Salmonella enterica isolates from layer farm environments are able to form biofilm on eggshell surfaces

Biofilm formation in food processing plants and novel control strategies to combat resistant biofilms: the case of Salmonella spp

Salmonella is one of the pathogens that cause many foodborne outbreaks throughout the world, representing an important global public health problem. Salmonella strains with biofilm-forming abilities have been frequently isolated from different food processing plants, especially in poultry industry. Biofilm formation of Salmonella on various surfaces can increase their viability, contributing to their persistence in food processing environments and cross-contamination of food products. In recent years, increasing concerns arise about the antimicrobial resistant and disinfectant tolerant Salmonella, while adaptation of Salmonella in biofilms to disinfectants exacerbate this problem. Facing difficulties to inhibit or remove Salmonella biofilms in food industry, eco-friendly and effective strategies based on chemical, biotechnological and physical methods are in urgent need. This review discusses biofilm formation of Salmonella in food industries, with emphasis on the current available knowledge related to antimicrobial resistance, together with an overview of promising antibiofilm strategies for controlling Salmonella in food production environments.

Efficacy of Plasma-Treated Water against Salmonella Typhimurium: Antibacterial Activity, Inhibition of Invasion, and Biofilm Disruption

Plasma-treated water (PTW) has emerged as a potential sanitizing agent. This study evaluated antibacterial activity, inhibition of invasion, and biofilm disruption effects of PTW against Salmonella Typhimurium. Minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) were determined for different PTW types. Time-kill assays were conducted to assess bactericidal effects, while polarized Caco-2 cells were used to evaluate invasion inhibition. Biofilm formation and cell viability were examined following PTW treatment using Salmonella Typhimurium isolates, while biofilm disruption and regrowth prevention were investigated using the Bioflux system. PTW exhibited antibacterial activity against all Salmonella Typhimurium isolates, with MICs of 25% for PTW1 and PTW2, and 50% for PTW3, PTW4, and PTW5. MBCs of 50% in media were observed for all PTW types. Undiluted PTW1 and PTW2 showed the highest bactericidal capacity, significantly reduced Salmonella viability, and completely inhibited bacterial invasion, while PTW3 and PTW5 also showed significant invasion reduction. Bioflux experiments confirmed the eradication of biofilms by PTW1 and PTW2, with no regrowth observed 72 h after PTW was removed. PTW demonstrated significant antibacterial activity, inhibition of invasion, biofilm disruption, and reduction of bacterial viability against Salmonella Typhimurium. This highlights PTW's potential as an effective sanitizer for reducing Salmonella contaminations.

Screening of lipid-A related genes and development of low-endotoxicity live-attenuated Salmonella gallinarum by arnT deletion that elicits immune responses and protection against fowl typhoid in chickens

In the present study, lipid-A gene mutants of Salmonella gallinarum (SG) were screened, and the arnT mutant exhibited optimal acidic and oxidative-stress and macrophage-survival. Modifying lipid-A by arnT-deletion resulted in significantly reduced endotoxicity, virulence, and mortality. Therefore, the arnT-deleted vaccine-candidate strain JOL2841 was constructed and demonstrated to be safe due to appropriate clearance by the chicken immune system. The reduced-endotoxicity of JOL2841 was evident from the downregulation of TNFα and IL-1β inflammatory cytokines, no inflammatory signs in organ gross-examination, and histopathological analysis. The IgY and IgA antibody titres, CD4, and CD8 T-cell population improvements, and IL-4, IL-2, and INFγ expression decipher the profound Th2 and Th1 immunogenicity. Consequently, JOL2841 exhibited prominent protection against wild-type SG challenge, as revealed by organ pathogen-load determination, organ gross-examination, and histopathological examination. Overall, the study represented the first report of arnT deficient SG resulted in negligible endotoxicity, low-virulence, safety and coordinated elicitation of humoral and cell-mediated immune response in chickens.

Prevalence of biofilm forming Salmonella in different seafood contact surfaces of fishing boats, fish landing centres, fish markets and seafood processing plants

The prevalence of biofilm forming Salmonella on different seafood contact surfaces was investigated. Out of 384 swab samples, 16.14 % and 1 % were confirmed biochemically and molecularly as Salmonella respectively. One out of four isolates was from the boat deck, and three were from the seafood processing plant. Salmonella was more prevalent in January, June, and September months. Different assays investigated the biofilm forming ability of isolates. Two out of four isolates have shown strong biofilms, and the others were moderate biofilm formers by microtitre plate assay. In the CRA assay, three isolates showed 'rdar' morphotype, and one showed 'bdar' morphotype. All isolates were positive for gcpA gene (~1700 bp), a critical gene found in Salmonella biofilms. The microbial load of Salmonella biofilms on different contact surfaces were determined, stainless steel and HDPE were found prone to biofilms. With this, a suitable mechanism shall be formulated to control the biofilms of Salmonella.

Effect of Essential Oils on the Inhibition of Biofilm and Quorum Sensing in Salmonella enteritidis 13076 and Salmonella typhimurium 14028

The emergence of multidrug-resistant microorganisms represents a global challenge that has led to a search for new antimicrobial compounds. Essential oils (EOs) from medicinal aromatic plants are a potential alternative for conventional antibiotics. In this study, the antimicrobial and anti-biofilm potential of 15 EOs was evaluated on planktonic and biofilm-associated cells of Salmonella enterica serovar Enteritidis ATCC 13076 (S. enteritidis) and Salmonella enterica serovar Typhimurium ATCC 14028 (S. typhimurium). In total, 4 out of 15 EOs showed antimicrobial activity and 6 EOs showed anti-biofilm activity against both strains. The EO from the Lippia origanoides chemotype thymol-carvacrol II (LTC II) presented the lowest minimum inhibitory concentration (MIC₅₀ = 0.37 mg mL^-1) and minimum bactericidal concentration (MBC = 0.75 mg mL^-1) values. This EO also presented the highest percentage of biofilm inhibition (>65%) on both microorganisms, which could be confirmed by scanning electron microscopy (SEM) images. Transcriptional analysis showed significant changes in the expression of the genes related to quorum sensing and the formation of the biofilm. EOs could inhibit the expression of genes involved in the quorum sensing mechanism (luxR, luxS, qseB, sdiA) and biofilm formation (csgA, csgB, csgD, flhD, fliZ, and motB), indicating their potential use as anti-biofilm antimicrobial agents. However, further studies are needed to elucidate the action mechanisms of essential oils on the bacterial cells under study.

Biofilm Formation by Salmonella enterica Strains

Biofilm formation by five different Salmonella enterica strains was assessed qualitatively and quantitatively under different incubation conditions. The strains exhibited different adherence abilities to test tubes. The isolates revealed Red Dry and Rough (RDAR) and Brown Dry and Rough (BDAR) morphotypes when cultured on Congo Red Agar (CRA). The pellicles formed by the tested strains ranged from strong to fragile when incubated in LB without NaCl at 27 °C. Smooth and White (SAW) morphotype on CRA and very weak pellicles were observed when the bacterial strains were incubated at 37 °C. The effect of temperature and media on biofilm formation by the tested strains was significant. Among the five Salmonella isolates, S. enteritidis TM 6 and S. enteritidis TM 68 formed strong biofilms when incubated in LB without NaCl at 27 °C for 24 h and consequently selected to be analysed under scanning electron microscope (SEM). Scanning electron micrographs revealed that S. enteritidis TM 6 formed more complex colonies when compared to those formed by S. enteritidis TM 68. As far as we know, this is the first study that provides quantitative and qualitative data for 5 Salmonella enterica isolates in different media mimicking four different nutritional conditions at two different temperatures after 24 and 48 h. The strains included two serovars S. bredeney and S. anatum, which are rarely accounted for. Additionally, the studies that described S. enteritidis biofilms under SEM are extremely limited, which makes it among the first comprehensive studies that screened for S. enteritidis biofilms.

Salmonella Biofilm Formation, Chronic Infection, and Immunity Within the Intestine and Hepatobiliary Tract

Within the species of Salmonella enterica, there is significant diversity represented among the numerous subspecies and serovars. Collectively, these account for microbes with variable host ranges, from common plant and animal colonizers to extremely pathogenic and human-specific serovars. Despite these differences, many Salmonella species find commonality in the ability to form biofilms and the ability to cause acute, latent, or chronic disease. The exact outcome of infection depends on many factors such as the growth state of Salmonella, the environmental conditions encountered at the time of infection, as well as the infected host and immune response elicited. Here, we review the numerous biofilm lifestyles of Salmonella (on biotic and abiotic surfaces) and how the production of extracellular polymeric substances not only enhances long-term persistence outside the host but also is an essential function in chronic human infections. Furthermore, careful consideration is made for the events during initial infection that allow for gut transcytosis which, in conjunction with host immune functions, often determine the progression of disease. Both typhoidal and non-typhoidal salmonellae can cause chronic and/or secondary infections, thus the adaptive immune responses to both types of bacteria are discussed with particular attention to the differences between Salmonella Typhi, Salmonella Typhimurium, and invasive non-typhoidal Salmonella that can result in differential immune responses. Finally, while strides have been made in our understanding of immunity to Salmonella in the lymphoid organs, fewer definitive studies exist for intestinal and hepatobiliary immunity. By examining our current knowledge and what remains to be determined, we provide insight into new directions in the field of Salmonella immunity, particularly as it relates to chronic infection.

Challenges in Vaccinating Layer Hens against Salmonella Typhimurium

Salmonella Typhimurium is among the most common causes of bacterial foodborne gastrointestinal disease in humans. Food items containing raw or undercooked eggs are frequently identified during traceback investigation as the source of the bacteria. Layer hens can become persistently infected with Salmonella Typhimurium and intermittently shed the bacteria over the course of their productive lifetime. Eggs laid in a contaminated environment are at risk of potential exposure to bacteria. Thus, mitigating the bacterial load on farms aids in the protection of the food supply chain. Layer hen producers use a multifaceted approach for reducing Salmonella on farms, including the all-in-all-out management strategy, strict biosecurity, sanitization, and vaccination. The use of live attenuated Salmonella vaccines is favored because they elicit a broader host immune response than killed or inactivated vaccines that have been demonstrated to provide cross-protection against multiple serovars. Depending on the vaccine, two to three doses of Salmonella Typhimurium vaccines are generally administered to layer hens within the first few weeks. The productive life of a layer hen, however, can exceed 70 weeks and it is unclear whether current vaccination regimens are effective for that extended period. The objective of this review is to highlight layer hen specific challenges that may affect vaccine efficacy.

Flagellar Motility Is Critical for Salmonella enterica Serovar Typhimurium Biofilm Development

The food-borne pathogen Salmonella enterica serovar Typhimurium (S. Typhimurium) causes self-limiting gastroenteritis in humans and is not easily eradicated because it often attaches to suitable surfaces to form biofilms that have high resistance to disinfectants and antimicrobials. To develop an alternative strategy for the treatment of biofilms, it is necessary to further explore the effects of flagellar motility on the development process of Salmonella biofilms. Here, we constructed flagella mutants (ΔflgE and ΔfliC) to systematically study this process. By comparing them with wild-type strains, we found that these mutants lacking flagellar motility form fewer biofilms in the early stage, and the formed mature biofilms contain more cells and extracellular polymeric substances (EPS). In addition, fewer mutant cells adhered to glass plates compared with wild-type cells even after 6 h of incubation, suggesting that flagellar motility plays a significant role in preliminary cell-surface interactions. More importantly, the motility of wild-type strain was greatly decreased when they were treated with carbonyl cyanide m-chlorophenylhydrazone, which inhibited flagellar motility and reduced biofilm formation, as in the case of the ΔflgE mutant. Overall, these findings suggest that flagellar motility plays an important role in Salmonella biofilm initiation and maturation, which can help us to counteract the mechanisms involved in biofilm formation and to develop more rational control strategies.

Viability of Salmonella Typhimurium biofilms on major food-contact surfaces and eggshell treated during 35 days with and without water storage at room temperature

Salmonella is one of the main foodborne pathogens that affect humans and farm animals. The Salmonella genus comprises a group of food-transmitted pathogens that cause highly prevalent foodborne diseases throughout the world. The aim of this study was to appraise the viability of Salmonella Typhimurium biofilm under water treatment at room temperature on different surfaces, specifically stainless steel (SS), plastic (PLA), rubber (RB), and eggshell (ES). After 35 D, the reduction of biofilm on SS, PLA, RB, and ES was 3.35, 3.57, 3.22, and 2.55 log CFU/coupon without water treatment and 4.31, 4.49, 3.50, and 1.49 log CFU/coupon with water treatment, respectively. The d_R value (time required to reduce bacterial biofilm by 99% via Weibull modeling) of S. Typhimurium without and with water treatment was the lowest on PLA (176.86 and 112.17 h, respectively) and the highest on ES (485.37 and 2,436.52 h, respectively). The viability of the S. Typhimurium on ES and the 3 food-contact surfaces was monitored for 5 wk (35 D). The results of this study provide valuable information for the control of S. Typhimurium on different surfaces in the food industry, which could reduce the risk to consumers.

In vivo and in vitro evaluation of tissue colonization and survival capacity of Salmonella Oranienburg in laying hens

Salmonella enterica serovar Oranienburg (SO) was linked to a human salmonellosis outbreak in the Midwest in 2015 and 2016 from consumption of eggs. However, unlike Salmonella enterica serovar Enteritidis (SE), little is known regarding the potential of SO to colonize in laying hens and contaminate eggs. We used in vivo and in vitro models to evaluate tissue colonization and survival capacity of SO. Twenty eight-week-old laying hens were each challenged with an oral dose of approximately 107 (n = 92) or 109 (n = 96) colony-forming units (CFU) in 1 mL saline and evaluated after 1, 2, and 4 wk. Standard microbiological methods with pre-enrichment and enrichment in selective media were used for detection of SO in tissues, egg shell wash, internal egg contents, and excreta. Peak colonization of spleen (86.9%), ovaries (31.6%), upper oviduct (15.8%), and lower oviduct (34.3%) was detected between 1 and 2 wk post-infection (pi), while at 4 wk SO was only recovered from spleens (25%). Salmonella enterica serovar Oranienburg was not recovered from internal egg contents. However, the presence of SO on egg shells was seen when there were traces of excreta. Shedding in excreta was found in 92 and 100% birds gavaged with 107 and 109 CFU at 2 wk pi, respectively. The invasion and proliferation of SO in ovarian granulosa cells (GC) was compared to that of SE, and while the invasion of SO into GC was comparable to SE, proliferation of SO was significantly lower (P < 0.05). The infective potential of SO was also assessed by enumerating survival in egg white over 4 wk under refrigerated conditions, resulting in 65% survival at 4 wk. Overall, our data suggested that SO infection in layers did not result in egg contamination via vertical transmission, and colonization of egg-forming tissues was limited to 2 wk pi. Survival within GC and egg white demonstrates the ability of SO to withstand antibacterial factors and the potential of SO to penetrate the yolk.

Salmonella and Campylobacter biofilm formation: a comparative assessment from farm to fork

It takes several steps to bring food from the farm to the fork (dining table), and contamination with food-borne pathogens can occur at any point in the process. Campylobacter spp. and Salmonella spp. are the main microorganisms responsible for foodborne disease in the EU. These two pathogens are able to persist throughout the food supply chain thanks to their ability to form biofilms. Owing to the high prevalence of Salmonella and especially of Campylobacter in the food supply chain and the huge efforts of food authorities to reduce these levels, it is of great importance to fully understand their mechanisms of persistence. Diverse studies have evaluated the biofilm-forming capacity of foodborne pathogens isolated at different steps of food production. Nonetheless, the principal obstacle of these studies is to reproduce the real conditions that microorganisms encounter in the food supply chain. While there are a wide number of Salmonella biofilm studies, information on Campylobacter biofilms is still limited. A comparison between the two microorganisms could help to develop new research in the field of Campylobacter biofilms. Therefore, this review evaluates relevant work in the field of Salmonella and Campylobacter biofilms and the applicability of the data obtained from these studies to real working conditions. © 2018 Society of Chemical Industry.

A Long-Term Efficacy Trial of a Live, Attenuated Salmonella Typhimurium Vaccine in Layer Hens

Salmonella remains one of the most common causes of bacterial foodborne gastrointestinal disease in humans. Raw eggs or food items containing undercooked eggs are frequently identified as the source of Salmonella. Salmonella Typhimurium contamination of table eggs most commonly occurs when they are laid in a contaminated environment. Several control strategies, including vaccination, are widely used to mitigate the total Salmonella load. It is unclear, however, whether live attenuated Salmonella vaccines are efficacious over the life span of a layer hen. Live attenuated Salmonella vaccines have been favored due to their ability to illicit a strong humoral immune response. The lifespan of a layer hen ranges between 60 and 80 weeks and the long term efficacy of attenuated vaccine strains has not been investigated. In this study, commercial brown layer chicks were vaccinated at day old, 6 weeks of age, and again at 10 weeks of age with the Bioproperties Vaxsafe^TM STM1 aroA mutant vaccine. Birds were challenged at 18 weeks of age with Salmonella Typhimurium DT9 (MLVA 03 15 08 11 550). Feces and eggs were monitored for S. Typhimurium for 40 weeks post-infection. Birds produced a strong immune response following the final dose which was administered intramuscularly. The serum antibody response to S. Typhimurium DT9 infection did not differ between challenged groups. Fecal shedding and egg contamination was highly variable and did not differ significantly between vaccinated and unvaccinated birds that had been challenged with S. Typhimurium DT9. Total bacterial load in feces was quantified using qPCR. No significant difference was detected between unvaccinated and vaccinated birds after challenge.

Absence of Curli in Soil-Persistent Escherichia coli Is Mediated by a C-di-GMP Signaling Defect and Suggests Evidence of Biofilm-Independent Niche Specialization

Escherichia coli is commonly viewed as a gastrointestinal commensal or pathogen although an increasing body of evidence suggests that it can persist in non-host environments as well. Curli are a major component of biofilm in many enteric bacteria including E. coli and are important for adherence to different biotic and abiotic surfaces. In this study we investigated curli production in a unique collection of soil-persistent E. coli isolates and examined the role of curli formation in environmental persistence. Although most soil-persistent E. coli were curli-positive, 10% of isolates were curli-negative (17 out of 170). Curli-producing E. coli (COB583, COB585, and BW25113) displayed significantly more attachment to quartz sand than the curli-negative strains. Long-term soil survival experiments indicated that curli production was not required for long-term survival in live soil (over 110 days), as a curli-negative mutant BW25113ΔcsgB had similar survival compared to wild type BW25113. Mutations in two genes associated with c-di-GMP metabolism, dgcE and pdeR, correlated with loss of curli in eight soil-persistent strains, although this did not significantly impair their survival in soil compared to curli-positive strains. Overall, the data indicate that curli-deficient and biofilm-defective strains, that also have a defect in attachment to quartz sand, are able to reside in soil for long periods of time thus pointing to the possibility that niches may exist in the soil that can support long-term survival independently of biofilm formation.

Characterization of Invasive Salmonella Serogroup C1 Infections in Mali

Nontyphoidal Salmonella (NTS) are the leading cause of foodborne infections worldwide and a major cause of bloodstream infections in infants and HIV-infected adults in sub-Saharan Africa (SSA). Salmonella Typhimurium (serogroup B) and Salmonella Enteritidis (serogroup D) are the most common serovars in this region. However, data describing rarer invasive NTS serovars, particularly those belonging to serogroups C1 and C2, circulating in SSA are lacking. We previously conducted systematic blood culture surveillance on pediatric patients in Bamako, Mali, from 2002 to 2014, and the results showed that serovars Typhimurium and Enteritidis accounted for 32% and 36% of isolates, respectively. Here, we present data on 27 Salmonella serogroup C1 strains that were isolated during this previous study. The strains were typed by serum agglutination and multilocus sequence typing (MLST). Sixteen strains were Salmonella Paratyphi C, four were Salmonella Colindale, and two were Salmonella Virchow. Interestingly, five strains were identified as the very rare Salmonella Brazzaville using a combination of serum agglutination and flagellin gene typing. Phenotypic characterization showed that Salmonella Brazzaville produced biofilm and exhibited catalase activity, which were not statistically different from the gastroenteritis-associated Salmonella Typhimurium sequence type (ST) 19. All tested Salmonella Paratyphi C strains were poor biofilm producers and showed significantly less catalase activity than Salmonella Typhimurium ST19. Overall, our study provides insight into the Salmonella serogroup C1 serovars that cause invasive disease in infants in Mali. In addition, we show that MLST and flagellin gene sequencing, in association with traditional serum agglutination, are invaluable tools to help identify rare Salmonella serovars.