Strain variability in biofilm formation: A food safety and quality perspective

Nasal carriage of Staphylococcus aureus in healthy dairy cows in Algeria: antibiotic resistance, enterotoxin genes and biofilm formation

BACKGROUND

Staphylococcus aureus can colonize and infect a variety of animal species. In dairy herds, it is one of the leading causes of mastitis cases. The objective of this study was to characterize the S. aureus isolates recovered from nasal swabs of 249 healthy cows and 21 breeders of 21 dairy farms located in two provinces of Algeria (Tizi Ouzou and Bouira).

METHODS

The detection of enterotoxin genes was investigated by multiplex PCRs. Resistance of recovered isolates to 8 antimicrobial agents was determined by disc-diffusion method. The slime production and biofilm formation of S. aureus isolates were assessed using congo-red agar (CRA) and microtiter-plate assay. Molecular characterization of selected isolates was carried out by spa-typing and Multi-Locus-Sequence-Typing (MLST).

RESULTS

S. aureus was detected in 30/249 (12%) and 6/13 (28.6%) of nasal swabs in cows and breeders, respectively, and a total of 72 isolates were recovered from positive samples (59 isolates from cows and 13 from breeders). Twenty-six of these isolates (36.1%) harbored genes encoding for staphylococcal enterotoxins, including 17/59 (28.8%) isolates from cows and 9/13 (69.2%) from breeders. Moreover, 49.1% and 92.3% of isolates from cows and breeders, respectively, showed penicillin resistance. All isolates were considered as methicillin-susceptible (MSSA). Forty-five (76.3%) of the isolates from cows were slime producers and 52 (88.1%) of them had the ability to form biofilm in microtiter plates. Evidence of a possible zoonotic transmission was observed in two farms, since S. aureus isolates recovered in these farms from cows and breeders belonged to the same clonal lineage (CC15-ST15-t084 or CC30-ST34-t2228).

CONCLUSIONS

Although healthy cows in this study did not harbor methicillin-resistant S. aureus isolates, the nares of healthy cows could be a reservoir of enterotoxigenic and biofilm producing isolates which could have implications in human and animal health.

The In Vitro Antibacterial Activity of Phytogenic and Acid-Based Eubiotics against Major Foodborne Zoonotic Poultry Pathogens

The aim of the study was to investigate in vitro the antibacterial activity of 8 commercial drinking water additives against major zoonotic poultry pathogens (Campylobacter spp., Escherichia coli, Salmonella Typhimurium, Staphylococcus aureus and Listeria spp.). We tested two essential oil-based phytogenics (Phyto CSC Liquide B, AEN 350 B Liquid), two acid-based eubiotics (Salgard® liquid, Intesti-Flora), and four blends of essential oils and organic acids (ProPhorceTM SA Exclusive, Herbal acid, Rigosol-N and Eubisan 3000). The antibacterial activity was determined by estimating the minimum inhibitory concentration (MIC) using a microdilution method. The MICs of the products against Campylobacter spp. ranged from 0.071% to 0.568% v/v, in which Herbal acid, a blend rich in lactic and phosphoric acids, also containing thyme and oregano oils, exhibited the highest efficacy (MIC: 0.071% v/v) against all the tested strains. The MICs of the tested products against Escherichia coli ranged between 0.071% and 1.894% v/v. Specifically, the MIC of Rigosol-N, a blend of high concentrations of lactic and acetic acid, was 0.142% v/v for both tested strains, whereas the MICs of Intesti-Flora, a mixture rich in lactic and propionic acid, ranged from 0.284% to 0.568% v/v. The MICs of the products against Salmonella Typhimurium were between 0.095% and 1.894% v/v. Specifically, the MIC of Eubisan 3000, a blend rich in oregano oil, was 0.284% v/v. The MICs against Staphylococcus aureus were between 0.142% and 9.090% v/v. The MICs of Phyto CSC Liquide B, which is rich in trans-cinnamaldehyde, were between 3.030% and 9.090% v/v, showing the highest MIC values of all tested products. Finally, the MIC values of the tested commercial products against Listeria spp. were 0.095% to 3.030% v/v. The MICs of ProPhorceTM SA Exclusive, a highly concentrated blend of formic acid and its salts, were 0.095-0.142% v/v against Listeria spp., while the MICs of AEN 350 B Liquid were between 0.284% and 1.894% exhibiting high Listeria spp. strain variability. In conclusion, all the selected commercial products exhibited more or less antibacterial activity against pathogenic bacteria and, thus, can be promising alternatives to antibiotics for the control of zoonotic poultry pathogens and the restriction of antimicrobial-resistant bacteria.

Biofilm formation by Listeria monocytogenes from the meat processing industry environment and the use of different combinations of detergents, sanitizers, and UV-A radiation to control this microorganism in planktonic and sessile forms

This study aimed to evaluate the ability of biofilm formation by L. monocytogenes from the meat processing industry environment, as well as the use of different combinations of detergents, sanitizers, and UV-A radiation in the control of this microorganism in the planktonic and sessile forms. Four L. monocytogenes isolates were evaluated and showed moderate ability to form biofilm, as well as carried genes related to biofilm production (agrB, agrD, prfA, actA, cheA, cheY, flaA, sigB), and genes related to tolerance to sanitizers (lde and qacH). The biofilm-forming isolates of L. monocytogenes were susceptible to quaternary ammonium compound (QAC) and peracetic acid (PA) in planktonic form, with minimum inhibitory concentrations of 125 and 75 ppm, respectively, for contact times of 10 and 5 min. These concentrations are lower than those recommended by the manufacturers, which are at least 200 and 300 ppm for QAC and PA, respectively. Biofilms of L. monocytogenes formed from a pool of isolates on stainless steel and polyurethane coupons were subjected to 14 treatments involving acid and enzymatic detergents, QAC and PA sanitizers, and UV-A radiation at varying concentrations and contact times. All treatments reduced L. monocytogenes counts in the biofilm, indicating that the tested detergents, sanitizers, and UV-A radiation exhibited antimicrobial activity against biofilms on both surface types. Notably, the biofilm formed on polyurethane showed greater tolerance to the evaluated compounds than the biofilm on stainless steel, likely due to the material's surface facilitating faster microbial colonization and the development of a more complex structure, as observed by scanning electron microscopy. Listeria monocytogenes isolates from the meat processing industry carry genes associated with biofilm production and can form biofilms on both stainless steel and polyurethane surfaces, which may contribute to their persistence within meat processing lines. Despite carrying sanitizer tolerance genes, QAC and PA effectively controlled these microorganisms in their planktonic form. However, combinations of detergent (AC and ENZ) with sanitizers (QAC and PA) at minimum concentrations of 125 ppm and 300 ppm, respectively, were the most effective.

The Effect of the PhoP/PhoQ System on the Regulation of Multi-Stress Adaptation Induced by Acid Stress in Salmonella Typhimurium

Acidic stress in beef cattle slaughtering abattoirs can induce the acid adaptation response of in-plant contaminated Salmonella. This may further lead to multiple resistance responses threatening public health. Therefore, the acid, heat, osmotic and antibiotic resistances of Salmonella typhimurium (ATCC14028) were evaluated after a 90 min adaption in a pH = 5.4 "mild acid" Luria-Bertani medium. Differences in such resistances were also determined between the ∆phoP mutant and wild-type Salmonella strains to confirm the contribution of the PhoP/PhoQ system. The transcriptomic differences between the acid-adapted and ∆phoP strain were compared to explore the role of the PhoP/Q two-component system in regulating multi-stress resistance. Acid adaptation was found to increase the viability of Salmonella to lethal acid, heat and hyperosmotic treatments. In particular, acid adaptation significantly increased the resistance of Salmonella typhimurium to Polymyxin B, and such resistance can last for 21 days when the adapted strain was stored in meat extract medium at 4 °C. Transcriptomics analysis revealed 178 up-regulated and 274 down-regulated genes in the ∆phoP strain. The Salmonella infection, cationic antimicrobial peptide (CAMP) resistance, quorum sensing and two-component system pathways were down-regulated, while the bacterial tricarboxylic acid cycle pathways were up-regulated. Transcriptomics and RT-qPCR analyses revealed that the deletion of the phoP gene resulted in the down-regulation of the expression of genes related to lipid A modification and efflux pumps. These changes in the gene expression result in the change in net negative charge and the mobility of the cell membrane, resulting in enhanced CAMP resistance. The confirmation of multiple stress resistance under acid adaptation and the transcriptomic study in the current study may provide valuable information for the control of multiple stress resistance and meat safety.

Genotype-phenotype evaluation of the heterogeneity in biofilm formation by diverse Bacillus licheniformis strains isolated from dairy products

The spoilage bacterium Bacillus licheniformis has been identified as a quick and strong biofilm former in the dairy industry. In our previous study, intra-species variation in bacterial biofilms has been observed in diverse B. licheniformis strains from different genetic backgrounds; however, the mechanisms driving the observed heterogeneity of biofilms remain to be determined. In this study, the genotype-phenotype evaluation of the heterogeneity in biofilm formation of four B. licheniformis strains were examined. The heterogeneity in biofilm phenotype was accessed in aspects of bacterial growth and motility, cell viability, biofilm matrix production, and biofilm architectures. The underlying mechanisms of the intra-species variability in biofilms were also explored by whole genome resequencing (WGR). Results from bacterial motility tests showed a diverse motility among the strains, but there was no clear correlation between bacterial motility and biofilm formation. The cell viability results showed a different number of live cells in biofilms at the intra-species level. Analysis of chemical components in biofilm matrix demonstrated the great intra-species differences regarding extracellular matrix composition, and a negative correlation between biofilm formation on stainless steel and the protein: carbohydrate ratio in biofilm matrix was observed. Confocal laser scanning microscopy analysis also revealed the intra-species variability by showing great differences in general properties of B. licheniformis biofilms. WGR results identified important pathways involved in biofilm formation, such as two-component systems, quorum sensing, starch and sucrose metabolism, ABC transporters, glyoxylate and dicarboxylate metabolism, purine metabolism, and a phosphotransferase system. Overall, the above results emphasize the necessity of exploring the intra-species variation in biofilms, and would provide in-depth knowledge for designing efficient biofilm control strategies in the dairy industry.

Characterization of a Straboviridae phage vB_AbaM-SHI and its inhibition effect on biofilms of Acinetobacter baumannii

Acinetobacter baumannii (A. baumannii) is a popular clinical pathogen worldwide. Biofilm-associated antibiotic-resistant A. baumannii infection poses a great threat to human health. Bacteria in biofilms are highly resistant to antibiotics and disinfectants. Furthermore, inhibition or eradication of biofilms in husbandry, the food industry and clinics are almost impossible. Phages can move across the biofilm matrix and promote antibiotic penetration. In the present study, a lytic A. baumannii phage vB_AbaM-SHI, belonging to family Straboviridae, was isolated from sauce chop factory drain outlet in Wuxi, China. The DNA genome consists of 44,180 bp which contain 93 open reading frames, and genes encoding products morphogenesis are located at the end of the genome. The amino acid sequence of vB_AbaM-SHI endolysin is different from those of previously reported A. baumannii phages in NCBI. Phage vB_AbaM-SHI endolysin has two additional β strands due to the replacement of a lysine (K) (in KU510289.1, NC_041857.1, JX976549.1 and MH853786.1) with an arginine (R) (SHI) at position 21 of A. baumannii phage endolysin. Spot test showed that phage vB_AbaM-SHI is able to lyse some antibiotic-resistant bacteria, such as A. baumannii (SL, SL1, and SG strains) and E. coli BL21 strain. Additionally, phage vB_AbaM-SHI independently killed bacteria and inhibited bacterial biofilm formation, and synergistically exerted strong antibacterial effects with antibiotics. This study provided a new perspective into the potential application value of phage vB_AbaM-SHI as an antimicrobial agent.

Control of Listeria monocytogenes in food industry by a combination treatment of natural aromatic compound with Listeria-specific bacteriophage cocktail

Most Listeria monocytogenes found in the food industry are listeriosis-causing pathogens and possess the ability to form biofilms on food and food contact materials (FCMs). This study aims to evaluate the efficacy of the combination treatment of natural aromatic compounds (thymol, eugenol, carvacrol, and citral) with a Listeria-specific phage cocktail in mitigating the threat posed by L. monocytogenes in the food industry. In vitro combination treatment of 1 minimal inhibitory concentration (MIC) of natural aromatic compound with phage cocktail at multiplicity of infection (MOI) 100 reduced more than 4 log CFU/mL of L. monocytogenes planktonic cells and inhibited biofilm formation. In addition, the expression of virulence-related genes (flaA, motB, hlyA, prfA, and actA) and the stress response (sigB) gene were significantly downregulated. The combination of natural aromatic compound with phage cocktail reduced the biofilm cell population on contaminated celery by more than 2 log CFU/g and by more than 2 log CFU/cm2 on already-formed biofilm on FCMs, but it was less effective on chicken meat, with an approximate reduction of only 1 log CFU/g. The antibiofilm activity toward preformed L. monocytogenes biofilms was also observed using field-emission scanning electron microscopy (FESEM) and confocal laser scanning microscopy (CLSM). COMSTAT analysis of the structural change of biofilms revealed that major biofilm structure parameters (biovolume, thickness, diffusion distance, and microcolonies at substratum) were reduced after treatment. Our findings suggest that the combination of natural aromatic compounds with a phage cocktail has enormous potential as an antimicrobial and antibiofilm agent for controlling L. monocytogenes in the food industry.

Durable superhydrophobic coatings for stainless-steel: An effective defense against Escherichia coli and Listeria fouling in the post-harvest environment

Increasing concerns revolve around bacterial cross-contamination of leafy green vegetables via food-contact surfaces. Given that stainless-steel is among the commonly used food-contact surfaces, this study reports a coating strategy enhancing its hygiene and microbiological safety through an antifouling approach via superhydrophobicity. The developed method involves growing a nickel-nanodiamond nanocomposite film on 304 stainless-steel via electroplating and sequential functionalization of the outer surface layer with nonpolar organosilane molecules via polydopamine moieties. The resultant superhydrophobic stainless-steel surfaces had a static water contact angle of 156.3 ± 1.9° with only 2.3 ± 0.5° contact angle hysteresis. Application of the coating to stainless-steel was demonstrated to yield 2.3 ± 0.6 log10 and 2.0 ± 0.9 log10 reductions in the number of adherent gram-negative Escherichia coli O157:H7 and gram-positive Listeria innocua cells, respectively. These population reductions were shown to be statistically significant (α = 0.05). Coated stainless-steel also resisted fouling when contacted with contaminated romaine lettuce leaves and maintained significant non-wetting character when abraded with sand or contacted with high concentration surfactant solutions. The incorporation of superhydrophobic stainless-steel surfaces into food processing equipment used for washing and packaging leafy green vegetables has the potential to mitigate the transmission of pathogenic bacteria within food production facilities.

Prevalence, Serotypes, Antimicrobial Resistance and Biofilm-Forming Ability of Listeria monocytogenes Isolated from Bulk-Tank Bovine Milk in Northern Greece

The prevalence of Listeria monocytogenes in bovine bulk-tank milk (BTM) in Greece has not been previously investigated. The aim of the study was to estimate the prevalence of L. monocytogenes in bovine BTM in Greece and to characterize the isolates in terms of carriage of genes encoding for pathogenic determinants, assess the isolates' biofilm-forming ability and determine their susceptibility against 12 antimicrobials. Samples (n = 138) of bovine BTM were obtained from farms located throughout Northern Greece and were analyzed qualitatively and quantitatively for L. monocytogenes. Five samples (3.6%) tested positive for L. monocytogenes. The pathogen's populations in these positive samples were below 5 CFU/mL. Most isolates belonged to the molecular serogroup "1/2a, 3a". All isolates carried the virulence genes inlA, inlC, inlJ, iap, plcA and hlyA, but actA was detected in only three isolates. The isolates displayed weak to moderate biofilm-forming ability and distinct antimicrobial resistance profiles. All isolates were characterized as multidrug resistant, with resistance to penicillin and clindamycin being a common feature. Considering that L. monocytogenes constitutes a serious public health threat, the key findings of the study, related to the carriage of virulence genes and multidrug resistance, highlight the importance of continued monitoring of the pathogen in farm animals.

PatA Regulates Isoniazid Resistance by Mediating Mycolic Acid Synthesis and Controls Biofilm Formation by Affecting Lipid Synthesis in Mycobacteria

Lipids are prominent components of the mycobacterial cell wall, and they play critical roles not only in maintaining biofilm formation but also in resisting environmental stress, including drug resistance. However, information regarding the mechanism mediating mycobacterial lipid synthesis remains limited. PatA is a membrane-associated acyltransferase and synthesizes phosphatidyl-myo-inositol mannosides (PIMs) in mycobacteria. Here, we found that PatA could regulate the synthesis of lipids (except mycolic acids) to maintain biofilm formation and environmental stress resistance in Mycolicibacterium smegmatis. Interestingly, the deletion of patA significantly enhanced isoniazid (INH) resistance in M. smegmatis, although it reduced bacterial biofilm formation. This might be due to the fact that the patA deletion promoted the synthesis of mycolic acids through an unknown synthesis pathway other than the reported fatty acid synthase (FAS) pathway, which could effectively counteract the inhibition by INH of mycolic acid synthesis in mycobacteria. Furthermore, the amino acid sequences and physiological functions of PatA were highly conserved in mycobacteria. Therefore, we found a mycolic acid synthesis pathway regulated by PatA in mycobacteria. In addition, PatA also affected biofilm formation and environmental stress resistance by regulating the synthesis of lipids (except mycolic acids) in mycobacteria. IMPORTANCE Tuberculosis, caused by Mycobacterium tuberculosis, leads to a large number of human deaths every year. This is so serious, which is due mainly to the drug resistance of mycobacteria. INH kills M. tuberculosis by inhibiting the synthesis of mycolic acids, which are synthesized by the FAS pathway. However, whether there is another mycolic acid synthesis pathway is unknown. In this study, we found a PatA-mediated mycolic acid synthesis pathway that led to INH resistance of in patA-deleted mutant. In addition, we first report the regulatory effect of PatA on mycobacterial biofilm formation, which could affect the bacterial response to environmental stress. Our findings represent a new model for regulating biofilm formation by mycobacteria. More importantly, the discovery of the PatA-mediated mycolic acid synthesis pathway indicates that the study of mycobacterial lipids has entered a new stage, and the enzymes might be new targets of antituberculosis drugs.

Investigation of differences in susceptibility of Campylobacter jejuni strains to UV light-emitting diode (UV-LED) technology

Campylobacter jejuni remains a high priority in public health worldwide. Ultraviolet light emitting-diode technology (UV-LED) is currently being explored to reduce Campylobacter levels in foods. However, challenges such as differences in species and strain susceptibilities, effects of repeated UV-treatments on the bacterial genome and the potential to promote antimicrobial cross-protection or induce biofilm formation have arisen. We investigated the susceptibility of eight C. jejuni clinical and farm isolates to UV-LED exposure. UV light at 280 nm induced different inactivation kinetics among strains, of which three showed reductions greater than 1.62 log CFU/mL, while one strain was particularly resistant to UV light with a maximum reduction of 0.39 log CFU/mL. However, inactivation was reduced by 0.46-1.03 log CFU/mL in these three strains and increased to 1.20 log CFU/mL in the resistant isolate after two repeated-UV cycles. Genomic changes related to UV light exposure were analysed using WGS. C. jejuni strains with altered phenotypic responses following UV exposure were also found to have changes in biofilm formation and susceptibility to ethanol and surface cleaners.

Attachment characteristics and kinetics of biofilm formation by Staphylococcus aureus on ready-to-eat cooked beef contact surfaces

Staphylococcus aureus is a food-borne pathogen that quickly forms biofilm on meat contact surfaces and thus poses a serious threat to the safety of the meat industry. This study evaluated the attachment, survival, and growth of S. aureus biofilm with exposure to environmental factors in the meat industry by simulated ready-to-eat (RTE) cooked beef product contamination scenarios. The results indicated that the meat-borne S. aureus biofilm formation dynamic could be divided into four different phases: initial adhesion (4-12 h), exponential (12-24 h), slow growth (1-3 days), and stationary (3-7 days). Meat-borne S. aureus has strong adhesion and biofilm formation ability, and its biofilm exhibits persistence, high-intensity metabolic activity, aerotaxis, and strain heterogeneity. This study has also demonstrated that in the long-term existence of meat-borne S. aureus biofilm on stainless steel and plexiglass surfaces (>7 days, 7.2-8.8 log CFU/cm² ), expose to RTE cooked beef products, may cause it to become high-risk contaminated food. Meat-borne S. aureus that forms a dense and rough concave-convex in the shape of biofilm architecture was observed by scanning electron microscopy, consisting of complex components and adhesion of living and dead cells. This was further confirmed by the meat-borne S. aureus biofilm on the stainless steel surface by attenuated total reflectance Fourier transformed infrared spectroscopy, and the dominant peaks in biofilm spectra were mainly associated with proteins, polysaccharides, amino acid residues, and phospholipids (>50%). These findings may help in the identification of the main sources of contamination within the meat industry and the subsequent establishment of strategies for biofilm prevention and removal. PRACTICAL APPLICATION: This study revealed the meat-borne S. aureus biofilm formation mechanism and found that it exhibited strong colonization and biofilm-forming ability, which can persist on the contact surfaces of ready-to-eat beef products. These initial findings could provide information on the behavior of meat-borne S. aureus biofilm attached to meat contact surfaces under conditions commonly encountered in meat environments, which help to support the determination of the main sources of contamination within the meat industry and the subsequent establishment of strategies for biofilm prevention and removal. It was also helpful in controlling biofilm contamination and improving meat safety to minimize it.

A desiccated dual-species subaerial biofilm reprograms its metabolism and affects water dynamics in limestone

Understanding the impact of sessile communities on underlying materials is of paramount importance in stone conservation. Up until now, the critical role of subaerial biofilms (SABs) whether they are protective or deteriorative remains unclear, especially under desiccation. The interest in desiccated SABs is raised by the prediction of an increase in drought events in the next decades that will affect the Mediterranean regions' rich stone heritage as never before. Thus, the main goal of this research is to study the effects of desiccation on both the biofilms' eco-physiology and its impacts on the lithic substrate. To this end, we used a dual-species model system composed of a phototroph and a chemotroph to simulate biofilm behavior on stone heritage. We found that drought altered the phototroph-chemotroph balance and enriched the biofilm matrix with proteins and DNA. Desiccated SABs underwent a shift in metabolism to fermentation and a decrease in oxidative stress. Additionally, desiccated SABs changed the water-related dynamics (adsorption, evaporation, and wetting properties) in limestone. Water absorption experiments showed that desiccated SABs protected the stone from rapid water uptake, while a thermographic survey indicated a delay in water evaporation. Spilling-drop tests revealed a change in the wettability of the stone-SAB interface, which affected the water transport properties of the stone. Finally, desiccated SABs reduced stone swelling in the presence of water vapor. The biodeteriorative and bioprotective implications of desiccated SABs on the stone were ultimately assessed.

Comparative genome identification of accessory genes associated with strong biofilm formation in Vibrio parahaemolyticus

Vibrio parahaemolyticus biofilms on the seafood processing plant surfaces are a potential source of seafood contamination and subsequent food poisoning. Strains differ in their ability to form biofilm, but little is known about the genetic characteristics responsible for biofilm development. In this study, pangenome and comparative genome analysis of V. parahaemolyticus strains reveals genetic attributes and gene repertoire that contribute to robust biofilm formation. The study identified 136 accessory genes that were exclusively present in strong biofilm forming strains and these were functionally assigned to the Gene Ontology (GO) pathways of cellulose biosynthesis, rhamnose metabolic and catabolic processes, UDP-glucose processes and O antigen biosynthesis (p < 0.05). Strategies of CRISPR-Cas defence and MSHA pilus-led attachment were implicated via Kyoto Encyclopedia of Genes and Genomes (KEGG) annotation. Higher levels of horizontal gene transfer (HGT) were inferred to confer more putatively novel properties on biofilm-forming V. parahaemolyticus. Furthermore, cellulose biosynthesis, a neglected potential virulence factor, was identified as being acquired from within the order Vibrionales. The cellulose synthase operons in V. parahaemolyticus were examined for their prevalence (22/138, 15.94 %) and were found to consist of the genes bcsG, bcsE, bcsQ, bcsA, bcsB, bcsZ, bcsC. This study provides insights into robust biofilm formation of V. parahaemolyticus at the genomic level and facilitates: identification of key attributes for robust biofilm formation, elucidation of biofilm formation mechanisms and development of potential targets for novel control strategies of persistent V. parahaemolyticus.

Prevalence, Infectious Characteristics and Genetic Diversity of Staphylococcus aureus and Methicillin-Resistant Staphylococcus aureus (MRSA) in Two Raw-Meat Processing Establishments in Northern Greece

In the present study, we investigated the isolation frequency, the genetic diversity, and the infectious characteristics of Staphylococcus aureus and methicillin-resistant S. aureus (MRSA) from the incoming meat and the meat products, the environment, and the workers' nasal cavities, in two meat-processing establishments in northern Greece. The isolated S. aureus strains were examined for their resistance to antimicrobials, carriage of the mecA and mecC genes, carriage of genes encoding for the production of nine staphylococcal enterotoxins, carriage of the Panton-Valentine Leukocidin and Toxic Shock Syndrome genes, and the ability to form biofilm. The genetic diversity of the isolates was evaluated using Pulsed Field Gel Electrophoresis (PFGE) and spa typing. S. aureus was isolated from 13.8% of the 160 samples examined, while only one sample (0.6%) was contaminated by MRSA carrying the mecA gene. The evaluation of the antimicrobial susceptibility of the isolates revealed low antimicrobial resistance. The higher resistance frequencies were observed for penicillin (68.2%), amoxicillin/clavulanic acid (36.4%) and tetracycline (18.2%), while 31.8% of the isolates were sensitive to all antimicrobials examined. Multidrug resistance was observed in two isolates. None of the isolates carried the mecC or lukF-PV genes, and two isolates (9.1%) harbored the tst gene. Eight isolates (36.4%) carried the seb gene, one carried the sed gene, two (9.1%) carried both the sed and sei genes, and one isolate (4.5%) carried the seb, sed and sei genes. Twenty-one (95.5%) of the isolates showed moderate biofilm production ability, while only one (4.5%) was characterized as a strong biofilm producer. Genotyping of the isolates by PFGE indicates that S. aureus from different meat-processing establishments represent separate genetic populations. Ten different spa types were identified, while no common spa type isolates were detected within the two plants. Overall, our findings emphasize the need for the strict application of good hygienic practices at the plant level to control the spread of S. aureus and MRSA to the community through the end products.

Biofilms as a microbial hazard in the food industry: A scoping review

Biofilms pose a serious public health hazard with a significant economic impact on the food industry. The present scoping review is designed to analyze the literature published during 2001-2020 on biofilm formation of microbes, their detection methods, and association with antimicrobial resistance (if any). The peer-reviewed articles retrieved from 04 electronic databases were assessed using PRISMA-ScR guidelines. From the 978 preliminary search results, a total of 88 publications were included in the study. On analysis, the commonly isolated pathogens were Listeria monocytogenes, Staphylococcus aureus, Salmonella spp., Escherichia coli, Bacillus spp., Vibrio spp., Campylobacter jejuni and Clostridium perfringens. The biofilm-forming ability of microbes was found to be influenced by various factors such as attachment surfaces, temperature, presence of other species, nutrient availability etc. A total of 18 studies characterized the biofilm-forming genes, particularly for S. aureus, Salmonella spp., and E. coli. In most studies, polystyrene plate and/or stainless-steel coupons were used for biofilm formation, and the detection was carried out by crystal violet assays and/or by plate counting method. The strain-specific significant differences in biofilm formation were observed in many studies, and few studies carried out analysis of multi-species biofilms. The association between biofilm formation and antimicrobial resistance wasn't clearly defined. Further, viable but non-culturable (VBNC) form of the foodborne pathogens is posing an unseen (by conventional cultivation techniques) but potent threat food safety. The present review recommends the need for carrying out systematic surveys and risk analysis of biofilms in food chain to highlight the evidence-based public health concerns, especially in regions where microbiological food hazards are quite prevalent.

Predictive models for the growth of Salmonella spp., Listeria spp., and Escherichia coli in lettuce harvested on Taiwanese farms

This study aimed at developing predictive models for Salmonella, Listeria, and E. coli in lettuce iceberg (Lactuca sativa) locally grown in Taiwan. The models were developed under constant temperature levels (5, 10, 15, 20, and 25°C) and validated under dynamic temperature conditions (18°C for 4 h, 7°C for 48 h, 23°C for 4 h). The result showed that (1) all strains were unable to grow at 5°C except for standard strain of Listeria obtained from the BCRC and (2) the growth rate of locally isolated strains of Salmonella and Listeria was higher than the standard one at certain temperature levels and lower than the growth rates of E. coli. The findings in this study enhance our understanding about the growth variability between Salmonella, Listeria, and E. coli strains on vegetables locally grown in Taiwan and may be used to improve the management of proper storage temperature in the lettuce supply chain in this country. Considering the temperature recommendation for refrigerated food in Taiwan, the findings in this study therefore recommend that fresh vegetables (e.g., lettuce) should be stored at 5°C or lower to prevent the rapid growth of these microorganisms. Finally, the developed models can be used in the assessment of the microbiological risk of Salmonella, Listeria, and E. coli contamination in lettuce locally grown in Taiwan. PRACTICAL APPLICATION: This study developed predictive models describing the growth of Salmonella, Listeria, and E. coli in lettuce locally grown in Taiwan. The models developed in this study can be used in quantitative microbial risk assessment.

Characterization of the Lytic Phage Flora With a Broad Host Range Against Multidrug-Resistant Escherichia coli and Evaluation of Its Efficacy Against E. coli Biofilm Formation

Escherichia coli is a gram-negative bacterium that is distributed widely throughout the world; it is mainly found in contaminated food, the poultry industry, and animal feces. The emergence of antibiotic-resistant E. coli poses a threat to human and animal health, which has led to renewed interest in phage-based therapy. E. coli biofilm control and prevention are of great importance. In this study, the isolated phages Flora and KM18 were found to belong to the family Myoviridae; the optimal preservation buffer was pH = 6~7, and the phage genome sizes were 168,909 (Flora) and 168,903 (KM18) bp. Phage Flora had a broader lytic spectrum than KM18. Phage Flora had a better antibiofilm effect than kanamycin sulfate in high-concentration E. coli cultures. A combination of the phage Flora and kanamycin sulfate showed better antibiofilm effects than Flora or kanamycin sulfate alone in low-concentration E. coli cultures. These characteristics can serve as a guideline for the selection of effective candidates for phage therapy, in this case antibiotic-resistant E. coli control in the poultry industry.

Biofilm formation and genomic features of Listeria monocytogenes strains isolated from meat and dairy industries located in Piedmont (Italy)

Listeria monocytogenes is considered a major challenge for the food industry as it can persist for long periods in food processing plants by forming biofilms. The aims of this study were: i) to assess the biofilm producing ability of 57 Listeria monocytogenes isolates previously subjected to whole-genome sequencing (WGS); ii) to compare the levels of biofilm formation with the presence or absence of biofilm associated genes. To determine the presence or absence of a known set of biofilm associated genes, a comparative genomic analysis was performed on each strain. Among Listeria monocytogenes isolates, 58 %, 38.5 % and 3.5 % exhibited weak, moderate or strong biofilm production, respectively. No difference in biofilm production was observed between food and environmental isolates. The percentage of Listeria monocytogenes strains isolated from meat products (57 %) classified as moderate or strong biofilm producers was higher than the percentage obtained for strains isolated from dairy products (28 %). The presence of the Stress Survival Islet 1, the arsD stress gene and the truncated inlA protein was significantly associated with increased levels of biofilm. Combining biofilm phenotype with molecular and genotyping data may provide the opportunity to better understand the relationship between genes linked to biofilm formation in Listeria monocytogenes.

Listeria monocytogenes - How This Pathogen Survives in Food-Production Environments?

The foodborne pathogen Listeria monocytogenes is the causative agent of human listeriosis, a severe disease, especially dangerous for the elderly, pregnant women, and newborns. Although this infection is comparatively rare, it is often associated with a significant mortality rate of 20-30% worldwide. Therefore, this microorganism has an important impact on food safety. L. monocytogenes can adapt, survive and even grow over a wide range of food production environmental stress conditions such as temperatures, low and high pH, high salt concentration, ultraviolet lights, presence of biocides and heavy metals. Furthermore, this bacterium is also able to form biofilm structures on a variety of surfaces in food production environments which makes it difficult to remove and allows it to persist for a long time. This increases the risk of contamination of food production facilities and finally foods. The present review focuses on the key issues related to the molecular mechanisms of the pathogen survival and adaptation to adverse environmental conditions. Knowledge and understanding of the L. monocytogenes adaptation approaches to environmental stress factors will have a significant influence on the development of new, efficient, and cost-effective methods of the pathogen control in the food industry, which is critical to ensure food production safety.

Polymeric Coatings and Antimicrobial Peptides as Efficient Systems for Treating Implantable Medical Devices Associated-Infections

Many infections are associated with the use of implantable medical devices. The excessive utilization of antibiotic treatment has resulted in the development of antimicrobial resistance. Consequently, scientists have recently focused on conceiving new ways for treating infections with a longer duration of action and minimum environmental toxicity. One approach in infection control is based on the development of antimicrobial coatings based on polymers and antimicrobial peptides, also termed as “natural antibiotics”.

Effect of pH and Salinity on the Ability of Salmonella Serotypes to Form Biofilm

Salmonella is a major cause of food-borne infections in Europe, and the majority of human infections are caused by only a few serotypes, among them are Salmonella enterica subsp. enterica serotype Enteritidis (hereafter Salmonella Enteritidis), Salmonella Typhimurium, and the monophasic variant of S. Typhimurium. The reason for this is not fully understood, but could include virulence factors as well as increased ability to transfer via the external environment. Formation of biofilm is considered an adaptation strategy used by bacteria to overcome environmental stresses. In order to assess the capability of different Salmonella serotypes to produce biofilm and establish whether this is affected by pH and salinity, 88 Salmonella isolates collected from animal, food, and human sources and belonging to 15 serotypes, including those most frequently responsible for human infections, were tested. Strains were grown in tryptic soy broth (TSB), TSB with 4% NaCl pH 4.5, TSB with 10% NaCl pH 4.5, TSB with 4% NaCl pH 7, or TSB with 10% NaCl pH 7, and biofilm production was assessed after 24 h at 37°C using crystal violet staining. A linear mixed effect model was applied to compare results from the different experimental conditions. Among the tested serotypes, S. Dublin showed the greatest ability to form biofilm even at pH 4.5, which inhibited biofilm production in the other tested serotypes. Salmonella Senftenberg and the monophasic variant of S. Typhimurium showed the highest biofilm production in TSB with 10% NaCl pH 7. In general, pH had a high influence on the ability to form biofilm, and most of the tested strains were not able to produce biofilm at pH 4.5. In contrast, salinity only had a limited influence on biofilm production. In general, serotypes causing the highest number of human infections showed a limited ability to produce biofilm in the tested conditions, indicating that biofilm formation is not a crucial factor in the success of these clones.

The Use of Ozone as an Eco-Friendly Strategy against Microbial Biofilm in Dairy Manufacturing Plants: A Review

Managing spoilage and pathogenic bacteria contaminations represents a major challenge for the food industry, especially for the dairy sector. Biofilms formed by these microorganisms in food processing environment continue to pose concerns to food manufacturers as they may impact both the safety and quality of processed foods. Bacteria inside biofilm can survive in harsh environmental conditions and represent a source of repeated food contamination in dairy manufacturing plants. Among the novel approaches proposed to control biofilm in food processing plants, the ozone treatment, in aqueous or gaseous form, may represent one of the most promising techniques due to its antimicrobial action and low environmental impact. The antimicrobial effectiveness of ozone has been well documented on a wide variety of microorganisms in planktonic forms, whereas little data on the efficacy of ozone treatment against microbial biofilms are available. In addition, ozone is recognized as an eco-friendly technology since it does not leave harmful residuals in food products or on contact surfaces. Thus, this review intends to present an overview of the current state of knowledge on the possible use of ozone as an antimicrobial agent against the most common spoilage and pathogenic microorganisms, usually organized in biofilm, in dairy manufacturing plants.

Modeling the combined effect of temperature, pH, acetic and lactic acid concentrations on the growth/no growth interface of acid-tolerant Bacillus spores

The application of minimal processing technologies has led to increased spoilage incidents in low-acid pasteurized sauces due to the outgrowth of acid-tolerant spore-forming spoilage bacteria (ATSSB). Controlling the germination and subsequent growth of ATSSB spores is vital to enhance the ambient storage stability of pasteurized sauces. This study developed and validated a set of growth/no growth (G/NG) models for spores of two ATSSB strains (Bacillus velezensis and Bacillus subtilis subsp. subtilis) isolated from pasteurized sauces. The G/NG data at two levels of temperature (22 and 30 °C) were collected in Nutrient Broth (a_w = 0.98 adjusted with NaCl) by a full factorial design with five equidistant levels of pH (4.4-5.6), four concentrations of total acetic acid (0.0-0.3% (w/w)), and four concentrations of total lactic acid (0.00-1.00% (w/w)). The growth, starting from heat-treated (10 min 80 °C) spores, of each strain was assessed under 160 combinations by regular optical density measurements during three months. Twelve replicates were made for each combination. The developed models demonstrate that without organic acids even the lowest pH (4.4) allows a high growth possibility of the ATSSB spores, while acetic and lactic acids exhibit a significant antibacterial activity, which can be enhanced at decreased pH. The growth starting from B. subtilis spores can be inhibited for at least three months with 1.0% (w/w) total lactic acid in the water phase at both temperatures, which was not the case for B. velezensis, while 0.3% acetic acid achieves a full inhibition on both strains at 22 °C. With a combination of 0.3% acetic acid and 0.7% lactic acid, no growth should occur in the investigated range. This research is one of the first studies exploring the feasibility of ambient storage for low-acid pasteurized sauces eliminating preservatives such as benzoic and sorbic acids, and proves the synergistic effect of decreased pH and the presence of acetic and lactic acids on inhibiting bacterial growth from ATSSB spores.

Promising strategies to control persistent enemies: Some new technologies to combat biofilm in the food industry-A review

Biofilm is an advanced form of protection that allows bacterial cells to withstand adverse environmental conditions. The complex structure of biofilm results from genetic-related mechanisms besides other factors such as bacterial morphology or substratum properties. Inhibition of biofilm formation of harmful bacteria (spoilage and pathogenic bacteria) is a critical task in the food industry because of the enhanced resistance of biofilm bacteria to stress, such as cleaning and disinfection methods traditionally used in food processing plants, and the increased food safety risks threatening consumer health caused by recurrent contamination and rapid deterioration of food by biofilm cells. Therefore, it is urgent to find methods and strategies for effectively combating bacterial biofilm formation and eradicating mature biofilms. Innovative and promising approaches to control bacteria and their biofilms are emerging. These new approaches range from methods based on natural ingredients to the use of nanoparticles. This literature review aims to describe the efficacy of these strategies and provide an overview of recent promising biofilm control technologies in the food processing sector.

Effect of Gaseous Ozone on Listeria monocytogenes Planktonic Cells and Biofilm: An In Vitro Study

Among food-borne pathogens, Listeria monocytogenes continues to pose concerns to food business operators due to its capacity to form biofilm in processing environments. Ozone may be an eco-friendly technology to control microbial contaminations, but data concerning its effect on Listeria monocytogenes biofilm are still limited. In this study, the effect of gaseous ozone at 50 ppm on planktonic cells and biofilm of reference and food-related Listeria monocytogenes strains was evaluated. Ozone caused a reduction in microbial loads of 3.7 ± 0.4 and 3.9 ± 0.4 Log10 CFU/mL after 10 and 30 min, respectively. A complete inactivation of planktonic cells after 6 h of treatment was observed. Biofilm inhibition and eradication treatments (50 ppm, 6 h) resulted in a significant decrease of the biofilm biomass for 59% of the strains tested, whilst a slight dampening of live cell loads in the biofilm state was observed. In conclusion, gaseous ozone is not sufficient to completely counteract Listeria monocytogenes biofilm, but it may be useful as an additional tool to contrast Listeria monocytogenes free-living cells and to improve the existing sanitization procedures in food processing environments.

Effect οf οxygen availability and pH οn adaptive acid tolerance response of immobilized Listeria monocytogenes in structured growth media

The aim of the present study was to evaluate the effect of oxygen availability (aerobic, hypoxic and anoxic conditions) and sub-optimal pH (6.2 and 5.5) in a structured medium (10% w/V gelatin) on the growth of two immobilized L. monocytogenes strains (C5, 6179) at 10 °C and their subsequent acid resistance (pH 2.0, e.g., gastric acidity). Anaerobic conditions resulted in lower bacterial population (P < 0.05) (7.8-8.2 log CFU/mL) at the end of storage than aerobic and hypoxic environment (8.5-9.0 log CFU/mL), a phenomenon that was intensified at lower pH (5.5), where no significant growth was observed for anaerobically grown cultures. Prolonged habituation of L. monocytogenes (15 days) at both pH increased its acid tolerance resulting in max. 10 times higher t_4D (appx. 60 min). The combined effect though of oxygen availability and suboptimal pH on L. monocytogenes acid resistance was found to vary with the strain. Anoxically grown cultures at pH 5.5 exhibited the lowest tolerance towards lethal acid stress, with countable survivors occurring only until 20 min of exposure at pH 2.0. Elucidating the role of oxygen limiting conditions, often encountered in structured foods, on acid resistance of L. monocytogenes, would assist in assessing the capacity of L. monocytogenes originated from different food-related niches to withstand gastric acidity and possibly initiate infection.

Analysis of the Phospholipid Profile of the Collection Strain PAO1 and Clinical Isolates of Pseudomonas aeruginosa in Relation to Their Attachment Capacity

Bacteria form multicellular and resistant structures named biofilms. Biofilm formation starts with the attachment phase, and the molecular actors involved in this phase, except adhesins, are poorly characterized. There is growing evidence that phospholipids are more than simple structural bricks. They are involved in bacterial adaptive physiology, but little is known about their role in biofilm formation. Here, we report a mass spectrometry analysis of the phospholipid (PL) profile of several strains of Pseudomonas aeruginosa isolated from cystic fibrosis patients. The aim of our study was to evaluate a possible link between the PL profile of a strain and its attachment phenotype. Our results showed that PL profile is strongly strain-dependent. The PL profile of P. aeruginosa PAO1, a collection strain, was different from those of 10 clinical isolates characterized either by a very low or a very high attachment capacity. We observed also that the clinical strain’s PL profiles varied even more importantly between isolates. By comparing groups of strains having similar attachment capacities, we identified one PL, PE 18:1-18:1, as a potential molecular actor involved in attachment, the first step in biofilm formation. This PL represents a possible target in the fight against biofilms.

Assessing the Biofilm Formation Capacity of the Wine Spoilage Yeast Brettanomyces bruxellensis through FTIR Spectroscopy

Brettanomyces bruxellensis is a wine spoilage yeast known to colonize and persist in production cellars. However, knowledge on the biofilm formation capacity of B. bruxellensis remains limited. The present study investigated the biofilm formation of 11 B. bruxellensis strains on stainless steel coupons after 3 h of incubation in an aqueous solution. FTIR analysis was performed for both planktonic and attached cells, while comparison of the obtained spectra revealed chemical groups implicated in the biofilm formation process. The increased region corresponding to polysaccharides and lipids clearly discriminated the obtained spectra, while the absorption peaks at the specific wavenumbers possibly reveal the presence of β-glucans, mannas and ergosterol. Unsupervised clustering and supervised classification were employed to identify the important wavenumbers of the whole spectra. The fact that all the metabolic fingerprints of the attached versus the planktonic cells were similar within the same cell phenotype class and different between the two phenotypes, implies a clear separation of the cell phenotype; supported by the results of the developed classification model. This study represents the first to succeed at applying a non-invasive technique to reveal the metabolic fingerprint implicated in the biofilm formation capacity of B. bruxellensis, underlying the homogenous mechanism within the yeast species.

Advanced Killing Potential of Thymol against a Time and Temperature Optimized Attached Listeria monocytogenes Population in Lettuce Broth

Fresh vegetables and salads are increasingly implicated in outbreaks of foodborne infections, such as those caused by Listeria monocytogenes, a dangerous pathogen that can attach to the surfaces of the equipment creating robust biofilms withstanding the killing action of disinfectants. In this study, the antimicrobial efficiency of a natural plant terpenoid (thymol) was evaluated against a sessile population of a multi-strain L. monocytogenes cocktail developed on stainless steel surfaces incubated in lettuce broth, under optimized time and temperature conditions (54 h at 30.6 °C) as those were determined following response surface modeling, and in comparison, to that of an industrial disinfectant (benzalkonium chloride). Prior to disinfection, the minimum bactericidal concentrations (MBCs) of each compound were determined against the planktonic cells of each strain. The results revealed the advanced killing potential of thymol, with a concentration of 625 ppm (= 4 × MBC) leading to almost undetectable viable bacteria (more than 4 logs reduction following a 15-min exposure). For the same degree of killing, benzalkonium chloride needed to be used at a concentration of at least 20 times more than its MBC (70 ppm). Discriminative repetitive sequence-based polymerase chain reaction (rep-PCR) also highlighted the strain variability in both biofilm formation and resistance. In sum, thymol was found to present an effective anti-listeria action under environmental conditions mimicking those encountered in the salad industry and deserves to be further explored to improve the safety of fresh produce.