Targeting Novel LPXTG Surface Proteins with Monoclonal Antibodies for Immunomagnetic Separation of Listeria monocytogenes.

The Gram-positive bacterium Listeria monocytogenes causes a significantly high percentage of fatalities among human foodborne illnesses. Surface proteins, specifically expressed from a wide range of L. monocytogenes serotypes under selective enrichment culture conditions, can serve as targets for the isolation of this pathogen using antibody-based methods to facilitate molecular detection. In this study, monoclonal antibodies (MAbs), previously raised against the L. monocytogenes LPXTG surface proteins LMOf2365_0639 and LMOf2365_0148, were investigated for their ability to isolate L. monocytogenes from bacterial samples with immunomagnetic separation (IMS). Only 1 out of 35 MAbs against LMOf2365_0639, M3644, was capable of capturing L. monocytogenes. Among all the 24 MAbs examined against LMOf2365_0148, 4 MAbs, M3686, M3697, M3699, and M3700, were capable of capturing L. monocytogenes cells specifically from abbreviated primary selective enrichment cultures in either Palcam or LEB/UVM1 media or from mixed samples containing target and nontarget bacteria. MAb M3686 showed a unique specificity with the capability to capture strains of seven L. monocytogenes serotypes (1/2a, 1/2b, 1/2c, 3a, 4a, 4b, and 4d). These promising MAbs were subsequently characterized by quantitative measurements of antigen-binding affinity using surface plasmon resonance analysis and epitope mapping using overlapping recombinant polypeptides. The usefulness of these MAbs to LMOf2365_0148 in bacterial capture was consistent with their high affinities with KD constants in the nanomolar range and can be explored further for the development of an automated IMS method suitable for routine isolation of L. monocytogenes from food and environmental samples.

Assessment of Listeria monocytogenes Surface Proteins Identified from Proteomics Analysis for Use as Diagnostic Biomarkers.

The Gram-positive bacterium Listeria monocytogenes is an important pathogen that causes a foodborne illness with a high percentage of fatalities. Surface proteins, specifically expressed from a wide range of L. monocytogenes serotypes under selective enrichment culture conditions, can serve as targets for the detection and isolation of this pathogen using antibody-based methods. Among a number of surface proteins identified by mass spectrometry in a previous proteomic study, six candidates (annotated as LMOf2365_0148, LMOf2365_0312, LMOf2365_0546, LMOf2365_1883, LMOf2365_2111, and LMOf2365_2742) were selected here for investigating their expression in the bacterial cells cultured in vitro by raising rabbit polyclonal antibodies (PAbs) against the recombinant form of each candidate. These protein candidates contained regions conserved among various L. monocytogenes isolates but variable in other Listeria species. LMOf2365_0148, an uncharacterized protein with a LPXTG motif accountable for covalent linkage to the cell wall peptidoglycan, exhibited a strong reaction signal from anti-LMOf2365_0148 PAb binding to the cell surface, as detected by immunofluorescence microscopy. Further study, through the generation of a panel of mouse monoclonal antibodies (MAbs) to the recombinant LMOf2365_0148, showed that one of the MAbs, M3686, reacted to bacterial isolates belonging to all three lineages of L. monocytogenes under Health Canada's standard enrichment culture conditions (MFHPB-07 and MFHPB-30). These results demonstrated the potential of using LMOf2365_0148 as a surface biomarker, in conjunction with specific MAbs developed here, for the isolation and detection of L. monocytogenes from foods and food processing environments. IMPORTANCE Strains of Listeria monocytogenes are differentiated serologically into at least 13 serotypes and grouped phylogenetically into 4 distinct lineages (I, II, III, and IV). No single monoclonal antibody (MAb) reported to date is capable of binding to the surface of L. monocytogenes strains representing all the serotypes. This study assessed the expression of six surface proteins selected from a previous proteomic study and demonstrated that surface protein LMOf2365_0148 has the greatest potential as a surface biomarker. A panel of 24 MAbs to LMOf2365_0148 were assessed extensively, revealing that one of the MAbs, M3686, reacted to a wide range of L. monocytogenes isolates (lineage I, II, and III isolates) grown under standard enrichment culture conditions and thus led to the conclusion that LMOf2365_0148 is a useful novel surface biomarker for identifying, detecting, and isolating the pathogen from food and environmental samples.

Two- step synthesis and luminescent properties of BaB2 O4 :Eu3+ nano/microphosphors prepared from Ba-B-O:Eu3+ precursor.

The BaB2 O4 :Eu3+ nano/microphosphors with sphere-, rod-, and granular-like morphologies were successfully obtained by a two-step method using Ba-B-O:Eu3+ as the precursor. The structure, morphology and photoluminescent properties of the products were characterized by Fourier transfer infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetry-differential thermal analysis (TG-DTA), scanning electron microscopy (SEM) and photoluminescence (PL). The formation mechanisms of Ba-B-O:Eu3+ and BaB2 O4 :Eu3+ were proposed. The results show that the BaB2 O4 :Eu3+ could retain the original morphologies of their respective precursors largely. The BaB2 O4 :Eu3+ prepared by this two-step method exhibited better morphology, smaller particle size and better crystallinity than when prepared by a solid-state method. The granular-like BaB2 O4 :Eu3+ red phosphor prepared by this two-step method exhibited stronger PL intensity and better red color purity than when prepared by a solid-state method.

Synthesis and luminescence properties of Ca3 (BO3 )2 :Eu3+ via two-step method.

Novel Ca2 B2 O5 ·H2 O:Eu3+ nanotubes, constructed with nanobelts, were prepared using a hydrothermal method. The Ca3 (BO3 )2 :Eu3+ nanobelts with a thickness of about 100 nm were made for the first time using a two-step hydrothermal process with Ca2 B2 O5 ·H2 O:Eu3+ as the precursor. The samples were characterized by energy dispersive X-ray spectroscopy, X-ray diffraction, Fourier transform infra-red spectroscopy, thermogravimetry differential thermal analysis and scanning electron microscopy. The relationship between Ca3 (BO3 )2 :Eu3+ and Ca2 B2 O5 ·H2 O:Eu3+ was also studied. Possible reaction and growth mechanisms for Ca2 B2 O5 ·H2 O:Eu3+ and Ca3 (BO3 )2 :Eu3+ were proposed. Ca3 (BO3 )2 :Eu3+ preserved the basic microstructure unit of Ca2 B2 O5 ·H2 O:Eu3+ . Both Ca2 B2 O5 ·H2 O:Eu3+ and Ca3 (BO3 )2 :Eu3+ exhibited red emissions centred at 614 nm, but the maximum excitation peaks for Ca2 B2 O5 ·H2 O:Eu3+ and Ca3 (BO3 )2 :Eu3+ differed. Ca3 (BO3 )2 :Eu3+ exhibited higher photoluminescence intensity but a lower R/O value than Ca2 B2 O5 ·H2 O:Eu3+ .

Identification of Surface Protein Biomarkers of Listeria monocytogenes via Bioinformatics and Antibody-Based Protein Detection Tools.

UNLABELLED: The Gram-positive bacterium Listeria monocytogenes causes a significant percentage of the fatalities among foodborne illnesses in humans. Surface proteins specifically expressed in a wide range of L. monocytogenes serotypes under selective enrichment culture conditions could serve as potential biomarkers for detection and isolation of this pathogen via antibody-based methods. Our study aimed to identify such biomarkers. Interrogation of the L. monocytogenes serotype 4b strain F2365 genome identified 130 putative or known surface proteins. The homologues of four surface proteins, LMOf2365_0578, LMOf2365_0581, LMOf2365_0639, and LMOf2365_2117, were assessed as biomarkers due to the presence of conserved regions among strains of L. monocytogenes which are variable among other Listeria species. Rabbit polyclonal antibodies against the four recombinant proteins revealed the expression of only LMOf2365_0639 on the surface of serotype 4b strain LI0521 cells despite PCR detection of mRNA transcripts for all four proteins in the organism. Three of 35 monoclonal antibodies (MAbs) to LMOf2365_0639, MAbs M3643, M3644, and M3651, specifically recognized 42 (91.3%) of 46 L. monocytogenes lineage I and II isolates grown in nonselective brain heart infusion medium. While M3644 and M3651 reacted with 14 to 15 (82.4 to 88.2%) of 17 L. monocytogenes lineage I and II isolates, M3643 reacted with 22 (91.7%) of 24 lineage I, II, and III isolates grown in selective enrichment media (UVM1, modified Fraser, Palcam, and UVM2 media). The three MAbs exhibited only weak reactivities (the optical densities at 414 nm were close to the cutoff value) to some other Listeria species grown in selective enrichment media. Collectively, the data indicate the potential of LMOf2365_0639 as a surface biomarker of L. monocytogenes, with the aid of specific MAbs, for pathogen detection, identification, and isolation in clinical, environmental, and food samples. IMPORTANCE: L. monocytogenes is traditionally divided into at least 12 serotypes. Currently, there are no monoclonal antibodies (MAbs) available that are capable of binding to the surface of L. monocytogenes strains representing all 12 serotypes. Such antibodies would be useful and are needed for the development of methods to detect and isolate L. monocytogenes from food samples. In our study, we aimed to identify surface proteins that possess regions of well-conserved amino acid sequences among various serotypes and then to employ them as antigen targets (biomarkers) for the development of MAbs. Through bioinformatics and protein expression analysis, we identified one of the four putative surface protein candidates, LMOf2365_0639, encoded by the genome of the L. monocytogenes serotype 4b strain F2365, as a useful surface biomarker. Extensive assessment of 35 MAbs raised against LMOf2365_0639 in our study revealed three MAbs (M3643, M3644, and M3651) that recognized a wide range of L. monocytogenes isolates.

Expression of Surface Protein LapB by a Wide Spectrum of Listeria monocytogenes Serotypes as Demonstrated with Anti-LapB Monoclonal Antibodies.

Protein antigens expressed on the surface of all strains of Listeria monocytogenes and absent from nonpathogenic Listeria spp. are presumably useful targets for pathogen identification, detection, and isolation using specific antibodies (Abs). To seek such surface proteins expressed in various strains of L. monocytogenes for diagnostic applications, we focused on a set of surface proteins known to be involved or putatively involved in L. monocytogenes virulence and identified Listeria adhesion protein B (LapB) as a candidate based on the bioinformatics analysis of whole-genome sequences showing that the gene coding for LapB was present in L. monocytogenes strains and absent from strains of other Listeria spp. Immunofluorescence microscopy (IFM), performed with rabbit polyclonal antibodies against the recombinant LapB protein (rLapB) of L. monocytogenes serotype 4b strain L10521, confirmed expression of LapB on the surface. A panel of 48 mouse monoclonal antibodies (MAbs) to rLaB was generated, and 7 of them bound strongly to the surface of L. monocytogenes cells as demonstrated using IFM. Further characterization of these 7 anti-LapB MAbs, using an enzyme-linked immunosorbent assay (ELISA), revealed that 6 anti-LapB MAbs (M3484, M3495, M3500, M3509, M3517, and M3519) reacted strongly with 46 (86.8%) of 53 strains representing 10 of the 12 serotypes tested (1/2a, 1/2b, 1/2c, 3a, 3b, 3c, 4ab, 4b, 4d, and 4e). These results indicate that LapB, together with companion anti-LapB MAbs, can be targeted as a biomarker for the detection and isolation of various L. monocytogenes strains from contaminated foods. IMPORTANCE: Strains of L. monocytogenes are traditionally grouped into serotypes. Identification of a surface protein expressed in all or the majority of at least 12 serotypes would aid in the development of surface-binding monoclonal antibodies (MAbs) for detection and isolation of L. monocytogenes from foods. Bioinformatics analysis revealed that the gene coding for Listeria adhesion protein B (LapB), a surface protein involved in L. monocytogenes virulence, was present in L. monocytogenes strains and absent from other Listeria spp. Polyclonal antibodies against recombinant LapB (rLapB) detected the exposed epitopes on the surface of L. monocytogenes Production and extensive assessment of 48 MAbs to rLapB showed that 6 anti-LapB MAbs (M3484, M3495, M3500, M3509, M3517, and M3519) detected the expression of LapB in a wide range of L. monocytogenes isolates representing 10 of 12 serotypes tested, suggesting that LapB, together with specific MAbs, can be targeted as a biomarker for pathogen detection and isolation.

Campylobacter species in animal, food, and environmental sources, and relevant testing programs in Canada.

Campylobacter species, particularly thermophilic campylobacters, have emerged as a leading cause of human foodborne gastroenteritis worldwide, with Campylobacter jejuni, Campylobacter coli, and Campylobacter lari responsible for the majority of human infections. Although most cases of campylobacteriosis are self-limiting, campylobacteriosis represents a significant public health burden. Human illness caused by infection with campylobacters has been reported across Canada since the early 1970s. Many studies have shown that dietary sources, including food, particularly raw poultry and other meat products, raw milk, and contaminated water, have contributed to outbreaks of campylobacteriosis in Canada. Campylobacter spp. have also been detected in a wide range of animal and environmental sources, including water, in Canada. The purpose of this article is to review (i) the prevalence of Campylobacter spp. in animals, food, and the environment, and (ii) the relevant testing programs in Canada with a focus on the potential links between campylobacters and human health in Canada.

Phenotypic screening of a targeted mutant library reveals Campylobacter jejuni defenses against oxidative stress.

During host colonization, Campylobacter jejuni is exposed to harmful reactive oxygen species (ROS) produced from the host immune system and from the gut microbiota. Consequently, identification and characterization of oxidative stress defenses are important for understanding how C. jejuni survives ROS stress during colonization of the gastrointestinal tract. Previous transcriptomic studies have defined the genes belonging to oxidant stimulons within C. jejuni. We have constructed isogenic deletion mutants of these identified genes to assess their role in oxidative stress survival. Phenotypic screening of 109 isogenic deletion mutants identified 22 genes which were either hypersensitive or hyposensitive to oxidants, demonstrating important roles for these genes in oxidant defense. The significance of these genes in host colonization was also assessed in an in vivo chick model of C. jejuni colonization. Overall, our findings identify an indirect role for motility in resistance to oxidative stress. We found that a nonmotile flagellum mutant, the ΔmotAB mutant, displayed increased sensitivity to oxidants. Restoration of sensitivity to superoxide in the ΔmotAB mutant was achieved by fumarate supplementation or tandem deletion of motAB with ccoQ, suggesting that disruption of the proton gradient across the inner membrane resulted in increased superoxide production in this strain. Furthermore, we have identified genes involved in cation transport and binding, detoxification, and energy metabolism that are also important factors in oxidant defense. This report describes the first isogenic deletion mutant library construction for screening of relevant oxidative stress defense genes within C. jejuni, thus providing a comprehensive analysis of the total set of oxidative stress defenses.

Complete genome sequences of a Canadian strain of enteroaggregative Escherichia coli (EAEC) with multiple metals and antimicrobial resistance genes isolated from municipal waste-activated sludge.

Enteroaggregative Escherichia coli (EAEC) is an emerging food-borne pathogen causing acute or persistent diarrhea in humans. Here, we report the complete genome sequence of a strain of EAEC with multiple metals and antimicrobial resistance genes isolated from a waste-activated sludge collected from a Canadian municipal wastewater treatment plant.

Ammonia-assisted Ni particle preferential deposition in Ni-Fe pyrophosphates on iron foam to improve the catalytic performance for overall water splitting.

Designing efficient and cost-effective electrocatalysts for overall water splitting remains a major challenge in hydrogen production. Herein, ammonia was introduced to pyrophosphate chelating solution assisted Ni particles preferential plating on porous Fe substrate to form coral-like Ni/NiFe-Pyro electrode. The pyrophosphate with multiple complex sites can couple with nickel and iron ions to form an integrated network structure, which also consists of metallic nickel due to the introduction of ammonia. The large network structure in Ni/NiFe-Pyro significantly enhances the synergistic effect between nickel and iron and then improves the electrocatalytic performance. As a result, the coral-like Ni/NiFe-Pyro@IF exhibits good electrocatalytic activity and stability for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The electrolyzer assembled with Ni/NiFe-Pyro@IF as cathode and anode just needs a low water-splitting voltage of 1.54 V to obtain the current density of 10 mA cm-2. Meanwhile, the stability test of Ni/NiFe-Pyro@IF is performed at the current densities ranging from 10 to 400 mA cm-2 for 50 h without any significant decay, indicating robust catalytic stability for overall water splitting. This strategy for synthesizing metal/metal pyrophosphate composites may provide a new avenue for future studies of efficient bifunctional electrocatalysts.

Proteomic identification of Listeria monocytogenes surface-associated proteins.

This study aimed to identify proteins exposed on the surface of Listeria monocytogenes cells for diagnostic reagent development. Brief trypsin treatment of L. monocytogenes cells followed by peptide separation and identification by nano-LC and online-MS/MS was performed. In parallel, as a negative control, proteins secreted into the digest buffer as well as proteins from cell lysis were identified. One hundred and seventy-four proteins were identified in at least two of three trials in either the negative control or during cell digest. Nineteen surface, 21 extracellularly secreted, 132 cytoplasmic, and two phage proteins were identified. Immunofluorescence microscopy of L. monocytogenes cells revealed the surface localization of two potential candidates for L. monocytogenes isolation and detection: lipoprotein LMOf2365_0546 and PBPD1 (LMOf2365_2742). In this report, we present the first data set of surface-exposed L. monocytogenes proteins currently available. The data have been deposited to the ProteomeXchange Consortium with identifier PXD000035.

Improvement of capture efficacy of immunomagnetic beads for Campylobacter jejuni using reagents that alter its motility.

Previous studies using the immunomagnetic beads separation (IMS) technique have shown high detection limits of live campylobacters but low detection limits of formalin-killed campylobacters. The present study investigated if the addition of various concentrations of reagents that alter the motility of live Campylobacter jejuni could enhance the recovery of the organisms by IMS. The addition of 5% glycerol, 0.001% formalin, 10% polyethylene glycol, or 0.001% agarose in a buffer slowed down the movement of C. jejuni and increased the recovery of live C. jejuni, using beads coated with specific monoclonal antibodies (mAbs). The highest recovery yielded was 5.2- ± 3.3-fold with 5% glycerol at 10(5) colony-forming units (CFU)·mL(-1). The addition of 5% glycerol also improved isolation at lower concentrations of C. jejuni (10(2) to 10(4) CFU·mL(-1)) in buffer. The recovery by IMS of C. jejuni killed by 1% formalin was increased up to as high as 17-fold compared with the recovery of live organisms, as detected using a real-time polymerase chain reaction assay. The reagents investigated did not enhance the immunological reactivity of the mAbs to this organism. These results indicate that the addition of several reagents enhanced the capture of C. jejuni by IMS, which could be partially due to the slowing down of the movement or the altering of the motility of C. jejuni and to the increasing of the contact time between C. jejuni and immunomagnetic beads.

Complete Genome Sequence of a Canadian Strain of Escherichia coli with Multiple Metal and Antimicrobial Resistance Genes That Was Isolated from Municipal Biosolids.

This announcement reports the complete genome sequence of a non-Shiga toxin-producing Escherichia coli strain that was isolated from municipal biosolids collected from a Canadian wastewater treatment plant. This strain contains multiple metal, antimicrobial, and heat resistance genes, as determined by genome sequencing, and could be a useful bacterial model for future studies.

One-Pot Conversion of Cellulose into 2,5-Hexanedione in H2O-Tetrahydrofuran Co-Solvents.

Catalytic conversion of cellulose into the novel platform molecule 2,5-hexanedione (HXD) is regarded as one feasible approach for high-value utilization of biomass resources. Here, we reported one efficient way of one-pot conversion of cellulose into HXD with high yield of 80.3% in H2O and tetrahydrofuran (THF) mixture within Al2(SO4)3 combined with Pd/C as a catalyst. In the catalytic reaction system, Al2(SO4)3 could catalyze the conversion of cellulose into 5-hydroxymethylfurfural (HMF), and Pd/C combined with Al2(SO4)3 could catalyze the hydrogenolysis of HMF into furanic intermediates such as 5-methylfurfuryl alcohol and 2,5-dimethylfuran (DMF) without causing over-hydrogenation of these furanic intermediates. These furanic intermediates were finally transformed into HXD catalyzed by Al2(SO4)3. Besides, the H2O/THF ratio could significantly influence the reactivity of the hydrolytic furanic ring-opening of the furanic intermediates. The catalytic system also showed excellent performance on the conversion of other carbohydrates (glucose and sucrose) into HXD.

Stack effects in tall building fires: a case study of Taiwan old apartment fire.

Tainan, a city that prospered early in Taiwan, has a hot and humid atmosphere. Hence, the grilled doors in numerous old buildings for ventilation and lighting to conserve energy. This study analyzed a fire incident that occurred during the late night of March 17, 2019 in a 38-year-old dwelling, where three residents were severely covered with soot. The site investigation showed that eight staircases lead to the same basement, which apparently created a stack effect and a makeup air phenomenon. Numerical simulations have been performed in this study to reconstruct the fire scene, whose results were consistent with the actual fire scene. In particular, the results showed that some staircases in the fire were blackened by smoke, while others acted as makeup air inlets. The temperature at the households' doors on all floors of Staircase 2, which was closest to the fire, exceeded 60 °C after four minutes. Furthermore, two immediately feasible improvement strategies according to the control volume theory of fluid mechanics were proposed in this study. Firstly, changing the grilled doors in the basement to a closed flat door style could effectively prevent smoke from flowing up in the staircases. Secondly, residents may consider closing the windows of the stairs at night to improve fire safety. The results showed that the chimney effect can be significantly reduced. These improvements could be a reference for other old dwellings to enhance their fire safety.

Complete Genome Sequence of a Listeria monocytogenes Strain with Antimicrobial Resistance Genes Isolated from Lettuce in Canada.

Listeria monocytogenes, a Gram-positive, rod-shaped, non-spore-forming bacterium, is an important foodborne bacterial pathogen for humans worldwide. Here, we report the complete genome sequence of a Canadian Listeria monocytogenes strain with an antimicrobial resistance (AMR) gene that was isolated from lettuce.

Complete Genome Sequence of a Listeria monocytogenes Strain Isolated from Sprouts and Carrying an Antimicrobial Resistance Gene.

Listeria monocytogenes, a Gram-positive, rod-shaped, non-spore-forming bacterium, is an important foodborne bacterial pathogen for humans worldwide, with a high mortality rate. Here, we report the complete genome sequence of a Listeria monocytogenes strain with an antimicrobial resistance (AMR) gene, isolated from sprouts in Canada.

Complete Genome Sequences of Three Listeria monocytogenes Strains from Microgreens Obtained with MinION and MiSeq Sequencing.

Listeria monocytogenes is a Gram-positive, rod-shaped, non-spore-forming bacterium which is an important foodborne bacterial pathogen for human worldwide with 20-30% mortality. Here, we report circular complete genome sequences of three Listeria monocytogenes strains isolated from the samples of microgreens in Canada.

Complete Genome Sequence of a Listeria monocytogenes Strain from a Sample of Kale Salad.

Listeria monocytogenes is a Gram-positive, rod-shaped, non-spore-forming bacterium that is an important foodborne bacterial pathogen for humans worldwide, with high mortality rates. Here, we report the complete genome sequence of a Listeria monocytogenes strain that was isolated from kale salad in Canada.

Application of a High-Throughput Targeted Sequence AmpliSeq Procedure to Assess the Presence and Variants of Virulence Genes in Salmonella.

We have developed a targeted, amplicon-based next-generation sequencing method to detect and analyze 227 virulence genes (VG) of Salmonella (AmpliSeqSalm_227VG) for assessing the pathogenicity potential of Salmonella. The procedure was developed using 80 reference genomes representing 75 epidemiologically-relevant serovars associated with human salmonellosis. We applied the AmpliSeqSalm_227VG assay to (a) 35 previously characterized field strains of Salmonella consisting of serovars commonly incriminated in foodborne illnesses and (b) 34 Salmonella strains with undisclosed serological or virulence attributes, and were able to divide Salmonella VGs into two groups: core VGs and variable VGs. The commonest serovars causing foodborne illnesses such as Enteritidis, Typhimurium, Heidelberg and Newport had a high number of VGs (217-227). In contrast, serovars of subspecies not commonly associated with human illnesses, such as houtenae, arizonae and salame, tended to have fewer VGs (177-195). Variable VGs were not only infrequent but, when present, displayed considerable sequence variation: safC, sseL, sseD, sseE, ssaK and stdB showed the highest variation and were linked to strain pathogenicity. In a chicken infection model, VGs belonging to rfb and sse operons showed differences and were linked with pathogenicity. The high-throughput, targeted NGS-based AmpliSeqSalm_227VG procedure provided previously unknown information about variation in select virulence genes that can now be applied to a much larger population of Salmonella for evaluating pathogenicity of various serovars of Salmonella and for risk assessment of foodborne salmonellosis.