Some Like It Hot: Heat Resistance of Escherichia coli in Food

Li, Hui; Gänzle, Michael G.

doi:10.3389/fmicb.2016.01763

Cited by 68 publications

(44 citation statements)

References 148 publications

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“…Bacteria have evolved elaborate strategies to counteract these effects. Cytosolic chaperone systems with protein folding capacities such as DnaKJE and GroESL, as well as ATP-dependent proteolytic systems such as the Clp ATPases are ubiquitous in bacterial species (Hecker et al, 1996; Frees et al, 2014; Li and Gänzle, 2016). However, we recently identified a novel Clp ATpase, ClpK, uniquely found in Gram-negative bacteria, which also confers heat resistance (Bojer et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

Turn Up the Heat—Food and Clinical Escherichia coli Isolates Feature Two Transferrable Loci of Heat Resistance

et al. 2017

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Heat treatment is a widely used process to reduce bacterial loads in the food industry or to decontaminate surfaces, e.g., in hospital settings. However, there are situations where lower temperatures must be employed, for instance in case of food production such as raw milk cheese or for decontamination of medical devices such as thermo-labile flexible endoscopes. A recently identified locus of heat resistance (LHR) has been shown to be present in and confer heat resistance to a variety of Enterobacteriaceae, including Escherichia coli isolates from food production settings and clinical ESBL-producing E. coli isolates. Here, we describe the presence of two distinct LHR variants within a particularly heat resistant E. coli raw milk cheese isolate. We demonstrate for the first time in this species the presence of one of these LHRs on a plasmid, designated pFAM21805, also encoding type 3 fimbriae and three bacteriocins and corresponding self-immunity proteins. The plasmid was highly transferable to other E. coli strains, including Shiga-toxin-producing strains, and conferred LHR-dependent heat resistance as well as type 3 fimbriae-dependent biofilm formation capabilities. Selection for and acquisition of this “survival” plasmid by pathogenic organisms, e.g., in food production environments, may pose great concern and emphasizes the need to screen for the presence of LHR genes in isolates.

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Section: Introductionmentioning

confidence: 99%

Turn Up the Heat—Food and Clinical Escherichia coli Isolates Feature Two Transferrable Loci of Heat Resistance

et al. 2017

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“…Even when considering that multiple copies of the LHR may be present in one strain, this study demonstrates that an increase of the fermentation temperature exerts a strong selective pressure for LHR-positive Enterobacteriaceae. A high frequency of LHR-positive Escherichia coli organisms has been previously found for meat (13), cheese (31), and wastewater (17); however, the LHR has not been identified in spontaneous solid-state fermentation or in K. cowanii. The temperature of Daqu ranged from 55 to 60°C for 6 days; at this temperature range, even LHR-positive Kosakonia and Enterobacter spp.…”

Section: Discussionmentioning

confidence: 93%

“…At the thermophilic stage, the temperature increased to about 60°C, followed by a decrease to 45°C at the cooling stage and a 13-day maturation stage at room temperature. A temperature of more than 55°C, which is typically sufficient to kill Enterobacteriaceae within minutes or hours (13,24), was maintained for more than 4 days.…”

Section: Resultsmentioning

confidence: 99%

“…Heat resistance of Enterobacteriaceae, including Escherichia coli, Salmonella, Cronobacter, and Enterobacter cloacae, is mediated by a genomic island termed the locus of heat resistance (LHR) (7,12). The LHR increases the D 60 value (decimal reduction time [i.e., the time required to kill 90% of the microorganisms] at 60°C) relative to that of LHR-negative strains of the same species 10-to 100-fold (13). LHR-encoded proteins include heat shock proteins that prevent or repair protein misfolding and aggregation (14,15).…”

mentioning

confidence: 99%

“…LHR-encoded proteins include heat shock proteins that prevent or repair protein misfolding and aggregation (14,15). Both the LHR and the spoVA 2mob operon are mobile genetic elements and may transfer to pathogenic bacteria or spoilage organisms; therefore, heat resistance provided by the LHR and the spoVA 2mob operon challenges the control of pathogens in food system by thermal processing (13,16).…”

mentioning

confidence: 99%

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Daqu Fermentation Selects for Heat-Resistant Enterobacteriaceae and Bacilli

Wang

Pan

et al. 2018

Appl Environ Microbiol

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Daqu is a spontaneous solid-state cereal fermentation used as saccharification and starter culture in Chinese vinegar and liquor production. The evolution of microbiota in this spontaneous fermentation is controlled by the temperature profile, which reaches temperatures from 50 to 65°C for several days. Despite these high temperatures, mesophilic (including) and bacilli are present throughout Daqu fermentation. This study aimed to determine whether Daqu spontaneous solid-state fermentation selects for heat-resistant variants of these organisms. Heat resistance in is mediated by the locus of heat resistance (LHR). One LHR-positive strain of was identified in Daqu, and it exhibited higher heat resistance than the LHR-negative isolated from malted oats. Heat resistance in endospores is mediated by the operon. Out of 10 Daqu isolates of the species, ,, , and, 5 did not contain , 3 contained one copy, and 2 contained two copies. The presence and copy number of the operon increased the resistance of spores to treatment with 110°C. To confirm the selection of LHR- and -positive strains during Daqu fermentation, the copy numbers of these genetic elements in Daqu samples were quantified by quantitative PCR (qPCR). The abundance of LHR and the operon in community DNA relative to that of total bacterial 16S rRNA genes increased 3-fold and 5-fold, respectively, during processing. In conclusion, culture-dependent and culture-independent analyses suggest that Daqu fermentation selects for heat-resistant and bacilli. Daqu fermentations select for mobile genetic elements conferring heat resistance in and bacilli. The locus of heat resistance (LHR), a genomic island conferring heat resistance in, and the operon, conferring heat resistance on bacterial endospores, were enriched 3- to 5-fold during Daqu fermentation and maturation. It is therefore remarkable that the LHR and the operon are accumulated in the same food fermentation. The presence of heat-resistant spp. and spp. in Daqu is not of concern for food safety; however, both genomic islands are mobile and transferable to pathogenic bacteria or toxin-producing bacteria by horizontal gene transfer. The identification of the LHR and the operon as indicators of fitness of and bacilli in Daqu fermentation provides insights into environmental sources of heat-resistant organisms that may contaminate the food supply.

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Sous vide processing: a viable approach for the assurance of microbial food safety

et al. 2022

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As consumer needs change, innovative food processing techniques are being developed that have minimal impact on food quality and ensure its microbiological safety. Sous vide (SV) is an emerging technology of cooking foods in vacuum pouches at specific temperatures, which results in even heat distribution. Presented here is an overview of the current state of the art in the application of SV techniques for processing and preserving foods. Unlike the conventional thermal food processing approach, the precise nature of the SV method improves food quality, nutrition and shelf-life while destroying microorganisms. Foods processed by SV are usually subjected to temperatures between 50 and 100 °C. Although sufficient for food preparation/ processing, its effectiveness in eliminating microbial pathogens, including viruses, parasites, vegetative and spore forms of bacteria, is limited. However, the inactivation of spore-forming microbes can be enhanced by combining the technique with other non-thermal methods that exert negligible impact on the nutritional, flavour and sensory characteristics of foods. In addition to exploring the mechanism of action of SV technology, the challenges related to its implementation in the food industry are also discussed. SV method potential, applications, and impacts on spore-forming microbes and spore inactivation are explored in this review. Through the debate and discussion presented, further research and industrial applications of this food processing method could be guided.

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Some Like It Hot: Heat Resistance of Escherichia coli in Food

Cited by 68 publications

References 148 publications

Turn Up the Heat—Food and Clinical Escherichia coli Isolates Feature Two Transferrable Loci of Heat Resistance

Turn Up the Heat—Food and Clinical Escherichia coli Isolates Feature Two Transferrable Loci of Heat Resistance

Daqu Fermentation Selects for Heat-Resistant Enterobacteriaceae and Bacilli

Sous vide processing: a viable approach for the assurance of microbial food safety

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