Salmonella biofilms: An overview on occurrence, structure, regulation and eradication

Raspberry Ketone-Mediated Inhibition of Biofilm Formation in Salmonella enterica Typhimurium-An Assessment of the Mechanisms of Action

Salmonella enterica is an important foodborne pathogen that causes gastroenteritis and systemic infection in humans and livestock. Salmonella biofilms consist of two major components-amyloid curli and cellulose-which contribute to the prolonged persistence of Salmonella inside the host. Effective agents for inhibiting the formation of biofilms are urgently needed. We investigated the antibiofilm effect of Raspberry Ketone (RK) and its mechanism of action against Salmonella Typhimurium 14028 using the Congo red agar method, Calcofluor staining, crystal violet method, pellicle assay, and the TMT-labeled quantitative proteomic approach. RK suppressed the formation of different types of Salmonella biofilms, including pellicle formation, even at low concentrations (200 µg/mL). Furthermore, at higher concentrations (2 mg/mL), RK exhibited bacteriostatic effects. RK repressed cellulose deposition in Salmonella biofilm through an unknown mechanism. Swimming and swarming motility analyses demonstrated reduced motility in RK-treated S. typhimurium. Proteomics analysis revealed that pathways involved in amyloid curli production, bacterial invasion, flagellar motility, arginine biosynthesis, and carbohydrate metabolism, were targeted by RK to facilitate biofilm inhibition. Consistent with the proteomics data, the expressions of csgB and csgD genes were strongly down-regulated in RK-treated S. typhimurium. These findings clearly demonstrated the Salmonella biofilm inhibition capability of RK, justifying its further study for its efficacy assessment in clinical and industrial settings.

An Explorative Review on Advanced Approaches to Overcome Bacterial Resistance by Curbing Bacterial Biofilm Formation

The continuous emergence of multidrug-resistant pathogens evoked the development of innovative approaches targeting virulence factors unique to their pathogenic cascade. These approaches aimed to explore anti-virulence or anti-infective therapies. There are evident concerns regarding the bacterial ability to create a superstructure, the biofilm. Biofilm formation is a crucial virulence factor causing difficult-to-treat, localized, and systemic infections. The microenvironments of bacterial biofilm reduce the efficacy of antibiotics and evade the host's immunity. Producing a biofilm is not limited to a specific group of bacteria; however, Pseudomonas aeruginosa, Acinetobacter baumannii, and Staphylococcus aureus biofilms are exemplary models. This review discusses biofilm formation as a virulence factor and the link to antimicrobial resistance. In addition, it explores insights into innovative multi-targeted approaches and their physiological mechanisms to combat biofilms, including natural compounds, phages, antimicrobial photodynamic therapy (aPDT), CRISPR-Cas gene editing, and nano-mediated techniques.

Molecular Detection of Virulence Factors in Salmonella serovars Isolated from Poultry and Human Samples

Salmonellosis is a common infectious disease in humans caused by Salmonella spp., which in recent years has shown an increase in its incidence, with products of avian origin being a common source of transmission. To present a successful infective cycle, there are molecular mechanisms such as virulence factors that provide characteristics that facilitate survival, colonization, and damage to the host. According to this, the study aims to characterize the virulence factors of Salmonella spp. strains isolated from broilers (n = 39) and humans (n = 10). The presence of 24 virulence genes was evaluated using end-point PCR. All the strains of Salmonella spp. isolated from broiler chickens revealed presence of 7/24 (29, 16%) virulence genes (lpfA, csgA, sitC, sipB, sopB, sopE, and sivH). Regarding the strains isolated from cases of gastroenteritis in humans, all strains contained (14/24, 58, 33%) virulence genes (lpfA, csgA, pagC, msgA, spiA, sitC, iroN, sipB, orgA, hilA, sopB, sifA, avrA, and sivH). In summary, the presence of virulence genes in different strains of Salmonella isolated from broilers and humans could be described as bacteria with potential pathogenicity due to the type and number of virulence genes detected. These findings are beneficial for the pathogenic monitoring of Salmonella in Colombia.

Antibiofilm Action of Plant Terpenes in Salmonella Strains: Potential Inhibitors of the Synthesis of Extracellular Polymeric Substances

Salmonella can form biofilms that contribute to its resistance in food processing environments. Biofilms are a dense population of cells that adhere to the surface, creating a matrix composed of extracellular polymeric substances (EPS) consisting mainly of polysaccharides, proteins, and eDNA. Remarkably, the secreted substances, including cellulose, curli, and colanic acid, act as protective barriers for Salmonella and contribute to its resistance and persistence when exposed to disinfectants. Conventional treatments are mostly ineffective in controlling this problem; therefore, exploring anti-biofilm molecules that minimize and eradicate Salmonella biofilms is required. The evidence indicated that terpenes effectively reduce biofilms and affect their three-dimensional structure due to the decrease in the content of EPS. Specifically, in the case of Salmonella, cellulose is an essential component in their biofilms, and its control could be through the inhibition of glycosyltransferase, the enzyme that synthesizes this polymer. The inhibition of polymeric substances secreted by Salmonella during biofilm development could be considered a target to reduce its resistance to disinfectants, and terpenes can be regarded as inhibitors of this process. However, more studies are needed to evaluate the effectiveness of these compounds against Salmonella enzymes that produce extracellular polymeric substances.

Nutrient Availability and Biofilm Polysaccharide Shape the Bacillaene-Dependent Antagonism of Bacillus subtilis against Salmonella Typhimurium

Salmonella enterica is one of the most common foodborne pathogens and, due to the spread of antibiotic resistance, new antimicrobial strategies are urgently needed to control it. In this study, we explored the probiotic potential of Bacillus subtilis PS-216 and elucidated the mechanisms that underlie the interactions between this soil isolate and the model pathogenic strain S. Typhimurium SL1344. The results reveal that B. subtilis PS-216 inhibits the growth and biofilm formation of S. Typhimurium through the production of the pks cluster-dependent polyketide bacillaene. The presence of S. Typhimurium enhanced the activity of the PpksC promoter that controls bacillaene production, suggesting that B. subtilis senses and responds to Salmonella. The level of Salmonella inhibition, overall PpksC activity, and PpksC induction by Salmonella were all higher in nutrient-rich conditions than in nutrient-depleted conditions. Although eliminating the extracellular polysaccharide production of B. subtilis via deletion of the epsA-O operon had no significant effect on inhibitory activity against Salmonella in nutrient-rich conditions, this deletion mutant showed an enhanced antagonism against Salmonella in nutrient-depleted conditions, revealing an intricate relationship between exopolysaccharide production, nutrient availability, and bacillaene synthesis. Overall, this work provides evidence on the regulatory role of nutrient availability, sensing of the competitor, and EpsA-O polysaccharide in the social outcome of bacillaene-dependent competition between B. subtilis and S. Typhimurium. IMPORTANCE Probiotic bacteria represent an alternative for controlling foodborne disease caused by Salmonella enterica, which constitutes a serious concern during food production due to its antibiotic resistance and resilience to environmental stress. Bacillus subtilis is gaining popularity as a probiotic, but its behavior in biofilms with pathogens such as Salmonella remains to be elucidated. Here, we show that the antagonism of B. subtilis is mediated by the polyketide bacillaene and that the production of bacillaene is a highly dynamic trait which depends on environmental factors such as nutrient availability and the presence of competitors. Moreover, the production of extracellular polysaccharides by B. subtilis further alters the influence of these factors. Hence, this work highlights the inhibitory effect of B. subtilis, which is condition-dependent, and the importance of evaluating probiotic strains under conditions relevant to the intended use.

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.

Salmonella Derby from pig production chain over a 10-year period: antimicrobial resistance, biofilm formation, and genetic relatedness

The aim of this study was to evaluate 140 Salmonella Derby isolates collected over a 10-year period from porcine origins (environment, pig carcass, lymph nodes, intestinal content, and pork) for their phenotypic and genotypic antimicrobial resistance, their ability to produce biofilm, and their genetic relatedness. The minimum inhibitory concentration (MIC) was determined using microdilution broth method and antimicrobial resistance genes were investigated by PCR. The quantification of biofilm formation was performed in sterile polystyrene microtiter plates. Genetic relatedness was determined by Xba-I macrorestriction analysis. The highest frequencies of non-wildtype (nWT) populations were observed against tetracycline (75.7%), streptomycin (70%), and colistin (11.4%), whereas wildtype populations were observed against ciprofloxacin, ceftazidime, and gentamicin. The resistance genes found were blaTEM (ampicillin), aadA variant (streptomycin/spectinomycin), tetA (tetracycline), and floR (florfenicol). On 96-well polystyrene microtiter plate, 68.6% of the isolates proved to be biofilm producers. Among 36 S. Derby isolates selected to PFGE analysis, 22 were clustered with 83.6% of similarity. Additionally, 27 isolates were clustered in 11 pulsotypes, which presented more than one strain with 100% of similarity. Most of S. Derby isolates were able to form biofilm and were classified as nWT or resistant to tetracycline, streptomycin, and colistin. PFGE allowed the identification of closely related S. Derby isolates that circulated in pig slaughterhouses and pork derived products along a decade.

The role and mechanisms of the two-component system EnvZ/OmpR on the intracellular survival of Aeromonas hydrophila

Aeromonas hydrophila infections are common in aquaculture. Our previous studies found that the A. hydrophila B11 strain can survive in fish macrophages for at least 24 h and the two-component system EnvZ/OmpR may be involved in intracellular survival. To reveal the role and mechanism of the two-component system EnvZ/OmpR in intracellular survival of A. hydrophila, the genes of envZ/ompR were silenced by shRNAi. The results showed that the survival rates of the envZ-RNAi and ompR-RNAi strains were only 2.05% and 3.75%, respectively, which were decreased by 91% and 83.6% compared with that of the wild-type strain. The escape ability of envZ-RNAi and ompR-RNAi was also decreased by 51.4% and 19.7%, respectively. The comparative transcriptome analysis revealed that the functional genes directly related to bacterial intracellular survival mainly included the genes related to anti-stress capacity, and the genes related to Zn²⁺ and Mg²⁺ transport. Further research confirmed that two-component system EnvZ/OmpR can regulate the expression of the important molecular chaperones, such as groEL, htpG, dnaK, clpB and grpE. The expression of these molecular chaperones in wild-type strain was up-regulated with the increase in H₂ O₂ concentrations, while the expression of these molecular chaperones in silent strains did not change significantly. Cells that phagocytosed wild-type strain had higher ROS content than cells that phagocytosed silent strains. Two-component system EnvZ/OmpR could also regulate zinc transporter (znuA, znuB, znuC) and zinc efflux protein (zntA) to maintain zinc homeostasis in cells, thus affecting the ability of bacteria to survive in phagocytes. Moreover, two-component system EnvZ/OmpR could affect the growth and intracellular survival of A. hydrophila by regulating the expression of MgtA, MgtC and MgtE and participating in bacterial Mg²⁺ homeostasis in fish macrophages.

Association between antimicrobial resistance and biofilm forming ability of Salmonella enterica serotypes from commercial broiler farms in Brazil

1. This study determined the antimicrobial resistance profile and the biofilm-forming ability of Salmonella enterica strains isolated from commercial broiler houses over a three-year period in southern Brazil.

2. Of the 720 drag swabs analysed, 37 (5.1%) tested positive for non-typhoidal Salmonella spp. and S. Heidelberg was the most frequent serovar.

3. Among the antimicrobial resistant strains (83.8%; 31/37), resistance was most common to tetracycline, ampicillin and nalidixic acid. Multidrug resistance was found in 65% (24/37) of the isolates, with a large proportion of multidrug resistant S. Heidelberg strains (81%; 13/16).

4. In total, 65% (24/37) of the isolates showed the ability to produce biofilm and multiple antimicrobial resistance was negatively correlated with biofilm formation.

5. Strains susceptible to all tested antimicrobials tended to form stronger biofilms than multidrug resistant ones. This suggested that Salmonella spp. with less antimicrobial resistance depend more on the protection provided by biofilm to survive in the farm environment.

Characterizing 5-oxoproline sensing pathways of Salmonella enterica serovar typhimurium

5-Oxoproline (5OP) is a poorly researched ubiquitous natural amino acid found in all life forms. We have previously shown that Salmonella enterica serovar Typhimurium (Salmonella) responds to 5OP exposure by reducing cyclic-di-GMP levels, and resultant cellulose dependent cellular aggregation in a YfeA and BcsA dependent manner. To understand if 5OP was specifically sensed by Salmonella we compared the interaction of Salmonella with 5OP to that of the chemically similar and biologically relevant molecule, l-proline. We show that l-proline but not 5OP can be utilized by Salmonella as a nutrient source. We also show that 5OP but not l-proline regulates cellulose dependent cellular aggregation. These results imply that 5OP is utilized by Salmonella as a specific signal. However, l-proline is a 5OP aggregation inhibitor implying that while it cannot activate the aggregation pathway by itself, it can inhibit 5OP dependent activation. We then show that in a l-proline transporter knockout mutant l-proline competition remain unaffected, implying sensing of 5OP is extracellular. Last, we identify a transcriptional effect of 5OP exposure, upregulation of the mgtCBR operon, known to be activated during host invasion. While mgtCBR is known to be regulated by both low pH and l-proline starvation, we show that 5OP regulation of mgtCBR is indirect through changes in pH and is not dependent on the 5OP chemical structure similarity to l-proline. We also show this response to be PhoPQ dependent. We further show that the aggregation response is independent of pH modulation, PhoPQ and MgtC and that the mgtCBR transcriptional response is independent of YfeA and BcsA. Thus, the two responses are mediated through two independent signaling pathways. To conclude, we show Salmonella responds to 5OP specifically to regulate aggregation and not specifically to regulate gene expression. When and where in the Salmonella life cycle does 5OP sensing takes place remains an open question. Furthermore, because 5OP inhibits c-di-GMP through the activation of an external sensor, and does not require an internalization step like many studied biofilm inhibitors, 5OP or derivatives might be developed into useful biofilm inhibitors.

Frequency of Salmonella serotypes among children in Iran: antimicrobial susceptibility, biofilm formation, and virulence genes

BACKGROUND/SIGNIFICANCE

Salmonella gastroenteritis causes significant morbidity among pediatric patients, mainly in developing world, such as the Middle East and North Africa (MENA) region. Concurrently, data from MENA countries like Iran, regarding prevalence of Salmonella serotypes, antimicrobial susceptibility, and biofilm production is scarce.

MATERIAL & METHODS

Slide agglutination was used to determine the serogroup of 140 Salmonella isolates recovered from 4477 stool specimens collected from children with gastroenteritis, and isolates were serotyped by PCR assay. The antimicrobial susceptibility of isolates to five first line drugs was assessed by disk diffusion assay using CLSI guidelines. Semi-quantitative evaluation of biofilm production was done by microtiter plate assay followed by PCR detection of biofilm-associated virulence genes csgD, pefA, and bcsA for each isolate.

RESULTS

Nearly 94% of Salmonella isolates were recovered from ≤ 5-year-old patients, and 99% of isolates were non-typhoidal. While we found extensive diversity among Salmonella isolates, serogroup D (46%) predominated, and Salmonella Enteritidis (41%) was the most common serotype that showed the highest antimicrobial susceptibility rate (> 96%). For the first time in Iran, S. Newport serotype from human specimens was isolated. Most isolates were sensitive to all test antimicrobials, but 35% of isolates were not-typed (NT) that showed the highest resistance with 48% being resistant to ≥ 1 test antimicrobial. Majority of isolates made weak (or no) biofilm, and we found a weak association between antimicrobial susceptibility, biofilm production, or virulence genes csgD, pefA, and bcsA.

CONCLUSIONS

The most effective measure that may control pediatric salmonellosis outbreaks is raising awareness of parents of preschoolers about food safety. Isolation of highly diverse Salmonella serotypes, including many commonly isolated from animals, indicates widespread contamination of the food chain. Majority of serotypes were sensitive to first-line antimicrobials, thus presently, pediatric Salmonella infections in this region may be controlled by conventional antimicrobials. However, despite the current trend, an imminent emergence of resistant Salmonella strains is foreseen, since various serotypes resistant to > 1 antimicrobial agent are typically associated with animals. Our results warrant further investigation that includes correlation analysis of clinical data regarding treatment outcomes, and serotype attributes like virulence genes.

Activity of Essential Oils Against Multidrug-Resistant Salmonella enteritidis

We have investigated the antibacterial, anti-biofilm, and anti-quorum sensing potencies of six Essential Oils (EOs) obtained from cinnamon (Cinnamomum verum), thyme (Thymus vulgaris), clove (Eugenia caryophyllata), curcuma (Curcuma longa L.), rosemary (Rosmarinus officinalis L.), and sage (Salvia officinalis). The study was conducted on 20 multidrug-resistant (MDR) S. enteritidis clinical strains. Minimum inhibitory concentrations and minimum bactericide concentrations were displayed by microdilution. The effect on biofilm formation was tested on polystyrene plates. The anti-quorum sensing effect was determined by measuring the inhibition of violacein production by Chromobacterium violaceum CV026. The influence of EOs on the adhesion of Salmonella strains to HT-29 cells was studied. The potency of S. enteritidis to infect and kill Caenorhabditis elegans was evaluated. The cinnamon, thyme, and clove EOs showed remarkable antibacterial properties. Biofilm formation was significantly reduced by the six EOs: 99.10% for cinnamon, 97.64% for clove, 95.90% for thyme, 79.84% for rosemary, 28.98% for curcuma, and 15.55% for sage. The MIC/2 of clove EO exhibited the highest percentage of inhibition of violacein production (99.03%), followed by thyme (91.68%) and cinnamon (84.13%) EOs. Thyme extracts exhibited an important anti-adhesive potency. Clove EO behaves as an effective regulator of Salmonella virulence in nematodes.

Salmonella enterica Serovar Typhimurium and Enteritidis Isolated from Raw Shrimp in Bangladesh: An Investigation Based on Molecular Characteristics, Survival, Virulence, Antibiotic Resistance, and Biofilm Formation Attributes

Shrimp is the white gold of Bangladesh, with the second-highest income source from exporting to foreign countries. Contamination with Salmonella spp. is now one of the significant issues for Bangladesh to export. Proper characterization of the salmonella pathogen is thus necessary to avoid undesirable losses due to the rejection of exported shrimp. In Bangladesh, the present condition of raw shrimp contamination with pathogenic Salmonella serovars and their survival/virulence properties was not adequately characterized. In this study, we collected 43 raw shrimps as samples from different farms in Jashore, Khulna, and Sathkhira regions. We then maintained standard cultural and biochemical protocols for isolating Salmonella strains, followed by the molecular identification of particular Salmonella serovars. The standard method for checking its credibility to form biofilm in 0–10% NaCl, tolerate acid/bile stress likewise in the gastrointestinal tract, and resist antimicrobial pressure was performed individually with the particular pathogenic strains. Our results successfully identified eleven Salmonella strains with three typhimurium serovars and three enteritidis serovars, which have biofilm-forming capability up to 4–8% NaCl, acid/bile habituation alike stomach/small intestine of humans, and resistance against necessary antibiotics generally used in treating human and poultry infection signifying the impending danger in the shrimp industry. While previous studies of Bangladesh successfully isolated Salmonella only presumptively, our research focused mainly on molecular characterization of the human Salmonella pathogen along with important survival and virulent attributes, such as biofilm formation, acid/bile tolerance, and antibiotic resistance of selected S. typhimurium and S. enteritidis strains. Further study with more sampling will be necessary to confer the transmission route of the pathogen from the natural reservoir to the shrimp industry.

Structural variations on Salmonella biofilm by exposition to river water

Biofilm formation, as adapting strategies, is the result of stressful conditions that Salmonella faces in hostile environments like surface water. We evaluated river water effect on Salmonella biofilm formation ability in terms of physical, morphological characteristics and chemical composition. A new morphotype SPAM (soft, pink and mucoid) was detected in Oranienburg strains S-76 and S-347 (environmental and clinical isolate). Oranienburg serotypes showed very marked behavior in adherence, pellicle liquid-air and resistance, being Oranienburg S-76 the strongest biofilm producer. All strains when exposed to river water presented an overlapping mucoid layer in the morphotype and increased their motility except Oranienburg S-347. The most motile was Typhimurium (control) and the least Infantis S-304 (clinical isolate). Mannose, glucose, galactose and ribose were the main biofilm sugar components; type and concentration of sugar suggest a morphotype/serotype dependent pattern. Strong morphotypes expressed in this study may be an effective protective strategy for Salmonella in hostile environments.

The CRISPR-Cas System Differentially Regulates Surface-Attached and Pellicle Biofilm in Salmonella enterica Serovar Typhimurium

The CRISPR-Cas mediated regulation of biofilm by Salmonella enterica serovar Typhimurium was investigated by deleting CRISPR-Cas components ΔcrisprI, ΔcrisprII, ΔΔcrisprI crisprII, and Δcas op. We determined that the system positively regulates surface biofilm while inhibiting pellicle biofilm formation. Results of real-time PCR suggest that the flagellar (fliC, flgK) and curli (csgA) genes were repressed in knockout strains, causing reduced surface biofilm. The mutants displayed altered pellicle biofilm architecture. They exhibited bacterial multilayers and a denser extracellular matrix with enhanced cellulose and less curli, ergo weaker pellicles than those of the wild type. The cellulose secretion was more in the knockout strains due to the upregulation of bcsC, which is necessary for cellulose export. We hypothesized that the secreted cellulose quickly integrates into the pellicle, leading to enhanced pellicular cellulose in the knockout strains. We determined that crp is upregulated in the knockout strains, thereby inhibiting the expression of csgD and, hence, also of csgA and bcsA. The conflicting upregulation of bcsC, the last gene of the bcsABZC operon, could be caused by independent regulation by the CRISPR-Cas system owing to a partial match between the CRISPR spacers and bcsC gene. The cAMP-regulated protein (CRP)-mediated regulation of the flagellar genes in the knockout strains was probably circumvented through the regulation of yddx governing the availability of the sigma factor σ²⁸ that further regulates class 3 flagellar genes (fliC, fljB, and flgK). Additionally, the variations in the lipopolysaccharide (LPS) profile and expression of LPS-related genes (rfaC, rfbG, and rfbI) in knockout strains could also contribute to the altered pellicle architecture. Collectively, we establish that the CRISPR-Cas system differentially regulates the formation of surface-attached and pellicle biofilm.

IMPORTANCE In addition to being implicated in bacterial immunity and genome editing, the CRISPR-Cas system has recently been demonstrated to regulate endogenous gene expression and biofilm formation. While the function of individual cas genes in controlling Salmonella biofilm has been explored, the regulatory role of CRISPR arrays in biofilm is less studied. Moreover, studies have focused on the effects of the CRISPR-Cas system on surface-associated biofilms, and comprehensive studies on the impact of the system on pellicle biofilm remain an unexplored niche. We demonstrate that the CRISPR array and cas genes modulate the expression of various biofilm genes in Salmonella, whereby surface and pellicle biofilm formation is distinctively regulated.

Inhibitory Effects of Compounds from Plumula nelumbinis on Biofilm and Quorum Sensing Against P. aeruginosa

Quorum sensing (QS), which controls the survival and virulence of Pseudomonas aeruginosa, including the formation of biofilm, is considered to be a new target to overcome pathogens. The aim of this study was to identify new QS inhibitors against P. aeruginosa and provide potential treatments for clinical infections. In this study, 25 compounds were isolated from Plumula nelumbini. Among these compounds, C25 showed the most significant biofilm inhibition activity, reaching 44.63% at 100 μM without inhibiting bacterial growth. Furthermore, C25 showed significant inhibition activity of rhamnolipid, pyocyanin, and elastase. Further mechanistic studies have confirmed that C25 could downregulate key genes in the QS system, including lasI, lasR, lasA, lasB, and pqsR, and Molecular docking studies have shown that C25 can bind to the active sites of the LasR and PqsR receptors. The present study suggests that C25 is a promising QS inhibitor for treating P. aeruginosa infections.

Modelling the Adhesion and Biofilm Formation Boundary of Listeria monocytogenes ST9

Listeria monocytogenes is a major foodborne pathogen that can adhere to or form a biofilm on food contact surfaces, depending on the environmental conditions. The purpose of this work is to determine the adhesion and biofilm formation boundaries for L. monocytogenes ST9 under the combination environments of temperature (5, 15, and 25 °C), NaCl concentration (0%, 3%, 6%, and 9% (w/v)) and pH (5.0, 6.0, 7.0, and 8.0). The probability models of adhesion and biofilm formation were built using the logistic regression. For adhesion, only the terms of linear T and NaCl are significant for L. monocytogenes ST9 (p < 0.05), whereas the terms of linear T, NaCl, and pH, and the interaction between T and pH were significant for biofilm formation (p < 0.05). By analyzing contour maps and their surface plots for two different states, we discovered that high temperature promoted adhesion and biofilm formation, whereas excessive NaCl concentration inhibited both of them. With a stringent threshold of 0.1667, the accuracy rate for identifying both adhesion/no-adhesion and biofilm formation/no-biofilm formation events were 0.929, indicating that the probability models are reasonably accurate in predicting the adhesion and biofilm formation boundary of L. monocytogenes ST9. The boundary model may provide a useful way for determining and further controlling L. monocytogenes adhesion and biofilm formation in various food processing environments.

Biofilm Formation of Listeria monocytogenes and Pseudomonas aeruginosa in a Simulated Chicken Processing Environment

This study aims to investigate the mono- and dual-species biofilm formation of Listeria monocytogenes and Pseudomonas aeruginosa incubated in different culture mediums, inoculum ratios, and incubation time. The planktonic cell population and motility were examined to understand the correlation with biofilm formation. The results showed that chicken juice significantly inhibited the biofilm formation of L. monocytogenes (p < 0.05). Pseudomonas aeruginosa was the dominant bacteria in the dual-species biofilm formation in the trypticase soy broth medium. The dynamic changes in biofilm formation were not consistent with the different culture conditions. The growth of planktonic L. monocytogenes and P. aeruginosa in the suspension was inconsistent with their growth in the biofilms. There was no significant correlation between motility and biofilm formation of L. monocytogenes and P. aeruginosa. Moreover, scanning electron microscopy (SEM) results revealed that the biofilm structure of L. monocytogenes was loose. At the same time, P. aeruginosa formed a relatively dense network in mono-species biofilms in an initial adhesion stage (24 h). SEM results also showed that P. aeruginosa was dominant in the dual-species biofilms. Overall, these results could provide a theoretical reference for preventing and controlling the biofilm formation of L. monocytogenes and P. aeruginosa in the food processing environment in the future.

The Complex Mechanism of the Salmonella typhi Biofilm Formation That Facilitates Pathogenicity: A Review

Salmonella enterica serovar Typhi (S. typhi) is an intracellular pathogen belonging to the Enterobacteriaceae family, where biofilm (aggregation and colonization of cells) formation is one of their advantageous traits. Salmonella typhi is the causative agent of typhoid fever in the human body and is exceptionally host specific. It is transmitted through the fecal-oral route by consuming contaminated food or water. This subspecies is quite intelligent to evade the innate detection and immune response of the host body, leading to systemic dissemination. Consequently, during the period of illness, the gallbladder becomes a harbor and may develop antibiotic resistance. Afterwards, they start contributing to the continuous damage of epithelium cells and make the host asymptomatic and potential carriers of this pathogen for an extended period. Statistically, almost 5% of infected people with Salmonella typhi become chronic carriers and are ready to contribute to future transmission by biofilm formation. Biofilm development is already recognized to link with pathogenicity and plays a crucial role in persistency within the human body. This review seeks to discuss some of the crucial factors related to biofilm development and its mechanism of interaction causing pathogenicity. Understanding the connections between these things will open up a new avenue for finding therapeutic approaches to combat pathogenicity.

Biofilm formation of Salmonella enterica serovar Enteritidis cocultured with Acanthamoeba castellanii responds to nutrient availability

Acanthamoeba spp. and Salmonella share common habitats, and their interaction may influence the biofilm-forming ability of Salmonella. In this study, biofilm formation of Salmonella enterica serovar Enteritidis cocultured with Acanthamoeba castellanii was examined in nutrient-rich and nutrient-deficient media. Furthermore, transcript copy number of biofilm-related genes in the biofilm cells of S. Enteritidis in monoculture was compared to those in coculture with A. castellanii. Results demonstrated that the presence of A. castellanii in the culture media activates the genes involved in the biofilm formation of S. Enteritidis, regardless of the nutrient availability. However, biofilm formation of S. Enteritidis cocultured with A. castellanii was not consistent with the transcript copy number results. In nutrient-rich medium, the number of Salmonella biofilm cells and the contents of the three main components of the biofilms including eDNA, protein, and carbohydrates were higher in the presence of A. castellanii compared to monocultures. However, in nutrient-deficient medium, the number of biofilm cells, and the amount of biofilm components in coculture conditions were less than the monocultures. These results indicate that despite activation of relevant genes in both nutrient-rich and nutrient-deficient media, biofilm formation of S. Enteritidis cocultured with A. castellanii responds to nutrient availability.

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

Stress response modulation: the key to survival of pathogenic and spoilage bacteria during poultry processing

The control of bacterial contaminants on meat is a key area of interest in the food industry. Bacteria are exposed to a variety of stresses during broiler processing which challenge bacterial structures and metabolic pathways causing death or sublethal injury. To counter these stresses, bacteria possess robust response systems that can induce shifts in the transcriptome and proteome to enable survival. Effective adaptive responses, such as biofilm formation, shock protein production and metabolic flexibility, require rapid induction and implementation at a cellular and community level to facilitate bacterial survival in adverse conditions. This review aims to provide an overview of the scientific literature pertaining to the regulation of complex adaptive processes used by bacteria to survive the processing environment, with particular focus on species that impact the quality and safety of poultry products like Campylobacter spp., Salmonella enterica and Pseudomonas spp.

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

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

Anti-Biofilms’ Activity of Garlic and Thyme Essential Oils against Salmonella typhimurium

Biofilm control by essential oil (EO) application has recently increased to preclude biofilm production on foods and environmental surfaces. In this work, the anti-biofilm effects of garlic and thyme essential oils using the minimum inhibitory concentration (MIC) method against Salmonella typhimurium recovered from different abattoir samples were investigated along with the virulence genes (InvA, SdiA and Stn genes), and the antimicrobial susceptibility profile of S. typhimurium as well. The obtained results revealed that S. typhimurium contaminated abattoir samples to varying degrees. The InvA gene was investigated in all isolates, whereas the SdiA and Stn genes were observed in four and three isolates, respectively. Utilizing the disc diffusion method, S. typhimurium isolates demonstrated substantial resistance to most of the examined antibiotics with a high multiple antibiotic resistance index. S. typhimurium isolates demonstrated biofilm formation abilities to various degrees at varied temperatures levels (4 °C and 37 °C). In conclusion, the obtained samples from the research area are regarded as a potential S. typhimurium contamination source. Furthermore, garlic essential oil (GEO) has more potential to inhibit S. typhimurium biofilm at different sub-minimum inhibitory concentrations as compared to thyme essential oil (TEO). Therefore, these EOs are considered as potential natural antibacterial options that could be applied in food industry.

Biofilm through the Looking Glass: A Microbial Food Safety Perspective

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

Antibacterial and Antibiofilm Activity of Selected Medicinal Plant Leaf Extracts Against Pathogens Implicated in Poultry Diseases

Antimicrobial resistant poultry pathogens are responsible for treatment failure and economic losses, and can also be a source of resistant zoonotic infections representing a risk to human health. In 2006 the European Union banned the use of antibiotics as growth promoters in farm animals and other regions are likely to follow suit. Alternative products and strategies are sought to help maintain animal gut health to reduce the prevalence of pathogens in the food chain. The minimum inhibitory concentration (MIC) of organic and aqueous leaf extracts of Alchornea laxiflora, Ficus exasperata, Morinda lucida, Jatropha gossypiifolia, Ocimum gratissimum, and Acalypha wilkesiana were tested against bacterial poultry pathogens including Staphylococcus aureus, Enterococcus faecalis, Salmonella spp., Escherichia coli, Campylobacter spp., and fungal species (Aspergillus fumigatus, Aspergillus flavus, and Candida albicans) using a 2-fold serial microdilution method. Activity of extracts against biofilms of the pathogens was done using a modified crystal violet staining in vitro assay. The safety of extracts was determined against Vero and Caco-2 cells using a tetrazolium-based in vitro assay. Acetone and cold water extracts of M. lucida had the best activity against three bacteria (MIC = 0.05-0.07 mg/ml) and two fungal (MIC = 0.03-0.15 mg/ml) organisms, respectively. The E. coli isolate and A. flavus were the most susceptible bacteria and fungi, respectively. Caco-2 cells generally displayed higher selectivity index (SI) values compared to Vero cells and average SI values against Vero and Caco-2 cells for both bacteria and fungi ranged from 0.01 to 4.48 and 0.005 to 16.41, respectively. All plant extracts had good anti-biofilm activity (>50%) against at least one organism. The disruption of established biofilm growth by the plant samples proved to be more difficult to achieve than efficacy against planktonic forms of bacteria. This study shows that some of the plant species are potential candidates as alternative feed additives in poultry production. In the future, a poultry feed trial to evaluate their in vivo efficacy as herbal feed additives will be conducted.

Determination of an effective agent combination using nisin against Salmonella biofilm

This present study aims to determine the lowest concentration effects of the assayed different antibiotics; antimicrobial agents alone and their combinations with nisin were investigated to prevent the biofilm formation and break down the biofilm structure of Salmonella. While the combination of nisin and EDTA showed a synergistic effect against Salmonella strain, chlorhexidine digluconate and streptomycin with nisin showed a partial synergetic effect; citric acid and sulfonamides with nisin showed an indifferent effect. The use of citric acid and chlorhexidine digluconate alone was very effective in Salmonella inhibition. While the citric acid combined with other agents had not much effect, the use of chlorhexidine digluconate combined with nisin and EDTA inactivated the total initial count within 24 h. Significantly, when citric acid and sulfonamides are used alone, they reduce by 64% and 44%, respectively. When they used nisin + EDTA, this ratio increased to 83% and 84%, respectively. For the prevention of biofilm, the most suitable conditions were determined as 97% biofilm inhibition. The results of this study can be used as a guide for the emergence of new approaches to ensure the food safety and quality of the food industry.

Relationship between growth ability, virulence, and resistance to food-processing related stresses in non-typhoidal Salmonellae

The ability of Salmonella to resist and adapt to harsh conditions is one of the major features that have made this microorganism such a relevant health hazard. However, the impact of these resistance responses on other aspects of Salmonella physiology, such as virulence and growth ability, is still not fully understood. The objective of this study was to determine the maximum growth rates (in three different media), virulence (adhesion and invasion of Caco-2 cells), and other phenotypic characteristics (biofilm-forming ability and antimicrobial resistance) of 23 Salmonella strains belonging to different serovars, and to compare them with their previously determined stress resistance parameters. Significant differences (p < 0.05) in growth rates, virulence, and biofilm-forming ability were found among the 23 strains studied. Nevertheless, whereas less than 3-fold change between the lowest and the highest growth rate was observed, the percentage of cells capable of invading Caco-2 cells varied more than 100-fold, that to form biofilms more than 30-fold, and the antibiotic MICs varied up to 512-fold, among the different strains. Results indicate that those strains with the highest cell adhesion ability were not always the most invasive ones and suggest that, in general terms, a higher stress resistance did not imply a reduced growth ability (rate). Similarly, no association between stress resistance and biofilm formation ability (except for acid stress) or antibiotic resistance (with minor exceptions) was found. Our data also suggest that, in Salmonella, acid stress resistance would be associated with virulence, since a positive correlation of that trait with adhesion and a negative correlation with invasion was found. This study contributes to a better understanding of the physiology of Salmonella and the relationship between bacterial stress resistance, growth ability, and virulence. It also provides new data regarding intra-specific variability of a series of phenotypic characteristics of Salmonella that are relevant from the food safety perspective.

A novel approach using growth curve analysis to distinguish between antimicrobial and anti-biofilm activities against Salmonella

Salmonella spp. are a commonly identified cause of outbreaks of food-borne diseases. Despite much research, there remains the need to find new antimicrobial and anti-biofilm agents against Salmonella. For this, it is necessary to distinguish between these two aspects. Agents that influence biofilm formation should not affect bacterial growth, to thus avoid further promotion of the development of resistance. In this study, we present the use of growth curves of Salmonella Infantis to simultaneously determine antimicrobial and anti-biofilm activities, for the screening for anti-Salmonella activities of 42 aqueous fungal extracts. The extract from Pseudohydnum gelatinosum showed good antimicrobial activity, and that from Pleurotus ostreatus showed good anti-biofilm activity. In extracts from Infundibulicybe geotropa and Infundibulicybe gibba, both activities were determined after fractionation. The antimicrobial activity was associated with protein-rich fractions and mediated by l-amino acid oxidase activity. The fractionation did not allow determination of the anti-biofilm active fraction, so further studies are needed to define these compounds. Growth curve analysis of S. Infantis is shown here to provide a fast and simple approach to distinguish between antimicrobial and anti-biofilm activities in a high-throughput setting, such that it can be easily implemented in screening and further bioassay-based purification of novel alternatives to antibiotics.

Action of carvacrol in Salmonella Typhimurium biofilm: A proteomic study

Carvacrol presents action in Salmonella Typhimurium biofilms, however the antibiofilm mechanism of this compound has not been fully established yet. In the present study, the aim was to evaluate protein profile changes in S. Typhimurium biofilm treated with carvacrol. Proteomic analysis of treated versus untreated biofilm showed several changes in proteins involved with S. Typhimurium biofilm and antioxidant activity. The proteins DsbA (thiol: disulfide interchange protein DsbA), LuxS (S-ribosylhomocysteine lyase), DksA (RNA polymerase binding transcription factor DksA), and SODs (superoxide dismutases) A, B and C had their synthesis decreased after treatment with carvacrol. These proteins play a key role in S. Typhimurium biofilm formation, demonstrating the dynamic antibiofilm action of carvacrol. The differentially expressed proteins identified provide possible action targets for future studies in order to gain more insight into the mechanism of action of carvacrol on S. Typhimurium biofilm.

Involvement of the Heat Shock Protein HtpG of Salmonella Typhimurium in Infection and Proliferation in Hosts

Salmonella Typhimurium is a common pathogen infecting the gastrointestinal tract of humans and animals, causing host gastroenteritis and typhoid fever. Heat shock protein (HtpG) as a molecular chaperone is involved in the various cellular processes of bacteria, especially under environmental stress. However, the potential association of HtpG with S. Typhimurium infection remains unknown. In this study, we clarified that HtpG could also play a role as an effector in S. Typhimurium infection. RNA-seq indicated that the flagellar assembly pathway, infection pathway, and chemotaxis pathway genes of S. Typhimurium were downregulated after the mutation of HtpG, which resulted in compromises of S. Typhimurium motility, biofilm formation, adhesion, invasion, and inflammation-inducing ability. In addition, HtpG recombinant protein was capable of promoting the proliferation of S. Typhimurium in host cells and the resultant inflammation. Collectively, our results illustrated an important role of HtpG in S. Typhimurium infection.

Water sorption characteristics of freeze-dried bacteria in low-moisture foods

Water sorption isotherms of bacteria reflect the water activity with the change of moisture content of bacteria at a specific temperature. The temperature-dependency of water activity change can help to understand the thermal resistance of bacteria during a thermal process. Thermal resistance of bacteria in low-moisture foods may differ significantly depending on the physiological characteristics of microorganisms, including cell structure, existence of biofilms, and growth state. Previous studies demonstrated that the incremental change of a_w in bacterial cells during thermal treatments resulted in changes in their thermotolerance. In this study, a pathogen associated with low-moisture foods outbreaks, Salmonella Enteritidis PT30 (in planktonic and biofilm forms), and its validated surrogate, Enterococcus faecium, were lyophilized and their water sorption isotherms (WSI) at 20, 40, and 60 °C were determined by using a vapor sorption analyzer and simulated by the Guggenheim, Anderson and De Boer model (GAB). The published thermal death times at 80 °C (D_{80 °C}-values) of these bacteria in low-moisture environments were related with their WSI-derived a_w changes. The results showed that planktonic E. faecium and biofilms of Salmonella, exhibiting higher thermal resistance compared to the planktonic cultures of Salmonella, had a smaller increase in a_w when thermally treated from 20 to 60 °C in sealed test cells. The computational modeling also showed that when temperature increased from 20 to 60 °C, with an increase in relative humidity from 10% to 60%, freeze-dried planktonic E. faecium and Salmonella cells would equilibrate to their surrounding environments in 0.15 s and 0.25 s, respectively, suggesting a rapid equilibration of bacterial cells to their microenvironment. However, control of bacteria with different cell structure and growth state would require further attentions on process design adjustment because of their different water sorption characteristics.

Differences in biofilm formation of Salmonella serovars on two surfaces under two temperature conditions

AIMS

Salmonella is extremely diverse, with >2500 serovars that are genetically and phenotypically diverse. The aim of this study was to build a collection of Salmonella isolates that are genetically diverse and to evaluate their ability to form biofilm under different conditions relevant to a processing environment.

METHODS AND RESULTS

Twenty Salmonella isolates representative of 10 serovars were subtyped using Clustered regularly interspaced short palindromic repeats (CRISPR)-typing to assess the genetic diversity between isolates of each serovar. Biofilm formation of the isolates on both plastic and stainless-steel surfaces at 25 and 15°C was assessed. At 25°C, 8/20 isolates each produced strong and moderate biofilm on plastic surface compared to stainless-steel (3/20 and 13/20 respectively). At 15°C, 5/20 produced strong biofilm on plastic surface and none on stainless-steel. Several isolates produced weak biofilm on plastic (11/20) and stainless-steel (16/20) surfaces. Serovar Schwarzengrund consistently produced strong biofilm while serovars Heidelberg and Newport produced weak biofilm.

CONCLUSION

These results suggest that Salmonellae differ in their attachment depending on the surface and temperature conditions encountered, which may influence persistence in the processing environment.

SIGNIFICANCE AND IMPACT OF STUDY

These differences in biofilm formation could provide useful information for mitigation of Salmonella in processing environments.

The role of antibiotics and heavy metals on the development, promotion, and dissemination of antimicrobial resistance in drinking water biofilms

Antimicrobial resistance (AMR), as well as the development of biofilms in drinking water distribution systems (DWDSs), have become an increasing concern for public health and management. As bulk water travels from source to tap, it may accumulate contaminants of emerging concern (CECs) such as antibiotics and heavy metals. When these CECs and other selective pressures, such as disinfection, pipe material, temperature, pH, and nutrient availability interact with planktonic cells and, consequently, DWDS biofilms, AMR is promoted. The purpose of this review is to highlight the mechanisms by which AMR develops and is disseminated within DWDS biofilms. First, this review will lay a foundation by describing how DWDS biofilms form, as well as their basic intrinsic and acquired resistance mechanisms. Next, the selective pressures that further induce AMR in DWDS biofilms will be elaborated. Then, the pressures by which antibiotic and heavy metal CECs accumulate in DWDS biofilms, their individual resistance mechanisms, and co-selection are described and discussed. Finally, the known human health risks and current management strategies to mitigate AMR in DWDSs will be presented. Overall, this review provides critical connections between several biotic and abiotic factors that influence and induce AMR in DWDS biofilms. Implications are made regarding the importance of monitoring and managing the development, promotion, and dissemination of AMR in DWDS biofilms.

Salmonella in Swine: Prevalence, Multidrug Resistance, and Vaccination Strategies

An estimated 1.3 million Salmonella infections and 420 deaths occur annually in the United States, with an estimated economic burden of $3.7 billion. More than 50% of US swine operations test positive for Salmonella according to the National Animal Health Monitoring System, and 20% of Salmonella from swine are multidrug resistant (resistant to ≥3 antimicrobial classes) as reported by the National Antimicrobial Resistance Monitoring System. This review on Salmonella in swine addresses the current status of these topics by discussing antimicrobial resistance and metal tolerance in Salmonella and the contribution of horizontal gene transfer. A major challenge in controlling Salmonella is that Salmonella is a foodborne pathogen in humans but is often a commensal in food animals and thereby establishes an asymptomatic reservoir state in such animals, including swine. As food animal production systems continue to expand and antimicrobial usage becomes more limited, the need for Salmonella interventions has intensified. A promising mitigation strategy is vaccination against Salmonella in swine to limit animal, environmental, and food contamination. Expected final online publication date for the Annual Review of Animal Biosciences, Volume 10 is February 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

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,&nbsp;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.

Evaluation of Sodium Bisulfate on Reducing Salmonella Heidelberg Biofilm and Colonization in Broiler Crops and Ceca

Salmonella Heidelberg (SH) on contaminated poultry causes economic and health risks to producers and consumers. We hypothesized that sodium bisulfate (SBS) would decrease SH biofilm on polyvinyl chloride (PVC) coupons and decrease the horizontal transfer of SH in broilers. Experiment 1: Salmonella Heidelberg biofilm was cultured with PVC coupons, which were treated with SBS at a pH of 3.5 for 10 min, 8 h, and 24 h. Experiment 2: Nine replicate pens per treatment were divided between two rooms. A seeder contact model was used to mimic a natural infection environment. Treatments consisted of tap water or sodium bisulfate in water at a pH of 3.5. Salmonella Heidelberg incidence and enumeration were measured in crops and ceca. Sodium bisulfate significantly reduced biofilm by 2.16 and 1.04 logs when treated for 8 and 24 h, respectively. Crop colonization was significantly decreased in trials 1 and 2 by 0.29 and 0.23 logs, respectively. Crop pH was significantly decreased in trial 2. Ceca colonization was significantly decreased in trial 1 by 0.39 logs. The results from the present study suggest that SBS may be administered to drinking water to decrease SH gut colonization and to reduce biofilm.

Bacterial Biofilms and Their Implications in Pathogenesis and Food Safety

Biofilm formation is an integral part of the microbial life cycle in nature. In food processing environments, bacterial transmissions occur primarily through raw or undercooked foods and by cross-contamination during unsanitary food preparation practices. Foodborne pathogens form biofilms as a survival strategy in various unfavorable environments, which also become a frequent source of recurrent contamination and outbreaks of foodborne illness. Instead of focusing on bacterial biofilm formation and their pathogenicity individually, this review discusses on a molecular level how these two physiological processes are connected in several common foodborne pathogens such as Listeria monocytogenes, Staphylococcus aureus, Salmonella enterica and Escherichia coli. In addition, biofilm formation by Pseudomonas aeruginosa is discussed because it aids the persistence of many foodborne pathogens forming polymicrobial biofilms on food contact surfaces, thus significantly elevating food safety and public health concerns. Furthermore, in-depth analyses of several bacterial molecules with dual functions in biofilm formation and pathogenicity are highlighted.