A multi-country outbreak ofListeria monocytogenesST6 linked to blanched frozen vegetables (bfV)took place in the EU (2015–2018). Evidence of food-borne outbreaks shows thatL. monocytogenesisthe most relevant pathogen associated with bfV. The probability of illness per serving of uncooked bfV,for the elderly (65–74 years old) population, is up to 3,600 times greater than cooked bfV and verylikely lower than any of the evaluated ready-to-eat food categories. The main factors affectingcontamination and growth ofL. monocytogenesin bfV during processing are the hygiene of the rawmaterials and process water; the hygienic conditions of the food processing environment (FPE); andthe time/Temperature (t/T) combinations used for storage and processing (e.g. blanching, cooling).Relevant factors after processing are the intrinsic characteristics of the bfV, the t/T combinations usedfor thawing and storage and subsequent cooking conditions, unless eaten uncooked. Analysis of thepossible control options suggests that application of a complete HACCP plan is either not possible orwould not further enhance food safety. Instead, specific prerequisite programmes (PRP) andoperational PRP activities should be applied such as cleaning and disinfection of the FPE, water control,t/T control and product information and consumer awareness. The occurrence of low levels ofL. monocytogenesat the end of the production process (e.g.<10 CFU/g) would be compatible with thelimit of 100 CFU/g at the moment of consumption if any labelling recommendations are strictly followed(i.e. 24 h at 5°C). Under reasonably foreseeable conditions of use (i.e. 48 h at 12°C),L. monocytogeneslevels need to be considerably lower (not detected in 25 g). Routine monitoring programmes forL. monocytogenesshould be designed following a risk-based approach and regularly revised based ontrend analysis, being FPE monitoring a key activity in the frozen vegetable industry.
Pesticides are broadly utilized in crop cultivation and could end up in wastewater of vegetable- and potato companies during water-consuming processing steps. To gain insight into the presence of pesticide residues in (waste)water of these industries, water was analysed and monitored from three vegetable- and two potato processing companies in Belgium. Samples were collected during one year of water before and after primary/secondary treatment (i.e. influent and effluent) and after tertiary treatment. Next to water, also (processed) carrot and potato products were analysed. Results show that boscalid (maximum: 18.32 μg/L) and terbuthylazine (maximum: 87.99 μg/L) are predominantly present in the vegetable industry and chlorpropham (maximum: 8.80x10⁶ μg/L) and terbuthylazine (maximum: 3.37x10⁵ μg/L) in the potato industry. The conventional treatment techniques seem to be insufficient for the removal of pesticides. Concentrations were even higher in the effluent than in the influent. Also, tertiary treatment techniques as ultra-filtration and reverse osmosis fail to reduce all pesticides below the European potable water limit of 0.1 μg/L. To meet this standard, the development and validation of new removal techniques are essential. Regarding product samples, almost no pesticide residues exceeded the MRL. Chlorpropham concentrations were statistically confirmed to be higher in potatoes and wastewater sampled when stored potatoes are processed.
Interfaces between air, liquid and walls (ALW interfaces) are known to be conducive to the formation of biofilms, at least in some bacteria, yet little information is available on the influence of material properties on the amount of biofilms formed and their resistance to a cleaning procedure. In this study, we investigated the ability of four bacterial strains (Pseudomonas fluorescens [Pf1], Escherichia coli [Ec-SS2], Bacillus cereus [Bc-98/4] and B. subtilis [Bs-PY79]) to form biofilms in static conditions at the ALW interface on four materials with very different topographic and hydrophilic/hydrophobic properties (stainless steels with 2R or 2B finishes, polypropylene and glass). Biofilms were observed after staining with orange acridine visually, by epifluorescence microscopy and by confocal scanner laser microscopy. The number of culturable cells within biofilms was also estimated after growth on agar. After one-day of incubation in a bacterial suspension, three strains (except Bc-PY79) were found to form large amounts of biofilm, easily observable to the naked eye. However, great differences were observed between strains in the number of CFU (between 4.7 and 7.4 log CFU cm⁻²), as well in the biofilm structure. Furthermore, the material also affected the amount and/or structure of biofilms, and a 3D-biofilm organisation was only observed for two of the four tested strains (Bc-98/4 and Pf1) on PP, a hydrophobic material. After a standard cleaning-in-place treatment involving NaOH 0.5% at 60 °C, cultivable cells were only detected from Bc-98/4 biofilms (growth on agar), while biofilms were also still visible on coupons contaminated with Pf1. Furthermore, most residual biofilms after cleaning appeared orange by epifluorescence microscopy after staining with orange acridine suggesting the presence of many viable but non-culturable cells within the residual biofilms. In Bc-98/4 biofilms, spores were also clearly observed by epifluorescence microscopy. Knowing their ability to survive the conditions encountered during cleaning procedures, this could account for the high level of CFU enumerated after cleaning. Lastly, Bc-98/4 biofilms formed on stainless steel 2R were more resistant to cleaning than on PP and glass. All of these results highlighted the importance of biofilms at the ALW interfaces in the control of surface hygiene, particularly in the food industry. We then investigated whether the shape of the menisci at the interfaces (convex vs concave, kinetics over time) could at least partly explain the shape or even the resistance to detachment of the ALW biofilms.
Aims The aim of this study was to evaluate the performance of sampling methods [contact plates, sponges, and swabs] in the recovery of biofilm Listeria monocytogenes populations considering the seafood environment conditions (nature of conditioning, of materials and bacterial species). Methods and results Different materials (stainless steel, polyvinyl chloride, polyurethane) were conditioned with two fish filtrates, the ready-to-eat the most consumed in Europe (smoked salmon, cod). After, we added the suspension of Listeria monocytogenes, alone or with Pseudomonas fluorescens or Carnobacterium strains, and incubated for 48 h at 8 °C. Then, the 48 h-biofilms were sampled with different methods (contact plates, sponges, and swabs). The cultivable bacterial populations were enumerated on agar, while the L. monocytogenes total and viable populations were quantified by qPCR and propidium monoazide-qPCR (PMA-qPCR), respectively. The amount of L. monocytogenes in biofilms was affected only by the nature of the conditioning with lowest adherent bacteria with cod versus with smoked salmon conditioning. Considering the amount of total population, the swab displayed the lowest values versus the sponges and the contact plates. An explanation was that the observations of the swab by microscopy showed the bacteria trapped within it. The recovery of cultivable bacterial populations was not significantly different with the three sampling methods. On the contrary, we showed that the VBNC populations were only detached by two of three methods (contact plates, sponges) while for the dead populations, those were contact plates and swabs. Conclusions The nature of the conditioning influenced the amount of the bacteria in biofilms. And the performance of the recovery of the bacterial populations (dead, VBNC, cultivable) was dependent on the methods used. Significance and impact of the study This study showed that the seafood environmental conditions influenced the biofilm formation and the assessment of the efficiency of cleaning and disinfectant operations could be significantly affected by the used sampling methods.
Surface contamination with droplets containing bacteria is of concern in the food industry and other environments where hygiene control is essential. Deposition patterns after the drying of contaminated droplets is affected by numerous parameters. The present study evaluated the rate of evaporation and the shape of deposition patterns after the drying of water droplets on a panel of materials with different surface properties (topography, hydrophobicity). The influence of the particle properties (in this study 1 μm-microspheres and two bacterial spores) was also investigated. Polystyrene microspheres were hydrophobic, while Bacillus spores were hydrophilic or hydrophobic, and surrounded by different surface features. In contrast to material topography, hydrophobicity was shown to deeply affect droplet evaporation, with the formation of small, thick deposits with microspheres or hydrophilic spores. Among the particle properties, the spore morphology (size and round/ovoid shape) did not clearly affect the deposition pattern. Conversely, hydrophobic spores aggregated to form clusters, which quickly settled on the materials and either failed to migrate, or only migrated to a slight extent on the surface, resulting in a steady distribution of spores or spore clusters over the whole contaminated area. Adherent bacteria or spores are known to be highly resistant to many stressful environmental conditions. In view of all the quite different patterns obtained following drying of spore-containing droplets, it seems likely that some of these would entail enhanced resistance to hygienic processes.