Prevalence, Molecular Typing, and Determination of the Biofilm-Forming Ability of Listeria monocytogenes Serotypes from Poultry Meat and Poultry Preparations in Spain

Characterization and long-read sequencing of biofilms formed by the microbiota present on inert surfaces in poultry slaughterhouses

Cross-contamination from inert slaughterhouse surfaces is among the main sources of contamination of poultry. The objective of the research reported here was to characterize the biofilms formed by the microbiota present on various surfaces in two poultry slaughterhouses in north-western Spain. Forty-four samples (22 from each slaughterhouse) were taken by swab rubbing at different points along the processing line (from stunning to cutting). The microbiota on all surfaces was able to form biofilms, which were studied by scanning confocal laser microscopy. The total biovolume in the observation field of 16,078.24 μm2 ranged from 22,106.8 ± 5544.3 μm3 to 414,229.6 ± 1621.0 μm3. Average values were higher in abattoir A than in abattoir B, with significant differences (P < 0.05) between surfaces. The percentage of biovolume of Gram-positive bacteria ranged between 0.02 % and 5.38 %. The highest percentages of Gram-positive bacteria were detected towards the beginning of the processing line. The microbiota of the biofilms was identified using long-read sequencing techniques (Oxford Nanopore). The predominant genera (found in >50.0 % of the biofilms) were Pseudomonas, Citrobacter, Klebsiella, Serratia, Escherichia, Enterobacter, Stenotrophomonas, Salmonella, Shewanella, Acinetobacter and Aeromonas. In addition, some pathogenic bacteria were detected, including Salmonella (31 surfaces), Yersinia enterocolitica (12), Escherichia coli O157:H7 (6), Campylobacter spp. (4) and Listeria monocytogenes (3). This research work has permitted identification of the most contaminated surfaces in poultry abattoirs and can serve as a starting point for the design of more effective cleaning and disinfection protocols.

Risk factor-based clustering of Listeria monocytogenes in food processing environments using principal component analysis

Listeria monocytogenes has a range of strategies that allow it to persist as biofilms in food processing environments (FPE), making it a pathogen of concern to the food industry. The properties of these biofilms are highly variable among strains, and this significantly affects the risk of food contamination. The present study therefore aims to conduct a proof-of-concept study to cluster strains of L. monocytogenes by risk potential using principal component analysis, a multivariate approach. A set of 22 strains, isolated from food processing environments, were typed by serogrouping and pulsed-field gel electrophoresis, showing a relatively high diversity. They were characterized in terms of several biofilm properties that might pose a potential risk of food contamination. The properties studied were tolerance to benzalkonium chloride (BAC), the structural parameters of biofilms (biomass, surface area, maximum and average thickness, surface to biovolume ratio and roughness coefficient) measured by confocal laser scanning microscopy and (3) transfer of biofilm cells to smoked salmon. The PCA correlation circle revealed that the tolerance of biofilms to BAC was positively correlated with roughness, but negatively with biomass parameters. On the contrary, cell transfers were not related to three-dimensional structural parameters, which suggests the role of other variables yet unexplored. Additionally, hierarchical clustering grouped strains into three different clusters. One of them included the strains with high tolerance to BAC and roughness. Another one consisted of strains with enhanced transfer ability, whereas the third cluster contained those that stood out for the thickness of biofilms. The present study represents a novel and effective way to classify L. monocytogenes strains according to biofilm properties that condition the potential risk of reaching the consumer through food contamination. It would thus allow the selection of strains representative of different worst-case scenarios for future studies in support of QMRA and decision-making analysis.

The Slaughterhouse as Hotspot of CC1 and CC6 Listeria monocytogenes Strains with Hypervirulent Profiles in an Integrated Poultry Chain of Italy

In Europe, very few studies are available regarding the diversity of Listeria monocytogenes (L. monocytogenes) clonal complexes (CCs) and sequence types (ST) in poultry and on the related typing of isolates using whole genome sequencing (WGS). In this study, we used a WGS approach to type 122 L. monocytogenes strains isolated from chicken neck skin samples collected in two different slaughterhouses of an integrated Italian poultry company. The studied strains were classified into five CCs: CC1-ST1 (21.3%), CC6-ST6 (22.9%), CC9-ST9 (44.2%), CC121-ST121 (10.6%) and CC193-ST193 (0.8%). CC1 and CC6 strains presented a virulence gene profile composed of 60 virulence genes and including the Listeria Pathogenicity Island 3, aut_IVb, gltA and gltB. According to cgMLST and SNPs analysis, long-term persistent clusters belonging to CC1 and CC6 were found in one of the two slaughterhouses. The reasons mediating the persistence of these CCs (up to 20 months) remain to be elucidated, and may involve the presence and the expression of stress response and environmental adaptation genes including heavy metals resistance genes (cadAC, arsBC, CsoR-copA-copZ), multidrug efflux pumps (mrpABCEF, EmrB, mepA, bmrA, bmr3, norm), cold-shock tolerance (cspD) and biofilm-formation determinants (lmo0673, lmo2504, luxS, recO). These findings indicated a serious risk of poultry finished products contamination with hypervirulent L. monocytogenes clones and raised concern for the consumer health. In addition to the AMR genes norB, mprF, lin and fosX, ubiquitous in L. monocytogenes strains, we also identified parC for quinolones, msrA for macrolides and tetA for tetracyclines. Although the phenotypical expression of these AMR genes was not tested, none of them is known to confer resistance to the primary antibiotics used to treat listeriosis The obtained results increase the data on the L. monocytogenes clones circulating in Italy and in particular in the poultry chain.

Quantification of Total and Viable Cells and Determination of Serogroups and Antibiotic Resistance Patterns of Listeria monocytogenes in Chicken Meat from the North-Western Iberian Peninsula

Twenty samples of minced chicken meat procured from butcher’s shops in León (Spain; 10 samples) and Vila Real (Portugal; 10 samples) were analyzed. Microbial concentrations (log10 cfu/g) of 7.53 ± 1.02 (viable aerobic microbiota), 7.13 ± 1.07 (psychrotrophic microorganisms), and 4.23 ± 0.88 (enterobacteria) were found. The detection method described in the UNE-EN ISO 11290-1 standard (based on isolation from the chromogenic medium OCLA) with confirmation by the polymerase chain reaction (PCR; lmo1030) (OCLA−PCR), revealed Listeria monocytogenes in 14 samples (70.0% of the total), nine of Spanish origin and five of Portuguese (p > 0.05). The levels of viable and inactivated L. monocytogenes in the samples were determined with a q-PCR using propidium monoazide (PMAxx) as a viability marker. Seven samples tested positive both with the OCLA−PCR and with the q-PCR, with estimated concentrations of viable cells varying between 2.15 log10 cfu/g (detection limit) and 2.94 log10 cfu/g. Three samples tested negative both with the OCLA−PCR and with the q-PCR. Seven samples were positive with the OCLA−PCR, but negative with the q-PCR, and three samples tested negative with the OCLA−PCR and positive with the q-PCR. The percentage of viable cells relative to the total ranged between 2.4% and 86.0%. Seventy isolates of L. monocytogenes (five from each positive sample) were classified in PCR serogroups with a multiplex PCR assay. L. monocytogenes isolates belonged to serogroups IIa (52 isolates; 74.3%), IIc (7; 10.0%), IVa (2; 2.9%), and IVb (9; 12.9%). The susceptibility of the 70 isolates to 15 antibiotics of clinical interest was tested. The strains presented resistance to between three and eight antibiotics. The average number of resistances was greater (p < 0.001) among strains isolated from Spanish samples (6.20 ± 1.08), than in those from Portugal (5.00 ± 1.08). In both groups of strains, a prevalence of resistance higher than 95% was observed for oxacillin, cefoxitin, cefotaxime, and cefepime. The need to handle minced chicken meat correctly, taking care to cook it sufficiently and to avoid cross-contamination, so as to reduce the danger of listeriosis, is emphasized. A combination of culture-dependent and culture-independent methods offers complementary routes for the detection in food of the cells of L. monocytogenes in various different physiological states.

Positive biofilms to guide surface microbial ecology in livestock buildings

The increase in human consumption of animal proteins implies changes in the management of meat production. This is followed by increasingly restrictive regulations on antimicrobial products such as chemical biocides and antibiotics, used in particular to control pathogens that can spread zoonotic diseases. Aligned with the One Health concept, alternative biological solutions are under development and are starting to be used in animal production. Beneficial bacteria able to form positive biofilms and guide surface microbial ecology to limit microbial pathogen settlement are promising tools that could complement existing biosecurity practices to maintain the hygiene of livestock buildings. Although the benefits of positive biofilms have already been documented, the associated fundamental mechanisms and the rationale of the microbial composition of these new products are still sparce. This review provides an overview of the envisioned modes of action of positive biofilms used on livestock building surfaces and the resulting criteria for the selection of the appropriate microorganisms for this specific application. Limits and advantages of this biosecurity approach are discussed as well as the impact of such practices along the food chain, from farm to fork.

Assessment of the molecular epidemiology and genetic multiplicity of Listeria monocytogenes recovered from ready-to-eat foods following the South African listeriosis outbreak

Following the recent listeriosis outbreak in South Africa, this study was carried out to assess the safety level of various common ready-to-eat foods (RTE) obtained from supermarkets and grocery stores in major towns and cities within the Amathole, Chris Hani and Sarah Baartman Districts Municipalities, Eastern Cape Province, South Africa. A sum of 239 food samples was collected from these locations, and Listeria monocytogenes (Lm) was isolated in line with the recommended techniques by the International Organization for Standardization EN ISO 11290:2017 parts 1 and 2. Identification of the pathogen and detection of various associated virulence genes was done using Polymerase Chain Reaction (PCR) techniques. From the RTE food samples processed, Lm was detected in 107 (44.77%) of the samples. Russian sausage was the most contaminated (78.57%), followed by sliced polony (61.90%), muffins (58.33%), polony (52.63%), and pies (52.38%), while all vetkoek samples examined were negative for Lm. Although the prevalence of Lm in the food samples was very high, concentrations were generally < 100 CFU/g. Strains of Lm recovered from the RTE foods were predominantly epidemiological strains belonging to serotypes 1/2a, 1/2b and 4b. The prevalence of 10 virulence genes including the inlA, InlC, inlJ, plcA, hlyA, plcB, prfA, mpl, inlB, and actA were detected among Lm isolates. Most of the isolates (69.07%) demonstrated the potential for biofilm formation and were categorized as weak (14.95%), moderate (13.40%) and strong (40.72) biofilm formers. Furthermore, molecular typing revealed high levels of genetic diversity among Lm isolates. The findings of this investigation suggested that the presence of Lm in the RTE foods may constitute potential threats to the food sector and could pose public health hazards to consumers, particularly the high-risk group of the population. We, therefore, recommend that adequate food monitoring for safety and proper regulation enforcement in the food sector must be ensured to avoid any future listeriosis outbreak that could be linked to RTE foods in South Africa.

Biofilm-Forming Ability of Microbacterium lacticum and Staphylococcus capitis Considering Physicochemical and Topographical Surface Properties

Biofilm characteristics of Microbacterium lacticum D84 (M. lacticum) and Staphylococcus capitis subsp. capitis (S. capitis) on polytetrafluoroethylene and AISI-304 stainless steel at early- (24, 48 h) and late-stage (144, 192 h) biofilm formation were investigated. M. lacticum biofilm structure was more developed compared to S. capitis, representing vastly mature biofilms with a strongly developed amorphous matrix, possibly extracellular polymeric substances (EPSs), at late-stage biofilm formation. S. capitis showed faster growth behavior but still resulted in a relatively flat biofilm structure. Strong correlations were found between several roughness parameters and S. capitis surface coverage (r ≥ 0.98), and between total surface free energy (γs) and S. capitis surface coverage (r = 0.89), while M. lacticum remained mostly unaffected. The pronounced ubiquitous biofilm characteristics make M. lacticum D84 a suitable model for biofilm research. Studying biofilm formation of these bacteria may help one understand bacterial adhesion on interfaces and hence reduce biofilm formation in the food industry.

Biovolume and spatial distribution of foodborne Gram-negative and Gram-positive pathogenic bacteria in mono- and dual-species biofilms

The objective of this study was to characterize the biofilms formed by Salmonella enterica serotype Agona, Listeria monocytogenes, methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus faecium (VRE) after 12, 48, 72, 120 and 240 h of incubation at 10 °C. Biofilms containing a single species, together with dual-species biofilms in which S. enterica and a Gram-positive bacterium existed in combination, were formed on polystyrene and evaluated by using confocal laser scanning microscopy (CLSM). All strains were able to form biofilm. The greatest biovolume in the observation field of 14,161 μm² was observed for mono-species biofilms after 72 h, where biovolumes of 94,409.0 μm³ ± 2131.0 μm³ (S. enterica), 58,418.3 μm³ ± 5944.9 μm³ (L. monocytogenes), 68,020.8 μm³ ± 5812.3 μm³ (MRSA) and 59,280.0 μm³ ± 4032.9 μm³ (VRE) were obtained. In comparison with single-species biofilms, the biovolume of S. enterica was higher in the presence of MRSA or VRE after 48, 72 and 120 h. In dual-species biofilms, the bacteria showed a double-layer distribution pattern, with S. enterica in the top layer and Gram-positive bacteria in the bottom layer. This spatial disposition should be taken into account when effective strategies to eliminate biofilms are being developed.

Architecture and Viability of the Biofilms Formed by Nine Listeria Strains on Various Hydrophobic and Hydrophilic Materials

Biofilms are a key factor in the persistence of Listeria in food processing plants, representing a potential source of foodstuff contamination. Nine Listeria strains (eight Listeria monocytogenes and one Listeria ivanovii) were studied by confocal laser scanning microscopy (CLSM) for their ability to form biofilm on glass, polystyrene, graphene and resin after 120 h of incubation at 12 °C. The relationship between cell surface hydrophobicity and biofilm formation was also investigated. On comparing the data for all the strains, similar (P > 0.05) biovolume values were obtained on glass (average 3.39 ± 1.69 µm3/µm2) and graphene (2.93 ± 1.14 µm3/µm2), while higher (P < 0.05) values were observed for polystyrene (4.39 ± 4.14 µm3/µm2). The highest (P < 0.01) biovolume levels were found in the biofilms formed on resin (7.35 ± 1.45 µm3/µm2), which also had the smallest biomass of inactivated cells (0.38 ± 0.37 µm3/µm2 vs. 1.20 ± 1.12 µm3/µm2 on the remaining surfaces; P < 0.001). No relationship was noted between cell surface hydrophobicity and biofilm-forming ability.