treatment on antimicrobial resistance genes and their potential uptake by other ‘live’ bacteria

James, Christian, Dixon, Ron, Talbot, Luke , James, Stephen, Willaims, Nicola and Onarinde, Bukola (2021) Assessing the impact of heat treatment on antimicrobial resistance genes and their potential uptake by other ‘live’ bacteria. Project Report. Food Standards Agency (FSA).

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Assessing the impact of heat treatment on antimicrobial resistance genes and their potential uptake by other ‘live’ bacteria
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Antimicrobial resistance (AMR) is a complex issue driven by a variety of interconnected factors enabling microorganisms to withstand the killing or microstatic effects of antimicrobial treatments, such as antibiotics, antifungals, disinfectants, preservatives. Microorganisms may be inherently resistant to such treatments or can change and adapt to overcome the effects of such treatments. Microorganisms can acquire antimicrobial resistance genes (ARGs) because of mutation or from other microorganisms through a range of mechanisms. The widespread use of
antimicrobial treatments is known to result in selection for AMR in microorganisms.

AMR and ARGs are a major public health issue worldwide and it is estimated that unless action is taken now to tackle AMR the global impact of AMR could be 10 million deaths annually by 2050 and cost up to US $100 trillion in cumulative lost economic output (O’Neill Report, 2014). It is recognised that anthropogenic, commensal, and environmental microorganisms all contribute to the reservoir of ARGs, collectively forming the antimicrobial resistome (Wright, 2007). Relatively little is known regarding the role of heat�treated/cooked food in disseminating AMR, and whether heating/cooking is sufficient to inactivate ARGs to the extent that resistance is not passed onto other ‘live’ bacteria.
This study was undertaken to critically review the available scientific literature for assessing the impact of heat treatment of food on ARGs, and the potential uptake of such ARGs by surrounding viable bacterial communities resident in other foods and the human gut.
For the purpose of this review, heat treatments were regarded as any thermal processes that are undertaken during the processing or prior to consumption of any foods. The review focused particularly, but not exclusively, on what scientific evidence exists that provides an understanding on whether cooking (heating) food to eliminate bacterial contamination can also induce sufficient damage to ARGs to 8 of 91 prevent their uptake by surrounding viable bacteria present in other settings, including other foods and the human gut.
The review question was defined as: “Do different heat treatments applied to eliminate bacterial contamination in
foods also induce sufficient damage to ARGs to prevent or inhibit their uptake by surrounding viable bacteria present in other settings, including the human gut and other foods?” Systemic searching of two literature databases (Web of Science, and PubMed) was undertaken, supplemented by additional records identified through other sources. A
total of 2681 of publications were identified between 1990 and May 2021, which were reduced to 247 after screening the titles and abstracts. This total was further reduced to 53, from which some data were extracted after appraising the full publications. This clearly indicated that literature relating to AMR bacteria and ARGs and heat treatments was sparse.
Of these 53 publications identified that were considered eligible for some data extraction, only four were found that had studied the impact of heat treatments on ARGs. The majority of publications identified related to the relative heat resistance of various AMR bacteria in comparison to non-AMR strains and serotypes/serovars. Nine publications were reviews with some mention of the impact of heat on AMR bacteria, while 17 had evidence on the relative heat resistance of AMR bacteria in comparison to non-AMR bacteria. These publications provide evidence that AMR
bacteria are likely to be no more heat-resistant than non-AMR bacteria. There is therefore evidence that heat treatments sufficient to kill non-AMR bacteria (such as 70°C for at least 2 min, or the equivalent) will be equally effective in killing AMR bacteria. 9 of 91 Most of these publications have not considered whether ARGs may persist after
such heat treatments, and whether these genes could be transferred to other bacteria.
Only four publications were identified that provide some evidence on the fate of ARGs after heat treatments. Due to the small number of publications identified and different laboratory methodologies used in the studies no statistical analysis was possible. Three of the four studies provided evidence that ARGs can at least be identified after heat treatments that are effective at inactivating AMR bacteria, but there is no certainty that such ARGs are intact and functional.
Of the four studies identified, one (Koncan et al., 2007) used in vitro experiments to mimic cooking processes. Another in vitro study (Taher et al., 2020a) mimicked commercial milk pasteurisation, whilst the third (Le Devendec et al., 2018) was not designed to mimic any particular heat treatment but did use strains originating from animal sources and temperatures and times similar to thermal processes used to treat and cook food. A further study on autoclaving (Masters et al., 1998) was considered relevant, but was not applied to food. The in vitro mimic of cooking processes study (Koncan et al., 2007) detected the presence of ARGs after cooking but did not demonstrate that these genes were
transferable to other bacteria. The other three studies did demonstrate that plasmid�encoded ARGs could be transferred to other bacteria following heat treatments under laboratory conditions.
The ARG considered by Koncan et al. (2007) was aac(6’)-Ie-aph(2’’)-Ia, while Taher et al. (2020a) considered blaZ, mecC, tetK, and Le Devendec et al. (2018) considered blaCTX-M-1, blaCMY-2, tetA, strA. Masters et al. (1998) did not give any
details of the gene considered. 10 of 91 These studies did not establish how likely was the occurrence of such transfer in the field. One of the studies (Le Devendec et al., 2018) theorised that natural transfer is probably rare.
None of the studies demonstrated whether ARGs from heat-treated AMR bacteria could be taken up by other live bacteria in the human gut after ingestion.

In conclusion, only a small number of studies were identified on the persistence of ARGs in heat-treated foods and their possible uptake by surrounding viable bacteria present in other settings, such as the human gut and other foods. Because of differences in conditions, these studies were not directly comparable. While the literature suggests that adequate heat treatment / cooking (e.g., cooking until the middle of the food commodity reaches 70°C for at least 2 min, or the equivalent) should be effective in ‘killing’ AMR bacteria in food, there is very little evidence if intact and functional ARGs are released from AMR bacteria following such heat treatments. Similarly, there does not appear to be any convincing data for the ready transfer of ARGs to the commensal bacteria of the mammalian gastrointestinal tract following cooking. Evidence to determine if there is a risk of transfer is sparse. We would therefore recommend further focused practical research be undertaken to provide evidence for a full assessment of risk in relation to transfer of ARGs from heat-treated foods to bacteria in other matrices.

Keywords:AMR, Heat treatment, ARGs, Bacteria
Subjects:C Biological Sciences > C510 Applied Microbiology
C Biological Sciences > C521 Medical Microbiology
C Biological Sciences > C500 Microbiology
Divisions:College of Science > National Centre for Food Manufacturing
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ID Code:46456
Deposited On:10 Nov 2021 10:58

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