Campylobacter biofilm phenotype exhibits reduced colonization potential in young chickens and altered in vitro virulence

Whole-Genome Sequencing and Phenotypic Analysis of Streptococcus equi subsp. zooepidemicus Sequence Type 147 Isolated from China

Streptococcus equi subsp. zooepidemicus (S. zooepidemicus) is one of the important zoonotic and opportunistic pathogens. In recent years, there has been growing evidence that supports the potential role of S. zooepidemicus in severe diseases in horses and other animals, including humans. Furthermore, the clinical isolation and drug resistance rates of S. zooepidemicus have been increasing yearly, leading to interest in its in-depth genomic analysis. In order to deepen the understanding of the S. zooepidemicus characteristics and genomic features, we investigated the genomic islands, mobile genetic elements, virulence and resistance genes, and phenotype of S. zooepidemicus strain ZHZ 211 (ST147), isolated from an equine farm in China. We obtained a 2.18 Mb, high-quality chromosome and found eight genomic islands. According to a comparative genomic investigation with other reference strains, ZHZ 211 has more virulence factors, like an iron uptake system, adherence, exoenzymes, and antiphagocytosis. More interestingly, ZHZ 211 has acquired a mobile genetic element (MGE), prophage Ph01, which was found to be in the chromosome of this strain and included two hyaluronidase (hyl) genes, important virulence factors of the strain. Moreover, two transposons and two virulence (virD4) genes were found to be located in the same genome island of ZHZ 211. In vitro phenotypic results showed that ZHZ 211 grows faster and is resistant to clarithromycin, enrofloxacin, and sulfonamides. The higher biofilm-forming capabilities of ZHZ 211 may provide a competitive advantage for survival in its niche. The results expand our understanding of the genomic, pathogenicity, and resistance characterization of Streptococcus zooepidemicus and facilitate further exploration of its molecular pathogenic mechanism.

A Guideline for Assessment and Characterization of Bacterial Biofilm Formation in the Presence of Inhibitory Compounds

Campylobacter jejuni, a zoonotic foodborne pathogen, is the worldwide leading cause of acute human bacterial gastroenteritis. Biofilms are a significant reservoir for survival and transmission of this pathogen, contributing to its overall antimicrobial resistance. Natural compounds such as essential oils, phytochemicals, polyphenolic extracts, and D-amino acids have been shown to have the potential to control biofilms formed by bacteria, including Campylobacter spp. This work presents a proposed guideline for assessing and characterizing bacterial biofilm formation in the presence of naturally occurring inhibitory molecules using C. jejuni as a model. The following protocols describe: i) biofilm formation inhibition assay, designed to assess the ability of naturally occurring molecules to inhibit the formation of biofilms; ii) biofilm dispersal assay, to assess the ability of naturally occurring inhibitory molecules to eradicate established biofilms; iii) confocal laser scanning microscopy (CLSM), to evaluate bacterial viability in biofilms after treatment with naturally occurring inhibitory molecules and to study the structured appearance (or architecture) of biofilm before and after treatment.

Extracellular c-di-GMP Plays a Role in Biofilm Formation and Dispersion of Campylobacter jejuni

Cyclic diguanosine monophosphate (c-diGMP) is a ubiquitous second messenger involved in the regulation of many signalling systems in bacteria, including motility and biofilm formation. Recently, it has been reported that c-di-GMP was detected in C. jejuni DRH212; however, the presence and the role of c-di-GMP in other C. jejuni strains are unknown. Here, we investigated extracellular c-di-GMP as an environmental signal that potentially triggers biofilm formation in C. jejuni NCTC 11168 using a crystal violet-based assay, motility-based plate assay, RT-PCR and confocal laser scanning microscopy (CLSM). We found that, in presence of extracellular c-di-GMP, the biofilm formation was significantly reduced (>50%) and biofilm dispersion enhanced (up to 60%) with no effect on growth. In addition, the presence of extracellular c-di-GMP promoted chemotactic motility, inhibited the adherence of C. jejuni NCTC 11168-O to Caco-2 cells and upregulated the expression of Cj1198 (luxS, encoding quarum sensing pathway component, autoinducer-2), as well as chemotaxis genes Cj0284c (cheA) and Cj0448c (tlp6). Unexpectedly, the expression of Cj0643 (cbrR), containing a GGDEF-like domain and recently identified as a potential diguanylate cyclase gene, required for the synthesis of c-di-GMP, was not affected. Our findings suggest that extracellular c-di-GMP could be involved in C. jejuni gene regulation, sensing and biofilm dispersion.

Bridging the Gap: A Role for Campylobacter jejuni Biofilms

Campylobacter jejuni is the leading cause of bacterial gastroenteritis in the developed world. Cases of Campylobacteriosis are common, as the organism is an avian commensal and is passed on to humans through contaminated poultry meat, water, and food preparation areas. Although typically a fastidious organism, C. jejuni can survive outside the avian intestinal tract until it is able to reach a human host. It has long been considered that biofilms play a key role in transmission of this pathogen. The aim of this review is to examine factors that trigger biofilm formation in C. jejuni. A range of environmental elements have been shown to initiate biofilm formation, which are then affected by a suite of intrinsic factors. We also aim to further investigate the role that biofilms may play in the life cycle of this organism.

pdh modulate virulence through reducing stress tolerance and biofilm formation of Streptococcus suis serotype 2

Streptococcus suis serotype 2 (S. suis 2) is a zoonotic pathogen. It causes meningitis, arthritis, pneumonia and sepsis in pigs, leading to extremely high mortality, which seriously affects public health and the development of the pig industry. Pyruvate dehydrogenase (PDH) is an important sugar metabolism enzyme that is widely present in microorganisms, mammals and higher plants. It catalyzes the irreversible oxidative decarboxylation of pyruvate to acetyl-CoA and reduces NAD+ to NADH. In this study, we found that the virulence of the S. suis ZY05719 sequence type 7 pdh deletion strain (Δpdh) was significantly lower than the wild-type strain (WT) in the mouse infection model. The distribution of viable bacteria in the blood and organs of mice infected with the Δpdh was significantly lower than those infected with WT. Bacterial survival rates were reduced in response to temperature stress, salt stress and oxidative stress. Additionally, compared to WT, the ability to adhere to and invade PK15 cells, biofilm formation and stress resistance of Δpdh were significantly reduced. Moreover, real-time PCR results showed that pdh deletion reduced the expression of multiple adhesion-related genes. However, there was no significant difference in the correlation biological analysis between the complemented strain (CΔpdh) and WT. Moreover, the survival rate of Δpdh in RAW264.7 macrophages was significantly lower than that of the WT strain. This study shows that PDH is involved in the pathogenesis of S. suis 2 and reduction in virulence of Δpdh may be related to the decreased ability to resist stress of the strain.

Polyphosphate and associated enzymes as global regulators of stress response and virulence in Campylobacter jejuni

Campylobacter jejuni (C. jejuni), a Gram-negative microaerophilic bacterium, is a predominant cause of bacterial foodborne gastroenteritis in humans worldwide. Despite its importance as a major foodborne pathogen, our understanding of the molecular mechanisms underlying C. jejuni stress survival and pathogenesis is limited. Inorganic polyphosphate (poly P) has been shown to play significant roles in bacterial resistance to stress and virulence in many pathogenic bacteria. C. jejuni contains the complete repertoire of enzymes required for poly P metabolism. Recent work in our laboratory and others have demonstrated that poly P controls a plethora of C. jejuni properties that impact its ability to survive in the environment as well as to colonize/infect mammalian hosts. This review article summarizes the current literature on the role of poly P in C. jejuni stress survival and virulence and discusses on how poly P-related enzymes can be exploited for therapeutic/prevention purposes. Additionally, the review article identifies potential areas for future investigation that would enhance our understanding of the role of poly P in C. jejuni and other bacteria, which ultimately would facilitate design of effective therapeutic/preventive strategies to reduce not only the burden of C. jejuni-caused foodborne infections but also of other bacterial infections in humans.

Adherence Reduction of Campylobacter jejuni and Campylobacter coli Strains to HEp-2 Cells by Mannan Oligosaccharides and a High-Molecular-Weight Component of Cranberry Extract

Campylobacter infections are a leading cause of human bacterial gastroenteritis in the United States and are a major cause of diarrheal disease throughout the world. Colonization and subsequent infection and invasion of Campylobacter require that the bacteria adhere to the surface of host cells. Agents that inhibit adherence could be used prophylactically to reduce Campylobacter carriage and infection. Mannan oligosaccharides (MOS) have been used as a feed supplement in livestock animals to improve performance and to replace growth-promoting antibiotics. However, MOS and other nondigestible oligosaccharides may also prevent pathogen colonization by inhibiting adherence in the gastrointestinal tract. In addition, plant extracts, including those derived from cranberries, have been shown to have antiadherence activity against pathogens. The goal of this study was to assess the ability of MOS and cranberry fractions to serve as antiadherence agents against strains of Campylobacter jejuni and Campylobacter coli. Adherence experiments were performed using HEp-2 cells. Significant reductions in adherence of C. jejuni 29438, C. jejuni 700819, C. jejuni 3329, and C. coli 43485 were observed in the presence of MOS (up to 40 mg/ml) and with a high-molecular-weight fraction of cranberry extract (up to 3 mg/ml). However, none of the tested materials reduced adherence of C. coli BAA-1061. No additive effect in adherence inhibition was observed for an MOS-cranberry blend. These results suggest that both components, MOS and cranberry, could be used to reduce Campylobacter colonization and carriage in livestock animals and potentially limit human exposure to this pathogen.

Methyl-accepting chemotaxis proteins 3 and 4 are responsible for Campylobacter jejuni chemotaxis and jejuna colonization in mice in response to sodium deoxycholate

Methyl-accepting chemotaxis proteins (MCPs), also termed transducer-like proteins (Tlps), serve as sensors in bacterial chemotactic signalling, and detect attractants and promote bacterial movement towards suitable sites for colonization. Campylobacter jejuni is a leading cause of human enteritis, but the mechanisms responsible for bacterial chemotaxis and early colonization in the jejunum of hosts are poorly understood. In the present study, we identified several types of bile and sodium deoxycholate (SDC) acting as chemotactic attractants of C. jejuni strain NCTC 11168-O in vitro, in which SDC was the most efficient chemoattractant. In mice with bile duct ligation, the wild-type strain displayed a markedly attenuated ability for colonization. Blockage of Tlp3 or Tlp4 protein with antibody or disruption of the tlp3 or tlp4 gene (Δtlp3 or Δtlp4) caused a significant inhibition of SDC-induced chemotaxis and attenuation for colonization on jejunal mucosa in mice of the bacterium. Disruption of both the genes (Δtlp3/Δtlp4) resulted in the absence of bacterial chemotaxis and colonization, while the tlp-gene-complemented mutants (CΔtlp3 and CΔtlp4) reacquired these abilities. The results indicate that SDC is an effective chemoattractant for C. jejuni, and Tlp3 and Tlp4 are the SDC-specific sensor proteins responsible for the bacterial chemoattraction.

Functional characterization of exopolyphosphatase/guanosine pentaphosphate phosphohydrolase (PPX/GPPA) of Campylobacter jejuni

The inorganic polyphosphate (poly-P) is a key regulator of stress responses and virulence in many bacterial pathogens including Campylobacter jejuni. The role of exopolyphosphatases/guanosine pentaphosphate (pppGpp) phosphohydrolases (PPX/GPPA) in poly-P homeostasis and C. jejuni pathobiology remains unexplored. Here, we analyzed deletion mutants (∆ppx1, ∆ppx2) and the double knockout mutant (dkppx), all ∆ppx mutants exhibited increased capacity to accumulate poly-P; however only ∆ppx1 and dkppx mutants showed decreased accumulation of ppGpp, an alarmone molecule that regulates stringent response in bacteria, suggesting potential dual role for PPX1/GPPA. Nutrient survival defect of ∆ppx mutants was rescued by the supplementation of specific amino acids implying that survival defect may be associated with decreased ppGpp and/ or increased poly-P in ∆ppx mutants. The ppk1 and spoT were upregulated in both ∆ppx1 and ∆ppx2 suggesting a compensatory role for SpoT and Ppk1 in poly-P and ppGpp homeostasis. The lack of ppx genes resulted in defects in motility, biofilm formation, nutrient stress survival, invasion and intracellular survival indicating that maintaining a certain level of poly-P is critical for ppx genes in C. jejuni pathophysiology. Both ppx1 and ppx2 mutants were resistant to human complement-mediated killing; however, the dkppx mutant was sensitive. The serum susceptibility did not occur in the presence of MgCl 2 and EGTA suggesting an involvement of the classical or lectin pathway of complement mediated killing. Interestingly, the chicken serum did not have any effect on the ∆ppx mutants' survival. The observed serum susceptibility was not related to C. jejuni surface capsule and lipooligosaccharide structures. Our study underscores the importance of PPX/GPPA proteins in poly-P and ppGpp homeostasis, two critical molecules that modulate environmental stress responses and virulence in C. jejuni.

Contribution of fibronectin-binding protein to pathogenesis of Streptococcus equi ssp. zooepidemicus

Streptococcus equi ssp. zooepidemicus (S. zooepidemicus) is responsible for a wide variety of infections in many species. Fibronectin-binding protein is a bacterial cell surface protein, which specifically binds fibronectin (FN). Considering the specific role of FN-binding protein in host-pathogen interactions, we investigated the function of a novel FN-binding domain in the FN-binding protein (FNZ) of S. zooepidemicus. Five recombinant FNZ gene fragments [N1 (amino acids, 38-197), N2 (amino acids, 38-603), N3 (amino acids, 41-315), N4 (amino acids, 192-370), and N5 (amino acids, 38-225)] were expressed in Escherichia coli, and their FN-binding activities were tested. The results showed that amino acids 192-225 in the NH2 -terminal region of FNZ could be responsible for binding fibronectin. The FNZ knockout mutant was constructed in S. zooepidemicus, which results in the reduced capacity to adhere to HEp-2 cell, defective virulence in vivo, decreased biofilm formation, and decreased colonization capacity in blood, liver, lung, and spleen tissues of mice as compared to the wild type. These results suggest that FNZ participates in biofilm formation, FN binding, cell adhesion, and pathogenesis of S. zooepidemicus. Furthermore, this work offers a novel FN-binding domain within FNZ, which will help in further characterization of S. zooepidemicus FN-binding properties.

Evaluation of Salmonella-vectored Campylobacter peptide epitopes for reduction of Campylobacter jejuni in broiler chickens

Campylobacter is a leading cause of bacterial gastroenteritis in humans and is often linked to contaminated poultry products. Live Salmonella vectors expressing three linear peptide epitopes from Campylobacter proteins Cj0113 (Omp18/CjaD), Cj0982c (CjaA), and Cj0420 (ACE393) were administered to chicks by oral gavage on the day of hatch, and the chicks were challenged with Campylobacter jejuni on day 21. All three candidate vaccines produced consistent humoral immune responses with high levels of serum IgG and mucosal secretory IgA (sIgA), with the best response from the Cj0113 peptide-expressing vector. Campylobacter challenge following vaccination of three candidate vaccine groups decreased Campylobacter recovery from the ileum compared to that for controls on day 32. The Cj0113 peptide-expressing vector reduced Campylobacter to below detectable levels. The Salmonella-vectored Cj0113 subunit vaccine appears to be an excellent candidate for further evaluation as a tool for the reduction of Campylobacter in poultry for improved food safety.

Evaluation of different selective media and culturing techniques for the quantification of Campylobacter ssp. from broiler litter

Poultry is a major reservoir for Campylobacter, the leading cause of foodborne illness in the United States, but how broilers become initially colonized is still under debate. Broiler litter is a potential source, but the best technique for quantifying Campylobacter from litter is still unknown. Therefore, our objectives were to determine if certain media are more selective for quantifying Campylobacter and if enrichment allows for the detection of stressed or viable but nonculturable cells from broiler litter samples. In this trial, 5 media and 2 culturing techniques were used to enumerate Campylobacter from broiler litter. The media used were campy-Line agar (CLA), campy-cefex agar (CCA), modified CCA, Campylobacter agar plates (CAP), and modified charcoal cefoperazone deoxycholate agar. Litter samples were obtained from a commercial broiler house. Each sample was equally divided and diluted 10-fold into peptone, for direct plating, or 4-fold into Campylobacter enrichment broth. Samples diluted in peptone were direct-plated onto each media and incubated under microaerophilic conditions for 48 h at 42 degrees C. Samples diluted in enrichment broth were incubated under the same conditions for 24 h, then further diluted to 10-fold before plating. Plates from enriched samples were incubated for an additional 24 h after plating. After incubation, all plates (direct and enriched) were counted and presumptive positive colonies were confirmed using a Campylobacter latex agglutination kit. Results indicated that there was no difference in the ability of any of the selective media tested to grow Campylobacter. Direct-plated samples had a higher Campylobacter isolation rate compared with enriched samples. The CLA and CAP were able to suppress total bacterial growth better than modified charcoal cefoperazone deoxycholate, modified CCA, and CCA. The CLA and CAP were the only media able to detect total bacterial population shifts over time. In conclusion, it is important before making a final decision on a selective medium to consider the medium's ability to suppress total bacterial growth as well as isolate Campylobacter.

Biofilm formation in bacterial pathogens of veterinary importance

Bacterial biofilms are structured communities of bacterial cells enclosed in a self-produced polymer matrix that is attached to a surface. Biofilms protect and allow bacteria to survive and thrive in hostile environments. Bacteria within biofilms can withstand host immune responses, and are much less susceptible to antibiotics and disinfectants when compared with their planktonic counterparts. The ability to form biofilms is now considered a universal attribute of micro-organisms. Diseases associated with biofilms require novel methods for their prevention, diagnosis and treatment; this is largely due to the properties of biofilms. Surprisingly, biofilm formation by bacterial pathogens of veterinary importance has received relatively little attention. Here, we review the current knowledge of bacterial biofilms as well as studies performed on animal pathogens.

Campylobacter jejuni 81-176 forms distinct microcolonies on in vitro-infected human small intestinal tissue prior to biofilm formation

Human small and large intestinal tissue was used to study the interaction of Campylobacter jejuni with its target tissue. The strain used for the study was 81-176 (+pVir). Tissue was processed for scanning and transmission electron microscopy, and by immunohistochemistry for light microscopy. Organisms adhered to the apical surface of ileal tissues at all time points in large numbers, in areas where mucus was present and in distinct groups. Microcolony formation was evident at 1-2 h, with bacteria adhering to mucus on the tissue surface and to each other by flagellar interaction. At later time points (3-4 h), biofilm formation on ileal tissue was evident. Flagellar mutants did not form microcolonies or biofilms in tissue. Few organisms were observed in colonic tissue, with organisms present but not as abundant as in the ileal tissue. This study shows that C. jejuni 81-176 can form microcolonies and biofilms on human intestinal tissue and that this may be an essential step in its ability to cause diarrhoea in man.

Biofilm formation by Campylobacter jejuni is increased under aerobic conditions

The microaerophilic human pathogen Campylobacter jejuni is the leading cause of food-borne bacterial gastroenteritis in the developed world. During transmission through the food chain and the environment, the organism must survive stressful environmental conditions, particularly high oxygen levels. Biofilm formation has been suggested to play a role in the environmental survival of this organism. In this work we show that C. jejuni NCTC 11168 biofilms developed more rapidly under environmental and food-chain-relevant aerobic conditions (20% O(2)) than under microaerobic conditions (5% O(2), 10% CO(2)), although final levels of biofilms were comparable after 3 days. Staining of biofilms with Congo red gave results similar to those obtained with the commonly used crystal violet staining. The level of biofilm formation by nonmotile aflagellate strains was lower than that observed for the motile flagellated strain but nonetheless increased under aerobic conditions, suggesting the presence of flagellum-dependent and flagellum-independent mechanisms of biofilm formation in C. jejuni. Moreover, preformed biofilms shed high numbers of viable C. jejuni cells into the culture supernatant independently of the oxygen concentration, suggesting a continuous passive release of cells into the medium rather than a condition-specific active mechanism of dispersal. We conclude that under aerobic or stressful conditions, C. jejuni adapts to a biofilm lifestyle, allowing survival under detrimental conditions, and that such a biofilm can function as a reservoir of viable planktonic cells. The increased level of biofilm formation under aerobic conditions is likely to be an adaptation contributing to the zoonotic lifestyle of C. jejuni.