Micro ecosystems from feed industry surfaces: a survival and biofilm study of Salmonella versus host resident flora strains

Role of Microbial Interactions across Food-Related Bacteria on Biofilm Population and Biofilm Decontamination by a TiO2-Nanoparticle-Based Surfactant

Microbial interactions play an important role in initial cell adhesion and the endurance of biofilm toward disinfectant stresses. The present study aimed to evaluate the effect of microbial interactions on biofilm formation and the disinfecting activity of an innovative photocatalytic surfactant based on TiO₂ nanoparticles. Listeria monocytogenes, Salmonella Enteritidis, Escherichia coli, Leuconostoc spp., Latilactobacillus sakei, Serratia liquefaciens, Serratia proteomaculans, Citrobacter freundii, Hafnia alvei, Proteus vulgaris, Pseudomonas fragi, and Brochothrix thermosphacta left to form mono- or dual-species biofilms on stainless steel (SS) coupons. The effectiveness of the photocatalytic disinfectant after 2 h of exposure under UV light on biofilm decontamination was evaluated. The effect of one parameter i.e., exposure to UV or disinfectant, was also determined. According to the obtained results, the microbial load of a mature biofilm depended on the different species or dual species that had adhered to the surface, while the presence of other species could affect the biofilm population of a specific microbe (p < 0.05). The disinfectant strengthened the antimicrobial activity of UV, as, in most cases, the remaining biofilm population was below the detection limit of the method. Moreover, the presence of more than one species affected the resistance of the biofilm cells to UV and the disinfectant (p < 0.05). In conclusion, this study confirms that microbial interactions affected biofilm formation and decontamination, and it demonstrates the effectiveness of the surfactant with the photocatalytic TiO₂ agent, suggesting that it could be an alternative agent with which to disinfect contaminated surfaces.

High biofilm-forming Pseudomonas strains isolated from poultry slaughterhouse surfaces: Their importance in the persistence of Salmonella enteritidis in slaughterhouses

The surfaces of poultry slaughterhouse equipment are significant sources of contamination with Pseudomonas strains, which leads to spoilage of poultry meat during subsequent refrigerated storage. In this study, Pseudomonas strains with high biofilm-forming ability were isolated from different surfaces of the poultry slaughterhouse equipment, identified based on molecular data, and characterized their biofilm-forming ability. After 24 h of incubation at 25 °C, 54 out of 58 Pseudomonas strains produced biofilm in vitro on polystyrene microplates. Seven isolates with high-ability to produce biofilm were identified as P. fragi (three strains), P. fluorescens (two strains), P. lundensis and P. cedrina. Despite their differences, these strains produced high amounts of biofilm in pure- and dual-species cultures with S. enteritidis on stainless steel surfaces. However, their ability to produce dual-species biofilms with S. enteritidis depends on whether S. enteritidis form the biofilm simultaneously with the Pseudomonas strains or whether Pseudomonas strains have already formed a biofilm. In concurrent inoculation, S. enteritidis participated in biofilm formation with all seven Pseudomonas strains with varying percent contributions. However, in delayed inoculation, S. enteritidis did not contribute in the biofilm formed by P. lundensis R26, P. fragi R39, and P. fluorescens R47. In addition to highlighting the complexity of bacterial interactions associated with Pseudomonas strains, these results showed that Pseudomonas strains can be implicated in Salmonella persistence in poultry slaughterhouses.

Mitigation of Salmonella on Food Contact Surfaces by Using Organic Acid Mixtures Containing 2-Hydroxy-4-(methylthio) Butanoic Acid (HMTBa)

Contaminated surfaces can transmit pathogens to food in industrial and domestic food-handling environments. Exposure to pathogens on food contact surfaces may take place via the cross-contamination of pathogens during postprocessing activities. Formaldehyde-based commercial sanitizers in recent years are less commonly being used within food manufacturing facilities due to consumer perception and labeling concerns. There is interest in investigating clean-label, food-safe components for use on food contact surfaces to mitigate contamination from pathogenic bacteria, including Salmonella. In this study, the antimicrobial effects of two types of organic acid mixtures containing 2-hydroxy-4-(methylthio) butanoic acid (HMTBa), Activate DA™ and Activate US WD-MAX™, against Salmonella when applied onto various food contact surfaces were evaluated. The efficacy of Activate DA (HMTBa + fumaric acid + benzoic acid) at 1% and 2% and Activate US WD-MAX (HMTBa + lactic acid + phosphoric acid) at 0.5% and 1% against Salmonella enterica (serovars Enteritidis, Heidelberg, and Typhimurium) were evaluated on six different material surfaces: plastic (bucket elevator and tote bag), rubber (bucket elevator belt and automobile tire), stainless steel, and concrete. There was a significant difference in the Salmonella log reduction on the material surfaces due to the organic acid treatments when compared to the untreated surfaces. The type of material surface also had an effect on the log reductions obtained. Stainless steel and plastic (tote) had the highest Salmonella log reductions (3-3.5 logs), while plastic (bucket elevator) and rubber (tire) had the lowest log reductions (1-1.7 logs) after treatment with Activate US WD-MAX. For Activate DA, the lowest log reductions (~1.6 logs) were observed for plastic (bucket elevator) and rubber (tire), and the highest reductions were observed for plastic (tote), stainless steel, and concrete (2.8-3.2 logs). Overall, the results suggested that Activate DA at 2% and Activate US WD-MAX at 1% are potentially effective at reducing Salmonella counts on food contact surfaces by 1.6-3.5 logs.

Evaluation of Liquid and Dry Chemical Treatments To Reduce Salmonella Typhimurium Contamination on Animal Food Manufacturing Surfaces

ABSTRACT

Salmonella can be isolated from animal food, ingredients, and animal food manufacturing surfaces. There are limited data regarding the sanitation of animal food manufacturing surfaces. This experiment evaluated the effects of nine chemical treatments on reduction of Salmonella Typhimurium contamination on various manufacturing surfaces. This experiment was a 9 × 5 factorial with nine chemical treatments and five surfaces. The nine chemical treatments included one with no inoculation or sanitation treatment (negative control). In the other eight treatments, inoculation with Salmonella Typhimurium was followed by either no sanitation treatment (positive control) or treatment with ground corn; liquid commercial formaldehyde; liquid food-grade sanitizer; liquid medium chain fatty acid blend of caprylic, caproic, and capric acids (MCFA); dry commercial calcium propionate; dry commercial acidulant; and dry commercial benzoic acid. The five surfaces included stainless steel, plastic, polypropylene tote bag, rubber belt, and rubber tire. Plastic had higher levels of Salmonella in the positive control than did the polypropylene tote bag; other surfaces had intermediate levels (P < 0.05). Surfaces treated with formaldehyde had no detectable Salmonella after treatment, and surfaces treated with MCFA had at least a 4-log reduction compared to the control (P < 0.05). The dry acidulant was the most effective dry sanitizer tested, but it had no impact on Salmonella concentration on rubber tires (P < 0.05). Whereas liquid sanitizers were the most effective in this experiment, they have limitations for use in dry bulk systems. In summary, formaldehyde, food-grade sanitizer, and MCFA were the most effective chemical treatments to reduce Salmonella surface contamination. Surface type can also influence Salmonella mitigation strategies; specifically, stainless steel and plastic can be more challenging to sanitize within animal food facilities.

HIGHLIGHTS

Antimicrobial-resistant Salmonella is detected more frequently in feed milling equipment than in raw feed components or processed animal feed

Food for human and animal consumption can provide a vehicle for the transfer of pathogenic and antimicrobial‐resistant bacteria into the food chain. We investigated the antimicrobial susceptibility of 453 Salmonella isolates collected from raw feed components, equipment and finished feed from 17 commercial feed mills in Australia between 2012 and 2021. Previous studies have found Salmonella prevalence and the diversity of Salmonella serotypes are greatest in the raw feed components. We, therefore, hypothesised that we would find a greater proportion of antimicrobial‐resistant Salmonella isolates in the raw feed components compared to other sample types. We found that of 453 isolates tested, 356 (0.80) were susceptible to all antimicrobials tested, 49 (0.11) were nonsusceptible to streptomycin only and 48 (0.11) were resistant to two or more antimicrobials. Of the 48 antimicrobial‐resistant isolates, 44 were found in feed milling equipment, two in raw feed components and two in finished feed. Statistical analysis, using a logistic regression with random effects model, found that the population‐adjusted mean probability of detecting antimicrobial‐resistant Salmonella isolates from feed milling equipment of 0.39, was larger than the probability of detecting resistant isolates in raw feed components 0.01, (P < 0.001) and in finished feed, 0.11, (P = 0.006). This propensity for antimicrobial‐resistant bacteria to colonise feed milling equipment has not been previously reported. Further studies are required to understand the ecology of antimicrobial‐resistant Salmonella in the feed milling environment.

Combined Effect of Temperature and Relative Humidity on the Survival of Salmonella Isolates on Stainless Steel Coupons

The survival on stainless steel of ten Salmonella isolates from food factory, clinical and veterinary sources was investigated. Stainless steel coupons inoculated with Salmonella were dried and stored at a range of temperatures and relative humidity (RH) levels representing factory conditions. Viability was determined from 1 to 22 days. Survival curves obtained for most isolates and storage conditions displayed exponential inactivation described by a log-linear model. Survival was affected by environmental temperatures and RH with decimal reduction times (DRTs) ranging from <1 day to 18 days. At 25 °C/15% RH, all isolates survived at levels of 10³ to 10⁵ cfu for >22 days. Furthermore, temperatures and RH independently influenced survival on stainless steel; increasing temperatures between 10 °C and 37 °C and increasing RH levels from 30–70% both decreased the DRT values. Survival curves displaying a shoulder followed by exponential death were obtained for three isolates at 10 °C/70% RH. Inactivation kinetics for these were described by modified Weibull models, suggesting that cumulative injury occurs before cellular inactivation. This study highlights the need to control temperature and RH to limit microbial persistence in the food manufacturing environment, particularly during the factory shut-down period for cleaning when higher temperature/humidity levels could be introduced.

Salmonella detection in commercially prepared livestock feed and the raw ingredients and equipment used to manufacture the feed: A systematic review and meta-analysis

Salmonella contamination of livestock feed is a serious veterinary and public health issue. In this study we used a systematic review to assess the prevalence and characterization of Salmonella isolates detected in raw feed components, feed milling equipment and finished feed from 97 studies published from 1955 to 2020 across seven global regions. Eighty-five studies were included in a meta-analyses to estimate the combined prevalence of Salmonella detection and to compare the risk of contamination associated with different sample types. We found the overall combined prevalence estimate of Salmonella detection was 0.14 with a prevalence of 0.18 in raw feed components, 0.09 in finished feed and 0.08 in feed milling equipment. Animal based raw feed components were 3.9 times more likely to be contaminated with Salmonella than plant based raw feed components. Differences between studies accounted for 99 % of the variance in the prevalence estimate for all sample types and there was no effect of region on the prevalence estimates. The combined prevalence of Salmonella detection in raw feed components decreased from 0.25 in 1955 to 0.11 in 2019. The proportion of Salmonella isolates that were resistant to antimicrobials was largest for amikacin (0.20), tetracycline (0.18) streptomycin (0.17), cefotaxime (0.14) and sulfisoxazole (0.11). The prevalence of Salmonella contamination of animal feed varies widely between individual studies and is an ongoing challenge for the commercial feed industry. Control relies on the vigilant monitoring and control of Salmonella in each individual mill.

Salmonella Typhimurium encoded cold shock protein E is essential for motility and biofilm formation

The ability of bacteria to form biofilms increases their survival under adverse environmental conditions. Biofilms have enormous medical and environmental impact; consequently, the factors that influence biofilm formation are an important area of study. In this investigation, the roles of two cold shock proteins (CSP) during biofilm formation were investigated in Salmonella Typhimurium, which is a major foodborne pathogen. Among all CSP transcripts studied, the expression of cspE (STM14_0732) was higher during biofilm growth. The cspE deletion strain (ΔcspE) did not form biofilms on a cholesterol coated glass surface; however, complementation with WT cspE, but not the F30V mutant, was able to rescue this phenotype. Transcript levels of other CSPs demonstrated up-regulation of cspA (STM14_4399) in ΔcspE. The cspA deletion strain (ΔcspA) did not affect biofilm formation; however, ΔcspEΔcspA exhibited higher biofilm formation compared to ΔcspE. Most likely, the higher cspA amounts in ΔcspE reduced biofilm formation, which was corroborated using cspA over-expression studies. Further functional studies revealed that ΔcspE and ΔcspEΔcspA exhibited slow swimming but no swarming motility. Although cspA over-expression did not affect motility, cspE complementation restored the swarming motility of ΔcspE. The transcript levels of the major genes involved in motility in ΔcspE demonstrated lower expression of the class III (fliC, motA, cheY), but not class I (flhD) or class II (fliA, fliL), flagellar regulon genes. Overall, this study has identified the interplay of two CSPs in regulating two biological processes: CspE is essential for motility in a CspA-independent manner whereas biofilm formation is CspA-dependent.

Review of multi-species biofilm formation from foodborne pathogens: multi-species biofilms and removal methodology

Multi-species biofilms are ubiquitous worldwide and are a concern in the food industry. Multi-species biofilms have a higher resistance to antimicrobial therapies than mono-species biofilms. In addition, multi-species biofilms can cause severe foodborne diseases. To remove multi-species biofilms, controlling the formation process of extracellular polymeric substances (EPS) and quorum sensing (QS) effects is essential. EPS disruption, inhibition of QS, and disinfection have been utilized to remove multi-species biofilms. This review presents information on the formation and novel removal methods for multi-species biofilms.

Comparison between cage and free-range egg production on microbial composition, diversity and the presence of Salmonella enterica

The microbial composition of the food production environment plays an important role in food safety and quality. This study employed both 16 S rRNA gene sequencing technology and culture-based techniques to investigate the bacterial microbiota of an egg production facility comprising of both free-range and conventional cage housing systems. The study also aimed to detect the presence of Salmonella enterica and determine whether its presence was positively or negatively associated with other taxa. Our findings revealed that microbiota profiles of free-range and cage houses differ considerably in relation to the relative abundance and diversity with a number of taxa unique to each system and to individual sampling sites within sheds. Core to each housing system were known inhabitants of the poultry gastrointestinal tracts, Romboutsia and Turicibacter, as well as common spoilage bacteria. Generally, free-range samples contained fewer taxa and were dominated by Staphylococcus equorum, differentiating them from the cage samples. Salmonella enterica was significantly associated with the presence of a taxa belonging to the Carnobacteriaceae family. The results of this study demonstrate that the diversity and composition of the microbiota is highly variable across egg layer housing systems, which could have implications for productivity, food safety and spoilage.

Pseudomonas putida as a potential biocontrol agent against Salmonella Java biofilm formation in the drinking water system of broiler houses

Background

Environmental biofilms can induce attachment and protection of other microorganisms including pathogens, but can also prevent them from invasion and colonization. This opens the possibility for so-called biocontrol strategies, wherein microorganisms are applied to control the presence of other microbes. The potential for both positive and negative interactions between microbes, however, raises the need for in depth characterization of the sociobiology of candidate biocontrol agents (BCAs). The inside of the drinking water system (DWS) of broiler houses is an interesting niche to apply BCAs, because contamination of these systems with pathogens plays an important role in the infection of broiler chickens and consequently humans. In this study, Pseudomonas putida, which is part of the natural microbiota in the DWS of broiler houses, was evaluated as BCA against the broiler pathogen Salmonella Java.

Results

To study the interaction between these species, an in vitro model was developed simulating biofilm formation in the drinking water system of broilers. Dual-species biofilms of P. putida strains P1, P2, and P3 with S. Java were characterized by competitive interactions, independent of P. putida strain, S. Java inoculum density and application order. When equal inocula of S. Java and P. putida strains P1 or P3 were simultaneously applied, the interaction was characterized by mutual inhibition, whereas P. putida strain P2 showed an exploitation of S. Java. Lowering the inoculum density of S. Java changed the interaction with P. putida strain P3 also into an exploitation of S. Java. A further increase in S. Java inhibition was established by P. putida strain P3 forming a mature biofilm before applying S. Java.

Conclusions

This study provides the first results showing the potential of P. putida as BCA against S. Java in the broiler environment. Future work should include more complex microbial communities residing in the DWS, additional Salmonella strains as well as chemicals typically used to clean and disinfect the system.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-020-02046-5.

Biofilm forming properties of quinolone resistant Escherichia coli from the broiler production chain and their dynamics in mixed biofilms

Background

Quinolone resistant Escherichia coli (QREC) have been found in samples from Norwegian broiler chicken, despite quinolones not being administered to poultry in Norway. Biofilm production may be one factor contributing to the observed persistence in the broiler production chain. In the present study, 158 QREC strains from chicken caecal and retail meat samples were screened for biofilm production in microtiter plates, biofilm morphotype on Congo Red (CR) agar plates and phylotype by multiplex PCR. Furthermore, the dynamics in mixed biofilms with strains of different morphotypes were studied on glass slides and on CR agar plates.

Results

All strains but one produced biofilm in microtiter plates and/or on CR agar plates at room temperature. There were no differences between strains from chicken caecum and chicken retail meat in the mean amount of biofilm produced in microtiter plates. Furthermore, no differences in biofilm production were observed between phylotypes. However, significant differences in biofilm production were found between biofilm morphotypes. The morphotype RDAR (red dry and rough, which has both curli and cellulose in the matrix, was displayed by 70% of the strains. Mean biofilm production by these strains were significantly higher than by strains with the morphotypes PDAR (pink dry and rough) with only cellulose or BDAR (brown dry and rough) with only curli. Interestingly, the two latter morphotypes produced biofilms with the morphotype RDAR when grown together. None of the strains achieved significantly higher numbers of colony forming units (cfu) in mixed biofilms than in single strain biofilms on glass slides.

Conclusions

The results indicate that QREC can form biofilm reservoirs on both inert and organic surfaces in production environments, as well as on meat. This may contribute to persistence and dissemination of the strains. Strains with both curli and cellulose in the biofilm matrix were significantly better biofilm formers than strains lacking one of these components. However, strains with only one of the components could compensate for this by producing mixed biofilms with strains having the other component, and thereby most likely enhance their probabilities of persistence in the production environment.

Impact of cleaning and disinfection procedures on microbial ecology and Salmonella antimicrobial resistance in a pig slaughterhouse

To guarantee food safety, a better deciphering of ecology and adaptation strategies of bacterial pathogens such as Salmonella in food environments is crucial. The role of food processing conditions such as cleaning and disinfection procedures on antimicrobial resistance emergence should especially be investigated. In this work, the prevalence and antimicrobial resistance of Salmonella and the microbial ecology of associated surfaces communities were investigated in a pig slaughterhouse before and after cleaning and disinfection procedures. Salmonella were detected in 67% of samples and isolates characterization revealed the presence of 15 PFGE-patterns belonging to five serotypes: S.4,5,12:i:-, Rissen, Typhimurium, Infantis and Derby. Resistance to ampicillin, sulfamethoxazole, tetracycline and/or chloramphenicol was detected depending on serotypes. 16S rRNA-based bacterial diversity analyses showed that Salmonella surface associated communities were highly dominated by the Moraxellaceae family with a clear site-specific composition suggesting a persistent colonization of the pig slaughterhouse. Cleaning and disinfection procedures did not lead to a modification of Salmonella susceptibility to antimicrobials in this short-term study but they tended to significantly reduce bacterial diversity and favored some genera such as Rothia and Psychrobacter. Such data participate to the construction of a comprehensive view of Salmonella ecology and antimicrobial resistance emergence in food environments in relation with cleaning and disinfection procedures.

Dynamics of Biofilm Formation by Salmonella Typhimurium and Beef Processing Plant Bacteria in Mono- and Dual-Species Cultures

This study aimed to determine the impact of bacteria from a beef plant conveyor belt on the biofilm formation of Salmonella in dual-species cultures. Beef plant isolates (50) including 18 Gram-negative aerobes (GNA), 8 Gram-positive aerobes (GPA), 5 lactic acid bacteria (LAB), 9 Enterobacteriaceae (EB), and 10 generic Escherichia coli (GEC) were included for developing biofilms in mono- and co-culture with S. Typhimurium at 15 °C for 6 days. Five selected cultures in planktonic form and in biofilms were tested for susceptibility to two commonly used sanitizers (i.e. E-San and Perox-E Plus). In mono-cultures, ≥ 80, 67, 61, 20, and 13% of GEC, EB, GNA, LAB, and GPA, respectively, developed measurable biofilms after 2 days, while all co-culture pairings with S. Typhimurium achieved some level of biofilm production. The predominant effect of EB and only effect of GEC strains on the biofilm formation of S. Typhimurium was antagonistic, while that of Gram-positive bacteria was synergistic, with the effect being more prominent on day 6. The effect was highly variable for the GNA isolates. Six aerobic isolates that formed moderate/strong biofilms by day 2 greatly boosted the co-culture biofilm formation. Seven Gram-negative bacteria were antagonistic against the biofilm formation of the co-cultures. Both sanitizers completely inactivated the selected planktonic cultures, but were largely ineffective against biofilms. In conclusion, all beef plant isolates assessed formed biofilms when paired with S. Typhimurium. Aerobic biofilm formers may create a more favorable condition for Salmonella biofilm formation, while some beef plant isolates have potential as a biocontrol strategy for Salmonella biofilms.

Comparison of 16S rDNA Next Sequencing of Microbiome Communities From Post-scalder and Post-picker Stages in Three Different Commercial Poultry Plants Processing Three Classes of Broilers

Poultry processing systems are a complex network of equipment and automation systems that require a proactive approach to monitoring in order to protect the food supply. Process oversight requires the use of multi-hurdle intervention systems to ensure that any undesirable microorganisms are reduced or eliminated by the time the carcasses are processed into final products. In the present study, whole bird carcass rinses (WBCR) collected at the post-scalder and post-picker locations from three different poultry processing facilities (Plant A: mid-weight broiler processing, B: large-weight broiler processing, C: young broiler (Cornish) processing) were subjected to next generation sequencing (NGS) and microbial quantification using direct plating methods to assess the microbial populations present during these stages of the poultry process. The quantification of aerobic plate counts (APC) and Enterobacteriaceae (EB) demonstrated that reductions for these microbial classes were not consistent between the two sampling locations for all facilities, but did not provide a clear picture of what microorganism(s) may be affecting those shifts. With the utilization of NGS, a more complete characterization of the microbial communities present including microorganisms that would not have been identified with the employed direct plating methodologies were identified. Although the foodborne pathogens typically associated with raw poultry, Salmonella and Campylobacter, were not identified, sequence analysis performed by Quantitative Insights of Microbiology Ecology (QIIME) indicated shifts of Erwinia, Serratia, and Arcobacter, which are microorganisms closely related to Salmonella and Campylobacter. Additionally, the presence of Chryseobacterium and Pseudomonas at both sampling locations and at all three facilities provides evidence that these microorganisms could potentially be utilized to assess the performance of multi-hurdle intervention systems.

Occurrence and characterisation of biofilms in drinking water systems of broiler houses

Background

Water quality in the drinking water system (DWS) plays an important role in the general health and performance of broiler chickens. Conditions in the DWS of broilers are ideal for microbial biofilm formation. Since pathogens might reside within these biofilms, they serve as potential source of waterborne transmission of pathogens to livestock and humans. Knowledge about the presence, importance and composition of biofilms in the DWS of broilers is largely missing. In this study, we therefore aim to monitor the occurrence, and chemically and microbiologically characterise biofilms in the DWS of five broiler farms.

Results

The bacterial load after disinfection in DWSs was assessed by sampling with a flocked swab followed by enumerations of total aerobic flora (TAC) and Pseudomonas spp. The dominant flora was identified and their biofilm-forming capacity was evaluated. Also, proteins, carbohydrates and uronic acids were quantified to analyse the presence of extracellular polymeric substances of biofilms. Despite disinfection of the water and the DWS, average TAC was 6.03 ± 1.53 log CFU/20cm². Enumerations for Pseudomonas spp. were on average 0.88 log CFU/20cm² lower. The most identified dominant species from TAC were Stenotrophomonas maltophilia, Pseudomonas geniculata and Pseudomonas aeruginosa. However at species level, most of the identified microorganisms were farm specific. Almost all the isolates belonging to the three most abundant species were strong biofilm producers. Overall, 92% of all tested microorganisms were able to form biofilm under lab conditions. Furthermore, 63% of the DWS surfaces appeared to be contaminated with microorganisms combined with at least one of the analysed chemical components, which is indicative for the presence of biofilm.

Conclusions

Stenotrophomonas maltophilia, Pseudomonas geniculata and Pseudomonas aeruginosa are considered as opportunistic pathogens and could consequently be a potential risk for animal health. Additionally, the biofilm-forming capacity of these organisms could promote attachment of other pathogens such as Campylobacter spp. and Salmonella spp.

Electronic supplementary material

The online version of this article (10.1186/s12866-019-1451-5) contains supplementary material, which is available to authorized users.

Pet Food Factory Isolates of Salmonella Serotypes Do Not Demonstrate Enhanced Biofilm Formation Compared to Serotype-Matched Clinical and Veterinary Isolates

Environmentally persistent Salmonella in the pet food factory environment has been described, with biofilm formation suggested as a candidate mechanism contributing to their persistence. In this study the ability of a panel of Salmonella isolates from factory, clinical, and veterinary sources was investigated for their ability to form biofilms at 24 and 48 hours. The effect of nutrient availability and incubation time on biofilm formation was investigated using full strength and diluted 1/20 TSB media at 37°C, 25°C, 15°C, and 10°C. Results highlighted that all the Salmonella isolates were able to form biofilms in both nutrient conditions and this was highly correlated with temperature. At 25°C, biofilm formation was enhanced in diluted 1/20 TSB and increased incubation time (48h) (p= <0.001). However, this was not observed at 10°C, 15°C, or 37°C. None of the factory isolates demonstrated enhanced biofilm formation in comparison to serotype-matched isolates from veterinary and clinical sources. Salmonella enterica Senftenberg 775W was the strongest biofilm former at 15°C, 25°C, and 37°C in all the conditions tested (p=<0.05). Biofilm formation is an important mechanism of environmental persistence in the food manufacturing environment; however, there is no evidence of an enhanced biofilm-producing phenotype in factory persistent strains.

Biofilm formation by Staphylococcus aureus and Salmonella spp. under mono and dual-species conditions and their sensitivity to cetrimonium bromide, peracetic acid and sodium hypochlorite

The aim of this study was evaluated the biofilm formation by Staphylococcus aureus 4E and Salmonella spp. under mono and dual-species biofilms, onto stainless steel 316 (SS) and polypropylene B (PP), and their sensitivity to cetrimonium bromide, peracetic acid and sodium hypochlorite. The biofilms were developed by immersion of the surfaces in TSB by 10 d at 37°C. The results showed that in monospecies biofilms the type of surface not affected the cellular density (p>0.05). However, in dual-species biofilms on PP the adhesion of Salmonella spp. was favored, 7.61±0.13Log10CFU/cm2, compared with monospecies biofilms onto the same surface, 5.91±0.44Log10CFU/cm2 (p<0.05). The mono and dual-species biofilms were subjected to disinfection treatments; and the most effective disinfectant was peracetic acid (3500ppm), reducing by more than 5Log10CFU/cm2, while the least effective was cetrimonium bromide. In addition, S. aureus 4E and Salmonella spp. were more resistant to the disinfectants in mono than in dual-species biofilms (p<0.05). Therefore, the interspecies interactions between S. aureus 4E and Salmonella spp. had a negative effect on the antimicrobial resistance of each microorganism, compared with the monospecies biofilms.

Bayesian model for tracing Salmonella contamination in the pig feed chain

Salmonella infections in pigs are in most cases asymptomatic, posing a risk of salmonellosis for pork consumers. Salmonella can transmit to pigs from various sources, including contaminated feed. We present an approach for quantifying the risk to pigs from contaminations in the feed chain, based on a Bayesian model. The model relies on Salmonella surveillance data and other information from surveys, reports, registries, statistics, legislation and literature regarding feed production and pig farming. Uncertainties were probabilistically quantified by synthesizing evidence from the available information over a categorically structured flow chain of ingredients mixed for feeds served to pigs. Model based probability for infection from feeds together with Salmonella subtyping data, were used to estimate the proportion of Salmonella infections in pigs attributable to feed. The results can be further used in assessments considering the human health risk linked to animal feed via livestock. The presented methods can be used to predict the effect of changes in the feed chain, and they are generally applicable to other animals and pathogens.

Dynamics of mono- and dual-species biofilm formation and interactions between Staphylococcus aureus and Gram-negative bacteria

Microorganisms are not commonly found in the planktonic state but predominantly form dual- and multispecies biofilms in almost all natural environments. Bacteria in multispecies biofilms cooperate, compete or have neutral interactions according to the involved species. Here, the development of mono- and dual-species biofilms formed by Staphylococcus aureus and other foodborne pathogens such as Salmonella enterica subsp. enterica serovar Enteritidis, potentially pathogenic Raoultella planticola and non-pathogenic Escherichia coli over the course of 24, 48 and 72 h was studied. Biofilm formation was evaluated by the crystal violet assay (CV), enumeration of colony-forming units (CFU cm-2 ) and visualization using confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). In general, Gram-negative bacterial species and S. aureus interacted in a competitive manner. The tested Gram-negative bacteria grew better in mixed dual-species biofilms than in their mono-species biofilms as determined using the CV assay, CFU ml-2 enumeration, and CLSM and SEM visualization. In contrast, the growth of S. aureus biofilms was reduced when cultured in dual-species biofilms. CLSM images revealed grape-like clusters of S. aureus and monolayers of Gram-negative bacteria in both mono- and dual-species biofilms. S. aureus clusters in dual-species biofilms were significantly smaller than clusters in S. aureus mono-species biofilms.

Characterizing Salmonella Contamination in Two Rendering Processing Plants

A microbiological investigation on Salmonella contamination was conducted in two U.S. rendering plants to investigate the potential cross-contamination of Salmonella in the rendering processing environment. Sampling locations were predetermined at the areas where Salmonella contamination may potentially occur, including raw materials receiving, crax (rendered materials before grinding process) grinding, and finished meal loading-out areas. Salmonella was either enumerated directly on xylose lysine Tergitol 4 agar plates or enriched in Rappaport-Vassiliadis and tetrathionate broths. The presumptive Salmonella isolates were confirmed using CHROMagar plating and latex agglutination testing and then characterized using pulsed-field gel electrophoresis, serotyping, and biofilm-forming determination. Among 108 samples analyzed, 79 (73%) samples were Salmonella positive after enrichment. Selected Salmonella isolates (n = 65) were assigned to 31 unique pulsed-field gel electrophoresis patterns, with 16 Salmonella serotypes, including Typhimurium and Mbandaka, identified as predominant serotypes and 10 Salmonella strains determined as strong biofilm formers. Our results indicated that the raw materials receiving area was the primary source of Salmonella and that the surfaces surrounding crax grinding and finished meal loading-out areas harbor Salmonella in biofilms that may recontaminate the finished meals. The same Salmonella serotypes found in both raw materials receiving and the finished meal loading-out areas suggested a potential of cross-contamination between different areas in the rendering processing environment.

Exopolysaccharide microchannels direct bacterial motility and organize multicellular behavior

The myxobacteria are a family of soil bacteria that form biofilms of complex architecture, aligned multilayered swarms or fruiting body structures that are simple or branched aggregates containing myxospores. Here, we examined the structural role of matrix exopolysaccharide (EPS) in the organization of these surface-dwelling bacterial cells. Using time-lapse light and fluorescence microscopy, as well as transmission electron microscopy and focused ion beam/scanning electron microscopy (FIB/SEM) electron microscopy, we found that Myxococcus xanthus cell organization in biofilms is dependent on the formation of EPS microchannels. Cells are highly organized within the three-dimensional structure of EPS microchannels that are required for cell alignment and advancement on surfaces. Mutants lacking EPS showed a lack of cell orientation and poor colony migration. Purified, cell-free EPS retains a channel-like structure, and can complement EPS⁻ mutant motility defects. In addition, EPS provides the cooperative structure for fruiting body formation in both the simple mounds of M. xanthus and the complex, tree-like structures of Chondromyces crocatus. We furthermore investigated the possibility that EPS impacts community structure as a shared resource facilitating cooperative migration among closely related isolates of M. xanthus.

Intra- and inter-species interactions within biofilms of important foodborne bacterial pathogens

A community-based sessile life style is the normal mode of growth and survival for many bacterial species. Under such conditions, cell-to-cell interactions are inevitable and ultimately lead to the establishment of dense, complex and highly structured biofilm populations encapsulated in a self-produced extracellular matrix and capable of coordinated and collective behavior. Remarkably, in food processing environments, a variety of different bacteria may attach to surfaces, survive, grow, and form biofilms. Salmonella enterica, Listeria monocytogenes, Escherichia coli, and Staphylococcus aureus are important bacterial pathogens commonly implicated in outbreaks of foodborne diseases, while all are known to be able to create biofilms on both abiotic and biotic surfaces. Particularly challenging is the attempt to understand the complexity of inter-bacterial interactions that can be encountered in such unwanted consortia, such as competitive and cooperative ones, together with their impact on the final outcome of these communities (e.g., maturation, physiology, antimicrobial resistance, virulence, dispersal). In this review, up-to-date data on both the intra- and inter-species interactions encountered in biofilms of these pathogens are presented. A better understanding of these interactions, both at molecular and biophysical levels, could lead to novel intervention strategies for controlling pathogenic biofilm formation in food processing environments and thus improve food safety.

Unraveling microbial biofilms of importance for food microbiology

The presence of biofilms is a relevant risk factors in the food industry due to the potential contamination of food products with pathogenic and spoilage microorganisms. The majority of bacteria are able to adhere and to form biofilms, where they can persist and survive for days to weeks or even longer, depending on the microorganism and the environmental conditions. The biological cycle of biofilms includes several developmental phases such as: initial attachment, maturation, maintenance, and dispersal. Bacteria in biofilms are generally well protected against environmental stress, consequently, extremely difficult to eradicate and detect in food industry. In the present manuscript, some techniques and compounds used to control and to prevent the biofilm formation are presented and discussed. Moreover, a number of novel techniques have been recently employed to detect and evaluate bacteria attached to surfaces, including real-time polymerase chain reaction (PCR), DNA microarray and confocal laser scanning microscopy. Better knowledge on the architecture, physiology and molecular signaling in biofilms can contribute for preventing and controlling food-related spoilage and pathogenic bacteria. The present study highlights basic and applied concepts important for understanding the role of biofilms in bacterial survival, persistence and dissemination in food processing environments.

Commonly used disinfectants fail to eradicate Salmonella enterica biofilms from food contact surface materials

Salmonellosis is the second most common cause of food-borne illness worldwide. Contamination of surfaces in food processing environments may result in biofilm formation with a risk of food contamination. Effective decontamination of biofilm-contaminated surfaces is challenging. Using the CDC biofilm reactor, the activities of sodium hypochlorite, sodium hydroxide, and benzalkonium chloride were examined against an early (48-h) and relatively mature (168-h) Salmonella biofilm. All 3 agents result in reduction in viable counts of Salmonella; however, only sodium hydroxide resulted in eradication of the early biofilm. None of the agents achieved eradication of mature biofilm, even at the 90-min contact time. Studies of activity of chemical disinfection against biofilm should include assessment of activity against mature biofilm. The difficulty of eradication of established Salmonella biofilm serves to emphasize the priority of preventing access of Salmonella to postcook areas of food production facilities.

Dual-species biofilm formation by Escherichia coli O157:H7 and environmental bacteria isolated from fresh-cut processing facilities

Biofilm formation is a mechanism adapted by many microorganisms that enhances the survival in stressful environments. In food processing facilities, foodborne bacterial pathogens, which many are poor biofilm formers, could potentially take advantage of this protective mechanism by interacting with other strong biofilm producers. The objective of this study was to determine the influence of bacteria native to fresh produce processing environments on the incorporation of Escherichia coli O157:H7 in biofilms. Bacteria strains representing 13 Gram-negative species isolated from two fresh produce processing facilities in a previous study were tested for forming dual-species biofilms with E. coli O157:H7. Strong biofilm producing strains of Burkholderia caryophylli and Ralstonia insidiosa exhibited 180% and 63% increase in biofilm biomass, and significant thickening of the biofilms (B. caryophylli not tested), when co-cultured with E. coli O157:H7. E. coli O157:H7 populations increased by approximately 1 log in dual-species biofilms formed with B. caryophylli or R. insidiosa. While only a subset of environmental isolates with strong biofilm formation abilities increased the presence of E. coli O157:H7 in biofilms, all tested E. coli O157:H7 exhibited higher incorporation in dual-species biofilms with R. insidiosa. These observations support the notion that E. coli O157:H7 and specific strong biofilm producing bacteria interact synergistically in biofilm formation, and suggest a route for increased survival potential of E. coli O157:H7 in fresh produce processing environments.

Cleaning of conveyor belt materials using ultrasound in a thin layer of water

Cleaning of conveyor belts in the food industry is imperative for preventing the buildup of microorganisms that can contaminate food. New technologies for decreasing water and energy consumption of cleaning systems are desired. Ultrasound can be used for cleaning a wide range of materials. Most commonly, baths containing fairly large amounts of water are used. One possibility to reduce water consumption is to use ultrasonic cavitation in a thin water film on a flat surface, like a conveyor belt. In order to test this possibility, a model system was set up, consisting of an ultrasound transducer/probe with a 70-mm-diameter flat bottom, operating at 19.8 kHz, and contaminated conveyor belt materials in the form of coupons covered with a thin layer of water or water with detergent. Ultrasound was then applied on the water surface at different power levels (from 46 to 260 W), exposure times (10 and 20 s), and distances (2 to 20 mm). The model was used to test two different belt materials with various contamination types, such as biofilms formed by bacteria in carbohydrate- or protein-fat-based soils, dried microorganisms (bacteria, yeasts, and mold spores), and allergens. Ultrasound treatment increased the reduction of bacteria and yeast by 1 to 2 log CFU under the most favorable conditions compared with water or water-detergent controls. The effect was dependent on the type of belt material, the power applied, the exposure time, and the distance between the probe and the belt coupon. Generally, dried microorganisms were more easily removed than biofilms. The effect on mold spores was variable and appeared to be species and material dependent. Spiked allergens were also efficiently removed by using ultrasound. The results in this study pave the way for new cleaning designs for flat conveyor belts, with possibilities for savings of water, detergent, and energy consumption.

Attachment and biofilm formation by foodborne bacteria in meat processing environments: causes, implications, role of bacterial interactions and control by alternative novel methods

Attachment of potential spoilage and pathogenic bacteria to food contact surfaces and the subsequent biofilm formation represent serious challenges to the meat industry, since these may lead to cross-contamination of the products, resulting in lowered-shelf life and transmission of diseases. In meat processing environments, microorganisms are sometimes associated to surfaces in complex multispecies communities, while bacterial interactions have been shown to play a key role in cell attachment and detachment from biofilms, as well as in the resistance of biofilm community members against antimicrobial treatments. Disinfection of food contact surfaces in such environments is a challenging task, aggravated by the great antimicrobial resistance of biofilm associated bacteria. In recent years, several alternative novel methods, such as essential oils and bacteriophages, have been successfully tested as an alternative means for the disinfection of microbial-contaminated food contact surfaces. In this review, all these aspects of biofilm formation in meat processing environments are discussed from a microbial meat-quality and safety perspective.

Salmonella serovars isolated for the first time in Poland, 1995-2007

OBJECTIVES

Almost each year, a few Salmonella serovars isolated for the first time are noted in Poland. Each such serovar should be regarded as potentially dangerous. Recognition of them and monitoring their occurrence and frequency of distribution in all sources is important to control salmonellosis, and is one of the roles of the National Salmonella Centre.

MATERIALS AND METHODS

Over 2000 Salmonella strains submitted to the National Salmonella Centre for reference identification were examined. All of them were isolated in Poland between 1995-2007 from human and non-human sources. They were serotyped and characterized biochemically according to standard techniques. The antigenic factors were identified by means of good-quality Salmonella specific rabbit antisera. The White-Kauffmann-Le Minor scheme was used to name the serovars.

RESULTS

One hundred and forty-five serovars were recognized. Fifty-two of them appeared for the first time in Poland. One serovar was found to be the new one. Its validation was done at the WHO Collaborating Centre for Reference and Research on Salmonella (Institut Pasteur, Paris, France). It will be included in the next (10th) edition of the White-Kauffmann-Le Minor scheme.

CONCLUSIONS

Salmonella will continue to be the feature of humans, animals and the general environment. For practical purposes, we have to accept that Salmonella will not be eliminated and we must address our efforts to its controlling. Measuring trends in Salmonella serovars over time ought to be done to provide information about the efficacy of prevention and control measures. Results of this study are significant for these activities. They have also allowed to update the list of Salmonella serovars isolated in Poland during the last fifty years (1957-2007) which is presented as well.

Biofilm building capacity of Salmonella enterica strains from the poultry farm environment

The Biofilm (BF) building capacity of different serotypes of Salmonella enterica derived from the poultry farm environment was investigated. Starting point for the investigation was the question if farm-isolated Salmonella serotypes with high importance for poultry meat and egg production are capable of forming a BF under defined laboratory conditions. Several isolates from different stages of the production cycle were chosen and compared to laboratory grown strains of the same serotype. BF building capacity was analyzed in a 96-well format during a time period of 2 days. Pulse field gel electrophoresis was used to establish a relationship between different isolates. The BF building capacity of a monospecies BF was strongly dependent on the temperature used for incubation. Results indicated further that certain farm isolates were capable of forming BF under laboratory conditions, whereas laboratory grown strains were not. Considerable differences between different field serovars and within one serovar exist. In conclusion, the BF building capacity of poultry-derived isolates is a function of adaptation to their host environment. Thus, the control of BF as a reservoir for Salmonella in the farm environment is of crucial importance for the overall improvement of food safety. Mechanical and substance-based approaches for this control exist in several variations, but overall decontamination success is difficult to achieve and needs to be especially adapted to the farm environment.

Differential biofilm formation and chemical disinfection resistance of sessile cells of Listeria monocytogenes strains under monospecies and dual-species (with Salmonella enterica) conditions

This study aimed to investigate the possible influence of bacterial intra- and interspecies interactions on the ability of Listeria monocytogenes and Salmonella enterica to develop mixed-culture biofilms on an abiotic substratum, as well as on the subsequent resistance of sessile cells to chemical disinfection. Initially, three strains from each species were selected and left to attach and form biofilms on stainless steel (SS) coupons incubated at 15°C for 144 h, in periodically renewable tryptone soy broth (TSB), under either monoculture or mixed-culture (mono-/dual-species) conditions. Following biofilm formation, mixed-culture sessile communities were subjected to 6-min disinfection treatments with (i) benzalkonium chloride (50 ppm), (ii) sodium hypochlorite (10 ppm), (iii) peracetic acid (10 ppm), and (iv) a mixture of hydrogen peroxide (5 ppm) and peracetic acid (5 ppm). Results revealed that both species reached similar biofilm counts (ca. 10(5) CFU cm(-2)) and that, in general, interspecies interactions did not have any significant effect either on the biofilm-forming ability (as this was assessed by agar plating enumeration of the mechanically detached biofilm bacteria) or on the antimicrobial resistance of each individual species. Interestingly, pulsed-field gel electrophoresis (PFGE) analysis clearly showed that the three L. monocytogenes strains did not contribute at the same level either to the formation of mixed-culture sessile communities (mono-/dual species) or to their antimicrobial recalcitrance. Additionally, the simultaneous existence inside the biofilm structure of S. enterica cells seemed to influence the occurrence and resistance pattern of L. monocytogenes strains. In sum, this study highlights the impact of microbial interactions taking place inside a mixed-culture sessile community on both its population dynamics and disinfection resistance.

The anti-biofilm activity secreted by a marine Pseudoalteromonas strain

Bacterial biofilms occur on all submerged structures in marine environments. The authors previously reported that the marine bacterium Pseudoalteromonas sp. 3J6 secretes antibiofilm activity. Here, it was discovered that another Pseudoalteromonas sp. strain, D41, inhibited the development of strain 3J6 in mixed biofilms. Confocal laser scanning microscope observations revealed that the culture supernatant of strain D41 impaired biofilm formation of strain 3J6 and another marine bacterium. A microtiter plate assay of the antibiofilm activity was set up and validated with culture supernatants of Pseudoalteromonas sp. 3J6. This assay was used to determine the spectra of action of strains D41 and 3J6. Each culture supernatant impaired the biofilm development of 13 marine bacteria out of 18. However, differences in the spectra of action and the physical behaviours of the antibiofilm molecules suggest that the latter are not identical. They nevertheless share the originality of being devoid of antibacterial activity against planktonic bacteria.

Streptococcus pneumoniae is desiccation tolerant and infectious upon rehydration

Streptococcus pneumoniae (pneumococcus) is a frequent colonizer of the nasopharynx and one of the leading causative agents of otitis media, pneumonia, and meningitis. The current literature asserts that S. pneumoniae is transmitted person to person via respiratory droplets; however, environmental surfaces (fomites) have been linked to the spread of other respiratory pathogens. Desiccation tolerance has been to shown to be essential for long-term survival on dry surfaces. This study investigated the survival and infectivity of S. pneumoniae following desiccation under ambient conditions. We recovered viable bacteria after all desiccation periods tested, ranging from 1 h to 4 weeks. Experiments conducted under nutrient limitation indicate that desiccation is a condition separate from starvation. Desiccation of an acapsular mutant and 15 different clinical isolates shows that S. pneumoniae desiccation tolerance is independent of the polysaccharide capsule and is a species-wide phenomenon, respectively. Experiments demonstrating that nondesiccated and desiccated S. pneumoniae strains colonize the nasopharynx at comparable levels, combined with their ability to survive long-term desiccation, suggest that fomites may serve as alternate sources of pneumococcal infection.

Even with the advent of multivalent capsular polysaccharide conjugate vaccines, S. pneumoniae continues to be a major cause of morbidity and mortality worldwide. Every year, there are approximately 7 million cases of pneumococcus-based otitis media in the United States alone, while pneumococcal invasive diseases are responsible for more than 1 million deaths globally. It is believed that the human upper respiratory tract is the sole niche of S. pneumoniae and, thus, that spread occurs via close contact with an infected individual. In this study, we characterized the desiccation tolerance of S. pneumoniae and found that it can survive for many weeks postdehydration and retain infectivity. Our results suggest that desiccation tolerance is an inherent trait of this genetically variable species and that fomites may be a source of transmission.