Biofilm formation and potential virulence factors of Salmonella strains isolated from ready-to-eat shrimps

Genome degradation promotes Salmonella pathoadaptation by remodeling fimbriae-mediated proinflammatory response

Understanding changes in pathogen behavior (e.g. increased virulence, a shift in transmission channel) is critical for the public health management of emerging infectious diseases. Genome degradation via gene depletion or inactivation is recognized as a pathoadaptive feature of the pathogen evolving with the host. However, little is known about the exact role of genome degradation in affecting pathogenic behavior, and the underlying molecular detail has yet to be examined. Using large-scale global avian-restricted Salmonella genomes spanning more than a century, we projected the genetic diversity of Salmonella Pullorum (bvSP) by showing increasingly antimicrobial-resistant ST92 prevalent in Chinese flocks. The phylogenomic analysis identified three lineages in bvSP, with an enhancement of virulence in the two recently emerged lineages (L2/L3), as evidenced in chicken and embryo infection assays. Notably, the ancestor L1 lineage resembles the Salmonella serovars with higher metabolic flexibilities and more robust environmental tolerance, indicating stepwise evolutionary trajectories towards avian-restricted lineages. Pan-genome analysis pinpointed fimbrial degradation from a virulent lineage. The later engineered fim-deletion mutant, and all other five fimbrial systems, revealed behavior switching that restricted horizontal fecal-oral transmission but boosted virulence in chicks. By depleting fimbrial appendages, bvSP established persistent replication with less proinflammation in chick macrophages and adopted vertical transovarial transmission, accompanied by ever-increasing intensification in the poultry industry. Together, we uncovered a previously unseen paradigm for remodeling bacterial surface appendages that supplements virulence-enhanced evolution with increased vertical transmission.

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.

Prevention and Control of Human Salmonella enterica Infections: An Implication in Food Safety

Salmonella is a foodborne zoonotic pathogen causing diarrhoeal disease to humans after consuming contaminated water, animal, and plant products. The bacterium is the third leading cause of human death among diarrhoeal diseases worldwide. Therefore, human salmonellosis is of public health concern demanding integrated interventions against the causative agent, Salmonella enterica. The prevention of salmonellosis in humans is intricate due to several factors, including an immune-stable individual infected with S. enterica continuing to shed live bacteria without showing any clinical signs. Similarly, the asymptomatic Salmonella animals are the source of salmonellosis in humans after consuming contaminated food products. Furthermore, the contaminated products of plant and animal origin are a menace in food industries due to Salmonella biofilms, which enhance colonization, persistence, and survival of bacteria on equipment. The contaminated food products resulting from bacteria on equipment offset the economic competition of food industries and partner institutions in international business. The most worldwide prevalent broad-range Salmonella serovars affecting humans are Salmonella Typhimurium and Salmonella Enteritidis, and poultry products, among others, are the primary source of infection. The broader range of Salmonella serovars creates concern over multiple strategies for preventing and controlling Salmonella contamination in foods to enhance food safety for humans. Among the strategies for preventing and controlling Salmonella spread in animal and plant products include biosecurity measures, isolation and quarantine, epidemiological surveillance, farming systems, herbs and spices, and vaccination. Other measures are the application of phages, probiotics, prebiotics, and nanoparticles reduced and capped with antimicrobial agents. Therefore, Salmonella-free products, such as beef, pork, poultry meat, eggs, milk, and plant foods, such as vegetables and fruits, will prevent humans from Salmonella infection. This review explains Salmonella infection in humans caused by consuming contaminated foods and the interventions against Salmonella contamination in foods to enhance food safety and quality for humans.

Salmonella T3SS effector SseK1 arginine-glycosylates the two-component response regulator OmpR to alter bile salt resistance

Type III secretion system (T3SS) effector proteins are primarily recognized for binding host proteins to subvert host immune response during infection. Besides their known host target proteins, several T3SS effectors also interact with endogenous bacterial proteins. Here we demonstrate that the Salmonella T3SS effector glycosyltransferase SseK1 glycosylates the bacterial two-component response regulator OmpR on two arginine residues, R15 and R122. Arg-glycosylation of OmpR results in reduced expression of ompF, a major outer membrane porin gene. Glycosylated OmpR has reduced affinity to the ompF promoter region, as compared to the unglycosylated form of OmpR. Additionally, the Salmonella ΔsseK1 mutant strain had higher bile salt resistance and increased capacity to form biofilms, as compared to WT Salmonella, thus linking OmpR glycosylation to several important aspects of bacterial physiology.

Human Salmonellosis: A Continuous Global Threat in the Farm-to-Fork Food Safety Continuum

Salmonella is one of the most common zoonotic foodborne pathogens and a worldwide public health threat. Salmonella enterica is the most pathogenic among Salmonella species, comprising over 2500 serovars. It causes typhoid fever and gastroenteritis, and the serovars responsible for the later disease are known as non-typhoidal Salmonella (NTS). Salmonella transmission to humans happens along the farm-to-fork continuum via contaminated animal- and plant-derived foods, including poultry, eggs, fish, pork, beef, vegetables, fruits, nuts, and flour. Several virulence factors have been recognized to play a vital role in attaching, invading, and evading the host defense system. These factors include capsule, adhesion proteins, flagella, plasmids, and type III secretion systems that are encoded on the Salmonella pathogenicity islands. The increased global prevalence of NTS serovars in recent years indicates that the control approaches centered on alleviating the food animals' contamination along the food chain have been unsuccessful. Moreover, the emergence of antibiotic-resistant Salmonella variants suggests a potential food safety crisis. This review summarizes the current state of the knowledge on the nomenclature, microbiological features, virulence factors, and the mechanism of antimicrobial resistance of Salmonella. Furthermore, it provides insights into the pathogenesis and epidemiology of Salmonella infections. The recent outbreaks of salmonellosis reported in different clinical settings and geographical regions, including Africa, the Middle East and North Africa, Latin America, Europe, and the USA in the farm-to-fork continuum, are also highlighted.

Surface conditioning with bacteriophages reduces biofilm formation of Salmonella Heidelberg

Salmonella remains one of the most common foodborne pathogens worldwide, and its resistance to antimicrobials has increased considerably over the years. In this context, was evaluated the action of three bacteriophages isolated or combined in inhibiting the adhesion and removal of Salmonella Heidelberg biofilm on a polystyrene surface. The bacteriophages UPF_BP1, UPF_BP2, UPF_BP3 and a pool of them were used for biocontrol of Salmonella Heidelberg biofilms on polystyrene surface in the action times of 3, 6 and 9 h. Individual and combined phages exhibited reductions in Salmonella Heidelberg adhesion of up to 83.4% and up to 64.0% in removal of preformed biofilm. The use of synergistic combinations between the phages is the most indicated option due to its potential to reduce biofilms. The use of the bacteriophage pool in surface conditioning is an alternative in the control of Salmonella Heidelberg biofilms.

Surveillance of Vibrio parahaemolyticus pathogens recovered from ready-to-eat foods

This study examined the occurrence of V. parahaemolyticus from ready-to-eat (RTE) food in Delta State, Nigeria. It also characterized antibiotic resistance and virulence gene profile patterns to determine the associated health risk hazard. Food samples total of 380 were collected randomly and assessed for V. parahaemolyticus. V. parahaemolyticus isolates were characterized for their virulence and antibiogram potentials using a phenotypic and polymerase chain reaction (PCR) approach. A total of 42 (11.1%) samples were contaminated with V. parahaemolyticus. In 17/42 (40.5%) of the V. parahaemolyticus-positive samples, the densities were < 10 MPN/g. However, 19/42 (45.2%) and 6/42 (14.3%) of the samples had densities of 10 - 10² and > 10² MPN/g, respectively. A total of 67 V. parahaemolyticus isolates were identified using PCR; 54(80.6%) isolates were multidrug resistant. A total of 22 (32.8%), 39 (58.2%), and 67 (100%) of the V. parahaemolyticus harbored the tdh, trh, and tlh toxin genes, respectively. The T3SS1 gene (vcrD1) was detected in 67 (100%) of the isolates. The T3SS2α genes which were vcrD2, vopB2, and vopT were detected in 21 (31.3%), 11 (16.4%) and 30 (44.8%) of the isolates respectively. Some of the V. parahaemolytics strains harbored the orf8 gene 20 (29.9%), and a combination of orf8 + tdh genes 12 (17.9%), categorized as pandemic strains. The antibiotic resistance genes detected in this study include bla_TEM 33 (49.3), tetM 19 (28.4), cmlA 32(47.8) and sul1 14 (20.9). The concentration levels and prevalence of V. parahaemolyticus in RTE foods indicate contamination of ready-to-eat foods, particularly street foods consumed in the Delta State of Nigeria, threatening public health and consumer safety.

Identification and characterization of MDR virulent Salmonella spp isolated from smallholder poultry production environment in Edo and Delta States, Nigeria

Salmonella is responsible for some foodborne disease cases worldwide. It is mainly transmitted to humans through foods of animal origin through the consumption of poultry products. The increased international trade and the ease of transboundary movement could propel outbreaks of local origin to translate into severe global threats. The present study aimed to characterize Salmonella serovars isolated from poultry farms in Edo and Delta States, Nigeria. A total of 150 samples (faecal, water and feed) were collected from ten poultry farms between January and August 2020 and analyzed for Salmonella characterization using standard bacteriological and molecular methods. Salmonella serovars identified include: Salmonella Enteritidis [n = 17 (39.5%)], Salmonella Typhimurium [n = 13 (30.2%)] and other Salmonella serovars [n = 13 (30.2%)]. All Salmonella serovars were cefotaxime and ampicillin resistant. The presence of the invA gene ranged from 9(69.2%) to 15(88.2%). The spvC gene ranged from 2(14.4%) to 10(58.8%). All Salmonella serovars had sdiA gene. The Salmonella isolates produced some extracellular virulence factors (such as protease, lipase, β-hemolytic activity, and gelatinase), while 13(30.2%) of the overall isolates formed strong biofilms. In conclusion, the detection of multiple antibiotic-resistant Salmonella serovars in faecal sources, which also exhibited virulence determinants, constituted a public health risk as these faecal samples have the potential as manure in the growing of crops. These pathogens can be transmitted to humans nearby and through poultry products, resulting in difficult-to-treat infections and economic loss.

The Prolonged Treatment of Salmonella enterica Strains with Human Serum Effects in Phenotype Related to Virulence

Salmonella enterica as common pathogens of humans and animals are good model organisms to conduct research on bacterial biology. Because these bacteria can multiply in both the external environments and in the living hosts, they prove their wide adaptability. It has been previously demonstrated that prolonged exposition of Salmonella serotype O48 cells to normal human serum led to an increase in resistance to sera in connection with the synthesis of very long O-antigen. In this work, we have studied the phenotype connected to virulence of Salmonella enterica strains that were subjected to consecutive passages in 50% human serum from platelet-poor plasma (SPPP). We found that eight passages in SPPP may not be enough for the bacteria to become serum-resistant (S. Typhimurium ATCC 14028, S. Senftenberg). Moreover, C1q and C3c complement components bound to Salmonellae (S. Typhimurium ATCC 14028, S. Hammonia) membrane proteins, which composition has been changed after passaging in sera. Interestingly, passages in SPPP generated genetic changes within gene fljB, which translated to cells’ motility (S. Typhimurium ATCC 14028, S. Erlangen). One strain, S. Hammonia exposed to a serum developed a multi-drug resistance (MDR) phenotype and two S. Isaszeg and S. Erlangen tolerance to disinfectants containing quaternary ammonium salts (QAS). Furthermore, colonial morphotypes of the serum adaptants were similar to those produced by starter cultures. These observations suggest that overcoming stressful conditions is manifested on many levels. Despite great phenotypic diversity occurring after prolonged exposition to SPPP, morphotypes of colonies remained unchanged in basic media. This work is an example in which stable morphotypes distinguished by altered virulence can be confusing during laboratory work with life-threatening strains.

Biofilms as a microbial hazard in the food industry: A scoping review

Biofilms pose a serious public health hazard with a significant economic impact on the food industry. The present scoping review is designed to analyze the literature published during 2001-2020 on biofilm formation of microbes, their detection methods, and association with antimicrobial resistance (if any). The peer-reviewed articles retrieved from 04 electronic databases were assessed using PRISMA-ScR guidelines. From the 978 preliminary search results, a total of 88 publications were included in the study. On analysis, the commonly isolated pathogens were Listeria monocytogenes, Staphylococcus aureus, Salmonella spp., Escherichia coli, Bacillus spp., Vibrio spp., Campylobacter jejuni and Clostridium perfringens. The biofilm-forming ability of microbes was found to be influenced by various factors such as attachment surfaces, temperature, presence of other species, nutrient availability etc. A total of 18 studies characterized the biofilm-forming genes, particularly for S. aureus, Salmonella spp., and E. coli. In most studies, polystyrene plate and/or stainless-steel coupons were used for biofilm formation, and the detection was carried out by crystal violet assays and/or by plate counting method. The strain-specific significant differences in biofilm formation were observed in many studies, and few studies carried out analysis of multi-species biofilms. The association between biofilm formation and antimicrobial resistance wasn't clearly defined. Further, viable but non-culturable (VBNC) form of the foodborne pathogens is posing an unseen (by conventional cultivation techniques) but potent threat food safety. The present review recommends the need for carrying out systematic surveys and risk analysis of biofilms in food chain to highlight the evidence-based public health concerns, especially in regions where microbiological food hazards are quite prevalent.

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.

Meta-Analysis for the Global Prevalence of Foodborne Pathogens Exhibiting Antibiotic Resistance and Biofilm Formation

Antimicrobial-resistant (AMR) foodborne bacteria causing bacterial infections pose a serious threat to human health. In addition, the ability of some of these bacteria to form biofilms increases the threat level as treatment options may become compromised. The extent of antibiotic resistance and biofilm formation among foodborne pathogens remain uncertain globally due to the lack of systematic reviews. We performed a meta-analysis on the global prevalence of foodborne pathogens exhibiting antibiotic resistance and biofilm formation using the methodology of a Cochrane review by accessing data from the China National Knowledge Infrastructure (CNKI), PubMed, and Web of Science databases between 2010 and 2020. A random effects model of dichotomous variables consisting of antibiotic class, sample source, and foodborne pathogens was completed using data from 332 studies in 36 countries. The results indicated AMR foodborne pathogens has become a worrisome global issue. The prevalence of AMR foodborne pathogens in food samples was greater than 10% and these foodborne pathogens were most resistant to β-lactamase antibiotics with Bacillus cereus being most resistant (94%). The prevalence of AMR foodborne pathogens in human clinical specimens was greater than 19%, and the resistance of these pathogens to the antibiotic class used in this research was high. Independently, the overall biofilm formation rate of foodborne pathogenic bacteria was 90% (95% CI, 68%–96%) and a direct linear relationship between biofilm formation ability and antibiotic resistance was not established. Future investigations should document both AMR and biofilm formation of the foodborne pathogen isolated in samples. The additional information could lead to alternative strategies to reduce the burden cause by AMR foodborne pathogens.

Processed ready-to-eat (RTE) foods sold in Yenagoa Nigeria were colonized by diarrheagenic Escherichia coli which constitute a probable hazard to human health

The study aimed to recover diarrheagenic Escherichia coli strains from processed ready-to-eat (RTE) foods in Yenagoa, Nigeria and characterize them using culture-based and molecular methods. Three hundred RTE food samples were collected randomly from different food outlets between February 2021 and August 2021 and assessed for the occurrence of E. coli using standard bacteriological procedures. The virulence factor formation and antibiotic susceptibility profile of the isolates was carried out using standard microbiological procedures. Polymerase chain reaction (PCR) was used to confirm the identity of the isolates via specific primers and further used to assay the diarrheagenic determinants of the E. coli isolates. The prevalence of E. coli positive samples based on the proliferation of E. coli on Chromocult coliform agar forming purple to violet colonies was 80(26.7%). The population density of E. coli from the RTE foods ranged from 0–4.3 × 10⁴ ± 1.47 CFU/g. The recovered E. coli isolates (n = 62) were resistant to antibiotics in different proportions such as ampicillin 62(100%), aztreonam 47(75.81%) and chloramphenicol 43(69.35%). All the recovered E. coli isolates were resistant to ≥ 2 antibiotics. The multiple antibiotic-resistant index (MARI) ranged from 0.13–0.94 with 47(75.8%) of isolates having MARI >2. A total of 48(77.4%) of the isolates were multidrug-resistant (MDR). The proportion of extracellular virulence factor formation is as follows: protease 12(19.35%), curli 39(62.9%), cellulose 21(33.89%), ornithine decarboxylase 19(30.65%) and aesculin hydrolysis 14(22.58%). The overall proportion of diarrheagenic E. coli was 33/62(53.2%). The distributions of typical diarrheagenic E. coli includes: tETEC 9(14.5%), tEPEC 13(20.9%), tEAEC 6(9.7%), tEIEC 2(3.2%) and tEHEC 3(4.8%). The proportions of atypical strains include aETEC 10(16.1%), aEAEC 5(8.1%), aEPEC 1(1.6%) and aEIEC 3(4.8%). This study demonstrated that some RTE foods sold in Yenagoa, Nigeria, are contaminated and constitute a probable human health hazard. Thus, there is a need for intensive surveillance of this isolate in RTE foods variety to spot evolving AMR phenotypes and avert food-borne infections.

Molecular and pathogenic characterization of Vibrio parahaemolyticus isolated from seafood

Gastroenteritis infections in humans are mainly associated with consumption of Vibrio parahaemolyticus contaminated shellfish, which causes health and economic loss. Virulence factor production, antibiotic resistance profile, and biofilm-forming capacity of Vibrio parahaemolyticus isolates on food and food contact surfaces at 30 °C were investigated to evaluate the antibiotic sensitivity and pathogenic level. Strains of V. parahaemolyticus were isolated from shellfish (e.g., Crassostrea gigas, Venerupis philippinarum, Mytilus coruscus, Anadara kagoshimensis) in Korea. When examined for 17 virulence factor-encoding genes, 53.3, 73.1, 87.1, 87.9, and 90.9% of the isolates were positive for genes encoding TDH, T6SS, T3SS1, T3SS2, and Type I pilus, respectively. All isolates showed resistance to vancomycin, tetracyclines, penicillin, nalidixic acid, and doxycycline, among 26 antibiotics tested, with most isolates resistant to kanamycin (93.5%), ampicillin (96.8%), clindamycin (96.8%), tobramycin (88.7%), amikacin (83.97%), and minocycline (80.7%). Biofilm formation, cell-cell attachment, and motility were high in most isolates. These findings may assist in monitoring the epidemics of the pathogen. Continuous monitoring could help to decrease V. parahaemolyticus infections and improve seafood safety.

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.

Prevalence and Characterization of Food-Borne Vibrio parahaemolyticus From African Salad in Southern Nigeria

The demand for minimally processed vegetables (African salad) has increased partly due to its inclusion in ready-to-eat foods. Nevertheless, the associated risk of the presence of emergent foodborne pathogens, such as Vibrio parahaemolyticus might be underestimated. The present study was designed to isolate and characterize foodborne V. parahaemolyticus from minimally processed vegetables using culture-based methods and molecular approach. A total of 300 samples were examined from retail outlets between November 2018 and August 2019 from Southern Nigeria. The prevalence of vibrios from the overall samples based on the colonial proliferation of yellow, blue-green and/or green colonies on thiosulfate citrate bile salts sucrose agar was 74/300 (24.6%). An average of two green or blue-green colonies from respective plates was screened for V. parahaemolyticus using analytical profile index (API) 20 NE. Polymerase chain reaction further confirmed the identity of positive V. parahaemolyticus. The counts of V. parahaemolyticus ranged from 1.5 to 1,000 MPN/g. A total of 63 recovered V. parahaemolyticus were characterized further. The resistance profile of the isolates include ampicillin 57/63 (90.5%), cefotaxime 41/63 (65.1%), ceftazidime 30/63 (47.6%), amikacin 32/63 (50.8%), kanamycin 15/63 (23.8%), and oxytetracycline 16/63 (25.4%). The multiple antibiotic index ranged from 0–0.81. The formation of biofilm by the isolates revealed the following: strong formation 15/63 (23.8%), moderate formation 31/63 (49.2%), weak formation 12/63 (19.1%), and no formation 5/63 (7.9%). A total of 63/63 (100%), 9/63 (14.3%), and 20/63 (31.8%) of the isolates harbored the tox R gene, TDH-related hemolysin (trh) and thermostable direct hemolysin (tdh) determinants respectively. The isolates with O2 serogroup were most prevalent via PCR. Isolates that were resistant to tetracycline, kanamycin, and chloramphenicol possessed resistant genes. The presence of multidrug-resistant vibrios in the minimally processed vegetables constitutes a public health risk and thus necessitates continued surveillance.

Salmonella spp. in Pet Reptiles in Portugal: Prevalence and Chlorhexidine Gluconate Antimicrobial Efficacy

A fraction of human Salmonella infections is associated with direct contact with reptiles, yet the number of reptile-associated Salmonellosis cases are believed to be underestimated. Existing data on Salmonella spp. transmission by reptiles in Portugal is extremely scarce. The aim of the present work was to evaluate the prevalence of Salmonella spp. in pet reptiles (snakes, turtles, and lizards), as well as evaluate the isolates' antimicrobial resistance and virulence profiles, including their ability to form biofilm in the air-liquid interface. Additionally, the antimicrobial effect of chlorhexidine gluconate on the isolates was tested. Salmonella was isolated in 41% of the animals sampled and isolates revealed low levels of antimicrobial resistance. Hemolytic and lypolytic phenotypes were detected in all isolates. The majority (90.63%) of the Salmonella isolates were positive for the formation of pellicle in the air-liquid interface. Results indicate chlorhexidine gluconate is an effective antimicrobial agent, against the isolates in both their planktonic and biofilm forms, demonstrating a bactericidal effect in 84.37% of the Salmonella isolates. This study highlights the possible role of pet reptiles in the transmission of non-typhoidal Salmonella to humans, a serious and increasingly relevant route of exposure in the Salmonella public health framework.

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.

Quorum sensing modulatory and biofilm inhibitory activity of Plectranthus barbatus essential oil: a novel intervention strategy

The essential oil (EO) from the roots of Plectranthus barbatus Andr. (Syn. Coleus forskohlii Briq.) was evaluated for quorum sensing (QS) inhibitory activity. P. barbatus EO was screened for inhibition of QS regulated violacein production in Chromobacterium violaceum (ATCC 12472) wild-type strain. At inhibitory (6.25% v/v) and sub-inhibitory concentrations (3.125% v/v) of the EO, dose-dependent response in the inhibition of violacein production was observed in C. violaceum. Similarly, sub-MIC (6.25% v/v) of P. barbatus EO disrupted QS regulated biofilm formation by 27.87% and inhibited swarming and twitching motility in Pseudomonas aeruginosa PA01 implying its anti-infective and QS modulatory activity. Fluorescence microscopy studies confirmed the disruption of biofilm formation by EO in P. aeruginosa PAO1. Promising antibacterial activity was recorded at concentrations as low as 3.12% v/v for Listeria monocytogenes (ATCC 13932) and at 6.25% v/v for both Salmonella enterica subsp. enterica serovar Typhimurium (ATCC 25241) and Escherichia coli (ATCC 11775). Furthermore, significant dose-dependent inhibition was observed for biofilm formation and motility in all the tested pathogens in different treated concentrations. GC-MS analysis revealed α-pinene, endo-borneol, bornyl acetate, 1-Hexyl-2-Nitrocyclohexane as the major phytoconstituents. P. barbatus EO or its constituent compounds with QS modulatory, antimicrobial and biofilm inhibitory property could be potential new-age dietary source based intervention and preservation technologies.

Synergistic Antimicrobial Effectiveness of Plant Essential Oil and Its Application in Seafood Preservation: A Review

The synergistic potential of plant essential oils (EOs) with other conventional and non-conventional antimicrobial agents is a promising strategy for increasing antimicrobial efficacy and controlling foodborne pathogens. Spoilage microorganisms are one of main concerns of seafood products, while the prevention of seafood spoilage principally requires exclusion or inactivation of microbial activity. This review provides a comprehensive overview of recent studies on the synergistic antimicrobial effect of EOs combined with other available chemicals (such as antibiotics, organic acids, and plant extracts) or physical methods (such as high hydrostatic pressure, irradiation, and vacuum-packaging) utilized to reduce the growth of foodborne pathogens and/or to extend the shelf-life of seafood products. This review highlights the synergistic ability of EOs when used as a seafood preservative, discovering the possible routes of the combined techniques for the development of a novel seafood preservation strategy.

Clarithromycin Exerts an Antibiofilm Effect against Salmonella enterica Serovar Typhimurium rdar Biofilm Formation and Transforms the Physiology towards an Apparent Oxygen-Depleted Energy and Carbon Metabolism

Upon biofilm formation, production of extracellular matrix components and alteration in physiology and metabolism allows bacteria to build up multicellular communities which can facilitate nutrient acquisition during unfavorable conditions and provide protection toward various forms of environmental stresses to individual cells. Thus, bacterial cells within biofilms become tolerant against antimicrobials and the immune system. In the present study, we evaluated the antibiofilm activity of the macrolides clarithromycin and azithromycin. Clarithromycin showed antibiofilm activity against rdar (red, dry, and rough) biofilm formation of the gastrointestinal pathogen Salmonella enterica serovar Typhimurium ATCC 14028 (Nal^r) at a 1.56 μM subinhibitory concentration in standing culture and dissolved cell aggregates at 15 μM in a microaerophilic environment, suggesting that the oxygen level affects the activity of the drug. Treatment with clarithromycin significantly decreased transcription and production of the rdar biofilm activator CsgD, with biofilm genes such as csgB and adrA to be concomitantly downregulated. Although fliA and other flagellar regulon genes were upregulated, apparent motility was downregulated. RNA sequencing showed a holistic cell response upon clarithromycin exposure, whereby not only genes involved in the biofilm-related regulatory pathways but also genes that likely contribute to intrinsic antimicrobial resistance, and the heat shock stress response were differentially regulated. Most significantly, clarithromycin exposure shifted the cells toward an apparent oxygen- and energy-depleted status, whereby the metabolism that channels into oxidative phosphorylation was downregulated, and energy gain by degradation of propane 1,2-diol, ethanolamine and l-arginine catabolism, potentially also to prevent cytosolic acidification, was upregulated. This analysis will allow the subsequent identification of novel intrinsic antimicrobial resistance determinants.

Identification and Characterization of Salmonella Serovars Isolated from Pig Farms in Benin City, Edo State, Nigeria: One Health Perspective

The present study was carried out to characterize Salmonella serovars from commercial pig farms in Benin City, Nigeria. A total of 81 samples were collected from the Agricultural Development Program farms between January and June 2017. Standard culture-based and polymerase chain reaction procedures were adopted in the isolation and identification of Salmonella serovars. Antibiotic susceptibility profiles of the isolates were conducted using the Kirby-Bauer disc diffusion method with prominent resistance determinants screened for using specific primer sets. The 84 identified Salmonella serovars include 15 Salmonella ser. Enteritidis, 11 Salmonella ser. Typhimurium, and 58 other Salmonella serovars. Phenotypic virulence factors include: hemolytic activity (51.7-100%), lipase activity (48.3-81.8%), protease activity (60.3-100%), gelatinase production (50-90.9%), DNA degrading activity (55.2-90.9%), and S-layer formation (63.8-100%). The biofilm formation profiles include nonbiofilm producers (0-12.1%), weak biofilm producers (0-20%), moderate biofilm producers (24.1-27.3%), and strong biofilm producers (48.3-72.7%). Salmonella serovars in this study harbored resistant determinants, such as tetA, tetC, ampC, sul1, sul2, sul3, floR, ermA, and ermC. The occurrence of resistance phenotype and determinants in pathogenic Salmonella serovars from pig farms is a significant public health concern, which could result in the dissemination of resistant elements within the environment.

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

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

Prevalence of Antimicrobial Resistance and Virulence Gene Elements of Salmonella Serovars From Ready-to-Eat (RTE) Shrimps

Gastrointestinal illnesses continue to be a global public health risk. Exposure to foodborne Salmonella directly or indirectly through consumption of ready-to-eat seafood can be an important route of infection to humans. This study was designed to estimate the population cell density, prevalence, virulence gene signatures, and antibiotic resistance of Salmonella serovars from ready-to-eat shrimps. Ready-to-eat (RTE) shrimp samples were obtained from different open markets in Delta and Edo States, Nigeria from November 2016 to October 2017. We employed classical and polymerase chain reaction (PCR) approaches. The mean Salmonella species enumerated from the RTE shrimps ranged from -0.301 to 5.434 log10 cfu/g with 210/1440 (14.58%) of the RTE shrimp samples harbored Salmonella species. After biochemical and PCR approach, the identified isolates were Salmonella Enteritidis 11(24.4%), Salmonella Typhimurium 14 (31.1%) and other Salmonella spp. 20 (44.4%). All Salmonella species recovered were resistant to penicillin and erythromycin with 100% sensitivity to cefotaxime, cephalothin, colistin, and polymyxin B. Findings on the multidrug-resistant (MDR) profile showed that a total of 9/14 (64.3%) of Salmonella Enteritidis were resistant to 5 antibiotics which belongs to 3 different groups of antimicrobials with a multiple antibiotic-resistant (MAR) index of 0.21; while 3/11 (27.3%) of Salmonella Typhimurium were resistant to 11 antibiotics which belongs to 7 different groups of antimicrobials with a MAR index of 0.46. Virulence genes (spiA, sipB, invA, sif A, fljB, and sefA) and resistance genes (class 1 and II integrase, sul2, catB3, flor, tmp, bla TEM, strB, dfr1, and tetC) were also detected in some of the Salmonella species with variable percentage. This study indicates that ready-to-eat shrimps are probable reservoirs harboring Salmonella strains. The identified Salmonella isolates which exhibited virulence determinants and antibiotic-resistant coupled with high MAR index constitute a consumer health risk to the communities.

Antimicrobial Resistance, Virulence Determinants, and Biofilm Formation of Enterococcus Species From Ready-to-Eat Seafood

Enterococcus species form an important population of commensal bacteria and have been reported to possess numerous virulence factors considered significantly important in exacerbating diseases caused by them. The present study was designed to characterize antibiotic-resistant and virulent enterococci from ready-to-eat (RTE) seafood. A total of 720 RTE shrimp samples comprising sauced shrimp (n = 288), boiled shrimp (n = 216), and smoked shrimp (n = 216) obtained from open markets in Delta State, Nigeria, were assessed. Standard classical methods and polymerase chain reaction (PCR) were used in identifying the Enterococcus species. Potential virulence factors (β-hemolysis, gelatinase activity, S-layer, and biofilm formation) were assessed using standard procedures. The antibiotic susceptibility profile of the identified enterococci isolates was assayed using the Kirby–Bauer disc diffusion method. PCR was further used to screen selected antibiotic resistance and virulence genes. Prevalence of Enterococcus species from shrimp varieties is as follows: sauced, 26 (9.03%); boiled, 6 (2.78%); and smoked, 27 (12.50%), with an overall prevalence of 59 (8.19%) based on the occurrence of black hallow colonies after incubation. Enterococcus species detected include E. faecalis, 17 (28.8%); E. faecium, 29 (49.2%); E. gallinarum, 6 (10.2%); E. casseliflavus, 2 (3.4%); E. hirae, 3 (5.1%); and E. durans, 2 (3.4%). Biofilm occurrence among the shrimp varieties is as follows: 19/26 (73.1%) for sauced shrimps, 5/6 (83.3%) for boiled shrimps, and 16/27 (59.3%) for smoked shrimps. The phenotypic expression of the enterococci virulence revealed the following: S-layer, 59 (100%); gelatinase production, 19 (32.2%); and β-hemolysis, 21 (35.6%). An average of 3–11 virulence genes were detected in the Enterococcus species. The resistance profile of Enterococcus species is as follows: erythromycin, 29 (49.2%); vancomycin, 22 (37.3%); and tetracycline, 27 (45.8%). The frequency of occurrence of antibiotic resistance genes from the phenotypic resistant enterococci isolates to the macrolide, glycopeptide, and tetracycline antibiotics is as follows: ermA, 13/29 (44.8%); vanA, 14/22 (63.6%); tetA, 14/27 (51.9%); tetM, 15/27 (55.6%); ermB, 4/29 (13.8%); and vanB, 5/22 (22.7%). Findings from this study reveal the antibiotic resistance of enterococci strains of such species as E. durans, E. casseliflavus, E. gallinarum, and E. hirae. This study further revealed that RTE food products are reservoirs of potential virulent enterococci with antibiotic-resistant capabilities. This provides useful data for risk assessment and indicates that these foods may present a potential public health risk to consumers.