Biofilm formation by Salmonella spp. in catfish mucus extract under industrial conditions

Microscopic Analysis of Temperature Effects on Surface Colonization and Biofilm Morphology of Salmonella enterica

Salmonella enterica represents a diverse group of pathogens commonly associated with food contamination including red meat. Even though pre- and post-harvest cleaning and sanitization procedures are widely implemented at meat processing plants to mitigate the hazard, S. enterica cells may escape the process by colonizing, on contact, surfaces in the form of a biofilm that functions as an aggregated microbial community to facilitate mutual protection, antimicrobial resistance, proliferation and dissemination. Biofilm development is a complex process that can be affected by a variety of factors including environmental temperature. We developed methods using scanning electron microscopy and confocal microscopy with a novel image analysis software tool to investigate the temperature influence on S. enterica cell colonization and biofilm formation by directly visualizing and comparing the biofilm matrix's morphological differences under various temperatures. Cocktails of S. enterica strains belonging to serovars, commonly isolated from meat samples, were applied to develop biofilms on a stainless steel surface at 7, 15, or 37 °C. Results of the microscopy analysis showed that as temperature increased, better-defined biofilm structures with extracellular polymeric structures (EPS) could be identified. However, S. enterica colonization and aggregated bacterial biomass were clearly observed at the low temperature (7 °C) as well. These results demonstrate that the environmental temperature significantly contributes to S. enterica biofilm formation as the higher temperatures encourage bacterial active proliferation and biofilm maturation leading to the development of well-pronounced structures, while the lower temperature may promote cell attachment but, meanwhile, limit the EPS biosynthesis and biofilm maturation. Our study indicates that the mature S. enterica biofilms formed under favorable conditions may protect the pathogens with the well-developed 3-demensional (3D) structure against routine treatment. Furthermore, the low temperatures commonly maintained at meat plants are not able to effectively prevent S. enterica colonization and biofilm formation since at such temperatures there could still be colonized biomass that can contaminate the products. Therefore, the temperature effect on pathogen colonization and biofilm development should be taken into consideration while evaluating hygiene standards and sanitization procedures at the processing facilities.

The impact of different acidic conditions and food substrates on Listeria monocytogenes biofilms development and removal using nanoencapsulated carvacrol

Listeria monocytogenes biofilms present a significant challenge in the food industry. This study explores the impact of different acidic conditions of culture media and food matrices on the development and removal of biofilms developed on stainless steel surfaces by wild-type (WT) L. monocytogenes strains as well as in two mutant derivatives, ΔsigB and ΔagrA, that have defects in the general stress response and quorum sensing, respectively. Additionally, the study investigates the efficacy of nanoencapsulated carvacrol as an antimicrobial against L. monocytogenes biofilms developed in Tryptic Soy Broth (TSB) culture media acidified to different pH conditions (3.5, 4.5, 5.5, 6.5), and in food substrates (apple juice, strained yogurt, vegetable soup, semi-skimmed milk) having the same pH levels. No biofilm formation was observed for all L. monocytogenes strains at pH levels of 3.5 and 4.5 in both culture media and food substrates. However, at pH 5.5 and 6.5, increased biofilm levels were observed in both the culture media and food substrates, with the WT strain showing significantly higher biofilm formation (3.04-6.05 log CFU cm-2) than the mutant strains (2.30-5.48 log CFU cm-2). For both applications, the nanoencapsulated carvacrol demonstrated more potent antimicrobial activity against biofilms developed at pH 5.5 with 2.23 to 3.61 log reductions, compared to 1.58-2.95 log reductions at pH 6.5, with mutants being more vulnerable in acidic environments. In food substrates, nanoencapsulated carvacrol induced lower log reductions (1.58-2.90) than the ones in TSB (2.02-3.61). These findings provide valuable insights into the impact of different acidic conditions on the development of L. monocytogenes biofilms on stainless steel surfaces and the potential application of nanoencapsulated carvacrol as a biofilm control agent in food processing environments.

Characterization of ready-to-eat fish surface as a potential source of contamination of Vibrio parahaemolyticus biofilms

The worldwide consumption of ready-to-eat seafood products has steadily increased due to a range of health benefits. However, depending on the handling or cutting process of raw fish, ready-to-eat sashimi can be exposed to microbiological risks that can lead to foodborne infection by marine pathogens. Since surface characteristics are key factors for microbial adhesion and biofilm formation, the present study aims to determine the correlation between raw fish skin properties and Vibrio parahaemolyticus biofilm formation. We analyzed V. parahaemolyticus biofilms (ATCC 17802; initially inoculated ca. 2 or 4 log CFU/cm²) on fish skin (gizzard shad, pomfret, red snapper, and mackerel; fish species served as sashimi without peeling the skin) formed under simulated marine environments (incubating in artificial seawater with rocking motion at 30 °C, the maximum temperature of seasonal seawater) for 24 h. The characteristics of fish skin were determined using confocal laser scanning microscopy/scanning electron microscopy. V. parahaemolyticus showed higher biofilm counts on fish skins than on stainless steel, which was used as a control (P < 0.05). In particular, V. parahaemolyticus formed biofilms with significantly higher levels of bacterial populations on gizzard shad and pomfret (ca. 5 log CFU/cm²; P < 0.05), highlighting the relationship between the biofilm formation level and the characteristics of gizzard shad and pomfret skins. The surface roughness of fish skins, including the main roughness parameters (Ra, Rq, and Rz), influenced the attachment of V. parahaemolyticus (P < 0.05). Additionally, images of V. parahaemolyticus biofilms suggested that different topographical profiles of fish species (e.g., mucus, unique structural features, etc.) could cause V. parahaemolyticus to exhibit different biofilm phenotypes, such as sticking to or entangling on the fish skin surface. The major findings of this study provide various phenotypic adhesions of V. parahaemolyticus to fish skin in considerations of the potential hazard for the consumption of ready-to-eat sashimi served with its skin.

Variations in the motility and biofilm formation abilities of Escherichia coli O157:H7 during noodle processing

Motility and biofilm formation help to protect bacteria from host immune responses and facilitate tolerance of environmental stimuli to improve their adaptability. However, few reports have investigated the adaptability of bacteria that live in food substrates undergoing food processing-induced stress. In this study, variations in the surface morphology, bacterial count, motility, and biofilm formation abilities of Escherichia coli O157:H7 NCTC12900 were investigated during noodle processing, including the kneading, squeezing, resting, and sheeting phases. The results showed that bacterial surface morphology, count, and motility were impaired in the squeezing phase, whereas biofilm biomass continuously increased across all processing phases. Twenty-one genes and sRNAs were measured using RT-qPCR to reveal the mechanisms underlying these changes. Of these, the genes adrA, csrA, flgM, flhD, fliM, ydaM, and the sRNA McaS were significantly upregulated, whereas the genes fliA, fliG, and the sRNAs CsrC, DsrA, GcvB, and OxyS were evidently repressed. According to the correlation matrix results based on the reference gene adrA, we found that csrA, GcvB, McaS, and OxyS were the most relevant genes and sRNAs for biofilm formation and motility. For each of them, their overexpressions was found to inhibit bacterial motility and biofilm formation to varying degrees during noodle processing. Among these, 12900/pcsrA had the highest inhibitory potential against motility, yielding a minimum of 11.2 mm motility diameter in the resting phase. Furthermore, 12900/pOxyS showed the most significant inhibitory effect against biofilm formation, yielding a minimum biofilm formation value of 5% of that exhibited the wild strain in the sheeting phase. Therefore, we prospect to find an effective and feasible novel approach to weaken bacterial survival during food processing by regulating the genes or sRNAs related to motility and biofilm formation.

Salmonella spp. in Aquaculture: An Exploratory Analysis (Integrative Review) of Microbiological Diagnoses between 2000 and 2020

The present study aimed to characterize, through descriptive statistics, data from scientific articles selected in a systematic integrative review that performed a microbiological diagnosis of Salmonella spp. in aquaculture. Data were obtained from research articles published in the BVS, Scielo, Science Direct, Scopus and Web of Science databases. The selected studies were published between 2000 and 2020 on samples of aquaculture animal production (fish, shrimp, bivalve mollusks, and other crustaceans) and environmental samples of aquaculture activity (farming water, soil, and sediments). After applying the exclusion criteria, 80 articles were selected. Data such as country of origin, categories of fish investigated, methods of microbiological diagnosis of Salmonella spp., sample units analyzed and most reported serovars were mined. A textual analysis of the word cloud and by similarity and descending hierarchical classification with the application of Reinert's algorithm was performed using R® and Iramuteq® software. The results showed that a higher percentage of the selected articles came from Asian countries (38.75%). Fish was the most sampled category, and the units of analysis of the culture water, muscle and intestine were more positive. The culture isolation method is the most widespread, supported by more accurate techniques such as PCR. The most prevalent Salmonella serovars reported were S. Typhimurium, S. Weltevreden and S. Newport. The textual analysis showed a strong association of the terms "Salmonella", "fish" and "water", and the highest hierarchical class grouped 25.4% of the associated text segments, such as "aquaculture", "food" and "public health". The information produced characterizes the occurrence of Salmonella spp. in the aquaculture sector, providing an overview of recent years. Future research focusing on strategies for the control and prevention of Salmonella spp. in fish production are necessary and should be encouraged.

A duplex real-time NASBA assay targeting serotype-specific gene for rapid detection of viable S. enterica serovar Paratyphi C in retail foods of animal origin

Salmonella enterica serovars Paratyphi C is highly adapted to humans and can cause a typhoid-like disease with high mortality rates. In this study, three serovar-specific genes were determined for S. Paratyphi C, SPC_0871，SPC_0872, and SPC_0908, by comparative genomics method. Based on SPC_0908 and xcd gene for testing Salmonella spp., we have developed a duplex real-time nucleic acid sequence-based amplification (real-time NASBA) with molecular beacon approach for simultaneous detection of viable cells of Salmonella spp. and serotype Paratyphi C. The test selectively and consistently detected 53 Salmonella spp. (representing 31 serotypes) and 18 non-Salmonella strains. Additionally, the method showed high resistance to interference by natural background flora in pork and chicken samples. The sensitivity of the established approach was determined to be 4.89 CFU/25 g in artificially contaminated pork and chicken samples after pre-enrichment. We propose this NASBA-based protocol as a potential detection method for Salmonella spp. and serotype Paratyphi C in food of animal origin.

Differential Effects of Growth Medium Salinity on Biofilm Formation of Two Salmonella enterica Strains

ABSTRACT

Salmonella enterica is a prominent foodborne pathogen, including diverse serotypes that are prolific biofilm formers. Its ability to form biofilm can be affected by multiple environmental factors. In this study, the effect of salinity on biofilm formation by S. enterica was evaluated by using two recently isolated strains of Salmonella serotypes Enteritidis and Newport. Although supplementing the growth medium with a low concentration (0.5 to 2%) of sodium chloride (NaCl) slightly enhanced biofilm formation for the strain S. enterica serovar Enteritidis 110, it sharply reduced or abolished biofilm formation by the strain S. enterica serovar Newport 193. This differential effect of salinity on S. enterica strains of different serotypes was poorly correlated with inhibition of planktonic growth but strongly correlated with cell motility. Examining genes known to affect biofilm formation showed that the expression of adrA, csgD, and fliC, which encode proteins required for surface adhesion and cell motility, was significantly downregulated with salinity increase in Salmonella Newport 193 but not in Salmonella Enteritidis 110. Therefore, it is plausible that the differential effect of salinity on biofilm formation by Salmonella Enteritidis 110 and Salmonella Newport 193 resulted from the differential regulation to genes required for cell adherence and motility.

HIGHLIGHTS

Antibiofilm activity of coenzyme Q0 against Salmonella Typhimurium and its effect on adhesion-invasion and survival-replication

Salmonella Typhimurium, a common Gram-negative foodborne pathogen, threatens public health and hinders the development of the food industry. In this study, we evaluated the antibiofilm activity of coenzyme Q0 (CoQ0) against S. Typhimurium. Besides, the inhibition of the S. Typhimurium's adhesion to and invasion of Caco-2 cells and its survival and replication in RAW 264.7 cells by CoQ0 were also explored. The minimum inhibitory concentrations and minimal bactericidal concentrations of CoQ0 against Salmonella were both 100-400 μg/mL. Salmonella Typhimurium biofilm formation was effectively inhibited by subinhibitory concentrations (SICs) of CoQ0. The CoQ0-affected biofilm morphology was observed with light microscopy and field-emission scanning electron microscopy. CoQ0 at SICs reduced the swimming motility and quorum sensing of S. Typhimurium and repressed the transcription of critical virulence-related genes. CoQ0 at SICs also clearly reduced the adhesion of S. Typhimurium to and its invasion of Caco-2 cells and reduced its survival and replication within RAW 264.7 macrophage cells. These findings suggest that CoQ0 has strong antibiofilm activity and can be used as an anti-infectious agent against Salmonella.

An ordinal logistic regression approach to predict the variability on biofilm formation stages by five Salmonella enterica strains on polypropylene and glass surfaces as affected by pH, temperature and NaCl

This study assessed the adhesion and formation of biofilm by five Salmonella enterica strains (S. Enteritidis 132, S. Infantis 176, S. Typhimurium 177, S. Heidelberg 281 and S. Corvallis 297) on polypropylene (PP) and glass (G) surfaces as affected by pH (4-7), NaCl concentration (0-10% w/v) and temperature (8-35 °C). Sessile counts <3 log CFU/cm² were considered lack of adhesion (category 1), while counts ≥ 3 and < 5 log CFU/cm² corresponded to adhesion (category 2) and counts ≥ 5 log CFU/cm² corresponded biofilm formation (category 3). The obtained results categorized in these three responses were used to develop ordinal regression models to predict the probability of biofilm stages on PP- and G-surfaces. The experimental outcomes for lack of adhesion were >90% on PP- and G-surfaces. Generally, adhesion outcomes corresponded to approximately 36% of the total, whereas biofilm outcomes were close to 65% in both PP- and G-surfaces. The biofilm stages varied among the strains studied and with the material surface under the same experimental conditions. According to the generated ordinal models, the probability of adhesion and biofilm formation on PP-surface by the five S. enterica strains tested decreased at pH 4 or 5 in NaCl concentrations >4% and at a temperature <20 °C. On G-surface, the probability of adhesion increased pH 6 or 7, in the absence of NaCl and temperatures <20 °C, while, the probability of biofilm formation increased in the same pH, NaCl concentration up to 4% and temperatures ≥20 °C. This is the first study assessing the biofilm formation through categorical, ordinal responses and it shows that ordinal regression models can be useful to predict biofilm stages of S. enterica as a function of pH, NaCl, and temperature or their interactions.

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.

Complete Genome Sequence of Salmonella enterica Serovar Enteritidis NCM 61, with High Potential for Biofilm Formation, Isolated from Meat-Related Sources

Here, we report the complete genome sequence of strain NMC 61 of Salmonella enterica serovar Enteritidis, which was previously isolated from conveyor belts during chicken slaughter and has the potential to form biofilms on several surfaces. The genome is predicted to contain 110 noncoding small RNAs on the chromosome.

Salmonella enterica growth and biofilm formation in flesh and peel cantaloupe extracts on four food-contact surfaces

Salmonella enterica is responsible for the highest number of foodborne disease outbreaks pertaining to cantaloupe industry. The objective of this study was to examine the growth and biofilm formation by outbreak strains of S. enterica ser. Poona (S. Poona), S. enterica ser. Stanley (S. Stanley) and S. enterica ser. Montevideo (S. Montevideo) on different food-contact processing surfaces in cantaloupe flesh and peel extracts at 22 °C and 10 °C. The generation time of all S. enterica strains tested was shorter in the high concentration (50 mg/ml) of cantaloupe extract and high temperature. In 50 mg/ml of cantaloupe flesh or peel extract, the populations of S. enterica were increased by 5 log CFU/ml in 24 h at 22 °C and 1 log CFU/ml in 72 h at 10 °C. In 2 mg/ml of cantaloupe flesh or peel extracts, the populations of S. enterica were increased by 3.5 log CFU/ml in 56 h at 22 °C, but there were no changes in 72 h at 10 °C. The biofilm production of S. enterica was greater at 50 mg/ml of cantaloupe extract and 22 °C, but no major differences (P ≥ 0.05) were found among the strains tested. In 50 mg/ml cantaloupe extract, S. enterica produced 5-6 log CFU/cm² biofilm in 4-7 d at 22 °C and approximately 3.5-4 log CFU/cm² in 7 d at 10 °C. In 2 mg/ml of cantaloupe extract, S. enterica produced 4-4.5 log CFU/cm² biofilms in 4-7 d at 22 °C and 3 log CFU/cm² in 7 d at 10 °C. Biofilm formation by S. Poona (01A4754) was lowest on buna-n rubber compared to stainless steel, polyethylene and polyurethane surfaces under the majority of conditions tested. Overall, these findings show that S. enterica strains can grow rapidly and form biofilms on different cantaloupe processing surfaces in the presence of low concentrations of cantaloupe flesh or peel extracts.

Scanning electron microscopy of Salmonella biofilms on various food-contact surfaces in catfish mucus

The objective of this study was to determine the growth and survival of Salmonella enterica in the presence of high and low concentrations (375 μg/ml and 15 μg/ml) of catfish mucus extract at 10 °C and 22 °C for 63 days. The second objective of this study was to investigate the biofilm formation of Salmonella enterica serovar Blockley (7175) in catfish mucus extract for 48 h at 22 °C on four food-contact surfaces and to observe the biofilm populations using Scanning Electron Microscopy (SEM). The surface properties, surface roughness and surface energies were determined using contact angle measurement and atomic force microscopy. In 375 μg/ml of catfish mucus extract that was inoculated with 3 log CFU/ml, the growth of Salmonella counts were increased to a maximum of 6-7 log CFU/ml at 10 °C and 7-8 log CFU/ml at 22 °C in 7-14 d and decreased by 1-2 log CFU/ml from these peak levels at both 10 °C and 22 °C from 21 to 63 d. In 15 μg/ml of catfish mucus extract, Salmonella counts were in the range of 4-5 log CFU/ml at 10 °C and 5-6 log CFU/ml at 22 °C over 7-63 d of storage. By contrast, Salmonella counts were non-detectable in the absence of catfish mucus by 21-28 d of storage at 10 °C or 22 °C. The biofilm counts of S. Blockley (7175) on a stainless steel surface were 4 log CFU/cm² and 5.5 log CFU/cm² in 15 μg/ml and 375 μg/ml of catfish mucus extract respectively after 48 h incubation at 22 °C. SEM revelead that biofilm formation by S. Blockley (7175) was less in 15 μg/ml than 375 μg/ml of catfish mucus extract on stainless steel. In addition, SEM indicated that the visible biofilms were least on buna-N rubber as compared to stainless steel, polyethylene and polyurethane surfaces. Contact angle and atomic force microscopy confirmed that buna-N rubber was highly hydrophobic with low surface energy and low roughness when compared to other three surfaces. These findings indicate that Salmonella can utilize catfish mucus as a nutrient source to survive for longer periods and promote biofilm formation for its persistence on different food-contact surfaces.