Adhesion, Biofilm Formation, and Genomic Features of Campylobacter jejuni Bf, an Atypical Strain Able to Grow under Aerobic Conditions

Mechanistic concepts involved in biofilm associated processes of Campylobacter jejuni: persistence and inhibition in poultry environments

Campylobacter species, predominantly Campylobacter jejuni, remains a significant zoonotic pathogen worldwide, with the poultry sector being the primary vector for human transmission. In recent years. there has been a notable rise in the incidence of human campylobacteriosis, necessitating a deeper understanding of the pathogen's survival mechanisms and transmission dynamics. Biofilm presence significantly contributes to C. jejuni persistence in poultry and subsequent food product contamination, and this review describes the intricate processes involved in biofilm formation. The ability of Campylobacter to form biofilms on various surfaces, including stainless steel, plastic, and glass, is a critical survival strategy. Campylobacter biofilms, with their remarkable resilience, protect the pathogen from environmental stresses such as desiccation, pH extremes, biocides and sanitizing agents. This review explores the molecular and genetic mechanisms of C. jejuni biofilm formation, highlighting regulatory genes involved in motility, chemotaxis, and stress responses. Flagellar proteins, particularly flaA, flaB, flaG, and adhesins like cadF and flpA, are identified as the main molecular components in biofilm development. The role of mixed-species biofilms, where C. jejuni integrates into existing biofilms of other bacteria to enhance pathogen resilience, is also discussed. This review also considers alternative interventions to control C. jejuni in poultry production, in the context of increasing antibiotic resistance. It explores the effectiveness of prebiotics, probiotics, synbiotics, bacteriocins, bacteriophages, vaccines, and organic acids, with a focus on their mechanisms of action in reducing bacterial colonization and biofilm formation. Studies show that mixtures of organic acids and compounds like Carvacrol and Eugenol significantly downregulate genes linked with motility and adhesion, thereby disrupting biofilm integrity. It discusses the impact of environmental factors, such as temperature and oxygen levels on biofilm formation, providing insights into how industrial conditions can be manipulated to reduce contamination. This paper stresses the need for a multifaceted approach to control Campylobacter in poultry, integrating molecular and genetic insights with practical interventions. By advancing our understanding of biofilm dynamics and gene regulation, we aim to inform the development of more effective strategies to enhance food safety and protect public health.

The role of cydB gene in the biofilm formation by Campylobacter jejuni

Campylobacter jejuni is a major cause of food- and water-borne bacterial infections in humans. A key factor helping bacteria to survive adverse environmental conditions is biofilm formation ability. Nonetheless, the molecular basis underlying biofilm formation by C. jejuni remains poorly understood. Around thirty genes involved in the regulation and dynamics of C. jejuni biofilm formation have been described so far. We applied random transposon mutagenesis to identify new biofilm-associated genes in C. jejuni strain 81-176. Of 1350 mutants, twenty-four had a decreased ability to produce biofilm compared to the wild-type strain. Some mutants contained insertions in genes previously reported to affect the biofilm formation process. The majority of identified genes encoded hypothetical proteins. In the library of EZ-Tn5 insertion mutants, we found the cydB gene associated with respiration that was not previously linked with biofilm formation in Campylobacter. To study the involvement of the cydB gene in biofilm formation, we constructed a non-marked deletion cydB mutant together with a complemented mutant. We found that the cydB deletion-mutant formed a weaker biofilm of loosely organized structure and lower volume than the parent strain. In the present study, we demonstrated the role of the cydB gene in biofilm formation by C. jejuni.

Aerotolerancy of Campylobacter spp.: A Comprehensive Review

Campylobacter spp. constitute a group of microaerophilic bacteria that includes strains that are aerotolerant and capable of surviving in aerobic conditions. Recent studies have shown that aerotolerant strains are highly prevalent in meats, animals, and clinical settings. Changes in growth media and other environmental conditions can affect the aerotolerance of Campylobacter strains and must be considered when studying their aerotolerance in vitro. Polymicrobial interactions and biofilms also play a significant role in the ability of Campylobacter to survive oxygen exposure. Continuous subculturing may foster aerotolerance, and studies have demonstrated a positive correlation between aerotolerance and virulence and between aerotolerance and the ability to survive stressful environmental conditions. Various mechanisms and genetic origins for aerotolerance have been proposed; however, most of the potential genes involved in aerotolerance require further investigation, and many candidate genes remain unidentified. Research is also needed to investigate if there are any clinical implications for Campylobacter aerotolerance. Understanding the aerotolerance of Campylobacter remains an important target for further research, and it will be an important step towards identifying potential targets for intervention against this clinically important food-borne pathogen.

The role of cydB gene in the biofilm formation by Campylobacter jejuni

Campylobacter jejuni is a major cause of food- and water-borne bacterial infections in humans. A key factor helping bacteria to survive adverse environmental conditions is biofilm formation ability. Nonetheless, the molecular basis underlying biofilm formation by C. jejuni remains poorly understood. Around thirty genes involved in the regulation and dynamics of C. jejuni biofilm formation have been described so far. We applied random transposon mutagenesis to identify new biofilm-associated genes in C. jejuni strain 81-176. Of 1350 mutants, twenty-four had a decreased ability to produce biofilm compared to the wild-type strain. Some mutants contained insertions in genes previously reported to affect the biofilm formation process. The majority of identified genes encoded hypothetical proteins. In the library of EZ-Tn5 insertion mutants, we found the cydB gene associated with respiration that was not previously linked with biofilm formation in Campylobacter. To study the involvement of the cydB gene in biofilm formation, we constructed a non-marked deletion cydB mutant together with a complemented mutant. We found that the cydB deletion-mutant formed a weaker biofilm of loosely organized structure and lower volume than the parent strain. In the present study, we demonstrated the role of the cydB gene in biofilm formation by C. jejuni.

Effect of biofilm formation in a hostile oxidative stress environment on the survival of Campylobacter jejuni recovered from poultry in Iraqi markets

Background and Aim

Campylobacter jejuni is a major contributor to bacterial enteritis, a common health problem. The resistance of this microaerophilic bacterium to oxidative stress allows it to thrive under aerobic conditions. This study aimed to investigate whether the capacity of C. jejuni to form biofilms in the presence of oxidative stress contributes to the pathogen's ability to thrive in agricultural settings as well as in chicken slaughter lines.

Materials and Methods

Twenty identified strains originating from chicken samples (eight from caeca contents and 12 from frozen chicken carcasses) were previously isolated and identified according to standard bacteriological protocols, followed by confirmation at the species level using multiplex polymerase chain reaction assay. Crystal violet staining was used to evaluate biofilm formation by these bacteria. Two exposure periods to gaseous ozone (1 and 2 min) were used to assess resistance to oxidative damage.

Results

Most of the strong biofilm-forming Campylobacter strains came from imported frozen chicken meat (25%), whereas only 10% came from caeca content. After exposure to gaseous ozone at 600 mg/h for 2 min, strong biofilm-producing strains exhibited a higher survival rate with a limited reduction of up to 3 logs, whereas negative biofilm-producing strains exhibited a limited survival rate with a reduction of 6 logs.

Conclusion

Based on our findings, we hypothesized that the presence of C. jejuni strains capable of forming biofilms in poultry farms and/or chicken production facilities triggers a public health alarm as this bacterium seems to be able to adapt more easily to live and thrive in hostile environmental conditions.

Oncogenic potential of Campylobacter infection in the gastrointestinal tract: narrative review

BACKGROUND

Campylobacter jejuni is the leading cause of zoonotic gastroenteritis. The other emerging group of Campylobacters spp. are part of human oral commensal, represented by C. concisus (CC), which has been recently linked to non-oral conditions. Although long-term gastrointestinal (GI) complications from these two groups of Campylobacters have been previously reviewed individually, overall impact of Campylobacter infection on GI carcinogenesis and their inflammatory precursor lesions has not been assessed collectively.

AIMS

To evaluate the available evidence concerning the association between Campylobacter infection/colonization and inflammatory bowel disease (IBD), reflux esophagitis/metaplasia colorectal cancer (CRC) and esophageal cancer (EC).

METHODS

We performed a comprehensive literature search of PubMed for relevant original publications and systematic reviews/meta-analyses of epidemiological and clinical studies. In addition, we gathered additional information concerning microbiological data, animal models and mechanistic data from in vitro studies.

RESULTS

Both retrospective and prospective studies on IBD showed relatively consistent increased risk associated with Campylobacter infection. Despite lack of supporting prospective studies, retrospective studies based on tissue/fecal microbiome revealed consistent enrichment of Campylobacter in CRC samples. Studies on EC precursor lesions (esophagitis and metaplasia) were generally supportive for the association with Campylobacter, while inconsistent observations on EC. Studies on both IBD and EC precursors suggested the predominant role of CC, but studies on CRC were not informative of species.

CONCLUSIONS

There is sufficient evidence calling for concerted effort in unveiling direct and indirect connection of this organism to colorectal and esophageal cancer in humans.

Positive biofilms to guide surface microbial ecology in livestock buildings

The increase in human consumption of animal proteins implies changes in the management of meat production. This is followed by increasingly restrictive regulations on antimicrobial products such as chemical biocides and antibiotics, used in particular to control pathogens that can spread zoonotic diseases. Aligned with the One Health concept, alternative biological solutions are under development and are starting to be used in animal production. Beneficial bacteria able to form positive biofilms and guide surface microbial ecology to limit microbial pathogen settlement are promising tools that could complement existing biosecurity practices to maintain the hygiene of livestock buildings. Although the benefits of positive biofilms have already been documented, the associated fundamental mechanisms and the rationale of the microbial composition of these new products are still sparce. This review provides an overview of the envisioned modes of action of positive biofilms used on livestock building surfaces and the resulting criteria for the selection of the appropriate microorganisms for this specific application. Limits and advantages of this biosecurity approach are discussed as well as the impact of such practices along the food chain, from farm to fork.

Inter-Relationship Between a Transcriptional Regulator of Flagella Genes cj0440c and Thiamine Metabolic Pathway in Campylobacter jejuni

Campylobacter jejuni is a major cause of gastroenteritis in humans. It has been reported that the pathogenesis of C. jejuni is closely related to the formation, adhesion, and invasion of flagella toxin in host epithelial cells. A putative transcriptional regulator, known as cj0440c, is thought to be involved in the regulation of flagellar synthesis. However, confirmation of this hypothesis requires deep insight into the regulation mechanism of cj0440c and its possible relationship with different antibiotics. Therefore, the study explained here was designed to determine the relationship and function (phenotypically and genotypically) of cj0440c in the flagellar synthesis of C. jejuni NCTC11168. The study determined the mode of expression of cj0440c and flagella-related genes under exposure to various drugs. To verify the involvement of cj0440c protein in the metabolic pathway of thiamine, an enzymatic hydrolysis experiment was performed and analyzed through the application of mass spectrometry. The overexpression vector of C. jejuni NCTC11168 was also constructed to find out whether or not target genes were regulated by cj0440c. The findings of the study showed that cj0440c and other flagella-related genes were expressed differentially under the influence of various antibiotics including erythromycin, tylosin, azithromycin, gentamicin, etimicin, enrofloxacin, gatifloxacin, tetracycline, and tigecycline. The analysis showed that the cj0440c protein did not catalyze the degradation of thiamine. In conclusion, the study aids in the understanding of the inter-relationship between the regulatory mechanism of flagella genes and the thiamine metabolic pathway.

Survival of Campylobacter jejuni Co-Cultured with Salmonella spp. in Aerobic Conditions

Campylobacter and Salmonella are responsible for the two major foodborne zoonotic diseases in Europe; poultry is the main infection source. Campylobacter cannot grow under aerobic conditions, but can show aerobic survival when co-cultured with other microorganisms; however, its interaction with Salmonella has not been studied yet. In this study, these two bacteria were co-cultured under controlled aerobic conditions. Different concentrations and strains of C. jejuni were incubated with or without different Salmonella serotypes (10 CFU) at 37 °C for 16 h. C. jejuni did not grow after incubation with or without Salmonella. The survival of C. jejuni was observed only for the highest initial concentration of 6 log CFU/mL with or without Salmonella. However, its survival was significantly higher when co-cultured with Salmonella. No survival was observed at lower concentrations. C. jejuni survival was positively affected by the presence of Salmonella but depended on the Salmonella serotype, the C. jejuni strain and the initial concentration. On the other hand, the Salmonella enumerations were not affected by C. jejuni. Our results suggest potential interactions between Salmonella and C. jejuni that require further investigations for a clearer understanding of their behavior in natural habitats.

Transcriptome analysis of biofilm formation under aerobic and microaerobic conditions in clinical isolates of Campylobacter spp

It has been well documented that Campylobacter is the leading cause of foodborne infections and bacterial enteritis in high-income countries. The gastrointestinal tract of most warm-blooded animals, such as mammals and poultry, is prone to this pathogen. Infections caused by this bacterium in humans have usually been associated with the consumption of contaminated poultry meat. The important point about Campylobacter is that this bacterium has adapted to harsh environmental conditions along the food chain (poultry digestive tract to the consumer's plate) and developed an adapted mechanism to those conditions. This study aimed to compare the ability of Campylobacter jejuni and Campylobacter coli strains to form biofilms under aerobic and microaerobic conditions. The presence and expression of flab, FliS, DnaK, luxs, CsrA, Cj0688, and cosR genes involved in biofilm formation were investigated. Finally, the correlation between the biofilm forming ability of Campylobacter isolates and the presence/expression of selected genes has been explored. A significant correlation was observed between the presence and expression of some genes and the degree of biofilm formation in C. jejuni and C. coli isolates. A strong biofilm production was detected in strains harboring all selected genes with greater expression levels. The ability of C. jejuni and C. coli strains in biofilm formation is associated with the coordinated function and convergent expression of the selected genes. Seemingly, stress response- and motility-related genes have the most involvement in biofilm formation of C. jejuni and C. coli strains, while other genes have an accessory role in this phenomenon.

Waterborne Isolates of Campylobacter jejuni Are Able to Develop Aerotolerance, Survive Exposure to Low Temperature, and Interact With Acanthamoeba polyphaga

Campylobacter jejuni is regarded as the leading cause of bacterial gastroenteritis around the world. Even though it is generally considered to be a sensitive microaerobic pathogen, it is able to survive in the environment outside of the intestinal tract of the host. This study aimed to assess the impact of selected environmental parameters on the survival of 14 C. jejuni isolates of different origins, including 12 water isolates. The isolates were tested for their antibiotic resistance, their ability to survive at low temperature (7°C), develop aerotolerance, and to interact with the potential protozoan host Acanthamoeba polyphaga. The antibiotic susceptibility was determined by standard disk diffusion according to EUCAST. Out of the 14 isolates, 8 were resistant to ciprofloxacin (CIP) and 5 to tetracycline (TET), while only one isolate was resistant to erythromycin (ERY). Five isolates were resistant to two different antibiotic classes. Tetracycline resistance was only observed in isolates isolated from wastewater and a clinical sample. Further, the isolates were tested for their survival at 7°C under both aerobic and microaerobic conditions using standard culture methods. The results showed that under microaerobic conditions, all isolates maintained their cultivability for 4 weeks without a significant decrease in the numbers of bacteria and variation between the isolates. However, significant differences were observed under aerobic conditions (AC). The incubation led to a decrease in the number of cultivable cells, with complete loss of cultivability after 2 weeks (one water isolate), 3 weeks (7 isolates), or 4 weeks of incubation (6 isolates). Further, all isolates were studied for their ability to develop aerotolerance by repetitive subcultivation under microaerobic and subsequently AC. Surprisingly, all isolates were able to adapt and grow under AC. As the last step, 5 isolates were selected to evaluate a potential protective effect provided by A. polyphaga. The cocultivation of isolates with the amoeba resulted in the survival of about 40% of cells treated with an otherwise lethal dose of gentamicin. In summary, C. jejuni is able to adapt and survive in a potentially detrimental environment for a prolonged period of time, which emphasizes the role of the environmental transmission route in the spread of campylobacteriosis.

Virulence Comparison of Salmonella enterica Subsp. enterica Isolates from Chicken and Whole Genome Analysis of the High Virulent Strain S. Enteritidis 211

Background: Salmonellaenterica is one of the common pathogens in both humans and animals that causes salmonellosis and threatens public health all over the world. Methods and Results: Here we determined the virulence phenotypes of nine Salmonellaenterica subsp. enterica (S. enterica) isolates in vitro and in vivo, including pathogenicity to chicken, cell infection, biofilm formation and virulence gene expressions. S. Enteritidis 211 (SE211) was highly pathogenic with notable virulence features among the nine isolates. The combination of multiple virulence genes contributed to the conferring of the high virulence in SE211. Importantly, many mobile genetic elements (MGEs) were found in the genome sequence of SE211, including a virulence plasmid, genomic islands, and prophage regions. The MGEs and CRISPR-Cas system might function synergistically for gene transfer and immune defense. In addition, the neighbor joining tree and the minimum spanning tree were constructed in this study. Conclusions: This study provided both the virulence phenotypes and genomic features, which might contribute to the understanding of bacterial virulence mechanisms in Salmonella enterica subsp. enterica. The first completed genomic sequence for the high virulent S. Enteritidis isolate SE211 and the comparative genomics and phylogenetic analyses provided a preliminary understanding of S. enterica genetics and laid the foundation for further study.

Whole Resistome Analysis in Campylobacter jejuni and C. coli Genomes Available in Public Repositories

Campylobacter spp. are the most frequent agent of human gastroenteritis worldwide, and the spread of multidrug-resistant strains makes the clinical treatment difficult. The current study presents the resistome analysis of 39,798 Campylobacter jejuni and 11,920 Campylobacter coli genomes available in public repositories. Determinants of resistance to β-lactams (Be) and tetracyclines (Te) were the most frequent for both species, with resistance to quinolones (Qu) as the third most important on C. jejuni and to aminoglycosides (Am) on C. coli. Moreover, resistance to Te, Qu, and Am was frequently found in co-occurrence with resistance to other antibiotic families. Geographical differences on clonal complexes distribution were found for C. jejuni and on resistome genotypes for both C. jejuni and C. coli species. Attending to the resistome patterns by isolation source, three main clusters of genomes were found on C. jejuni genomes at antimicrobial resistance gene level. The first cluster was formed by genomes from human, food production animals (e.g., sheep, cow, and chicken), and food (e.g., dairy products) isolates. The higher incidence of tet(O), associated with tetracycline resistance, and the gyrA (T86I) single-nucleotide polymorphism (SNP), associated with quinolone resistance, among genomes from this cluster could be due to the intense use of these antibiotics in veterinary and human clinical settings. Similarly, a high incidence of tet(O) genes of C. coli genomes from pig, cow, and turkey was found. Moreover, the cluster based on resistome patterns formed by C. jejuni and C. coli genomes of human, turkey, and chicken origin is in agreement with previous observations reporting chicken or poultry-related environments as the main source of human campylobacteriosis infections. Most clonal complexes (CCs) associated with chicken host specialization (e.g., ST-354, ST-573, ST-464, and ST-446) were the CCs with the highest prevalence of determinants of resistance to Be, Qu, and Te. Finally, a clear trend toward an increase in the occurrence of Te and Qu resistance determinants on C. jejuni, linked to the spread of the co-occurrence of the bla_OXA–61 and tet(O)-tet(O/W/O) genes and the gyrA (T86I) SNP, was found from 2001 to date in Europe.

Bacillaene Mediates the Inhibitory Effect of Bacillus subtilis on Campylobacter jejuni Biofilms

Biofilms are the predominant bacterial lifestyle and can protect microorganisms from environmental stresses. Multispecies biofilms can affect the survival of enteric pathogens that contaminate food products, and thus, investigating the underlying mechanisms of multispecies biofilms is essential for food safety and human health. In this study, we investigated the ability of the natural isolate Bacillus subtilis PS-216 to restrain Campylobacter jejuni biofilm formation and adhesion to abiotic surfaces as well as to disrupt preestablished C. jejuni biofilms. Using confocal laser scanning microscopy and colony counts, we demonstrate that the presence of B. subtilis PS-216 prevents C. jejuni biofilm formation, decreases growth of the pathogen by 4.2 log₁₀, and disperses 26-h-old preestablished C. jejuni biofilms. Furthermore, the coinoculation of B. subtilis and C. jejuni interferes with the adhesion of C. jejuni to abiotic surfaces, reducing it by 2.4 log₁₀. We also show that contact-independent mechanisms contribute to the inhibitory effect of B. subtilis PS-216 on C. jejuni biofilm. Using B. subtilis mutants in genes coding for nonribosomal peptides and polyketides revealed that bacillaene significantly contributes to the inhibitory effect of B. subtilis PS-216. In summary, we show a strong potential for the use of B. subtilis PS-216 against C. jejuni biofilm formation and adhesion to abiotic surfaces. Our research could bring forward novel applications of B. subtilis in animal production and thus contribute to food safety. IMPORTANCE Campylobacter jejuni is an intestinal commensal in animals (including broiler chickens) but also the most frequent cause of bacterial foodborne infection in humans. This pathogen forms biofilms which enhance survival of C. jejuni in food processing and thus threaten human health. Probiotic bacteria represent a potential alternative in the prevention and control of foodborne infections. The beneficial bacterium Bacillus subtilis has an excellent probiotic potential to reduce C. jejuni in the animal gastrointestinal tract. However, data on the effect of B. subtilis on C. jejuni biofilms are scarce. Our study shows that the B. subtilis natural isolate PS-216 prevents adhesion to the abiotic surfaces and the development of submerged C. jejuni biofilm during coculture and destroys the preestablished C. jejuni biofilm. These insights are important for development of novel applications of B. subtilis that will reduce the use of antibiotics in human and animal health and increase productivity in animal breeding.

Quantification of Campylobacter jejuni gene expression after successive stresses mimicking poultry slaughtering steps

Broiler meat is considered as the most important source of the foodborne pathogen Campylobacter jejuni. Exposure to stress conditions encountered during the slaughtering process may induce bacterial adaptation mechanisms, and enhance or decrease pathogen resistance to subsequent stress. This adaptation may result from changes in bacterial gene expression. This study aims to accurately quantify the expression of selected C. jejuni genes after stresses inspired from the poultry slaughtering process. RT-qPCR was used to quantify gene expression of 44 genes in three strains after successive heat and cold stresses. Main results indicated that 26 genes out of 44 were differentially expressed following the successive thermal stresses. Three clusters of genes were differentially expressed according to the strain and the stress condition. Up-regulated genes mainly included genes involved in the heat shock response, whereas down-regulated genes belonged to metabolic pathways (such as lipid, amino-acid metabolisms). However, four genes were similarly overexpressed in the three strains; they might represent indicators of the thermal stress response at the species scale. Advances in the molecular understanding of the stress response of pathogenic bacteria, such as Campylobacter, in real-life processing conditions will make it possible to identify technological levers and better mitigate the microbial risk.

Biofilm-forming ability of poultry Campylobacter jejuni strains in the presence and absence of Pseudomonas aeruginosa

The aims of this study were to evaluate the ability of Campylobacter jejuni isolated from a poultry slaughterhouse to form biofilm in the presence and absence of Pseudomonas aeruginosa, and the effect of surface (stainless steel, polystyrene), temperature (7, 25, and 42 °C), and oxygen concentration (microaerophilic and aerobic conditions) on the formation of biofilm. The genes ahpC, cadF, clpP, dnaJ, docA, flaA, flaB, katA, kpsM, luxS, racR, and sodB, related to biofilm formation by C. jejuni, were also investigated. All isolates formed biofilm on stainless steel and on polystyrene, in both aerobic and microaerophilic atmospheres, including temperatures not optimal for C. jejuni growth (7 and 25 °C), and biofilm also was formed in the presence of P. aeruginosa. In dual-species biofilm on stainless steel, biofilm formation was 2-6 log CFU·cm^-2 higher at 7 °C for all isolates, in comparison with monospecies biofilm. Ten genes (ahpC, cadF, clpP, dnaJ, docA, flaA, flaB, luxS, racR, and sodB) were detected in all isolates, but katA and kpsM were found in four and six isolates, respectively. The results obtained are of concern because the poultry C. jejuni isolates form biofilm in different conditions, which is enhanced in the presence of other biofilm formers, such as P. aeruginosa.

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.

Review on Stress Tolerance in Campylobacter jejuni

Campylobacter spp. are the leading global cause of bacterial colon infections in humans. Enteropathogens are subjected to several stress conditions in the host colon, food complexes, and the environment. Species of the genus Campylobacter, in collective interactions with certain enteropathogens, can manage and survive such stress conditions. The stress-adaptation mechanisms of Campylobacter spp. diverge from other enteropathogenic bacteria, such as Escherichia coli, Salmonella enterica serovar Typhi, S. enterica ser. Paratyphi, S. enterica ser. Typhimurium, and species of the genera Klebsiella and Shigella. This review summarizes the different mechanisms of various stress-adaptive factors on the basis of species diversity in Campylobacter, including their response to various stress conditions that enhance their ability to survive on different types of food and in adverse environmental conditions. Understanding how these stress adaptation mechanisms in Campylobacter, and other enteric bacteria, are used to overcome various challenging environments facilitates the fight against resistance mechanisms in Campylobacter spp., and aids the development of novel therapeutics to control Campylobacter in both veterinary and human populations.

Revisiting Campylobacter jejuni Virulence and Fitness Factors: Role in Sensing, Adapting, and Competing

Campylobacter jejuni is the leading cause of bacterial foodborne gastroenteritis world wide and represents a major public health concern. Over the past two decades, significant progress in functional genomics, proteomics, enzymatic-based virulence profiling (EBVP), and the cellular biology of C. jejuni have improved our basic understanding of this important pathogen. We review key advances in our understanding of the multitude of emerging virulence factors that influence the outcome of C. jejuni–mediated infections. We highlight, the spatial and temporal dynamics of factors that promote C. jejuni to sense, adapt and survive in multiple hosts. Finally, we propose cohesive research directions to obtain a comprehensive understanding of C. jejuni virulence mechanisms.

High prevalence of Campylobacter jejuni CC21 and CC257 clonal complexes in children with gastroenteritis in Tehran, Iran

BACKGROUND

Campylobacter jejuni (C. jejuni) is a leading cause of acute gastroenteritis in human worldwide. The aim of study was to assess the distribution of sialylated lipooligosaccharide (LOS) classes and capsular genotypes in C. jejuni isolated from Iranian children with gastroenteritis. Furthermore, the level of dnaK gene expression in C. jejuni strains with selected capsular genotypes and LOS classes was intended. Moreover, a comprehensive study of C. jejuni MLST-genotypes and inclusive comparison with peer sequences worldwide was intended.

METHODS

Twenty clinical C. jejuni strains were isolated from fecal specimens of 280 children aged 0-5 years, suspected of bacterial gastroenteritis, which admitted to 3 children hospitals from May to October, 2018. Distribution of sialylated LOS classes and specific capsular genotypes were investigated in C. jejuni of clinical origin. The expression of dnaK in C. jejuni strains was measured by Real-Time-PCR. MLST-genotyping was performed to investigate the clonal relationship of clinical C. jejuni strains and comparison with inclusive sequences worldwide.

RESULTS

C. jejuni HS23/36c was the predominant genotype (45%), followed by HS2 (20%), and HS19 and HS4 (each 10%). A total of 80% of isolates were assigned to LOS class B and C. Higher expression level of dnaK gene was detected in strains with HS23/36c, HS2 and HS4 capsular genotypes and sialylated LOS classes B or C. MLST analysis showed that isolates were highly diverse and represented 6 different sequence types (STs) and 3 clonal complexes (CCs). CC21 and CC257 were the most dominant CCs (75%) among our C. jejuni strains. No new ST and no common ST with our neighbor countries was detected.

CONCLUSIONS

The C. jejuni isolates with LOS class B or C, and capsular genotypes of HS23/36, HS2, HS4 and HS19 were dominant in population under study. The CC21 and CC257 were the largest CCs among our isolates. In overall picture, CC21 and CC353 complexes were the most frequently and widely distributed clonal complexes worldwide, although members of CC353 were not detected in our isolates. This provides a universal picture of movement of dominant Campylobacter strains worldwide.

Adhesion, Biofilm Formation, and luxS Sequencing of Campylobacter jejuni Isolated From Water in the Czech Republic

The microaerophilic pathogen Campylobacter jejuni is a leading bacterial cause of human gastroenteritis in developed countries. Even though it has a reputation as a fastidious organism, C. jejuni is widespread and can be easily isolated from various animals, food, and environmental sources. It is suggested that an ability to form biofilms is probably necessary for the survival of C. jejuni under harsh environmental conditions. The first step required for successful biofilm formation is adhesion to a suitable surface. Therefore, in this work, the degree of adhesion was evaluated, followed by characterization and quantification of biofilms using confocal laser scanning microscopy (CLSM). A total of 15 isolates of C. jejuni were used in the experiments (12 isolates from surface and waste waters, 1 human clinical, 1 food and 1 ACTT BAA-2151 collection strain, all samples originated from the Czech Republic). Regardless of the sample origin, all C. jejuni isolates were able to adhere to the polystyrene surface within 30 min, with the number of attached cells increasing with the time of incubation. The resulting data showed that all isolates were able to form complex voluminous biofilms after 24 h of cultivation. The average amount of biovolume ranged from 3.59 × 106 µm3 to 17.50 × 106 µm3 in isolates obtained from different sources of water, 16.79 × 106 µm3 in the food isolate and 10.92 × 106 µm3 in the collection strain. However, the highest amount of biomass was produced by the human clinical isolate (25.48 × 106 µm3). Similar to the quantity, the architecture of the biofilms also differed, from a rugged flat monolayer of cells to large clustered structures. Further, all isolates were tested for the presence of the luxS gene, as the luxS/AI-2 (autoinducer-2) quorum sensing pathway has been previously connected with enhanced biofilm formation. Two isolates originated from surface waters did not possess the luxS gene. These isolates formed thinner and sparser biofilms lacking the presence of significant clusters. However, the ability to adhere to the surface was preserved. The sequencing of the luxS-containing fragments shown a high similarity of the luxS gene among the isolates.

Biofilm formation and extracellular microvesicles-The way of foodborne pathogens toward resistance

Almost all known foodborne pathogens are able to form biofilms as one of the strategies for survival under harsh living conditions, to ward off the inhibition and the disinfection during food production, transport and storage, as well as during cleaning and sanitation of corresponding facilities. Biofilms are communities where microbial cells live under constant intracellular interaction and communication. Members of the biofilm community are embedded into extracellular matrix that contains polysaccharides, DNA, lipids, proteins, and small molecules that protect microorganisms and enable their intercellular communication under stress conditions. Membrane vesicles (MVs) are produced by both Gram positive and Gram negative bacteria. These lipid membrane-enveloped nanoparticles play an important role in biofilm genesis and in communication between different biofilm members. Furthermore, MVs are involved in other important steps of bacterial life like cell wall modeling, cellular division, and intercellular communication. They also carry toxins and virulence factors, as well as nucleic acids and different metabolites, and play a key role in host infections. After entering host cells, MVs can start many pathologic processes and cause serious harm and cell death. Prevention and inhibition of both biofilm formation and shedding of MVs by foodborne pathogens has a very important role in food production, storage, and food safety in general. Better knowledge of biofilm formation and maintaining, as well as the role of microbial vesicles in this process and in the process of host cells' infection is essential for food safety and prevention of both food spoilage and host infection.

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

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

Virulence Traits of Inpatient Campylobacter jejuni Isolates, and a Transcriptomic Approach to Identify Potential Genes Maintaining Intracellular Survival

There are still major gaps in our understanding of the bacterial factors that influence the outcomes of human Campylobacter jejuni infection. The aim of this study was to compare the virulence-associated features of 192 human C. jejuni strains isolated from hospitalized patients with diarrhoea (150/192, 78.1%), bloody diarrhoea (23/192, 11.9%), gastroenteritis (3/192, 1.6%), ulcerative colitis (3/192, 1.5%), and stomach ache (2/192, 1.0%). Traits were analysed with genotypic and phenotypic methods, including PCR and extracellular matrix protein (ECMP) binding, adhesion, and invasion capacities. Results were studied alongside patient symptoms, but no distinct links with them could be determined. Since the capacity of C. jejuni to invade host epithelial cells is one of its most enigmatic attributes, a high throughput transcriptomic analysis was performed in the third hour of internalization with a C. jejuni strain originally isolated from bloody diarrhoea. Characteristic groups of genes were significantly upregulated, outlining a survival strategy of internalized C. jejuni comprising genes related (1) to oxidative stress; (2) to a protective sheath formed by the capsule, LOS, N-, and O- glycosylation systems; (3) to dynamic metabolic activity supported by different translocases and the membrane-integrated component of the flagellar apparatus; and (4) to hitherto unknown genes.

CRISPR-cas3 of Salmonella Upregulates Bacterial Biofilm Formation and Virulence to Host Cells by Targeting Quorum-Sensing Systems

Salmonella is recognized as one of the most common microbial pathogens worldwide. The bacterium contains the clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR-associated (Cas) systems, providing adaptive immunity against invading foreign nucleic acids. Previous studies suggested that certain bacteria employ the Cas proteins of CRISPR-Cas systems to target their own genes, which also alters the virulence during invasion of mammals. However, whether CRISPR-Cas systems in Salmonella have similar functions during bacterial invasion of host cells remains unknown. Here, we systematically analyzed the genes that are regulated by Cas3 in a type I-E CRISPR-Cas system and the virulence changes due to the deletion of cas3 in Salmonella enterica serovar Enteritidis. Compared to the cas3 gene wild-type (cas3 WT) Salmonella strain, cas3 deletion upregulated the lsrFGBE genes in lsr (luxS regulated) operon related to quorum sensing (QS) and downregulated biofilm-forming-related genes and Salmonella pathogenicity island 1 (SPI-1) genes related to the type three secretion system (T3SS). Consistently, the biofilm formation ability was downregulated in the cas3 deletion mutant (Δcas3). The bacterial invasive and intracellular capacity of Δcas3 to host cells was also reduced, thereby increasing the survival of infected host cells and live chickens. By the transcriptome-wide screen (RNA-Seq), we found that the cas3 gene impacts a series of genes related to QS, the flagellum, and SPI-1-T3SS system, thereby altering the virulence phenotypes. As QS SPI-1-T3SS and CRISPR-Cas systems are widely distributed in the bacteria kingdom, our findings extend our understanding of virulence regulation and pathogenicity in mammalian hosts for Salmonella and potentially other bacteria.

Trans-Cinnamaldehyde, Eugenol and Carvacrol Reduce Campylobacter jejuni Biofilms and Modulate Expression of Select Genes and Proteins

Campylobacter jejuni is the leading cause of human foodborne illness globally, and is strongly linked with the consumption of contaminated poultry products. Several studies have shown that C. jejuni can form sanitizer tolerant biofilm leading to product contamination, however, limited research has been conducted to develop effective control strategies against C. jejuni biofilms. This study investigated the efficacy of three generally recognized as safe status phytochemicals namely, trans-cinnamaldehyde (TC), eugenol (EG), or carvacrol (CR) in inhibiting C. jejuni biofilm formation and inactivating mature biofilm on common food contact surfaces at 20 and 37°C. In addition, the effect of phytochemicals on biofilm architecture and expression of genes and proteins essential for biofilm formation was evaluated. For the inhibition study, C. jejuni was allowed to form biofilms either in the presence or absence of sub-inhibitory concentrations of TC (0.75 mM), EG (0.61 mM), or CR (0.13 mM) for 48 h and the biofilm formation was quantified at 24-h interval. For the inactivation study, C. jejuni biofilms developed at 20 or 37°C for 48 h were exposed to the phytochemicals for 1, 5, or 10 min and surviving C. jejuni in the biofilm were enumerated. All phytochemicals reduced C. jejuni biofilm formation as well as inactivated mature biofilm on polystyrene and steel surface at both temperatures (P < 0.05). The highest dose of TC (75.64 mM), EG (60.9 mM) and CR (66.56 mM) inactivated (>7 log reduction) biofilm developed on steel (20°C) within 5 min. The genes encoding for motility systems (flaA, flaB, and flgA) were downregulated by all phytochemicals (P < 0.05). The expression of stress response (cosR, ahpC) and cell surface modifying genes (waaF) was reduced by EG. LC-MS/MS based proteomic analysis revealed that TC, EG, and CR significantly downregulated the expression of NapA protein required for oxidative stress response. The expression of chaperone protein DnaK and bacterioferritin required for biofilm formation was reduced by TC and CR. Scanning electron microscopy revealed disruption of biofilm architecture and loss of extracellular polymeric substances after treatment. Results suggest that TC, EG, and CR could be used as a natural disinfectant for controlling C. jejuni biofilms in processing areas.

Antifungal activities against Candida albicans, of cell-free supernatants obtained from probiotic Pediococcus acidilactici HW01

OBJECTIVE

The aim of this study was to investigate the antifungal activities of cell-free supernatants of a probiotic strain, Pediococcus acidilactici HW01, against Candida albicans.

DESIGN

C. albicans was cultured in the presence of different concentration of cell-free supernatants obtained from P. acidilactici HW01 (HW01 CFS) and the growth of C. albicans was determined. C. albicans was incubated with HW01 CFS for 24 h and the biofilm formation of C. albicans was determined by staining crystal violet and by using a scanning electron microscope. Biofilm quantification was determined by 2, 3-Bis (2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT) assay.

RESULTS

HW01 CFS inhibitedC. albicans growth, whereas bacteriocin, which is a well-known antimicrobial peptide of lactic acid bacteria, failed to inhibit C. albicans growth. Pre-treatment and simultaneous treatment with HW01 CFS exhibited a significant inhibition of C. albicans biofilm. Although post-treatment with HW01 CFS did not disrupt the established biofilm of C. albicans at 3 h-incubation, significant reduced C. albicans biofilm was observed after 6 h-incubation in the presence of HW01 CFS.

CONCLUSION

These results suggested that the CFS fromP. acidilactici HW01 was revealed as an effective antifungal agent against C. albicans by reducing the growth and biofilm formation.

Campylobacter coli From Retail Liver and Meat Products Is More Aerotolerant Than Campylobacter jejuni

Aerotolerance in the microaerophilic species Campylobacter was previously reported and could increase bacterial survival and transmission in foods during stressful processing and storage conditions. In this study, 167 Campylobacter isolates (76 C. jejuni and 91 C. coli) were screened for aerotolerance; these strains were previously isolated from retail chicken meat, chicken livers, chicken gizzards, turkey, pork, and beef liver samples. Bacterial cultures were incubated aerobically in Mueller Hinton broth with agitation and viable cell counts were taken at 0, 6, 12, and 24 h. Approximately 47% of the screened Campylobacter isolates were aerotolerant (viable after a 12-h aerobic incubation period), whereas 24% were hyper-aerotolerant (viable after a 24-h aerobic incubation). A greater prevalence of aerotolerant strains (80%) was found among C. coli isolates as compared to C. jejuni isolates (6%). Differences in the oxidative stress response related genes were detected among C. jejuni and C. coli isolates when comparative genomics was used to analyze 17 Whole Genome Sequenced (WGS) strains from our laboratory. Genes encoding putative transcriptional regulator proteins and a catalase-like heme binding protein were found in C. coli genomes, but were absent in the genomes of C. jejuni. PCR screening showed the presence of a catalase-like protein gene in 75% (68/91) of C. coli strains, which was absent in all tested C. jejuni strains. While about 79% (30/38) of the hyper-aerotolerant C. coli strains harbored the catalase-like protein gene, the gene was also present in a number of the aerosensitive strains. The Catalase like protein gene was found to be expressed in both aerobic and microaerobic conditions with a 2-fold higher gene expression detected in aerobic conditions for an aerosensitive strain. However, the exact function of the gene remains unclear and awaits further investigation. In conclusion, aerotolerant Campylobacter strains (especially C. coli) are prevalent in various retail meats. Further studies are needed to investigate whether the genes encoding catalase-like heme binding protein and putative transcriptional regulators in C. coli strains are involved in stress response.

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.

The Novel Protein Cj0371 Inhibits Chemotaxis of Campylobacter jejuni

cj0371 is a novel gene that is associated with Campylobacter jejuni virulence, and an isogenic mutant of cj0371 showed hyper chemotaxis and motility. Chemotactic motility is an important virulence factor and is involved in C. jejuni pathogenesis. Campylobacter sp. has specific variations of the common chemotaxis components, including histidine autokinase CheA, coupling scaffold protein CheV, chemotaxis response regulator protein CheY and several chemoreceptor proteins. In this study, we used immunoprecipitation combined with LC-MS/MS analyses to screen six chemotaxis pathway proteins that potentially interact with the putative protein Cj0371. qRT-PCR was used to quantitatively analyze the expression of these chemotaxis genes and basic flagella genes. The results showed that the expression of cheV, cj1110c, and cj0262c was significantly up-regulated, and four flagella genes also had up-regulated expression in the cj0371 mutant. GST pull-down analyses found that Cj0371 interacted with the receiver domain of the CheV protein. Enzyme-coupled spectrophotometric assays showed that the ATPase activity of CheA was higher when Cj0371 was not present in the chemotaxis reaction medium. Therefore, we concludes that cj0371 has a negative influence on C. jejuni chemotaxis, which may occur by adjusting the receiver domain of CheV to influence chemotaxis. This paper provides a new component in the chemotaxis pathway of C. jejuni for the first time and highlight the complexity of this remarkable pathway.

Salmonella and Campylobacter biofilm formation: a comparative assessment from farm to fork

It takes several steps to bring food from the farm to the fork (dining table), and contamination with food-borne pathogens can occur at any point in the process. Campylobacter spp. and Salmonella spp. are the main microorganisms responsible for foodborne disease in the EU. These two pathogens are able to persist throughout the food supply chain thanks to their ability to form biofilms. Owing to the high prevalence of Salmonella and especially of Campylobacter in the food supply chain and the huge efforts of food authorities to reduce these levels, it is of great importance to fully understand their mechanisms of persistence. Diverse studies have evaluated the biofilm-forming capacity of foodborne pathogens isolated at different steps of food production. Nonetheless, the principal obstacle of these studies is to reproduce the real conditions that microorganisms encounter in the food supply chain. While there are a wide number of Salmonella biofilm studies, information on Campylobacter biofilms is still limited. A comparison between the two microorganisms could help to develop new research in the field of Campylobacter biofilms. Therefore, this review evaluates relevant work in the field of Salmonella and Campylobacter biofilms and the applicability of the data obtained from these studies to real working conditions. © 2018 Society of Chemical Industry.

An adapted in vitro assay to assess Campylobacter jejuni interaction with intestinal epithelial cells: Taking into stimulation with TNFα

Campylobacter jejuni is the most prevalent foodborne bacterial infection agent. This pathogen seems also involved in inflammatory bowel diseases in which pro-inflammatory cytokines, such as tumor necrosis factor α (TNFα), play a major role. C. jejuni pathogenicity has been extensively studied using in vitro cell culture methods, and more precisely "healthy" cells. In fact, no information is available regarding the behavior of C. jejuni in contact with TNFα-stimulated cells. Therefore, this research was designed to investigate the effect of TNFα on C. jejuni interaction with human intestinal epithelial cells (HT29 and HT29-MTX). To ensure IL-8 production induced by TNFα, human rtTNFα was added to HT29 and HT29-MTX before adhesion and invasion assays. About 10⁸ CFU bacteria of C. jejuni strains cells were added to measure their adherence and invasion abilities using TNFα-stimulated cells versus non stimulated cells. Exposure to TNFα results in IL-8 overproduction by intestinal epithelial cells. In addition, the effect of TNFα pre-treatment on C. jejuni adhesion and internalization into eukaryotic cells is strain-dependent. Indeed, the adhesion/invasion process is affected in <50% of the strains tested when TNFα is added to the intestinal cells. Interestingly, TNFα affects more strains in their ability to adhere to and invade the mucus-secreting HT29-MTX cells. Among the 10 strains tested, the aero-tolerant C. jejuni Bf strain is one of the most virulent. These results suggest that the TNFα signalling pathway could participate in the internalization of C. jejuni in human intestinal cells and can help in understanding the pathogenicity of this microorganism in contact with TNFα-stimulated cells.

Campylobacteriosis, Salmonellosis, Yersiniosis, and Listeriosis as Zoonotic Foodborne Diseases: A Review

Zoonoses are diseases transmitted from animals to humans, posing a great threat to the health and life of people all over the world. According to WHO estimations, 600 million cases of diseases caused by contaminated food were noted in 2010, including almost 350 million caused by pathogenic bacteria. Campylobacter, Salmonella, as well as Yersinia enterocolitica and Listeria monocytogenes may dwell in livestock (poultry, cattle, and swine) but are also found in wild animals, pets, fish, and rodents. Animals, often being asymptomatic carriers of pathogens, excrete them with faeces, thus delivering them to the environment. Therefore, pathogens may invade new individuals, as well as reside on vegetables and fruits. Pathogenic bacteria also penetrate food production areas and may remain there in the form of a biofilm covering the surfaces of machines and equipment. A common occurrence of microbes in food products, as well as their improper or careless processing, leads to common poisonings. Symptoms of foodborne infections may be mild, sometimes flu-like, but they also may be accompanied by severe complications, some even fatal. The aim of the paper is to summarize and provide information on campylobacteriosis, salmonellosis, yersiniosis, and listeriosis and the aetiological factors of those diseases, along with the general characteristics of pathogens, virulence factors, and reservoirs.

Genome-Enabled Insights into the Ecophysiology of the Comammox Bacterium "Candidatus Nitrospira nitrosa"

Nitrospira-like bacteria are among the most diverse and widespread nitrifiers in natural ecosystems and the dominant nitrite oxidizers in wastewater treatment plants (WWTPs). The recent discovery of comammox-like Nitrospira strains, capable of complete oxidation of ammonia to nitrate, raises new questions about specific traits responsible for the functional versatility and adaptation of this genus to a variety of environments. The availability of new Nitrospira genome sequences from both nitrite-oxidizing and comammox bacteria offers a way to analyze traits in different Nitrospira functional groups. Our comparative genomics analysis provided new insights into the adaptation of Nitrospira strains to specific lifestyles and environmental niches.

The recently discovered comammox bacteria have the potential to completely oxidize ammonia to nitrate. These microorganisms are part of the Nitrospira genus and are present in a variety of environments, including biological nutrient removal (BNR) systems. However, the physiological traits within and between comammox and nitrite-oxidizing bacterium (NOB)-like Nitrospira species have not been analyzed in these ecosystems. In this study, we identified Nitrospira strains dominating the nitrifying community of a sequencing batch reactor (SBR) performing BNR under microaerobic conditions. We recovered metagenome-derived draft genomes from two Nitrospira strains: (i) Nitrospira sp. strain UW-LDO-01, a comammox-like organism classified as “Candidatus Nitrospira nitrosa,” and (ii) Nitrospira sp. strain UW-LDO-02, a nitrite-oxidizing strain belonging to the Nitrospira defluvii species. A comparative genomic analysis of these strains with other Nitrospira-like genomes identified genomic differences in “Ca. Nitrospira nitrosa” mainly attributed to each strain’s niche adaptation. Traits associated with energy metabolism also differentiate comammox from NOB-like genomes. We also identified several transcriptionally regulated adaptive traits, including stress tolerance, biofilm formation, and microaerobic metabolism, which might explain survival of Nitrospira under multiple environmental conditions. Overall, our analysis expanded our understanding of the genetic functional features of “Ca. Nitrospira nitrosa” and identified genomic traits that further illuminate the phylogenetic diversity and metabolic plasticity of the Nitrospira genus.

IMPORTANCENitrospira-like bacteria are among the most diverse and widespread nitrifiers in natural ecosystems and the dominant nitrite oxidizers in wastewater treatment plants (WWTPs). The recent discovery of comammox-like Nitrospira strains, capable of complete oxidation of ammonia to nitrate, raises new questions about specific traits responsible for the functional versatility and adaptation of this genus to a variety of environments. The availability of new Nitrospira genome sequences from both nitrite-oxidizing and comammox bacteria offers a way to analyze traits in different Nitrospira functional groups. Our comparative genomics analysis provided new insights into the adaptation of Nitrospira strains to specific lifestyles and environmental niches.

Author Video: An author video summary of this article is available.

Intrinsic and Extrinsic Aspects on Campylobacter jejuni Biofilms

Biofilm represents a way of life that allows greater survival of microorganisms in hostile habitats. Campylobacter jejuni is able to form biofilms in vitro and on surfaces at several points in the poultry production chain. Genetic determinants related to their formation are expressed differently between strains and external conditions are decisive in this respect. Our approach combines phylogenetic analysis and the presence of seven specific genes linked to biofilm formation in association with traditional microbiology techniques, using Mueller Hinton and chicken juice as substrates in order to quantify, classify, determine the composition and morphology of the biomass of simple and mixed biofilms of 30 C. jejuni strains. It also evaluates the inhibition of its formation by biocides commonly used in industry and also by zinc oxide nanoparticles. Genetic analysis showed high heterogeneity with the identification of 23 pulsotypes. Despite the diversity, the presence of flaA, cadF, luxS, dnaJ, htrA, cbrA, and sodB genes in all strains shows the high potential for biofilm formation. This ability was only expressed in chicken juice, where they presented phenotype of a strong biofilm producer, with a mean count of 7.37 log CFU/mL and an ultrastructure characteristic of mature biofilm. The composition of simple and mixed biofilms was predominantly composed by proteins. The exceptions were found in mixed biofilms with Pseudomonas aeruginosa, which includes a carbohydrate-rich matrix, lower ability to sessile form in chicken juice and compact architecture of the biofilm, this aspects are intrinsic to this species. Hypochlorite, chlorhexidine, and peracetic acid were more effective in controlling viable cells of C. jejuni in biofilm, but the existence of tolerant strains indicates exposure to sublethal concentrations and development of adaptation mechanisms. This study shows that in chicken juice C. jejuni presents greater potential in producing mature biofilms.

Characterisation of Aerotolerant Forms of a Robust Chicken Colonizing Campylobacter coli

Campylobacter contaminated poultry meat is a major source of human foodborne illness. Campylobacter coli strain OR12 is a robust colonizer of chickens that was previously shown to outcompete and displace other Campylobacter strains from the chicken's gastrointestinal tract. This strain is capable of aerobic growth on blood agar. Serial aerobic passage increased this aerotolerance as assessed by quantitative assays for growth and survival on solid media. Aerotolerance was also associated with increased peroxide stress resistance. Aerobic passage did not alter cellular morphology or motility or hinder the microaerobic growth rate. Colonization of broiler chickens by aerotolerant C. coli OR12 was significantly lower than the wild-type strain at 3 days after challenge but not by 7 days, suggesting adaptation had occurred. Bacteria recovered from chickens had retained their aerotolerance, indicating this trait is stable. Whole genome sequencing enabled comparison with the wild-type sequence. Twenty-three point mutations were present, none of which were in genes known to affect oxidative stress resistance. Insertions or deletions caused frame shifts in several genes including, phosphoglycerate kinase and the b subunit of pyruvate carboxylase that suggest modification of central and carbohydrate metabolism in response to aerobic growth. Other genes affected include those encoding putative carbonic anhydrase, motility accessory factor, filamentous haemagglutinin, and aminoacyl dipeptidase proteins. Aerotolerance has the potential to affect environmental success and survival. Increased environmental survival outside of the host intestinal tract may allow opportunities for transmission between hosts. Resistance to oxidative stress may equate to increased virulence by virtue of reduced susceptibility to oxidative free radicals produced by host immune responses. Finally, resistance to ambient atmospheric oxygen may allow increased survival on chicken skin, and therefore constitutes an increased risk to public health.