Escherichia coli O157:H7 Strains Isolated from High-Event Period Beef Contamination Have Strong Biofilm-Forming Ability and Low Sanitizer Susceptibility, Which Are Associated with High pO157 Plasmid Copy Number

Evaluating disinfectant efficacy on mixed biofilms comprising Shiga toxigenic Escherichia coli, lactic acid bacteria, and spoilage microorganisms

This study aimed to investigate the impact of temperature and the presence of other microorganisms on the susceptibility of STEC to biocides. Mature biofilms were formed at both 10°C and 25°C. An inoculum of planktonic bacteria comprising 106 CFU/mL of spoilage bacteria and 103 CFU/mL of a single E. coli strain (O157, O111, O103, and O12) was used to form mixed biofilms. The following bacterial combinations were tested: T1: Carnobacterium piscicola + Lactobacillus bulgaricus + STEC, T2: Comamonas koreensis + Raoultella terrigena + STEC, and T3: Pseudomonas aeruginosa + C. koreensis + STEC. Tested biocides included quaternary ammonium compounds (Quats), sodium hypochlorite (Shypo), sodium hydroxide (SHyd), hydrogen peroxide (HyP), and BioDestroy®-organic peroxyacetic acid (PAA). Biocides were applied to 6-day-old biofilms. Minimum Bactericidal Concentrations (MBC) and Biofilm Eradication Concentrations (BEC) were determined. Planktonic cells and single-species biofilms exhibited greater susceptibility to sanitizers (p < 0.0001). Lactobacillus and Carnobacterium were more susceptible than the rest of the tested bacteria (p < 0.0001). Single species biofilms formed by E. coli O111, O121, O157, and O45 showed resistance (100%) to Shypo sanitizer (200 ppm) at 25°C. From the most effective to the least effective, sanitizer performance on single-species biofilms was PAA > Quats > HyP > SHyd > Shypo. In multi-species biofilms, spoilage bacteria within T1, T2, and T3 biofilms showed elevated resistance to SHyd (30%), followed by quats (23.25%), HyP (15.41%), SHypo (9.70%), and BioDestroy® (3.42%; p < 0.0001). Within T1, T2, and T3, the combined STEC strains exhibited superior survival to Quats (23.91%), followed by HyP (19.57%), SHypo (18.12%), SHyd (16.67%), and BioDestroy® (4.35%; p < 0.0001). O157:H7-R508 strains were less tolerant to Quats and Shypo when combined with T2 and T3 (p < 0.0001). O157:H7 and O103:H2 strains in mixed biofilms T1, T2, and T3 exhibited higher biocide resistance than the weak biofilm former, O145:H2 (p < 0.0001). The study shows that STEC within multi-species biofilms' are more tolerant to disinfectants.

Relationship between Desiccation Tolerance and Biofilm Formation in Shiga Toxin-Producing Escherichia coli

Shiga toxin-producing Escherichia coli (STEC) is a major concern in the food industry and requires effective control measures to prevent foodborne illnesses. Previous studies have demonstrated increased difficulty in the control of biofilm-forming STEC. Desiccation, achieved through osmotic stress and water removal, has emerged as a potential antimicrobial hurdle. This study focused on 254 genetically diverse E. coli strains collected from cattle, carcass hides, hide-off carcasses, and processing equipment. Of these, 141 (55.51%) were STEC and 113 (44.48%) were generic E. coli. The biofilm-forming capabilities of these isolates were assessed, and their desiccation tolerance was investigated to understand the relationships between growth temperature, relative humidity (RH), and bacterial survival. Only 28% of the STEC isolates had the ability to form biofilms, compared to 60% of the generic E. coli. Stainless steel surfaces were exposed to different combinations of temperature (0 °C or 35 °C) and relative humidity (75% or 100%), and the bacterial attachment and survival rates were measured over 72 h and compared to controls. The results revealed that all the strains exposed to 75% relative humidity (RH) at any temperature had reduced growth (p < 0.001). In contrast, 35 °C and 100% RH supported bacterial proliferation, except for isolates forming the strongest biofilms. The ability of E. coli to form a biofilm did not impact growth reduction at 75% RH. Therefore, desiccation treatment at 75% RH at temperatures of 0 °C or 35 °C holds promise as a novel antimicrobial hurdle for the removal of biofilm-forming E. coli from challenging-to-clean surfaces and equipment within food processing facilities.

Driving forces shaping the microbial ecology in meat packing plants

Meat production is a complex system, continually receiving animals, water, air, and workers, all of which serve as carriers of bacteria. Selective pressures involved in different meat processing stages such as antimicrobial interventions and low temperatures, may promote the accumulation of certain residential microbiota in meat cutting facilities. Bacteria including human pathogens from all these sources can contaminate meat surfaces. While significant advancements have been made in enhancing hygienic standards and pathogen control measures in meat plants, resulting in a notable reduction in STEC recalls and clinical cases, STEC still stands as a predominant contributor to foodborne illnesses associated with beef and occasionally with pork. The second-and third-generation sequencing technology has become popular in microbiota related studies and provided a better image of the microbial community in the meat processing environments. In this article, we reviewed the potential factors influencing the microbial ecology in commercial meat processing facilities and conducted a meta-analysis on the microbiota data published in the last 10 years. In addition, the mechanisms by which bacteria persist in meat production environments have been discussed with a focus on the significant human pathogen E. coli O157:H7 and generic E. coli, an indicator often used for the hygienic condition in food production.

Listeria monocytogenes Biofilms in Food-Associated Environments: A Persistent Enigma

Listeria monocytogenes (LM) is a bacterial pathogen responsible for listeriosis, a foodborne illness associated with high rates of mortality (20-30%) and hospitalisation. It is particularly dangerous among vulnerable groups, such as newborns, pregnant women and the elderly. The persistence of this organism in food-associated environments for months to years has been linked to several devastating listeriosis outbreaks. It may also result in significant costs to food businesses and economies. Currently, the mechanisms that facilitate LM persistence are poorly understood. Unravelling the enigma of what drives listerial persistence will be critical for developing more targeted control and prevention strategies. One prevailing hypothesis is that persistent strains exhibit stronger biofilm production on abiotic surfaces in food-associated environments. This review aims to (i) provide a comprehensive overview of the research on the relationship between listerial persistence and biofilm formation from phenotypic and whole-genome sequencing (WGS) studies; (ii) to highlight the ongoing challenges in determining the role biofilm development plays in persistence, if any; and (iii) to propose future research directions for overcoming these challenges.

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.

Evaluation of Salmonella Biofilm Cell Transfer from Common Food Contact Surfaces to Beef Products

ABSTRACT

Meat contamination by Salmonella enterica is a serious public health concern. Available data have suggested that biofilm formation at processing plants and contaminated contact surfaces might contribute to meat contamination. Because transfer from contact surfaces to food products via direct contact has been deemed the most common bacteria transmission route that can lead to contamination, we evaluated the effect of Salmonella biofilm forming ability, contact surface material, and beef surface tissue type on Salmonella biofilm transfer from hard surfaces to beef products. Salmonella biofilms developed on the common contact surfaces stainless steel (SS) and polyvinylchloride (PVC) were transferred consecutively via 30 s of direct contact to either lean muscle or adipose tissue surfaces of 15 pieces of beef trim. The Salmonella biofilm cells could be effectively transferred multiple times from the contact surfaces to the beef trim as indicated by quantifiable Salmonella cells on most meat samples. Biofilm forming ability had the most significant impact (P < 0.05) on transfer efficiency. More cells of Salmonella strains that formed strong biofilms were transferred after each contact and contaminated more meat samples with quantifiable cells compared with strains that formed weak biofilms. Contact surface materials also affected transferability. Salmonella biofilms on SS transferred more efficiently than did those on PVC. In contrast, the two types of meat surface tissues were not significantly different (P > 0.05) in biofilm transfer efficiency. Beef trim samples that were in contact with biofilms but did not have quantifiable Salmonella cells were positive for Salmonella after enrichment culture. Our results indicate the high potential of Salmonella biofilms on common contact surfaces in meat processing plants to cause product cross-contamination.

HIGHLIGHTS

Nature-Inspired Antimicrobial Surfaces and Their Potential Applications in Food Industries

Antimicrobial resistance (AMR) is a growing global concern and has called for the integration of different areas of expertise for designing robust solutions. One such approach is the development of antimicrobial surfaces to combat the emerging resistance in microbes against drugs and disinfectants. This review is a compressive summary of the work done in the field of material science, chemistry, and microbiology in the development of antimicrobial materials and surfaces that are inspired by examples in nature. The focus includes examples of natural antimicrobial surfaces, such as cicada wings or nanopillars, dragonfly wings, shrimp shells, taro leaves, lotus leaves, sharkskin, gecko skin, and butterfly wings, along with their mechanism of action. Techniques, compositions, and combinations that have been developed to synthetically mimic these surfaces against bacterial/viral and fungal growth in food-processing areas have also been discussed. The applications of synthetic mimics of natural antimicrobial surfaces in food-processing environments is still a naïve area of research. However, this review highlights the potential applications of natural antimicrobial surfaces in the food-processing environment as well as outlines the challenges that need mitigations.

Biofilm through the Looking Glass: A Microbial Food Safety Perspective

Food-processing facilities harbor a wide diversity of microorganisms that persist and interact in multispecies biofilms, which could provide an ecological niche for pathogens to better colonize and gain tolerance against sanitization. Biofilm formation by foodborne pathogens is a serious threat to food safety and public health. Biofilms are formed in an environment through synergistic interactions within the microbial community through mutual adaptive response to their long-term coexistence. Mixed-species biofilms are more tolerant to sanitizers than single-species biofilms or their planktonic equivalents. Hence, there is a need to explore how multispecies biofilms help in protecting the foodborne pathogen from common sanitizers and disseminate biofilm cells from hotspots and contaminate food products. This knowledge will help in designing microbial interventions to mitigate foodborne pathogens in the processing environment. As the global need for safe, high-quality, and nutritious food increases, it is vital to study foodborne pathogen behavior and engineer new interventions that safeguard food from contamination with pathogens. This review focuses on the potential food safety issues associated with biofilms in the food-processing environment.

Consecutive Treatments with a Multicomponent Sanitizer Inactivate Biofilms Formed by Escherichia coli O157:H7 and Salmonella enterica and Remove Biofilm Matrix

ABSTRACT

Many foodborne pathogens, including Escherichia coli O157:H7 and Salmonella enterica, can develop biofilms on contact surfaces at meat processing plants. Owing to the high tolerance of the biofilm cells associated with the three-dimensional biofilm structure and the well-expressed bacterial extracellular polymeric substances, it is a real challenge to completely inactivate and remove mature biofilms, as well as further prevent biofilm reoccurrence and pathogen survival. In the present study, we evaluated the effectiveness of consecutive treatments (10 to 120 min per treatment) by repeatedly applying a multicomponent sanitizer, based on a functional mechanism by synergistic combination of hydrogen peroxide and quaternary ammonia compounds, against biofilms formed by E. coli O157:H7 and S. enterica strains. Biofilms on stainless steel surfaces were treated with 2.5, 5, or 10% (recommended working concentration) of the sanitizer applied as a foam or liquid solution. Our results showed that the multicomponent sanitizer significantly (P < 0.05) reduced the amount of viable biofilm cells at all concentrations, as enumerable bacteria were only detected after low-concentration treatments (2.5 or 5%) with short exposure periods (10 or 20 min per treatment). Treatments with high concentrations (5 or 10%) of the sanitizer, multiple consecutive treatments (2 or 3 treatments), and sufficient exposure time (>60 min per treatment) effectively controlled pathogen survival postsanitization. Examination with a scanning electron microscope showed that treatment with the sanitizer at 5% strength significantly dissolved the connecting extracellular polysaccharide matrix and removed the majority of the biofilm matrix. No intact biofilm structure was detected after the 10% sanitizer treatment; instead, scattered individual bacteria with visibly altered cell morphology were observed. The treated bacteria exhibited indented and distorted shapes with shortened cell length and increased surface roughness, indicating severe cell injury and death. Our observations indicated that consecutive treatments with the multicomponent sanitizer was effective in inactivating E. coli O157:H7 and S. enterica biofilms and preventing pathogen reoccurrence.

HIGHLIGHTS

Impact of mixed biofilm formation with environmental microorganisms on E. coli O157:H7 survival against sanitization

Biofilm formation by foodborne pathogens is a serious threat to food safety and public health. Meat processing plants may harbor various microorganisms and occasional foodborne pathogens; thus, the environmental microbial community might impact pathogen survival via mixed biofilm formation. We collected floor drain samples from two beef plants with different E. coli O157:H7 prevalence history and investigated the effects of the environmental microorganisms on pathogen sanitizer tolerance. The results showed that biofilm forming ability and bacterial species composition varied considerably based on the plants and drain locations. E. coli O157:H7 cells obtained significantly higher sanitizer tolerance in mixed biofilms by samples from the plant with recurrent E. coli O157:H7 prevalence than those mixed with samples from the other plant. The mixed biofilm that best protected E. coli O157:H7 also had the highest species diversity. The percentages of the species were altered significantly after sanitization, suggesting that the community composition affects the role and tolerance level of each individual species. Therefore, the unique environmental microbial community, their ability to form biofilms on contact surfaces and the interspecies interactions all play roles in E. coli O157:H7 persistence by either enhancing or reducing pathogen survival within the biofilm community.

Bacteriophage biocontrol of Shiga toxigenic Escherichia coli (STEC) O145 biofilms on stainless steel reduces the contamination of beef

Shiga toxigenic Escherichia coli (STEC) can form biofilms and frequently cause serious foodborne illnesses. A strain of STEC O145:H25 (EC19990166) known to be a strong biofilm former was used to evaluate the efficacy of bacteriophage AZO145A against biofilms formed on stainless steel (SS) coupons. Exposure of STEC O145:H25 to phage AZO145A (10¹⁰ PFU/mL) for 2 h resulted in a 4.0 log₁₀ reduction (P < 0.01) of planktonic cells grown in M9 broth at 24 °C for 24 h, while reductions were 2.0 log₁₀ CFU/mL if these cells were grown for 48 h or 72 h prior to phage treatment. STEC O145 biofilms formed on SS coupons for 24, 48 and 72 h were reduced (P < 0.01) 2.9, 1.9 and 1.9 log₁₀ CFU/coupon by phages. STEC O145 cells in biofilms were readily transferred from the surface of the SS coupon to beef (3.6 log₁₀ CFU/coupon) even with as little as 10 s of contact with the meat surface. However, transfer of STEC O145 cells from biofilms that formed on SS coupons for 48 h to beef was reduced (P < 0.01) by 3.1 log₁₀ CFU by phage (2 × 10¹⁰ PFU/mL) at 24 °C. Scanning electron microscopy revealed that bacterial cells within indentations on the surface of SS coupons were reduced by phage. These results suggest that bacteriophage AZO145A could be effective in reducing the viability of biofilm-adherent STEC O145 on stainless steel in food industry environments.

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

The inherent differences in microbial behavior among identically treated strains of the same microbial species, referred to as "strain variability", are regarded as an important source of variability in microbiological studies. Biofilms are defined as the structured multicellular communities with complex architecture that enable microorganisms to grow adhered to abiotic or living surfaces and constitute a fundamental aspect of microbial ecology. The research studies assessing the strain variability in biofilm formation are relatively few compared to the ones evaluating other aspects of microbial behavior such as virulence, growth and stress resistance. Among the available research data on intra-species variability in biofilm formation, compiled and discussed in the present review, most of them refer to foodborne pathogens as compared to spoilage microorganisms. Molecular and physiological aspects of biofilm formation potentially related to strain-specific responses, as well as information on the characterization and quantitative description of this type of biological variability are presented and discussed. Despite the considerable amount of available information on the strain variability in biofilm formation, there are certain data gaps and still-existing challenges that future research should cover and address. Current and future advances in systems biology and omics technologies are expected to aid significantly in the explanation of phenotypic strain variability, including biofilm formation variability, allowing for its integration in microbiological risk assessment.

Biofilm Formation by Shiga Toxin-Producing Escherichia coli on Stainless Steel Coupons as Affected by Temperature and Incubation Time

Forming biofilm is a strategy utilized by Shiga toxin-producing Escherichia coli (STEC) to survive and persist in food processing environments. We investigated the biofilm-forming potential of STEC strains from 10 clinically important serogroups on stainless steel at 22 °C or 13 °C after 24, 48, and 72 h of incubation. Results from crystal violet staining, plate counts, and scanning electron microscopy (SEM) identified a single isolate from each of the O113, O145, O91, O157, and O121 serogroups that was capable of forming strong or moderate biofilms on stainless steel at 22 °C. However, the biofilm-forming strength of these five strains was reduced when incubation time progressed. Moreover, we found that these strains formed a dense pellicle at the air-liquid interface on stainless steel, which suggests that oxygen was conducive to biofilm formation. At 13 °C, biofilm formation by these strains decreased (P < 0.05), but gradually increased over time. Overall, STEC biofilm formation was most prominent at 22 °C up to 24 h. The findings in this study identify the environmental conditions that may promote STEC biofilm formation in food processing facilities and suggest that the ability of specific strains to form biofilms contributes to their persistence within these environments.

Biofilms in Food Processing Environments: Challenges and Opportunities

This review examines the impact of microbial communities colonizing food processing environments in the form of biofilms on food safety and food quality. The focus is both on biofilms formed by pathogenic and spoilage microorganisms and on those formed by harmless or beneficial microbes, which are of particular relevance in the processing of fermented foods. Information is presented on intraspecies variability in biofilm formation, interspecies relationships of cooperativism or competition within biofilms, the factors influencing biofilm ecology and architecture, and how these factors may influence removal. The effect on the biofilm formation ability of particular food components and different environmental conditions that commonly prevail during food processing is discussed. Available tools for the in situ monitoring and characterization of wild microbial biofilms in food processing facilities are explored. Finally, research on novel agents or strategies for the control of biofilm formation or removal is summarized.

Biofilms and Meat Safety: A Mini-Review

Biofilms are surface-attached microbial communities with distinct properties, which have a tremendous impact on public health and food safety. In the meat industry, biofilms remain a serious concern because many foodborne pathogens can form biofilms in areas at meat plants that are difficult to sanitize properly, and biofilm cells are more tolerant to sanitization than their planktonic counterparts. Furthermore, nearly all biofilms in commercial environments consist of multiple species of microorganisms, and the complex interactions within the community significantly influence the architecture, activity, and sanitizer tolerance of the biofilm society. This review focuses on the effect of microbial coexistence on mixed biofilm formation with foodborne pathogens of major concern in the fresh meat industry and their resultant sanitizer tolerance. The factors that would affect biofilm cell transfer from contact surfaces to meat products, one of the most common transmission routes that could lead to product contamination, are discussed as well. Available results from recent studies relevant to the meat industry, implying the potential role of bacterial persistence and biofilm formation in meat contamination, are reviewed in response to the pressing need to understand the mechanisms that cause "high event period" contamination at commercial meat processing plants. A better understanding of these events would help the industry to enhance strategies to prevent contamination and improve meat safety.

Ability of Shiga toxigenic Escherichia coli to survive within dry-surface biofilms and transfer to fresh lettuce

Biofilms are known to play important roles in bacterial survival and persistence in food-processing environments. This study aimed to determine the ability of the top 7 STEC serotypes to form biofilms on polystyrene (POL) and stainless steel (SS) plates and to quantify their survival and transfer from dry-surface biofilms to lettuce pieces. The ability of 14 STEC strains to form biofilms on these two materials at different exposure times and temperatures was assessed using crystal violet, Congo red and SEM. At 10 °C all serotypes were weak biofilm producers on both surfaces. In contrast, serotypes O45-040, O45-445, O103-102, O103-670 and O157-R508 were strong biofilm producers at 25 °C. Strains O103-102, O103-670, O111-CFS, O111-053 and O157:H7-R508 were expressers of curli. Under scanning electron microscopy, strains O103-670, O111-CFS, O157-R508, and O121-083 formed more discernible multilayer, mature biofilms on SS coupons. Regardless of the surface (POL/SS), all STEC strains were able to transfer viable cells onto fresh lettuce within a short contact time (2 min) to varying degrees (up to 6.35 log cfu/g). On POL, viable cell of almost all serotypes exhibited decreased detachment (p = 0.001) over 6 days; while after 30 days on SS, serotypes O45-040, O103-102, O103-670, O111-053, O111-CFS, O121-083, O145-231 O157:H7-R508 and O157:H7-122 were transferred to lettuce. After enrichment, all 14 STEC strains were recovered from dry-surface biofilms on POL and SS plates after 30 days. Results demonstrated that the top 7 STEC remained viable within dry-surface biofilms for at least 30 days, transferring to lettuce within 2 min of exposure and acting as a source of adulteration.

Biofilm Formation, Antimicrobial Resistance, and Sanitizer Tolerance of Salmonella enterica Strains Isolated from Beef Trim

In the beef industry, product contamination by Salmonella enterica is a serious public health concern, which may result in human infection and cause significant financial loss due to product recalls. Currently, the precise mechanism and pathogen source responsible for Salmonella contamination in commercial establishments are not well understood. We characterized 89 S. enterica strains isolated from beef trim with respect to their biofilm-forming ability, antimicrobial resistance, and biofilm cell survival/recovery growth after sanitizer exposure. A total of 28 Salmonella serovars was identified within these strains. The most common serovars identified were Anatum, Dublin, Montevideo, and Typhimurium, with these accounting for nearly half of the total strains. The vast majority (86%) of the strains was able to develop strong biofilms, and the biofilm-forming ability was highly strain dependent and related to cell surface expression of extracellular polymeric structures. These strains also demonstrated strong tolerance to quaternary ammonium chloride (QAC) and chlorine dioxide (ClO₂), but were more sensitive to chlorine treatment. Sanitizer tolerance and bacterial postsanitization recovery growth were closely associated with strains' biofilm-forming ability. Thirty percent of the examined strains were found resistant to multiple antimicrobial agents and the resistance phenotypes were serovar associated, but not related to strains' biofilm-forming ability. Pulsed-field gel electrophoresis analysis tended to group strains by serovar rather than by biofilm-forming ability. Collectively, these data indicate that the strong biofilm formers of certain S. enterica strains/serovars possess significant potential for causing meat product contamination in meat processing environment.