Identification of potential Campylobacter jejuni genes involved in biofilm formation by EZ-Tn5 Transposome mutagenesis

Association between ability to form biofilm and virulence factors of poultry extra-intestinal Campylobacter jejuni and Campylobacter coli

Campylobacter species are known to be able to produce biofilm, which represents an ideal protective environment for the maintenance of such fragile bacteria. Since the genetic mechanisms promoting biofilm formation are still poorly understood, in this study we assessed the ability of C. jejuni (n = 7) and C. coli (n = 3) strains isolated from diseased poultry, and previously characterized by whole genome sequencing, to form biofilm. The in vitro analyses were carried out by using a microtiter based protocol including biofilm culturing and fixation, staining with crystal violet, and measurement of the optical density (OD₅₇₀). The ability to form biofilm was categorized into four classes (no, weak, moderate, and strong producers). Potential correlations between OD₅₇₀ and the presence/absence of virulence determinants were examined. The C. jejuni were classified as no (n = 3), weak (n = 2), and moderate (n = 2) biofilm producers; however, all possessed genes involved in chemotaxis, adhesion, and invasion to the host cells. No genes present exclusively in biofilm producers or in non-biofilm producers were identified. All C. coli were classified as weak producers and showed a similar set of virulence genes between each other. A trend of increased mean OD₅₇₀ was observed in the presence of flaA and maf7 genes. No association between biofilm production classes and the explanatory variables considered was observed. The results of this study suggest that further investigations are needed to better identify and characterize the genetic determinants involved in extra-intestinal Campylobacter biofilm formation.

Impact of Bacillus subtilis Antibiotic Bacilysin and Campylobacter jejuni Efflux Pumps on Pathogen Survival in Mixed Biofilms

The foodborne pathogen Campylobacter jejuni is typically found in an agricultural environment; in animals, such as birds, as an intestinal commensal; and also in food products, especially fresh poultry meat. Campylobacter interactions within mixed species biofilms are poorly understood, especially at the microscale. We have recently shown that the beneficial bacterium Bacillus subtilis reduces C. jejuni survival and biofilm formation in coculture by secreting the antibiotic bacillaene. We extend these studies here by providing evidence that besides bacillaene, the antagonistic effect of B. subtilis involves a nonribosomal peptide bacilysin and that the fully functional antagonism depends on the quorum-sensing transcriptional regulator ComA. Using confocal laser scanning microscopy, we also show that secreted antibiotics influence the distribution of C. jejuni and B. subtilis cells in the submerged biofilm and decrease the thickness of the pathogen's biofilm. Furthermore, we demonstrate that genes encoding structural or regulatory proteins of the efflux apparatus system (cmeF and cmeR), respectively, contribute to the survival of C. jejuni during interaction with B. subtilis PS-216. In conclusion, this study demonstrates a strong potential of B. subtilis PS-216 to reduce C. jejuni biofilm growth, which supports the application of the PS-216 strain to pathogen biofilm control. IMPORTANCE Campylobacter jejuni is a prevalent cause of foodborne infections worldwide, while Bacillus subtilis as a potential probiotic represents an alternative strategy to control this alimentary infection. However, only limited literature exists on the specific mechanisms that shape interactions between B. subtilis and C. jejuni in biofilms. This study shows that in the two species biofilms, B. subtilis produces two antibiotics, bacillaene and bacilysin, that inhibit C. jejuni growth. In addition, we provide the first evidence that specific pathogen efflux pumps contribute to the defense against B. subtilis attack. Specifically, the CmeDEF pump acts during the defense against bacilysin, while CmeR-dependent overexpression of CmeABC nullifies the bacillaene attack. The role of specific B. subtilis antibiotics and these polyspecific pumps, known for providing resistance against medically relevant antibiotics, has not been studied during bacterial competition in biofilms before. Hence, this work broadens our understanding of mechanisms that shape antagonisms and defense during probiotic-pathogen interactions.

Assessment of biofilm formation by Campylobacter spp. isolates mimicking poultry slaughterhouse conditions

This research aimed to assess the biofilm formation ability of Campylobacter strains under temperature and oxygen stress conditions, similar to those found in the industrial environment, to explain the persistence of this pathogen on the poultry slaughter line. A collection of C. jejuni and C. coli isolates (n = 143) obtained from poultry samples (cecal content and neck skin), collected at slaughterhouse level, from diverse flocks, on different working days, was genotyped by flaA-restriction fragment length polymorphism (RFLP) typing method. A clustering analysis resulted in the assignment of 10 main clusters, from which 15 strains with different flaA-RFLP genotypes were selected for the assessment of biofilm formation ability and antimicrobial susceptibility. Biofilm assays, performed by crystal violet staining method, were conducted with the goal of mimicking some conditions present at the slaughterhouse environment, based on temperature, atmosphere, and contamination levels. Results indicated that many C. jejuni strains with similar flaA-RFLP profiles were present at the slaughterhouse on different processing days. All the strains tested (n = 15) were multidrug-resistant except for one. Biofilm formation ability was strain-dependent, and it appeared to have been affected by inoculum concentration, temperature, and tolerance to oxygen levels. At 10°C, adherence levels were significantly lower than at 42°C. Under microaerobic and aerobic atmospheres, at 42°C, 3 strains (C. jejuni 46E, C. jejuni 61C, and C. coli 65B) stood out, exhibiting significant levels of biofilm formation. C. jejuni strains 46E and 61C were inserted in clusters with evidence of persistence at the slaughterhouse for a long period of time. This study demonstrated that Campylobacter strains from broilers are capable of forming biofilms under conditions resembling the slaughterhouse environment. These results should be seen as a cue to improve the programs of hygiene implemented, particularly in those zones that can promote biofilm formation.

Antibiotic Resistance in the Alternative Lifestyles of Campylobacter jejuni

Campylobacter jejuni is the main pathogen identified in cases of foodborne gastroenteritis worldwide. Its importance in poultry production and public health is highlighted due to the growing antimicrobial resistance. Our study comparatively investigated the effect of five different classes of antimicrobials on the planktonic and biofilm forms of 35 strains of C. jejuni with high phylogenetic distinction in 30 of them. In the planktonic form, the existence of susceptible strains to colistin (7/35 - 20%) and resistance to meropenem (3/35 - 8.6%) represent a novelty in strains evaluated in Brazil. In biofilms formed with the addition of chicken juice, the number of resistant strains was significantly higher for colistin, erythromycin and meropenem (100%), but the susceptibility to tetracycline was shown as a control strategy for specific cases. High concentrations (1,060 ± 172.1mg/L) of antibiotics were necessary to control the biofilm structure in susceptible strains in the planktonic form, which is consistent with the high biomass produced in these strains. Stainless steel and polyurethane were the most (BFI=2.1) and least (BFI=1.6) favorable surfaces for the production of biomass treated with antimicrobials. It is concluded that the antimicrobial action was detected for all tested drugs in planktonic form. In sessile forms, the biomass production was intensified, except for tetracycline, which showed an antibiofilm effect.

Molecular Mechanisms of Campylobacter Biofilm Formation and Quorum Sensing

Even though Campylobacter spp. are known to be fastidious organisms, they can survive within the natural environment. One mechanism to withstand unfavourable conditions is the formation of biofilms, a multicellular structure composed of different bacterial and other microbial species which are embedded in an extracellular matrix. High oxygen levels, low substrate concentrations and the presence of external DNA stimulate the biofilm formation by C. jejuni. These external factors trigger internal adaptation processes, e.g. via regulating the expression of genes encoding proteins required for surface structure formation, as well as motility, stress response and antimicrobial resistance. Known genes impacting biofilm formation will be summarized in this review. The formation of biofilms as well as the expression of virulence genes is often regulated in a cell density depending manner by quorum sensing, which is mediated via small signalling molecules termed autoinducers. Even though quorum sensing mechanisms of other bacteria are well understood, knowledge on the role of these mechanisms in C. jejuni biofilm formation is still scarce. The LuxS enzyme involved in generation of autoinducer-2 is present in C. jejuni, but autoinducer receptors have not been identified so far. Phenotypes of C. jejuni strains lacking a functional luxS like reduced growth, motility, oxygen stress tolerance, biofilm formation, adhesion, invasion and colonization are also summarized within this chapter. However, these phenotypes are highly variable in distinct C. jejuni strains and depend on the culture conditions applied.

Comparative Genomics of the Transport Proteins of Ten Lactobacillus Strains

The genus Lactobacillus includes species that may inhabit different anatomical locations in the human body, but the greatest percentage of its species are inhabitants of the gut. Lactobacilli are well known for their probiotic characteristics, although some species may become pathogenic and exert negative effects on human health. The transportome of an organism consists of the sum of the transport proteins encoded within its genome, and studies on the transportome help in the understanding of the various physiological processes taking place in the cell. In this communication we analyze the transport proteins and predict probable substrate specificities of ten Lactobacillus strains. Six of these strains (L. brevis, L. bulgaricus, L. crispatus, L. gasseri, L. reuteri, and L. ruminis) are currently believed to be only probiotic (OP). The remaining four strains (L. acidophilus, L. paracasei, L. planatarum, and L. rhamnosus) can play dual roles, being both probiotic and pathogenic (PAP). The characteristics of the transport systems found in these bacteria were compared with strains (E. coli, Salmonella, and Bacteroides) from our previous studies. Overall, the ten lactobacilli contain high numbers of amino acid transporters, but the PAP strains contain higher number of sugar, amino acid and peptide transporters as well as drug exporters than their OP counterparts. Moreover, some of the OP strains contain pore-forming toxins and drug exporters similar to those of the PAP strains, thus indicative of yet unrecognized pathogenic potential. The transportomes of the lactobacilli seem to be finely tuned according to the extracellular and probiotic lifestyles of these organisms. Taken together, the results of this study help to reveal the physiological and pathogenic potential of common prokaryotic residents in the human body.

Identification of Genes Involved in Antifungal Activity of Burkholderia seminalis Against Rhizoctonia solani Using Tn5 Transposon Mutation Method

Rhizoctonia solani is the causative agent of rice sheath blight disease. In a previous study, we found that the growth of R. solani was inhibited by Burkholderia seminalis strain R456. Therefore, the present study was conducted to identify the genes involved in the antifungal activity of B. seminalis strain R456 by using a Tn5 transposon mutation method. Firstly, we constructed a random insertion transposon library of 997 mutants, out of which 11 mutants showed the defective antifungal activity against R. solani. Furthermore, the 10 antagonism-related genes were successfully identified based on analysis of the Tn5 transposon insertion site. Indeed, this result indicated that three mutants were inserted on an indigenous plasmid in which the same insertion site was observed in two mutants. In addition, the remaining eight mutants were inserted on different genes encoding glycosyl transferase, histone H1, nonribosomal peptide synthetase, methyltransferase, MnmG, sulfate export transporter, catalase/peroxidase HPI and CysD, respectively. Compared to the wild type, the 11 mutants showed a differential effect in bacteriological characteristics such as cell growth, biofilm formation and response to H₂O₂ stress, revealing the complexity of action mode of these antagonism-related genes. However, a significant reduction of cell motility was observed in the 11 mutants compared to the wild type. Therefore, it can be inferred that the antifungal mechanism of the 10 above-mentioned genes may be, at least partially, due to the weakness of cell motility. Overall, the result of this study will be helpful for us to understand the biocontrol mechanism of this bacterium.

Comparative genomics of transport proteins in seven Bacteroides species

The communities of beneficial bacteria that live in our intestines, the gut microbiome, are important for the development and function of the immune system. Bacteroides species make up a significant fraction of the human gut microbiome, and can be probiotic and pathogenic, depending upon various genetic and environmental factors. These can cause disease conditions such as intra-abdominal sepsis, appendicitis, bacteremia, endocarditis, pericarditis, skin infections, brain abscesses and meningitis. In this study, we identify the transport systems and predict their substrates within seven Bacteroides species, all shown to be probiotic; however, four of them (B. thetaiotaomicron, B. vulgatus, B. ovatus, B. fragilis) can be pathogenic (probiotic and pathogenic; PAP), while B. cellulosilyticus, B. salanitronis and B. dorei are believed to play only probiotic roles (only probiotic; OP). The transport system characteristics of the four PAP and three OP strains were identified and tabulated, and results were compared among the seven strains, and with E. coli and Salmonella strains. The Bacteroides strains studied contain similarities and differences in the numbers and types of transport proteins tabulated, but both OP and PAP strains contain similar outer membrane carbohydrate receptors, pore-forming toxins and protein secretion systems, the similarities were noteworthy, but these Bacteroides strains showed striking differences with probiotic and pathogenic enteric bacteria, particularly with respect to their high affinity outer membrane receptors and auxiliary proteins involved in complex carbohydrate utilization. The results reveal striking similarities between the PAP and OP species of Bacteroides, and suggest that OP species may possess currently unrecognized pathogenic potential.

The Involvement of the Cas9 Gene in Virulence of Campylobacter jejuni

Campylobacter jejuni is considered as the leading cause of gastroenteritis all over the world. This bacterium has the CRISPR–cas9 system, which is used as a gene editing technique in different organisms. However, its role in bacterial virulence has just been discovered; that discovery, however, is just the tip of the iceberg. The purpose of this study is to find out the relationship between cas9 and virulence both phenotypically and genotypically in C. jejuni NCTC11168. Understanding both aspects of this relationship allows for a much deeper understanding of the mechanism of bacterial pathogenesis. The present study determined virulence in wild and mutant strains by observing biofilm formation, motility, adhesion and invasion, intracellular survivability, and cytotoxin production, followed by the transcriptomic analysis of both strains. The comparative gene expression profile of wild and mutant strains was determined on the basis of De-Seq transcriptomic analysis, which showed that the cas9 gene is involved in enhancing virulence. Differential gene expression analysis revealed that multiple pathways were involved in virulence, regulated by the CRISPR-cas9 system. Our findings help in understanding the potential role of cas9 in regulating the other virulence associated genes in C. jejuni NCTC11168. The findings of this study provide critical information about cas9's potential involvement in enhancing the virulence of C. jejuni, which is a major public health threat.

Genotypic diversity, antimicrobial resistance and biofilm-forming abilities of Campylobacter isolated from chicken in Central China

Background

Campylobacter is considered to be the leading cause of human bacterial gastroenteritis, of which poultry is the main reservoir. Campylobacter contaminated chicken products are a major cause of human Campylobacter infection. In this study, the prevalence of Campylobacter in chicken in central China was investigated, and the genotypic diversity, antimicrobial resistance and biofilm of these isolates were characterized.

Results

A total of 206 Campylobacter isolates, including 166 C. jejuni and 40 C. coli, were isolated from chicken farms and live poultry markets in central China. Multilocus sequence typing and phylogenetic analysis showed that the Campylobacter isolates had diverse genetic backgrounds, which covered most of the dominant clone complexes (CCs) reported throughout China. The most prevalent CCs were CC-464, CC-1150, CC-353, and CC-828. All the isolates showed resistance to norfloxacin, ciprofloxacin and Cefazolin, and a prevalent resistance to fluoroquinolones, β-lactams and tetracyclines was also observed. Among all the isolates, 133 strains showed the ability to form biofilm, thereinto, the isolates in two genetic branches, mainly including CC-21, CC-48, CC-677 and CC-45, showed a significantly lower ability to form biofilm than other genetic branches (p < 0.05). However, in general, the ability to form biofilm varied among different genetic branches, suggesting a complex genetic background to biofilm formation, but not only the genetic lineages. Compared with the strains unable to form biofilm, biofilm-producing strains possessed a significantly higher resistance to ampicillin, neomycin, sulfamethoxazole, amikacin, clindamycin and erythromycin (p < 0.05).

Conclusions

To the best of our knowledge, this is the first report on the relationship of the genotypic diversity, antimicrobial resistance and biofilm-forming abilities of Campylobacter isolated from chicken in Central China, which showed the potential importance of biofilm in antimicrobial resistance. This study will help us better understand the epidemiology and antimicrobial resistance of Campylobacter.