LygA retention on the surface of Listeria monocytogenes via its interaction with wall teichoic acid modulates bacterial homeostasis and virulence.

Wall teichoic acid (WTA) is the abundant cell wall-associated glycopolymer in Gram-positive bacteria, playing crucial roles in surface proteins retention, bacterial homeostasis, and virulence. The WTA glycosylation of Listeria monocytogenes is essential for surface anchoring of virulence factors, whereas the nature and function of the noncovalent interactions between cell wall-associated proteins and WTA are less unknown. In this study, we found that galactosylated WTA (Gal-WTA) of serovar (SV) 4h L. monocytogenes plays a key role in modulating the novel glycine-tryptophan (GW) domain-containing autolysin protein LygA through direct interactions. Gal-deficient WTA of Lm XYSN (ΔgalT) showed a dramatic reduction of LygA on the cell surface. We demonstrated that LygA binds to Gal-WTA through the GW domains, and the binding affinity is associated with the number of GW motifs. Moreover, we confirmed the direct Gal-dependent binding of the GW protein Auto from the type I WTA strain, which has no interaction with rhamnosylated WTA, indicating that the complexity of both WTA and GW proteins affect the coordination patterns. Importantly, we revealed the crucial roles of LygA in facilitating bacterial homeostasis as well as crossing the intestinal and blood-brain barriers. Altogether, our findings suggest that both the glycosylation patterns of WTA and a fixed numbers of GW domains are closely associated with the retention of LygA on the cell surface, which promotes the pathogenesis of L. monocytogenes within the host.

The haemagglutinin-neuraminidase protein of velogenic Newcastle disease virus enhances viral infection through NF-κB-mediated programmed cell death.

The haemagglutinin-neuraminidase (HN) protein, a vital membrane glycoprotein, plays a pivotal role in the pathogenesis of Newcastle disease virus (NDV). Previously, we demonstrated that a mutation in the HN protein is essential for the enhanced virulence of JS/7/05/Ch, a velogenic variant NDV strain originating from the mesogenic vaccine strain Mukteswar. Here, we explored the effects of the HN protein during viral infection in vitro using three viruses: JS/7/05/Ch, Mukteswar, and an HN-replacement chimeric NDV, JS/MukHN. Through microscopic observation, CCK-8, and LDH release assays, we demonstrated that compared with Mukteswar and JS/MukHN, JS/7/05/Ch intensified the cellular damage and mortality attributed to the mutant HN protein. Furthermore, JS/7/05/Ch induced greater levels of apoptosis, as evidenced by the activation of caspase-3/8/9. Moreover, JS/7/05/Ch promoted autophagy, leading to increased autophagosome formation and autophagic flux. Subsequent pharmacological experiments revealed that inhibition of apoptosis and autophagy significantly impacted virus replication and cell viability in the JS/7/05/Ch-infected group, whereas less significant effects were observed in the other two infected groups. Notably, the mutant HN protein enhanced JS/7/05/Ch-induced apoptosis and autophagy by suppressing NF-κB activation, while it mitigated the effects of NF-κB on NDV infection. Overall, our study offers novel insights into the mechanisms underlying the increased virulence of NDV and serves as a reference for the development of vaccines.

Development and evaluation of rapid and accurate one-tube RPA-CRISPR-Cas12b-based detection of mcr-1 and tet(X4).

The emergence and quick spread of the plasmid-mediated tigecycline resistance gene tet(X4) and colistin resistance gene mcr-1 have posed a great threat to public health and raised global concerns. It is imperative to develop rapid and accurate detection systems for the onsite surveillance of mcr-1 and tet(X4). In this study, we developed one-tube recombinase polymerase amplification (RPA) and CRISPR-Cas12b integrated mcr-1 and tet(X4) detection systems. We identified mcr-1- and tet(X4)-conserved and -specific protospacers through a comprehensive BLAST search based on the NCBI nt database and used them for assembling the detection systems. Our developed one-tube RPA-CRISPR-Cas12b-based detection systems enabled the specific detection of mcr-1 and tet(X4) with a sensitivity of 6.25 and 9 copies within a detection time of ~ 55 and ~ 40 min, respectively. The detection results using pork and associated environmental samples collected from retail markets demonstrated that our developed mcr-1 and tet(X4) detection systems could successfully monitor mcr-1 and tet(X4), respectively. Notably, mcr-1- and tet(X4)-positive strains were isolated from the positive samples, as revealed using the developed detection systems. Whole-genome sequencing of representative strains identified an mcr-1-carrying IncI2 plasmid and a tet(X4)-carrying IncFII plasmid, which are known as important vectors for mcr-1 and tet(X4) transmission, respectively. Taken together, our developed one-tube RPA-CRISPR-Cas12b-based mcr-1 and tet(X4) detection systems show promising potential for the onsite detection of mcr-1 and tet(X4). KEY POINTS: • One-tube RPA-CRISPR-Cas12b-based mcr-1 and tet(X4) detection systems were developed based on identified novel protospacers. • Both detection systems exhibited high sensitivity and specification with a sample-to-answer time of less than 1 h. • The detection systems show promising potential for onsite detection of mcr-1 and tet(X4).

Invited review: Role of Bacillus licheniformis in the dairy industry-Friends or foes?

Bacillus licheniformis is one of the major spore-forming bacteria with great genotypic diversity in raw milk, dairy ingredients, and final dairy products; it is found throughout the dairy-processing continuum. Although being widely used as a probiotic strain, this species also serves as a potential risk in the dairy industry based on its roles in foodborne illness and dairy spoilage. Biofilm formation of B. licheniformis, combined with the heat resistance of its spores, make it impossible to prevent the presence of B. licheniformis in final dairy products by using traditional cleaning and disinfection procedures. Despite the extensive efforts to identify B. licheniformis in various dairy samples, no reviews have been written on both hazards and benefits of this sporeformer. This review discusses the prevalence of B. licheniformis from raw milk to commercial dairy products, biofilm formation and spoilage potential of B. licheniformis, and possible prevention methods. In addition, the potential benefits of B. licheniformis in the dairy industry are also summarized.

Mobile Colistin Resistance and Plasmid-Mediated Quinolone Resistance Genes in Escherichia coli from China, 1993-2019.

Plasmid-mediated quinolone resistance (PMQR) genes and mobile colistin resistance (MCR) genes in Escherichia coli (E. coli) have been widely identified, which is considered a global threat to public health. In the present study, we conducted an analysis of MCR genes (mcr-1, mcr-2, mcr-3, mcr-4, and mcr-5) and PMQR genes [qnrA, qnrB, qnrC, qnrD, qnrE1, qnrVC, qnrS, aac(6')-Ib-cr, qepA, and oqxAB] in E. coli from China, 1993-2019. From the 3,663 E. coli isolates examined, 1,613 (44.0%) tested positive for PMQR genes, either individually or in combination. Meanwhile, 262 isolates (7.0%) carried the MCR genes. Minimum inhibitory concentration (MIC) analyses of 17 antibiotics for the MCR gene-carrying strains revealed universal multidrug resistance. Resistance to polymyxin varied between 4 µg/mL and 64 µg/mL, with MIC50 and MIC90 at 8 µg/mL and 16 µg/mL, respectively. In addition, fluctuations in the detection rates of these resistant genes correlated with the introduction of antibiotic policies, host origin, temporal trends, and geographical distribution. Continuous surveillance of PMQR and MCR variants in bacteria is required to implement control and prevention strategies.

Assessment of beneficial effects and identification of host adaptation-associated genes of Ligilactobacillus salivarius isolated from badgers.

BACKGROUND: Ligilactobacillus salivarius has been frequently isolated from the gut microbiota of humans and domesticated animals and has been studied as a candidate probiotic. Badger (Meles meles) is known as a "generalist" species that consumes complex foods and exhibits tolerance and resistance to certain pathogens, which can be partly attributed to the beneficial microbes such as L. salivarius in the gut microbiota. However, our understanding of the beneficial traits and genomic features of badger-originated L. salivarius remains elusive. RESULTS: In this study, nine L. salivarius strains were isolated from wild badgers' feces, one of which exhibited good probiotic properties. Complete genomes of the nine L. salivarius strains were generated, and comparative genomic analysis was performed with the publicly available complete genomes of L. salivarius obtained from humans and domesticated animals. The strains originating from badgers harbored a larger genome, a higher number of protein-coding sequences, and functionally annotated genes than those originating from humans and chickens. The pan-genome phylogenetic tree demonstrated that the strains originating from badgers formed a separate clade, and totally 412 gene families (12.6% of the total gene families in the pan-genome) were identified as genes gained by the last common ancestor of the badger group. The badger group harbored significantly more gene families responsible for the degradation of complex carbohydrate substrates and production of polysaccharides than strains from other hosts; many of these were acquired by gene gain events. CONCLUSIONS: A candidate probiotic and nine L. salivarius complete genomes were obtained from the badgers' gut microbiome, and several beneficial genes were identified to be specifically present in the badger-originated strains that were gained in the evolution. Our study provides novel insights into the adaptation of L. salivarius to the intestinal habitat of wild badgers and provides valuable strain and genome resources for the development of L. salivarius as a probiotic.

Activation dynamics of antigen presenting cells in vivo against Mycobacterium bovis BCG in different immunized route.

BACKGROUND: Control of Tuberculosis (TB) infection is mainly the result of productive teamwork between T-cell populations and antigen presenting cells (APCs). However, APCs activation at the site of initiating cellular immune response during BCG early infection is not completely understood. METHODS: In this study, we injected C57BL/6 mice in intravenous (i.v) or subcutaneous (s.c) route, then splenic or inguinal lymph node (LN) DCs and MΦs were sorted, and mycobacteria uptake, cytokine production, antigen presentation activity, and cell phenotype were investigated and compared, respectively. RESULTS: Ag85A-specific T-cell immune response began at 6 days post BCG infection, when BCG was delivered in s.c route, Th17 immune response could be induced in inguinal LN. BCG could induce high level of activation phenotype in inguinal LN MΦs, while the MHC II presentation of mycobacteria-derived peptides by DCs was more efficient than MΦs. CONCLUSIONS: The results showed that BCG immunized route can decide the main tissue of T-cell immune response. Compared with s.c injected route, APCs undergo more rapid cell activation in spleen post BCG i.v infection.

Isolation and genomic characterization of Vmp-1 using Vibrio mimicus as the host: A novel virulent bacteriophage capable of cross-species lysis against three Vibrio spp.

Vibrio mimicus is a zoonotic pathogen that is widely distributed in aquatic habitats/environments (marine coastal water, estuaries, etc). The development of biocontrol agents for V. mimicus is imperative for the prevention and control of aquatic animal diseases and human food-borne infections. In this study, a broad-spectrum bacteriophage Vmp-1 was isolated from dealt aquatic product in a local market by double-layer agar plate method using V. mimicus CICC21613 as the host bacteria. Results indicated that Vmp-1, which belongs to the family Podoviridae, showed good pH tolerance (pH 3.0-12.0) and thermal stability (30-50 °C). The optimal multiplicity of infection (MOI) of Vmp-1 was 0.001 for a 20-min incubation and 100-min lysis period. Vmp-1 effectively controlled V. mimicus CICC21613 in LBS model (MOI = 0.0001, 0.001, 0.01, 0.1, 1) within 8 h. The full length of the Vmp-1 genome was 43,312 bp, with average GC content of 49.5%, and a total of 44 protein-coding regions. This study provides a novel phage strain that has the highest homology with vB_VpP_HA5 (GenBank: OK585159.1, 95.96%) for the development of biocontrol agents for V. mimicus.

A live attenuated DIVA vaccine affords protection against Listeria monocytogenes challenge in sheep.

Listeria monocytogenes (Lm) is a deadly foodborne pathogen that comprises 14 serotypes, among which, serotype 4b Lm is the primary cause of listeriosis outbreaks in humans and animals. Here, we evaluated the safety, immunogenicity, and protective efficacy of a serotype 4b vaccine candidate Lm NTSNΔactA/plcB/orfX in sheep. The infection dynamics, clinical features, and pathological observation verified that the triple genes deletion strain has adequate safety for sheep. Moreover, NTSNΔactA/plcB/orfX significantly stimulated humoral immune response and provided 78% immune protection to sheep against lethal wild-type strain challenge. Notably, the attenuated vaccine candidate could differentiate infected and vaccinated animals (DIVA) via serology determination of the antibody against listeriolysin O (LLO, encoded by hly) and phosphatidylinositol-specific phospholipase C (PI-PLC, encoded by plcB). These data suggest that the serotype 4b vaccine candidate has high efficacy, safety, and DIVA characteristics, and may be used to prevent Lm infection in sheep. Our study provides a theoretical basis for its future application in livestock and poultry breeding.

First Detection of blaNDM-1-Haboring IncHI2 Plasmid in Escherichia coli Strain Isolated from Goose in China.

Carbapenem-resistant Enterobacteriaceae infections are among the most serious threats to human and animal health worldwide. Of the 1013 strains of Escherichia coli isolated and identified in 14 regions of China from 2007 to 2018, seven strains were resistant to meropenem and all were positive for blaNDM. The seven New Delhi metallo-ß-lactamase (NDM)-positive strains belonged to five different sequence types, indicating that most of the NDM-positive strains were nonclonal. An IncHI2 plasmid carrying the blaNDM-1 element was identified in the C1147 strain from a goose source and reported for the first time, showing a specific structure. Conjugation experiments revealed that the IncHI2 plasmid was conjugatable, and the horizontal propagation of the plasmid led to the rapid propagation of NDM in the same and different strains. This study revealed that waterfowl, as a potential transmission factor for carbapenem-resistant blaNDM-1, poses a threat to human health.

Comparision of biological and genomic characteristics of five virulent bacteriophages against Enterobacter hormaechei.

Enterobacter hormaechei is a zoonotic bacteria that may cause respiratory diseases in animals and neonatal sepsis in humans. Bacteriophages are increasingly considered as potential biocontrol agents to control pathogens in the food industry. In this study, five E. hormaechei virulent phages, named as Ehp-YZU08, Ehp-YZU10, Ehp-YZU9-1, Ehp-YZU9-2 and Ehp-YZU9-3, were isolated from sewage in China and analyzed for their biological and whole-genome characteristics, and a comparative genomic analysis was performed to study the functional genes and phylogenetic evolution of phages. The results showed that four of the phage strains belong to the Podoviridae family and one belongs to the Myoviridae family. The burst sizes were 70-283 PFU/cell after a latent period of 5-40 min. Phages were able to survive in a pH range of 5-10 and resist temperatures up to 60 °C for 60 min. The sequencing results showed that the full length of the genomes of the five phages ranged from 39,502 to 173,418 bp. Each phage contained multiple genes related to phage replication, and genes related to bacterial virulence or drug resistance were not found. The five phages belonged to three different groups by a construction of a phylogenetic tree, and the significant genetic evolutionary distance from each E. hormaechei phage was observed. The inhibition assay showed that all five phages could completely inhibit the growth of E. hormaechei at 37 °C within 8 h, suggesting that the phages in this study have great potential for the development of biocontrol agents against E. hormaechei in the food industry.

A balanced gut microbiota is essential to maintain health in captive sika deer.

Certain animals harbor a high proportion of pathogens, particular the zoonotic pathogens, in their gut microbiome but are usually asymptomic; however, their carried pathogens may seriously threaten the public health. By understanding how the microbiome overcomes the negative effects of pathogens to maintain host health, we can develop novel solutions to control animal-mediated pathogen transmission including identification and application of beneficial microbes. Here, we analyzed the gut microbiota of 10 asymptomic captive sika deer individuals by full-length 16S rDNA sequencing. Twenty-nine known pathogens capable of infecting humans were identified, and the accumulated proportions of the identified pathogens were highly variable among individuals (2.33 to 39.94%). The relative abundances of several beneficial bacteria, including Lactobacillus and Bifidobacterium, were found to be positively correlated with the relative abundances of accumulated pathogens. Whole-genome metagenomic analysis revealed that the beneficial- and pathogenic-associated functions, such as genes involved in the synthesis of short chain fatty acids and virulence factors, were also positively correlated in the microbiome, indicating that the beneficial and pathogenic functions were maintained at a relatively balanced ratio. Furthermore, the bacteriophages that target the identified pathogens were found to be positively correlated with the pathogenic content in the microbiome. Several high-quality genomes of beneficial bacteria affiliated with Lactobacillus and Bifidobacterium and bacteriophages were recovered from the metagenomic data. Overall, this study provides novel insights into the interplay between beneficial and pathogenic content to ensure maintenance of a healthy gut microbiome, and also contributes to discovery of novel beneficial microbes and functions that control pathogens. KEY POINTS: • Certain asymptomic captive sika deer individuals harbor relatively high amounts of zoonotic pathogens. • The beneficial microbes and the beneficial functions are balanced with the pathogenic contents in the gut microbiome. • Several high-quality genomes of beneficial bacteria and bacteriophages are recovered by metagenomics.

Salmonella Typhimurium ST34 Isolate Was More Resistant than the ST19 Isolate in China, 2007 - 2019.

To disclose the antimicrobial susceptibility and wide adaptability of commonly occurring genotypes of Salmonella enterica serovar Typhimurium, the antimicrobial resistance and multilocus sequence typing (MLST) profiles of 196 Salmonella Typhimurium isolates (136 from food-producing animals, 19 from environments, 15 from markets, and 26 from humans) in China between 2007 and 2019 were analyzed. Tests of susceptibility to 19 antimicrobial agents using the broth microdilution method showed that 84.7% of the isolates were resistant to at least one antimicrobial. Antimicrobial susceptibility analysis demonstrated that 66.8% of the isolates were multidrug-resistant (MDR) strains, with resistance to three or more antimicrobials. The highest antidrug resistance was to ampicillin, amoxicillin/clavulanic acid, and tetracycline. Three MLST types were detected, and sequence type (ST) 19 was the most common ST. However, ST34 was associated with a higher MDR rate and more complex MDR patterns, than ST19 and ST99, although the exact mechanism has not been reported. Our study highlights the variation of drug resistance and STs from different sources and the association between STs and drug resistance, providing useful information for epidemiological research and developing a public health strategy.

Isolation and genomic characterization of P.A-5, a novel virulent bacteriophage against Enterobacter hormaechei.

Enterobacter hormaechei is a foodborne pathogen responsible for neonatal sepsis in humans and respiratory disease in animals. In this work, a new virulent phage (P.A-5) infecting E. hormaechei was isolated from domestic sewage samples and characterized. Transmission electron microscopy revealed that P.A-5 belonged to the family Myoviridae having a head size of 77.53 nm and a tail length of 72.24 nm. The burst size was 262 PFU/cell after a latent period of 20 min. Phage P.A-5 was able to survive in a pH range of 4-9 and resist temperatures up to 55 °C for 60 min. The genome sequence of P.A-5 had homology most similar to that of Shigellae phage MK-13 (GenBank: MK509462.1). Pork artificially contaminated with E. hormaechei was used as a model to evaluate the potential of P.A-5. The results clearly showed that P.A-5 treatment can completely inhibit E. hormaechei growth in pork within 8 h, indicating the potential use of P.A-5 as a biocontrol agent for E. hormaechei.

Isolation of virulent phages infecting dominant mesophilic aerobic bacteria in cucumber pickle fermentation.

Pickle is a type of mildly lactic acid fermented vegetable and is a traditional dish favored in China, Japan, and Korea. Corruption of spoilage bacteria and accumulation of nitrite during vegetable fermentation are common problems that affect the pickle industry and consumer health. In this work, cucumber juice was used as a vegetable model to study the dominant mesophilic aerobic bacteria (MAB) producing nitrite during pickle fermentation. Virulent phages infecting the dominant MABs combined with Lactobacillus plantarum M6 were used to control these bacteria. Enterobacter cloacae and Pseudomonas fluorescens are the dominant MABs in the fermentation of cucumber juice containing 4% or 8% NaCl, with isolation percentages reaching 30.6% and 23.1%, respectively. Virulent phages PspYZU5415 and EcpYZU01 were isolated using P. fluorescens J5415 and E. cloacae J01 as the host bacteria, respectively. These two phages show a broad host range and strong lytic activity, and their genomes contain no toxins and antibiotic resistance genes. PspYZU5415 and EcpYZU01 were combined into a cocktail (designated as Phage MIX) that effectively inhibits the growth of E. cloacae and P. fluorescens in cucumber juice with different salt concentrations. PhageMIX combined with L. plantarum M6 decreased the counts of P. mendocina and E. cloacae to undetectable levels at 48 h during the fermentation of cucumber juice artificially contaminated with P. mendocina and E. cloacae. In addition, nitrite content increased to 11.3 mg/L at 20 h and then degraded completely at 36 h. By contrast, P. mendocina and E. cloacae remained in the groups without PhageMIX during fermentation (0-48 h). Nitrite content rapidly increased to 65.7 mg/L at 12 h and then decreased to 21.6 mg/L at 48 h in the control group. This study suggests that PhageMIX combined with lactic acid bacterial strains can be used as an ecological starter for controlling the dominant MABs P. mendocina and E. cloacae and for reducing nitrate production during the early stage of pickle fermentation.

Epidemiology of Human Listeriosis in China During 2008-2017.

Listeria monocytogenes is a facultative, intracellular foodborne pathogen that causes listeriosis and is prevalent worldwide. However, our knowledge of this bacterium and the listeriosis it causes is still extremely limited until now. Therefore, this retrospective study of patients in mainland China over 10 years (2008-2017) was performed to better understand the demographic trends and clinical features of listeriosis in China. Both electronic and manual retrieval systems were used to collect the relevant literature on listeriosis in mainland China. A total of 759 cases were reported from 22 provinces. Among the clinical cases, septicemia was the most common presentation (49%), followed by central nervous system infection (25%). The overall case fatality rate was 18%, with a higher rate among neonatal patients (73%). In recent years, listeriosis has been reported annually and even peaked in 2014. The median age of nonperinatal cases was 36 years (range, 0-102), with a predominance of male cases (52%). Sporadic cases were frequent from March to May. Efforts to prevent and control the spread of listeriosis are required through further research and collaborative efforts to improve the capacities of clinical diagnosis and treatment.

Multidrug-Resistant Escherichia coli Strain Isolated from Swine in China Harbors mcr-3.1 on a Plasmid of the IncX1 Type That Cotransfers with mcr-1.1.

An Escherichia coli strain isolated from the feces of swine at a pork slaughterhouse in Henan province China was found to possess two colistin-resistance genes, mcr-1 and mcr-3, plus 16 additional resistance genes. Genes mcr-1.1 and mcr-3.1 were identified on IncHI2 and IncX1 type plasmids, respectively. Transconjugants (containing mcr-3, mcr-1&mcr-3) were obtained that were 64- and 512-fold higher than the minimum inhibitory concentration of colistin on the recipient bacteria (E. coli C600), respectively. The IncX1 plasmid containing mcr-3.1 displayed a very specific structure compared with previous mcr-3. Variable and stable regions were similar across different plasmids, multiple insertion sequences and transposases.

Genetic Diversity of Listeria monocytogenes Isolates from Invasive Listeriosis in China.

Listeria monocytogenes is a deadly foodborne pathogen, and infections can result in meningoencephalitis and sepsis with mortality rates of up to 30%. In this study, we performed comparative whole-genome analysis of 30 clinical isolates sequenced together with 32 previously sequenced clinical and food isolates from China. The data indicate that L. monocytogenes isolates belonging to the clonal complexes (CC) -1, -8, -9, -87, -121, and -155 are present in human clinical cases. The majority of isolates are from CC-87, 9, and 8 and overlap with those CCs previously reported on the basis of multilocus sequence typing for isolates from Chinese food products. Detailed genome analysis of isolates, representative of CCs in clinical and food products, revealed strong similarities both in their core- and accessory genomes indicating that they are highly related. When compared to genome sequences of isolates of a given CC worldwide, clinical isolates of China were distinct and clustered in unified clades. Our data indicate that epidemic clones of L. monocytogenes (CC-87, 9, and 8) with unusually high occurrence of plasmids are unique to China and suggest that common populations of L. monocytogenes clones are present in both clinical and food products in China.

MoS2 decorated nanocomposite: Fe2O3@MoS2 inhibits the conjugative transfer of antibiotic resistance genes.

Nanomaterials of Al2O3 and TiO2 have been proved to promote the spread of antibiotic resistance genes (ARGs) by horizontal gene transfer. In this work, we found that Fe2O3@MoS2 nanocomposite inhibited the horizontal gene transfer (HGT) by inhibiting the conjugative transfer mediated by RP4-7 plasmid. To discover the mechanism of Fe2O3@MoS2 inhibiting HGT, the bacterial cells were collected under the optimal mating conditions. The collected bacterial cells were used for analyzing the expression levels of genes unique to the plasmid and the bacterial chromosome in the conjugation system by qPCR. The results of genes expression demonstrated that the mechanism of Fe2O3@MoS2 inhibited conjugation by promoting the expression of global regulatory gene (trbA) and inhibiting the expression of conjugative transfer genes involved in mating pair formation (traF, trbB) and DNA replication (trfA). The risk assessment of Fe2O3@MoS2 showed that it had very low toxicity to organisms. The findings of this paper showed that Fe2O3@MoS2, as an inhibitor of horizontal gene transfer, is an environment-friendly material.

Insights into the impact of flhF inactivation on Campylobacter jejuni colonization of chick and mice gut.

BACKGROUND: Campylobacter jejuni (C. jejuni) is a leading cause of foodborne gastroenteritis worldwide. This bacterium lacks many of the classical virulence factors, and flagellum-associated persistent colonization has been shown to be crucial for its pathogenesis. The flagellum plays a multifunctional role in C. jejuni pathogenesis, and different flagellar elements make diverse contributions. The flhF gene encodes the flagellar biosynthesis regulator, which is important for flagellar biosynthesis. In this study, the influence of flhF on C. jejuni colonization was systematically studied, and the possible mechanisms were also analyzed. RESULTS: The flhF gene has a significant influence on C. jejuni colonization, and its inactivation resulted in severe defects in the commensal colonization of chicks, with approximately 104- to 107-fold reductions (for NCTC 11168 and a C. jejuni isolate respectively) observed in the bacterial caecal loads. Similar effects were observed in mice where the flhF mutant strain completely lost the ability to continuously colonize mice, which cleared the isolate at 7 days post inoculation. Characterization of the phenotypic properties of C. jejuni that influence colonization showed that the adhesion and invasion abilities of the C. jejuni flhF mutant were reduced to approximately 52 and 27% of that of the wild-type strain, respectively. The autoagglutination and biofilm-formation abilities of the flhF mutant strain were also significantly decreased. Further genetic investigation revealed that flhF is continuously upregulated during the infection process, which indicates a close association of this gene with C. jejuni pathogenesis. The transcription of some other infection-related genes that are not directly involved in flagellar assembly were also influenced by its inactivation, with the flagellar coexpressed determinants (Feds) being apparently affected. CONCLUSIONS: Inactivation of flhF has a significant influence on C. jejuni colonization in both birds and mammals. This defect may be caused by the decreased adhesion, invasion, autoagglutination and biofilm-formation abilities of the flhF mutant strain, as well as the influence on the transcription of other infection related genes, which provides insights into this virulence factor and the flagellum mediated co-regulation of C. jejuni pathogenesis.