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

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ABSTRACT

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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Midpoint-rooted maximum-likelihood phylogenetic tree of aligned LHR sequences (>80% coverage of LHR1FAM21805) from different bacterial species. Two distinct clusters representing predominantly Enterobacteriaceae and strains of Pseudomonas, respectively, are observed. LHR2 of FAM21805 and C604-10 cluster within the Pseudomonas group.
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Figure 3: Midpoint-rooted maximum-likelihood phylogenetic tree of aligned LHR sequences (>80% coverage of LHR1FAM21805) from different bacterial species. Two distinct clusters representing predominantly Enterobacteriaceae and strains of Pseudomonas, respectively, are observed. LHR2 of FAM21805 and C604-10 cluster within the Pseudomonas group.

Mentions: Previous studies have described the presence of LHR in several distinct pathogenic species, including E. coli, K. pneumoniae, Enterobacter species, and Pseudomonas aeruginosa (Bojer et al., 2010; Gajdosova et al., 2011; Lee et al., 2015; Mercer et al., 2015). Based on a BLAST search using the entire LHR, Mercer et al. recently observed two distinct phylogenetic groups harboring LHRs—one predominantly comprising Enterobacteriaceae and one primarily comprising P. aeruginosa (Mercer et al., 2015). We performed the same analysis using LHR2 from FAM21805 as input, which retrieved 27 sequences with more than 80% coverage. SNPs within the LHRs were identified and used to calculate a maximum-likelihood phylogenetic tree. As expected, LHR1FAM21805 and LHR1C604−10 both clustered tightly with the other E. coli LHR1s within the Enterobacteriaceae group (Figure 3). Not surprisingly, LHR2FAM21805 and LHR2C604−10 both clustered tightly together. Remarkably, however, they were located within the Pseudomonas group of the phylogenetic tree. These findings demonstrate the ability of E. coli to acquire LHRs from both phylogenetic groups.


Turn Up the Heat — Food and Clinical Escherichia coli Isolates Feature Two Transferrable Loci of Heat Resistance
Midpoint-rooted maximum-likelihood phylogenetic tree of aligned LHR sequences (>80% coverage of LHR1FAM21805) from different bacterial species. Two distinct clusters representing predominantly Enterobacteriaceae and strains of Pseudomonas, respectively, are observed. LHR2 of FAM21805 and C604-10 cluster within the Pseudomonas group.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5383660&req=5

Figure 3: Midpoint-rooted maximum-likelihood phylogenetic tree of aligned LHR sequences (>80% coverage of LHR1FAM21805) from different bacterial species. Two distinct clusters representing predominantly Enterobacteriaceae and strains of Pseudomonas, respectively, are observed. LHR2 of FAM21805 and C604-10 cluster within the Pseudomonas group.
Mentions: Previous studies have described the presence of LHR in several distinct pathogenic species, including E. coli, K. pneumoniae, Enterobacter species, and Pseudomonas aeruginosa (Bojer et al., 2010; Gajdosova et al., 2011; Lee et al., 2015; Mercer et al., 2015). Based on a BLAST search using the entire LHR, Mercer et al. recently observed two distinct phylogenetic groups harboring LHRs—one predominantly comprising Enterobacteriaceae and one primarily comprising P. aeruginosa (Mercer et al., 2015). We performed the same analysis using LHR2 from FAM21805 as input, which retrieved 27 sequences with more than 80% coverage. SNPs within the LHRs were identified and used to calculate a maximum-likelihood phylogenetic tree. As expected, LHR1FAM21805 and LHR1C604−10 both clustered tightly with the other E. coli LHR1s within the Enterobacteriaceae group (Figure 3). Not surprisingly, LHR2FAM21805 and LHR2C604−10 both clustered tightly together. Remarkably, however, they were located within the Pseudomonas group of the phylogenetic tree. These findings demonstrate the ability of E. coli to acquire LHRs from both phylogenetic groups.

View Article: PubMed Central - PubMed

ABSTRACT

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.

No MeSH data available.


Related in: MedlinePlus