The physiology of Campylobacter species and its relevance to their role as foodborne pathogens

Comparative quantification of Campylobacter jejuni from environmental samples using traditional and molecular biological techniques

Campylobacter jejuni is one of the most common causes of gastroenteritis in the world. Given the potential risks to human, animal, and environmental health, the development and optimization of methods to quantify this important pathogen in environmental samples is essential. Two of the most commonly used methods for quantifying C. jejuni are selective plate counting and quantitative real-time PCR (qPCR). Unfortunately, little comparative research has been performed to evaluate the accuracy of these methods for quantification of C. jejuni in aqueous and solid matricies. In this study, the limit of detection and the level of resolution obtained using these 2 methods was evaluated for C. jejuni and compared with that of the common indicator organism Escherichia coli. The use of selective plate count media for quantification of C. jejuni resulted in a 0.7-1.2 log underestimation of cell concentrations, compared with qPCR in both water and column leachate samples, whereas E. coli concentrations were found to be similar with either technique. For C. jejuni, only the qPCR assay accurately measured 2-fold changes in cell concentrations in water samples, whereas concentrations of E. coli were accurately measured regardless of method. Based on these data, qPCR assays were found to be more accurate than selective plate counts for quantification of C. jejuni from environmental samples.

Analysis of the pan genome of Campylobacter jejuni isolates recovered from poultry by pulsed-field gel electrophoresis, multilocus sequence typing (MLST), and repetitive sequence polymerase chain reaction (rep-PCR) reveals different discriminatory capabilities

Campylobacter jejuni is one of the leading bacterial causes of food-borne illness in the USA. Molecular typing methods are often used in food safety for identifying sources of infection and pathways of transmission. Moreover, the identification of genetically related isolates (i.e., clades) may facilitate the development of intervention strategies for control and prevention of food-borne diseases. We analyzed the pan genome (i.e., core and variable genes) of 63 C. jejuni isolates recovered from chickens raised in conventional, organic, and free-range poultry flocks to gain insight into the genetic diversity of C. jejuni isolates recovered from different environments. We assessed the discriminatory power of three genotyping methods [i.e., pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST), and repetitive extragenic palindromic polymerase chain reaction (rep-PCR)]. The rep-PCR fingerprint was generated by determining the presence of repetitive sequences that are interspersed throughout the genome via repetitive extragenic palindromic PCR, enterobacterial repetitive intergenic consensus sequence PCR (ERIC-PCR), and BOX element PCR (BOX-PCR) and combining the data to form a composite fingerprint. The genetic fingerprints were subjected to computer-assisted pattern analysis. Comparison of the three genotypic methods revealed that repREB-PCR showed greater discriminatory power than PFGE and MLST. ERIC-PCR and BOX-PCR yielded the highest number of PCR products and greatest reproducibility. Regardless of the genotyping method, C. jejuni isolates recovered from chickens reared in conventional, organic, and free-range environments all exhibit a high level of genotypic diversity.

Atypical roles for Campylobacter jejuni amino acid ATP binding cassette transporter components PaqP and PaqQ in bacterial stress tolerance and pathogen-host cell dynamics

Campylobacter jejuni is a human pathogen causing severe diarrheal disease; however, our understanding of the survival of C. jejuni during disease and transmission remains limited. Amino acid ATP binding cassette (AA-ABC) transporters in C. jejuni have been proposed as important pathogenesis factors. We have investigated a novel AA-ABC transporter system, encoded by cj0467 to cj0469, by generating targeted deletions of cj0467 (the membrane transport component) and cj0469 (the ATPase component) in C. jejuni 81-176. The analyses described here have led us to designate these genes paqP and paqQ, respectively (pathogenesis-associated glutamine [q] ABC transporter permease [P] and ATPase [Q]). We found that loss of either component resulted in amino acid uptake defects, most notably diminished glutamine uptake. Altered resistance to a series of environmental and in vivo stresses was also observed: both mutants were hyperresistant to aerobic and organic peroxide stress, and while the DeltapaqP mutant was also hyperresistant to heat and osmotic shock, the DeltapaqQ mutant was more susceptible than the wild type to the latter two stresses. The DeltapaqP and DeltapaqQ mutants also displayed a surprising but statistically significant increase in recovery from macrophages and epithelial cells in short-term intracellular survival assays. Annexin V, 4',6-diamidino-2-phenylindole (DAPI), and Western blot analyses revealed that macrophages infected with the DeltapaqP or DeltapaqQ mutant exhibited transient but significant decreases in cell death and extracellular signal-regulated kinase-mitogen-activated protein kinase activation compared to levels in wild-type-infected cells. The DeltapaqP mutant was not defective in either short-term or longer-term mouse colonization, consistent with its increased stress survival and diminished host cell damage phenotypes. Collectively, these results demonstrate a unique correlation of an AA-ABC transporter with bacterial stress tolerances and host cell responses to pathogen infection.

Intracellular pH as an indicator of viability and resuscitation of Campylobacter jejuni after decontamination with lactic acid

The aim of the study was to determine intracellular pH (pH(i)) as an indicator of the physiological state of two Campylobacter jejuni strains (603 and 608) at the single cell level after bactericidal treatment with lactic acid (3% v/v lactic acid, pH 4.0, 0.85% w/v NaCl) and during recovery and survival using Fluorescence Ratio Imaging Microscopy (FRIM). After exposure to lactic acid solution a decline in pH(i) to 5.5 (FRIM detection limit) was observed in the majority of cells (75-100%) within 2 min. The enumeration data revealed that after 2 min of lactic acid exposure, approx. 90% of the initial population became unculturable. In the following 10 min of exposure, a further decrease in the cell count was observed resulting in 3.53 and 3.21 log CFU/ml reduction of culturable cells at the end of the treatment. On the contrary, the FRIM results revealed that the subpopulations with pH(i)>5.5 increased between 2 and 12 min of exposure to lactic acid. Removing the acid stress and incubating the cells suspension under the more favourable conditions resulted in an immediate increase in cell population with pH(i)>pH(ex) for both C. jejuni strains. Further 24 h incubation at 37 degrees C resulted in increased pH(i) and colony count (recovery study). On the contrary, 24 h incubation at suboptimal temperature of 4 degrees C, showed pH(i) decrease to pH(ex)=6.0 (no pH gradient) in the whole population of C. jejuni cells. Rather than dying, cells exposed for longer time (72 and 120 h) to 4 degrees C increased the subpopulation of the cells with positive pH gradient, mostly comprised of the cells with DeltapH>0.5, indicating the ability of C. jejuni cells to regulate their metabolic activity under suboptimal conditions.

In vitro antimicrobial and antioxidant activity of commercial rosemary extract formulations

Phenolic plant extracts are sources of natural bioactive compounds, which can inhibit the rate of food spoilage. MIC and MBC concentrations of four oil- or water-soluble rosemary (Rosmarinus officinalis) extracts against gram-positive (Bacillus and Staphylococcus) and gram-negative (Campylobacter and Salmonella) bacteria were determined by using disk diffusion, agar dilution, and broth microdilution methods, as well as bacterial survival kinetics in a macrodilution test. To describe the antioxidant properties of the extracts, the reducing power, free radical scavenging effectiveness, and beta-carotene bleaching test were used. The antimicrobial and antioxidant activity depended on the concentration and chemical nature of the phenolic compounds in the extracts. Gram-positive bacteria were more sensitive than were gram-negative bacteria, especially for oil-soluble extracts with carnosic acid as the major phenolic compound. A microdilution method based on ATP measurement was found to be a useful, rapid technique for determining antibacterial efficiency, and its results correlated well with MICs from survival curve measurement. Reducing power and free radical scavenging effectiveness was higher in water-soluble formulations, according to their higher total phenolic content, but in an aqueous emulsion system of linoleic acid, they exhibited lower antioxidant activity. This correlated well with the higher efficiency of antimicrobial activity of oil-soluble formulations, despite the lower total phenolic content of these extracts.

Evaluation of TECRA broth, Bolton broth, and direct plating for recovery of Campylobacter spp, from broiler carcass rinsates from commercial processing plants

The purpose of this study was to compare a conventional culture broth method (Bolton enrichment), a newly developed proprietary broth method (TECRA Campylobacter enrichment), and direct plating for recovery of Campylobacter spp. from chicken carcass rinsates. Whole carcass rinses were taken from 140 carcasses at rehang (immediately after defeathering but before evisceration) and from 140 carcasses at postchill from eight different processing plants in the United States. The rinsate samples were packed in ice and shipped overnight to the laboratory. Aliquots of the rinsate were transferred into Bolton and TECRA enrichment broths and were direct plated. Standard laboratory procedures with Campy-cefex plates were followed for recovery of Campylobacter spp. For rehang carcasses, 94% were positive for Campylobacter spp. with the TECRA enrichment broth and 74% were positive with the Bolton enrichment broth. For postchill carcasses, 74% were positive for Campylobacter spp. with the TECRA enrichment broth and 71% were positive with the Bolton enrichment broth. Compared with the Bolton enrichment broth, TECRA enrichment broth significantly suppressed non-Campylobacter microflora (P < 0.05). Overall, TECRA enrichment broth yielded an 11% higher total number of Campylobacter-positive samples compared with the Bolton enrichment broth. Campylobacter spp. detection in postchill samples was significantly greater (P < 0.05) by enrichment (84%) than by direct plating (19%). The high number of Campylobacter-positive samples obtained with all procedures indicated that 99% of the carcass rinsates obtained at rehang and 84% obtained at postchill contained Campylobacter spp.

A longitudinal study of Campylobacter distribution in a turkey production chain

Background

Campylobacter is the most common cause of bacterial enteritis worldwide. Handling and eating of contaminated poultry meat has considered as one of the risk factors for human campylobacteriosis.Campylobacter contamination can occur at all stages of a poultry production cycle. The objective of this study was to determine the occurrence of Campylobacter during a complete turkey production cycle which lasts for 1,5 years of time. For detection of Campylobacter, a conventional culture method was compared with a PCR method. Campylobacter isolates from different types of samples have been identified to the species level by a multiplex PCR assay.

Methods

Samples (N = 456) were regularly collected from one turkey parent flock, the hatchery, six different commercial turkey farms and from 11 different stages at the slaughterhouse. For the detection of Campylobacter, a conventional culture and a PCR method were used. Campylobacter isolates (n = 143) were identified to species level by a multiplex PCR assay.

Results

No Campylobacter were detected in either the samples from the turkey parent flock or from hatchery samples using the culture method. PCR detected Campylobacter DNA in five faecal samples and one fluff and eggshell sample. Six flocks out of 12 commercial turkey flocks where found negative at the farm level but only two were negative at the slaughterhouse.

Conclusion

During the brooding period Campylobacter might have contact with the birds without spreading of the contamination within the flock. Contamination of working surfaces and equipment during slaughter of a Campylobacter positive turkey flock can persist and lead to possible contamination of negative flocks even after the end of the day's cleaning and desinfection. Reduction of contamination at farm by a high level of biosecurity control and hygiene may be one of the most efficient ways to reduce the amount of contaminated poultry meat in Finland. Due to the low numbers of Campylobacter in the Finnish turkey production chain, enrichment PCR seems to be the optimal detection method here.

Epidemiological surveillance of Campylobacter jejuni in chicken, dairy cattle and diarrhoea patients

Campylobacter jejuni of different subtypes were identified in chicken, dairy cattle and diarrhoea patients in China from 2005 to 2006, using multiplex PCR and RFLP. The results indicated that, of the three types of samples, C. jejuni was most frequently detected in poultry of the three types of samples, with an average isolation rate of up to 18.61% and a flock contamination rate of 86.67%. The average incidence of C. jejuni in overall cattle and environmental samples, milk cows, heifers and diarrhoea patients was 7.77, 5.02, 8.70 and 4.84%, respectively. A higher prevalence was detected in outpatients than ward patients (P<0.01), and in patients aged <7 years than in older patients (P<0.01). The 265 isolates of C. jejuni were classified into 20 distinct types by PCR-RFLP analysis of the flaA gene, with the genotype distribution in humans overlapping that in poultry and cattle. This suggests that certain C. jejuni strains circulate between humans and domestic animals such as cattle and poultry.

Inhibition by yeast-derived mannoproteins of adherence to and invasion of Caco-2 cells by Campylobacter jejuni

The main objective of the present work was to study the influence of yeast-derived mannoproteins on the adherence to and invasion of Caco-2 cells by Campylobacter jejuni. Mannoprotein fractions were prepared by enzymatic and thermal extraction methods. The method used to prepare the mannoprotein extracts influenced their composition and determined the efficacy of the extract against C. jejuni adherence and/or invasion. The availability of mannose in the mannoprotein fraction seemed to be important for inhibiting effective adherence and invasion of Caco-2-cells by C. jejuni, although protein moieties also played a role in the process. The study of the mechanisms involved in the inhibition of C. jejuni adherence and invasion by mannoproteins may have further implications in the control of this foodborne pathogen.

Survival of stress exposed Campylobacter jejuni in the murine macrophage J774 cell line

Although campylobacters are relatively fragile and sensitive to environmental stresses, Campylobacter jejuni has evolved mechanisms for survival in diverse environments, both inside and outside the host. Their survival properties and pathogenic potential were assessed after subjecting food and clinical C. jejuni isolates to different stress conditions. After exposure to starvation (5 h and 15 h of nutrient depletion), a temperature shock (3 min at 55 degrees C) or oxidative stress (5 h and 15 h of atmospheric oxygen) we studied the culturability, viability and capability of adhesion, internalization and survival within the in vitro cell culture model using J774 murine macrophages. Starvation severely impaired C. jejuni culturability, particularly after 15 h of nutrient depletion. The number of viable cells decreased by 30-40%. Starved bacterial cells also showed a lower capability of adhesion, internalization and survival within macrophages. Despite the reduced culturability and viability of the heat treated cells, C. jejuni efficiently adhered to, and entered murine macrophages. However, the number of heat treated cells started to decrease more quickly than non-stressed cells. Within 24 h post infection all the cells were killed. The bacterial mechanisms involved in inactivating toxic oxygen products may enhance bacterial persistence through increased binding, entry and survival of both oxidatively stressed C. jejuni isolates inside the macrophages. Oxygen exposure increased the internalization and intracellular survival, although the cells cannot remain viable for extended periods within murine macrophages. However, any prolongation of survival in macrophages may increase the probability of transmission of bacteria in the host organism and have further implications in the pathogenesis of campylobacteriosis. This indicates that environmental stress conditions may be involved.

Contribution of the stereospecific methionine sulphoxide reductases MsrA and MsrB to oxidative and nitrosative stress resistance in the food-borne pathogen Campylobacter jejuni

The microaerophilic food-borne pathogen Campylobacter jejuni is exposed to highly variable oxygen concentrations during its life cycle and employs a variety of protection mechanisms to resist oxidative stress. However, not all of the enzymes that mediate such protection have yet been identified. Two genes in strain NCTC 11168, Cj0637c and Cj1112c, are predicted to encode unrelated methionine sulphoxide reductases, which may repair oxidized methionine residues in proteins and thus contribute to oxidative stress defence. Cj0637 and Cj1112 were overexpressed, purified and shown by a coupled thioredoxin-thioredoxin reductase-NADPH assay to catalyse the stereospecific reduction of the S and R diastereoisomers, respectively, of the model compound methyl p-tolyl sulphoxide. Cj0637 is thus identified as MsrA and Cj1112 as MsrB. The contribution of these enzymes to oxidative and nitrosative stress resistance in C. jejuni was assessed by phenotypic analysis of a set of isogenic msrA, msrB and msrA/B insertion mutants. As RT-PCR data suggested a polar effect on Cj1111c in the msrB mutant, an msrB/msrB(+) merodiploid complementation strain was also constructed. The msrA/B strain was severely growth inhibited under standard microaerobic conditions, whereas the msrA and msrB strains grew normally. Agar plate disc diffusion assays showed that all mutants displayed increased sensitivity to hydrogen peroxide, organic peroxide, superoxide, and nitrosative and disulphide stress, but quantitative cell viability assays showed that the msrA/B double mutant was markedly more sensitive to both oxidative and nitrosative stress. All of the stress-sensitivity phenotypes observed for the msrB mutant were restored to wild-type in the msrB/msrB(+) merodiploid. It is concluded that MsrA and MsrB make a significant contribution to the protection of C. jejuni against oxidative and nitrosative stress.

Incidence and ecology of Campylobacter jejuni and coli in animals

Since its initial emergence in the 1970s, Campylobacter has become one of the most common causative agents of bacterial foodborne illness. Campylobacter species readily colonize the gastrointestinal tracts of domestic, feral and wild animals and while they rarely cause clinical disease in food animals, they can produce severe acute gastroenteritis in humans. Prevalence of Campylobacter in food animals can exceed 80% thus challenging processors to employ post-harvest pathogen reduction strategies. Reduction of pathogens before arrival to the abattoir is also of interest because the implementation of pre-harvest interventions may compliment existing post-harvest control techniques to further diminish possible retail sources of infection. Such multiple hurdle approaches that simultaneously utilize pre- and post-harvest control techniques are expected to be the most effective approach for decreasing human illness associated with foodborne pathogens.

Cross-contamination in the kitchen: effect of hygiene measures

AIMS

To determine the effect of hygiene measures on cross-contamination of Campylobacter jejuni at home and to select a safe tracer organism for C. jejuni.

METHODS AND RESULTS

Comparative tests were conducted with nonpathogenic Escherichia coli and Lactobacillus casei and L. casei was chosen as the safe tracer organism. Salads containing chicken breast fillet contaminated with a known number of C. jejuni and L. casei were prepared according to different cross-contamination scenarios and contamination levels of salads were determined. Cross-contamination could be strongly reduced when cleaning cutting board and cutlery with hot water (68 degrees C), but generally was not prevented using consumer-style cleaning methods for hands and cutting board.

CONCLUSIONS

Dish-washing does not sufficiently prevent cross-contamination, thus different cutting boards for raw meat and other ingredients should be used and meat-hand contact should be avoided or hands should be thoroughly cleaned with soap. Lactobacillus casei can be used as a safe tracer organism for C. jejuni in consumer observational studies.

SIGNIFICANCE AND IMPACT OF THE STUDY

Cross-contamination plays an important role in the transmission of food-borne illness, especially for C. jejuni. This study delivers suitable data to quantitatively assess the risk of campylobacteriosis caused by cross-contamination and it shows the effect of different preventive hygiene measures.

Expression, purification, and structural characterization of CfrA, a putative iron transporter from Campylobacter jejuni

The gene for the Campylobacter ferric receptor (CfrA), a putative iron-siderophore transporter in the enteric food-borne pathogen Campylobacter jejuni, was cloned, and the membrane protein was expressed in Escherichia coli, affinity purified, and then reconstituted into model lipid membranes. Fourier transform infrared spectra recorded from the membrane-reconstituted CfrA are similar to spectra that have been recorded from other iron-siderophore transporters and are highly characteristic of a beta-sheet protein (approximately 44% beta-sheet and approximately 10% alpha-helix). CfrA undergoes relatively extensive peptide hydrogen-deuterium exchange upon exposure to (2)H(2)O and yet is resistant to thermal denaturation at temperatures up to 95 degrees C. The secondary structure, relatively high aqueous solvent exposure, and high thermal stability are all consistent with a transmembrane beta-barrel structure containing a plug domain. Sequence alignments indicate that CfrA contains many of the structural motifs conserved in other iron-siderophore transporters, including the Ton box, PGV, IRG, RP, and LIDG motifs of the plug domain. Surprisingly, a homology model reveals that regions of CfrA that are expected to play a role in enterobactin binding exhibit sequences that differ substantially from the sequences of the corresponding regions that play an essential role in binding/transport by the E. coli enterobactin transporter, FepA. The sequence variations suggest that there are differences in the mechanisms used by CfrA and FepA to interact with bacterial siderophores. It may be possible to exploit these structural differences to develop CfrA-specific therapeutics.

Isolation of Campylobacter jejuni and coliform bacilli from bile and liver obtained from slaughter cattle in Western Japan

A total of 290 bile samples from 143 Japanese Brown, 97 Japanese Black, and 50 Holstein cattle, and a total of 148 liver samples from 81 Japanese Brown, 49 Japanese Black, and 18 Holstein cattle were examined for the presence of Campylobacter jejuni by direct plating. The bile samples were also subjected to enumeration of coliform bacilli. Sixty-eight (23%) bile samples and 2 (1.4%) liver samples were positive for C. jejuni. A significantly higher isolation rate was observed from bile samples from Holstein (50%) than from Japanese Black (22%) and Japanese Brown (15%) cattle. C. jejuni was isolated from 52 of 232 bile samples that contained < 30 CFU/ml (under the detection threshold) of coliform bacilli. The presence of C. jejuni from bile was observed throughout the year. Fifty-four of the 68 bile isolates were serologically typed into eight groups. Serotypes O:4 complex (28 isolates) and O:2 (11 isolates), which were commonly isolated from human patients in Japan, accounted for 57% of the isolates. These observations suggest that bile can be a cause of contamination with C. jejuni even though it contains only a low number of coliforms.

The Campylobacter jejuni thiol peroxidases Tpx and Bcp both contribute to aerotolerance and peroxide-mediated stress resistance but have distinct substrate specificities

The microaerophilic food-borne pathogen Campylobacter jejuni experiences variable oxygen concentrations during its life cycle, especially during transitions between the external environment and the avian or mammalian gut. Single knockout mutations in either one of two related thiol peroxidase genes, tpx and bcp, resulted in normal microaerobic growth (10% [vol/vol] oxygen) but poorer growth than that of the wild type under high-aeration conditions (21% [vol/vol] oxygen). However, a tpx/bcp double mutant had a severe microaerobic growth defect and did not grow at high aeration in shake flasks. Although the single mutant strains were no more sensitive than the wild-type strains in disc diffusion assays with hydrogen peroxide, organic peroxides, superoxide, or nitrosative stress agents, in all cases the double mutant was hypersensitive. Quantitative cell viability and cellular lipid peroxidation assays indicated some increased sensitivity of the single tpx and bcp mutants to peroxide stress. Protein carbonylation studies revealed that the tpx/bcp double mutant had a higher degree of oxygen- and peroxide-induced oxidative protein damage than did either of the single mutants. An analysis of the peroxidase activity of the purified recombinant enzymes showed that, surprisingly, Tpx reduced only hydrogen peroxide as substrate, whereas Bcp also reduced organic peroxides. Immunoblotting of wild-type cell extracts with Tpx- or Bcp-specific antibodies showed increased abundance of both proteins under high aeration compared to that under microaerobic growth conditions. Taken together, the results suggest that Tpx and Bcp are partially redundant antioxidant enzymes that play an important role in protection of C. jejuni against oxygen-induced oxidative stress.

Quantification of Campylobacter jejuni cross-contamination via hands, cutlery, and cutting board during preparation of a chicken fruit salad

Using artificially contaminated chicken, the quantitative overall effect of Campylobacter jejuni cross-contamination, either via cutlery, cutting board, or hands, on the microbiological quality of a chicken salad was tested to identify the most critical transfer route. The end contamination level of salads prepared according to different scenarios, with or without cross-contamination, was compared. It was shown that the mean transfer rate calculated for all salads prepared allowing cross-contamination was 0.12% of the initial number of C. jejuni on the chicken fillet (8.8 +/- 0.2 log CFU). The difference in calculated transfer rates for the tested cross-contamination routes was not significantly different (P > 0.05). The prevention of cross-contamination by replacing cutlery and cutting board after handling raw chicken and the prevention of hand contact resulted in considerably reduced end contamination levels (< 2.4 log CFU) or noncontaminated end products. The results of this study emphasize the importance of preventing cross-contamination during food handling in reducing the risks of foodborne infections, and they provide useful data for quantitative microbiological risk assessment.

Pyruvate relieves the necessity of high induction levels of catalase and enables Campylobacter jejuni to grow under fully aerobic conditions

AIMS

Several cases of campylobacteriosis reported worldwide seemingly conflict with the strict growth requirements and sensitivity to environmental stress of Campylobacter jejuni. In this study, the need for a micro-aerobic environment [dissolved oxygen tension (DOT): 0.1-90%; 100% air saturation)] and the adaptive responses to oxygen stress were studied.

METHODS AND RESULTS

The growth of C. jejuni in continuous culture was assessed under different DOT in the presence or absence of pyruvate. In a medium without pyruvate, continuous cultures of C. jejuni showed typically micro-aerobic behaviour and cells were unable to grow under fully aerobic conditions. However in the presence of pyruvate (25 mmol l(-1)), continuous cultures of C. jejuni were able to grow in a broad DOT range, varying from 0.1% to at least 90%, and the catalase activity was decreased.

CONCLUSIONS

Addition of pyruvate results in the decrease in the concentration of hydrogen peroxide, which enables C. jejuni to grow aerobically.

SIGNIFICANCE AND IMPACT OF THE STUDY

New information on the oxidative physiology of C. jejuni and its ability to grow aerobically in media supplemented with pyruvate is presented.

Impacts of treatment parameters on the inactivation of Campylobacter jejuni by high pressure: a statistical study of main effects and interactions

AIM

The influence of environmental (temperature and pH) and biological (strain) parameters on the inactivation of Campylobacter jejuni by high hydrostatic pressure (HHP) was investigated.

METHODS AND RESULTS

Two clinical strains harvested in stationary phase were pressurized at 20 degrees C and 37 degrees C within a range of 50-400 MPa, in a phosphate (pH 7.0) or a citrate phosphate buffer (pH 5.6), for 10 min. Treatment efficiencies were determined by logarithmic comparisons of culturable cells on blood agar before and after treatment. Results were statistically compared using an anova of culturable cells after treatment to evaluate the effect of all factors. At least a 7-log reduction in cell numbers was observed for both strains. The pH and the strains had no effect on HHP treatment at 20 degrees C while at 37 degrees C, both pH and strain influenced significantly the HHP treatment on C. jejuni.

CONCLUSIONS

The pressure efficacy on C. jejuni eradication was affected by both environmental and biological factors.

SIGNIFICANCE AND IMPACT OF THE STUDY

Depending on the treatment conditions, C. jejuni sensitivity to HHP can significantly vary. The determination of the inactivation treatment by HPP has to be normalized considering the interaction of environmental and biological factors.

Survival of Campylobacter jejuni and Escherichia coli in groundwater during prolonged starvation at low temperatures

AIMS

To evaluate the survival of Campylobacter jejuni relative to that of Escherichia coli in groundwater microcosms varying in nutrient composition.

METHODS AND RESULTS

Studies were conducted in groundwater and deionized water incubated for up to 470 days at 4 degrees C. Samples were taken for culturable and total cell counts, nutrient and molecular analysis. Die-off in groundwater microcosms was between 2.5 and 13 times faster for C. jejuni than for E. coli. Campylobacter jejuni had the lowest decay rate and longest culturability in microcosms with higher dissolved organic carbon (4 mg l(-1)). Escherichia coli survival was the greatest when the total dissolved nitrogen (12.0 mg l(-1)) was high. The transition of C. jejuni to the coccoid stage was independent of culturability.

CONCLUSION

The differences in the duration of survival and response to water nutrient composition between the two organisms suggest that E. coli may be present in the waters much longer and respond to water composition much differently than C. jejuni.

SIGNIFICANCE AND IMPACT OF THE STUDY

The data from these studies would aid in the evaluation of the utility of E. coli as an indicator of C. jejuni. This study also provided new information about the effect of nutrient composition on C. jejuni viability.

Nutrition-based health in animal production

Events such as BSE, foot and mouth disease and avian influenza illustrate the importance of animal health on a global basis. The only practical solution to deal with such problems has usually been mass culling of millions of animals at great effort and expense. Serious consideration needs to be given to nutrition as a practical solution for health maintenance and disease avoidance of animals raised for food. Health or disease derives from a triad of interacting factors; diet–disease agent, diet–host and disease agent–host. Various nutrients and other bioactive feed ingredients, nutricines, directly influence health by inhibiting growth of pathogens or by modulating pathogen virulence. It is possible to transform plant-based feed ingredients to produce vaccines against important diseases and these could be fed directly to animals. Nutrients and nutricines contribute to three major factors important in the diet–host interaction; maintenance of gastrointestinal integrity, support of the immune system and the modulation of oxidative stress. Nutrition-based health is the next challenge in modern animal production and will be important to maintain economic viability and also to satisfy consumer demands in terms of food quality, safety and price. This must be accomplished largely through nutritional strategies making optimum use of both nutrients and nutricines.

Campylobacter jejuni inactivation in New Zealand soils

AIM

The study was undertaken to determine the inactivation rate of Campylobacter jejuni in New Zealand soils.

METHODS AND RESULTS

Farm dairy effluent (FDE) inoculated at c. 10(5) ml(-1) with C. jejuni was applied to intact soil cores at a rate of 2 l m(-2). Four soils were used: Hamilton (granular); Taupo (pumice); Horotiu and Waihou (allophanic). After FDE application cores were incubated at 10 degrees C for up to 32 days. For all four soils all the FDE remained within the cores and at least 99% of C. jejuni were retained in the top 5 cm. Campylobacter jejuni had declined to the limit of detection (two C. jejuni 100 g(-1)) by 25 days in Hamilton and Taupo soils and by 32 days in Waihou soil. In contrast, in Horotiu soil the decline was only three orders of magnitude after 32 days. Simulated heavy rainfall was applied 4 and 11 days after FDE application and only about 1% of the applied C. jejuni were recovered in leachates.

CONCLUSIONS

This study demonstrated that at least 99% of applied C. jejuni were retained in the top 5 cm of four soils where they survived for at least 25 days at 10 degrees C.

SIGNIFICANCE AND IMPACT OF THE STUDY

Soil retention of C. jejuni is efficient at FDE application rates that prevent drainage losses. The low infectious dose of C. jejuni and its ability to survive up to 25 days have implications for stock management on dairy farms.

Optimising the viability during storage of freeze-dried cell preparations of Campylobacter jejuni

Freeze-dried cultures of Campylobacter jejuni are used in the food and microbiological industry for reference materials and culture collections. However, C. jejuni is very susceptible to damage during freeze-drying and subsequent storage and it would be useful to have longer-lasting cultures. The survival of C. jejuni during freeze-drying and subsequent storage was investigated with the aim of optimising survival. C. jejuni was freeze-dried using cultures of different age (24-120 h), various lyoprotectants (10% phytone peptone, proteose peptone, peptonized milk, trehalose, soytone and sorbitol), various storage (air, nitrogen and vacuum) and re-hydration (media, temperature and time) conditions. One-day-old cultures had significantly greater survival after freeze-drying than older cultures. The addition of trehalose to inositol broth as a lyoprotectant resulted in almost 2 log(10) increase in survival after 2 months storage at 4 degrees C. Storage in a vacuum atmosphere and re-hydration in inositol broth at 37 degrees C increased recovery by 1-2 log(10) survival compared to re-hydration in maximal recovery diluent (MRD) after storage at 4 degrees C. Survival during storage was optimal when a one-day-old culture was freeze-dried in inositol broth plus 10% (w/v) trehalose, stored under vacuum at 4 degrees C and re-hydrated at the same incubation temperature (37 degrees C) in inositol broth for 30 min. The results demonstrate that the survival of freeze-dried cells of C. jejuni during storage can be significantly increased by optimising the culture age, the lyoprotectant, and the storage and re-hydration conditions. The logarithmic rate of loss of viability (K) followed very well an inverse dependence on the absolute temperature, i.e., the Arrhenius rate law. Extrapolation of the results to a more typical storage temperature (4 degrees C) predicted a very low K value of 1.5 x 10(-3). These results will be useful to the development of improved reference materials and samples held in culture collections.

A major role for intestinal epithelial nucleotide oligomerization domain 1 (NOD1) in eliciting host bactericidal immune responses to Campylobacter jejuni

Campylobacter jejuni is the foremost cause of bacterial-induced diarrhoeal disease worldwide. Although it is well established that C. jejuni infection of intestinal epithelia triggers host innate immune responses, the mechanism(s) involved remain poorly defined. Innate immunity can be initiated by families of structurally related pattern-recognition receptors (PRRs) that recognize specific microbial signature motifs. Here, we demonstrated maximal induction of epithelial innate responses during infection with live C. jejuni cells. In contrast when intestinal epithelial cells (IECs) were exposed to paraformaldehyde-fixed bacteria, host responses were minimal and a marked reduction in the number of intracellular bacteria was noted in parallel. These findings suggested a role for intracellular host-C. jejuni interactions in eliciting early innate immunity. We therefore investigated the potential involvement of a family of intracellular, cytoplasmic PRRs, the nucleotide-binding oligomerization domain (NOD) proteins in C. jejuni recognition. We identified NOD1, but not NOD2, as a major PRR for C. jejuni in IEC. We also found that targeting intestinal epithelial NOD1 with small interfering RNA resulted in an increase in number of intracellular C. jejuni, thus highlighting a critical role for NOD1-mediated antimicrobial defence mechanism(s) in combating this infection at the gastrointestinal mucosal surface.

Environmental stress factors affecting survival and virulence of Campylobacter jejuni

Enteric pathogens are constantly exposed to stressful conditions in their natural habitat in the host and even more in the extra-host environment, including food processing. The aim of this study was to evaluate the effect of selected environmental stress factors: temperature shift, starvation and atmospheric oxygen concentration on culturability/viability of two Campylobacter jejuni isolates. Additionally, after stress exposure, in an in vitro cell culture model using Caco-2 cells, the adhesion, invasion and intracellular survival of C. jejuni were studied. Nutrient insufficiency was the most powerful stress factor which significantly affected C. jejuni culturability and viability, as well as, adhesion and invasion properties. Temperature elevation induced a transient growth arrest, and temporary loss of pathogenic potential as indicated by impaired adhesion and invasion efficiency of C. jejuni. However, bacteria recovered within 24-48h inside the Caco-2 cells. Oxidative stress neither affected C. jejuni growth nor reduced the binding and invasion into Caco-2 cells. Only 5h oxygen exposure increased the invasion capability and intraepithelial survival of the clinical isolate. Modulation of C. jejuni virulence in response to environmental stress factors may have further implications in the pathogenesis of campylobacteriosis.

Campylobacters as zoonotic pathogens: a food production perspective

Campylobacters remain highly important zoonotic pathogens worldwide which infect an estimated 1% of the population of Western Europe each year. Certain campylobacters are also important in infections of animals, particularly of the reproductive tract, and some are involved in periodontal disease. This paper focuses, however, on the two species which are most important in food-borne infections of humans, Campylobacter (C.) jejuni and C. coli. Infection with these campylobacters is serious in its own right but can also have long-term sequelae such as reactive arthritis and Guillain-Barré syndrome. The pathogens are ubiquitous in nature and in domestic animals and, as a consequence, are found frequently in the environment and on many raw foods, of both plant and animal origin and bacterial numbers can be very high on certain key foods like raw poultry meat. Although all commercial poultry species can carry campylobacters, the risk is greater from chicken because of the high levels of consumption. Campylobacters are relatively 'new' zoonotic pathogens as routine culture from clinical specimens only became possible in the late 1970s. As a consequence there is much that still needs to be understood about the behaviour and pathogenicity of these highly important bacteria. In particular, and from a food industry/food safety perspective, it is important to better understand the behaviour of C. jejuni and C. coli in the food production environment, and how this affects their ability to survive certain food production processes. There is a belief that campylobacters are much more sensitive to hostile conditions than either salmonellas or Escherichia coli. Much of data to support this view have been derived from laboratory experiments and may not fully represent the natural situation. Studies are showing that campylobacters may be more robust than previously thought and thus may represent a greater challenge to food safety. We recommend that research is undertaken to better understand how campylobacters behave in the food chain and how responses to relevant conditions affect their ability to survive processing and their virulence. There is also a need to better understand the reasons why campylobacters are capable of frequent change, particularly in the expression of surface antigens.

Prevalence, Molecular Characterization and Antimicrobial Resistance of Thermophilic Campylobacter Isolates from Cattle, Hens, Broilers and Broiler Meat in South-eastern Italy

Eleven cattle farms, 8 layer farms, 7 broiler farms and 30 broiler meat samples were investigated in south-eastern Italy throughout 2003 to evaluate the prevalence, the molecular type and antimicrobial resistance of thermophilic Campylobacters. A total of 398 samples were analysed. One Campylobacter isolate for each positive faecal swab and three isolates per positive broiler meat sample were selected for further analysis. Multiplex PCR was performed for species-level identification and PCR-RFLP of the flagellin A gene for genotyping. Resistance to 14 antimicrobials was studied in 188 Campylobacter isolates. Prevalence of campylobacters was high both on farms (100%) and in food samples (73%). On 4/11 cattle farms and on 10/15 poultry farms more than one species was isolated. The presence of more than one genotype was found on 8/11 cattle farms, on 10/15 poultry farms and in 8/22 Campylobacter-positive food samples. High rates of resistance to quinolone were observed: 9/31 (29%) C. jejuni bovine isolates, 4/22 (18%) C. jejuni poultry isolates, and 14/26 (54%) C. coli poultry isolates. Resistance to sulphamethoxazole-trimethoprim was also observed frequently: 18/26 (69%) of the avian C. coli strains, 25/31 (80%) of the C. jejuni strains isolated from poultry and 15/22 (68%) of those isolated from cattle were resistant. There was a significant difference between the rate of resistance to macrolides of C. coli and C. jejuni isolated in poultry, which amounted to 23% and 3%, respectively. This study provided data on the prevalence and antimicrobial resistance of thermophilic campylobacters in south-eastern Italy and confirmed that flaA-typing is an efficient tool to study the epidemiology of Campylobacter strains in short-term investigations.

Stress Response of Campylobacter spp. and its Role in Food Processing

In many temperate countries Campylobacter spp. are the most common bacterial causes of human infectious intestinal disease. Yet the aetiology of this infection has only partly been described. A majority of human campylobacteriosis cases are associated with food of animal origin. Despite being very sensitive to environmental stressors Campylobacter spp. are able to persist in the food chain and can pose a threat to the consumer. In this review, the survival potential and stress response of Campylobacter spp. in food will be summarized and the importance of food preservation technologies will be discussed.

Cj1496c encodes a Campylobacter jejuni glycoprotein that influences invasion of human epithelial cells and colonization of the chick gastrointestinal tract

Campylobacter jejuni has an N-linked protein glycosylation pathway that is required for efficient cell invasion and chick gastrointestinal colonization by the microbe. In this study, we constructed insertion mutants of 22 putative glycoprotein genes and examined the ability of each to invade the human intestinal epithelial cell line INT-407. Among the mutants tested, one carrying an insertion in Cj1496c was defective for invasion into INT-407 cells; this defect was also observed in an in-frame deletion mutant of Cj1496c (delta Cj1496c). The delta Cj1496c mutant C. jejuni also showed a reduced ability to colonize chick ceca. Site-specific mutagenesis combined with Western blot analysis suggested that the Cj1496c protein is glycosylated at N73 and N169. However, the delta Cj1496c mutant expressing a nonglycosylated form of Cj1496c exhibited levels of invasion and colonization equivalent to those of the parent strain, suggesting that glycans are not directly involved in the function of Cj1496c.

Survival and stress induced expression of groEL and rpoD of Campylobacter jejuni from different growth phases

Although Campylobacter jejuni is the leading cause of bacterial diarrhoeal disease in humans worldwide, its potential to adapt to the stressful conditions and survive in extra-intestinal environment is still poorly understood. We tested the effect of heat shock (55 degrees C, 3 min) and oxidative stress (3 mM H2O2 for 10 min or prolonged incubation at atmosphere oxygen concentration) on non-starved and starved cells of Campylobacter jejuni from different growth phases. Viability as assessed with the Bacterial Viability Kit LIVE/DEAD BacLighttrade mark dying before fluorescent microscopy and culturability of the cells (CFU ml(-1)) from both growth phases showed that starvation increased heat but not oxidative resistance. High temperature and oxidative stress invoked quick transformation from culturable spiral shaped to nonculturable spiral and coccoid cells. Despite physiological changes of the cells we were not able to document clear differences in the expression of heat shock and starvation genes (dnaK, htpG, groEL), oxidative (ahpC, sodB), virulence (flaA) and housekeeping genes (16S rRNA, rpoD) after heat treatment (55 degrees C, 3 min) or oxidative stresses applied. When starving, no induction of expression of any of these genes was noticed, chloramphenicol had no influence on their gene expression. Quantitative real-time PCR analyses showed that at least 10-20 min of heat shock was necessary to evidently increase the amount of groEL and rpoD transcripts.

Analysis of covariance patterns in gene expression data and FT-IR spectra

The aim of this study was to detect and interpret correlation patterns in several large data matrices from the same biological system using Partial Least Squares Regression (PLSR) in order to get information on the system under investigation. To do this, DNA microarray data and Fourier Transform Infrared (FT-IR) spectra from a designed study where Campylobacter jejuni was exposed to environmental stress conditions, were used. The experimental design included variation in atmospheric conditions, temperature and time. PLSR was first used to analyse each of the two data types separately in order to explore the effect of the experimental parameters on the data. The results showed that both the gene expression and FT-IR spectra were affected by the variations in atmosphere, temperature and time, but that the effect was different for the two types of data. When the DNA microarray data and FT-IR spectra were linked together by PLSR, covariation due to temperature was seen. Both specific genes and ranges in the FT-IR spectra that were connected to the variation in temperature were detected. Some of these are possibly connected to properties of the cell wall of the bacteria. The results in this study show the potential of PLSR for investigation of covariance structures in biological data. By doing this, valuable information about the biological system can be detected and interpreted. It was also shown that the use of FT-IR spectroscopy provided important information about the stress responses in the bacteria, information that was not detected from the DNA microarray data.

Campylobacter in poultry: filling an ecological niche

Epidemiological studies indicate that Campylobacter species may be responsible for the majority of cases of sporadic gastroenteritis in humans. These studies also suggest that poultry may be one of the most common sources of the bacteria for humans. Campylobacter and related genera in the family Campylobacteraceae are oral and intestinal commensals of vertebrates and some nonvertebrates, a characteristic that complicates rational approaches to controlling Campylobacter contamination of poultry. This review will discuss the phylogeny, genomics, and physiology of campylobacters with the intention of revealing how these organisms have evolved to fill their intestinal ecological niche in poultry and how their physiology must be understood in order to enact effective control strategies.

Environmental survival mechanisms of the foodborne pathogen Campylobacter jejuni

Campylobacter spp. continue to be the greatest cause of bacterial gastrointestinal infections in humans worldwide. They encounter many stresses in the host intestinal tract, on foods and in the environment. However, in common with other enteric bacteria, they have developed survival mechanisms to overcome these stresses. Many of the survival mechanisms used by Campylobacter spp. differ from those used by other bacteria, such as Escherichia coli and Salmonella spp. This review summarizes the mechanisms by which Campylobacter spp. adapt to stress conditions and thereby increase their ability to survive on food and in the environment.

Antimicrobial susceptibilities of Campylobacter jejuni isolates from poultry from Alberta, Canada

One hundred four isolates of Campylobacter jejuni from poultry in Alberta, Canada, collected during 2001 were tested for resistance to 10 antimicrobial agents using agar dilution. This study provides a baseline of resistance profiles and the mechanisms of resistance observed in C. jejuni in poultry from Alberta, Canada.

Transcriptional and translational expression patterns associated with immobilized growth of Campylobacter jejuni

AlthoughCampylobacter jejuniis a leading cause of food-borne illness, little is known about the mechanisms by which this pathogen mediates prolonged environmental survival or host cell virulence. Although these behaviours represent distinct phenotypes, they share a common requirement of an immobilized state. In order to understand the cellular mechanisms that facilitate a surface-associated lifestyle, transcriptional and translational expression profiles were determined for sessile and planktonicC. jejuni. These investigations indicate that the immobilized bacteria undergo a shift in cellular priorities away from metabolic, motility and protein synthesis capabilities towards emphasis on iron uptake, oxidative stress defence and membrane transport. This pattern of expression partially overlaps those reported for Campylobacter during host colonization, as well as for other species of bacteria involved in biofilms, highlighting common adaptive responses to the conserved challenges within each of these phenotypes. The adaptation of Campylobacter to immobilized growth may represent a quasi-differentiated state that functions as a foundation for further specialization towards phenotypes such as biofilm formation or host cell virulence.

Development of a real-time NASBA assay for the detection of Campylobacter jejuni cells

The objectives of this study were the development of a real-time NASBA assay for the detection of Campylobacter jejuni mRNA and the evaluation of its potential to determine the viability of the detected C. jejuni cells. A set of specific primers and probes was chosen to amplify the mRNA of the tuf-gene and the GTPase-gene. Only the tuf-assay was able to detect as low as 10(2) cells per NASBA reaction and was specific for Campylobacter. However, as the assay was able to detect dead cells, it cannot be used to demonstrate the viability of C. jejuni cells. The tuf-gene mRNA is no good viability indicator due to its stability.

Growth of Campylobacter in media supplemented with organic acids

The growth of Campylobacter spp. in media supplemented with organic acids was examined. A Bioscreen C Microbiology Reader was used to measure growth of cultures incubated at 37 degrees C for 48 h in a tryptose-yeast extract basal broth medium and in basal broth supplemented with 10, 20, 30, 40, or 50 mM citric, fumaric, lactic, malic, or succinic acid. Growth of three of six isolates was significantly greater (P < or = 0.05) in media supplemented with 20 to 50 mM citric acid than in nonsupplemented media, growth of five of six isolates was significantly greater in media supplemented with 10 to 50 mM succinic acid than in nonsupplemented media, and growth of six of six isolates was significantly greater in media supplemented with 10 to 50 mM fumaric or malic acid or with 20 to 50 mM lactic acid than in nonsupplemented media. Isolates were also cultured in basal media supplemented with a mixture of 10, 20, 30, 40, or 50 mM fumaric, malic, lactic, and succinic acids. Results indicated that the growth of all Campylobacter isolates was significantly greater in media supplemented with mixtures containing each of these organic acids at 10 to 40 mM than in nonsupplemented media. These findings indicate that in vitro growth of Campylobacter spp. may be significantly enhancedin media supplemented with organic acids that support the growth of these bacteria.

Influence of inoculation levels and processing parameters on the survival of Campylobacter jejuni in German style fermented turkey sausages

This study investigated the influence of inoculum levels and manufacturing methods on the survival of Campylobacter (C.) jejuni in raw fermented turkey sausages. Sausages were prepared and inoculated with C. jejuni. After inoculation, these sausages were processed and ripened for 8 days. Samples were taken throughout the ripening process. The presence of C. jejuni was established bacteriologically. Additionally, lactic acid bacteria were enumerated, pH values and water activity were measured to verify the ripening process. To detect changes in genotype and verify the identity of the recovered clones, AFLP analysis was carried out on the re-isolated strains. Whereas no C. jejuni were detectable when inoculating the sausages with the lowest inoculum (0.08-0.44 log(10) cfu/g sausage emulsion), C. jejuni were detectable for 12-24h by enrichment when inoculated with approximately 2 log(10) cfu/g. After inoculation with 4 and 6 log(10) cfu/g respectively, C. jejuni were detectable without enrichment for 12-48 h and by enrichment for 144 h at the most. The greatest decrease of the C. jejuni population occurred during the first 4 h of ripening. Only a very high inoculum level allowed the survival of the organism during a fermentation process and during ripening to pose a potential risk for consumers. Lower initial Campylobacter inoculums will be eliminated during proper ripening of the sausages, if sufficient decrease in water activity and pH-value is ensured.

The Campylobacter jejuni stringent response controls specific stress survival and virulence-associated phenotypes

Campylobacter jejuni is a highly prevalent food-borne pathogen that causes diarrhoeal disease in humans. A natural zoonotic, it must overcome significant stresses both in vivo and during transmission despite the absence of several traditional stress response genes. Although relatively little is understood about its mechanisms of pathogenesis, its ability to interact with and invade human intestinal epithelial cells closely correlates with virulence. A C. jejuni microarray-based screen revealed that several known virulence genes and several uncharacterized genes, including spoT, were rapidly upregulated during infection of human epithelial cells. spoT and its homologue relA have been shown in other bacteria to regulate the stringent response, an important stress response that to date had not been demonstrated for C. jejuni or any other epsilon-proteobacteria. We have found that C. jejuni mounts a stringent response that is regulated by spoT. Detailed analyses of a C. jejuni delta spoT mutant revealed that the stringent response is required for several specific stress, transmission and antibiotic resistance-related phenotypes. These include stationary phase survival, growth and survival under low CO2/high O2 conditions, and rifampicin resistance. A secondary suppressor strain that specifically rescues the low CO2 growth defect of the delta spoT mutant was also isolated. The stringent response additionally proved to be required for the virulence-related phenotypes of adherence, invasion, and intracellular survival in two human epithelial cell culture models of infection; spoT is the first C. jejuni gene shown to participate in longer term survival in epithelial cells. Microarray analyses comparing wild-type to the delta spoT mutant also revealed a strong correlation between gene expression profiles and phenotype differences observed. Together, these data demonstrate a critical role for the C. jejuni stringent response in multiple aspects of C. jejuni biology and pathogenesis and, further, may lend novel insight into unexplored features of the stringent response in other prokaryotic organisms.