The phylogeny, identification, and characterization of 33 B. cereus sensu lato isolates originating from 17 agricultural soils from 11 countries were analyzed on the basis of whole genome sequencing. Phylogenetic analyses revealed all isolates are divided into six groups, which follows the generally accepted phylogenetic division of B. cereus sensu lato isolates. Four different identification methods resulted in a variation in the identity of the isolates, as none of the isolates were identified as the same species by all four methods—only the recent identification method proposed directly reflected the phylogeny of the isolates. This points to the importance of describing the basis and method used for the identification. The presence and percent identity of the protein product of 19 genes potentially involved in pathogenicity divided the 33 isolates into groups corresponding to phylogenetic division of the isolates. This suggests that different pathotypes exist and that it is possible to differentiate between them by comparing the percent identity of proteins potentially involved in pathogenicity. This also reveals that a basic link between phylogeny and pathogenicity is likely to exist. The geographical distribution of the isolates is not random: they are distributed in relation to their division into the six phylogenetic groups, which again relates to different ecotypes with different temperature growth ranges. This means that we find it easier to analyze and understand the results obtained from the 33 B. cereus sensu lato isolates in a phylogenetic, patho-type and ecotype-oriented context, than in a context based on uncertain identification at the species level.

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Climate change and its worldwide effects are undeniable. Temperature increase due to climate change may affect foodborne pathogen survival on fresh produce. This study aimed to present an evaluation of climate change impact regarding temperature rise situations, on attachment of different pathogenic Escherichia coli strains on cress grown under controlled conditions. EHEC O157:H7, EAEC O104:H4 and EPEC O26 were inoculated with initial inoculum concentration of 8 log MPN/mL at different stages during growth to observe how inoculation time (7, 14, 21 and 28 days post sowing; dps) and route (seed and leaves) affect pathogen load on fresh produce. This study revealed that temperature increase designed according to mitigation scenarios for climate change (+2, +4 and +6 °C) did not cause any considerable change in pathogen persistence on leaf at 30 dps (~4.5 to 7 log MPN/g). In plants contaminated at later stage (21 and 28 dps), higher bacterial populations were obtained for all temperatures studied. Our results show that E. coli translocated towards leaf portions from seed and established significant amount of pathogen load on leaf (~4 to 5.3 log MPN/g). Also, inoculated bacteria have tightly bound to leaf (~3.5 to 7 log MPN/g) and cannot be eliminated by washing. Although persistence of E. coli O157:H7, O104:H4 and O26 did not differ significantly according to temperature, the bacterial load on the leaves was above infectious dose for humans.

PurposeThis study aimed to investigate how enteric pathogens and their biofilm populations on fresh produce survive according to time that contamination has occurred on leaves and contamination route: seed irrigation water.Design/methodology/approachCress was contaminated in two different ways: contamination of seeds and irrigation water with 8-log MPN/mL bacterial load, Salmonella Newport, Escherichia coli O157:H7, O104:H4 or O78:H2. While contaminated seeds were cultivated for seed contamination, contaminated irrigation was applied at the end of each week to separate groups of samples obtained from cultivated surface-sterile seeds to understand how long these pathogens could survive until harvest.FindingsThe results indicated these pathogens survived until harvest, and formed biofilms on cress leaves grown using both contaminated seeds and irrigation water. No significant difference was observed among populations of Salmonella and E. coli groups in terms of survival (∼4.5–6.0 log MPN/g) and biofilm formation (∼4.4–5.7 log MPN/g) for contamination by seed. Also, SEM images revealed biofilm-like structures, the proofs of the attachment of these pathogens on leaf surfaces.Originality/valueFrom our knowledge this is the first study focusing on the survival and biofilm formation of one Salmonella serotype (Newport) and three E. coli serotypes (O157:H7, O104:H4, and O78:H2), representing enterohemorrhagic and enteroaggregative E. coli pathogenic subgroups, under the same irrigation and growth schemes. Furthermore, this study mimics the contamination of seeds and irrigation water with sewage or wastewater and may shed light on contamination of fresh produce grown using poor wastewater treatment.