Development of a PCR assay combined with a short enrichment culture for detection of Campylobacter jejuni in estuarine surface waters

DNA Supercoiling Regulates the Motility of Campylobacter jejuni and Is Altered by Growth in the Presence of Chicken Mucus

Campylobacter jejuni is the leading cause of bacterial gastroenteritis in humans, but relatively little is known about the global regulation of virulence factors during infection of chickens or humans. This study identified DNA supercoiling as playing a key role in regulating motility and flagellar protein production and found that this supercoiling-controlled regulon is induced by growth in chicken mucus. A direct correlation was observed between motility and resting DNA supercoiling levels in different strains of C. jejuni, and relaxation of DNA supercoiling resulted in decreased motility. Transcriptional analysis and Western immunoblotting revealed that a reduction in motility and DNA supercoiling affected the two-component regulatory system FlgRS and was associated with reduced FlgR expression, increased FlgS expression, and aberrant expression of flagellin subunits. Electron microscopy revealed that the flagellar structure remained intact. Growth in the presence of porcine mucin resulted in increased negative supercoiling, increased motility, increased FlgR expression, and reduced FlgS expression. Finally, this supercoiling-dependent regulon was shown to be induced by growth in chicken mucus, and the level of activation was dependent on the source of the mucus from within the chicken intestinal tract. In conclusion, this study reports for the first time the key role played by DNA supercoiling in regulating motility in C. jejuni and indicates that the induction of this supercoiling-induced regulon in response to mucus from different sources could play a critical role in regulating motility in vivo.

Although Campylobacter jejuni is the leading cause of bacterial gastroenteritis, very little is understood about how this pathogen controls the expression of genes involved in causing disease. This study for the first time identifies DNA supercoiling as a key regulator of motility in C. jejuni, which is essential for both pathogenesis and colonization. Altering the level of DNA supercoiling results in changes in motility levels, as well as changes in the expression of genes involved in flagellar gene regulation. Furthermore, spontaneous clones of the organism with different motility profiles have altered DNA supercoiling levels. Finally, mucus was identified as a key stimulator of changes in DNA supercoiling, and it was shown that mucus from different sites in the chicken intestine induced different levels of DNA supercoiling. In conclusion, this study implicates DNA supercoiling as a key regulator of motility in C. jejuni in vivo during colonization of the mucus layer.

Environmental monitoring of waterborne Campylobacter: evaluation of the Australian standard and a hybrid extraction-free MPN-PCR method

Campylobacter is the leading agent of diarrheal disease worldwide. This study evaluates a novel culture-PCR hybrid (MPN-PCR) assay for the rapid enumeration of Campylobacter spp. from estuarine and wastewater systems. To first evaluate the current, culture-based, Australian standard, an inter-laboratory study was conducted on 69 subsampled water samples. The proposed Most-Probable Number (MPN)-PCR method was then evaluated, by analysing 147 estuarine samples collected over a 2 year period. Data for 14 different biological, hydrological and climatic parameters were also collated to identify pathogen-environment relationships and assess the potential for method specific bias. The results demonstrated that the intra-laboratory performance of the MPN-PCR was superior to that of AS/NZS (σ = 0.7912, P < 0.001; κ = 0.701, P < 0.001) with an overall diagnostic accuracy of ~94%. Furthermore, the analysis of both MPN-PCR and AS/NZS identified the potential for the introduction of method specific bias during assessment of the effects of environmental parameters on Campylobacter spp. numbers.

Determination of the optimal culture conditions for detecting thermophilic campylobacters in environmental water

This study evaluated alternative protocols for culturing thermophilic campylobacters in environmental water. All samples were filtered through a sterile 0.45μm pore-size membrane, which was then incubated in Preston enrichment broth. Four variables were compared: water sample volume (2000mL vs. 500mL), enrichment broth volume (25mL vs. 100mL), enrichment incubation duration (24h vs. 48h), and number of enrichment passages (one vs. two). In addition, DNA extracts were prepared from all final broths and analyzed using three rRNA PCR assays. River water was collected at 3 sampling sites weekly for 9 weeks. Among these 27 collections, 25 (93%) yielded Campylobacter spp. under at least one of the 16 culture conditions. By univariate analysis, yields were significantly better for the 2000mL sample volume (68.5% vs. 43.0%, p<0.0001) and the 25mL enrichment broth volume (64.5% vs. 47.0%, p<0.0004). Neither of the enrichment period had a significant effect, although there was a trend in favor of 48h incubation (59.5% vs. 52.0%, p=0.13). The three PCR methods gave concordant results for 66 (33%) of the culture-negative samples and 103 (50%) of the culture-positive samples. Compared with culture results, Lubeck's 16S PCR assay had the best performance characteristics, with a sensitivity of 82% and a specificity of 94%. Of the 12 culture-negative samples positive by Lubeck's PCR assay, 11 (92%) samples were also positive by Denis' 16S PCR assay, suggesting that in these cases the culture might have been falsely negative. Based on our results, we conclude that the optimal conditions for detecting Campylobacter spp. in natural waters include 2000mL sample volume and a single enrichment broth of 25mL PB incubated for 48h.

Polymerase chain reaction for the diagnosis of bovine genital campylobacteriosis

Bovine genital campylobacteriosis is a common venereal disease of cattle; the prevalence of this disease can be underestimated mostly because of the nature of the etiological agent, the microaerobic Campylobacter fetus subspecies venerealis. The purpose of the current study was to evaluate the utilization of polymerase chain reaction (PCR) in the diagnosis of genital campylobacteriosis in samples obtained from bull prepuce aspirate, cow cervical mucus, and abomasum contents of aborted fetuses, collected into enrichment medium. Five different DNA extraction protocols were tested: thermal extraction, lysis with proteinase K, lysis with guanidine isothiocyanate, lysis with DNAzol, and lysis with hexadecyltrimethylammonium bromide (CTAB). The specificity, sensitivity, and technical application of the PCR assay were also evaluated with clinical samples and compared to bacterial isolation by standard culture. DNA extraction by the CTAB protocol provided better results in PCR, and it was able to detect 63 colony-forming units per ml of C. fetus. Out of 277 clinical samples tested, 68 (24%) were positive for Campylobacter fetus using PCR, while only 8 (2.8%) of the samples were positive by bacterial isolation in solid medium, proving the superiority of the PCR technique when compared to the standard isolation method, and providing evidence for its usefulness as a better screening test in cattle for the diagnosis of bovine genital campylobacteriosis.

Rapid and accurate detection of Arcobacter contamination in commercial chicken products and wastewater samples by real-time polymerase chain reaction

An SYBR Green real-time polymerase chain reaction (PCR) assay was developed for Arcobacter detection in food and wastewater samples. The assay was applied to 36 chicken and 33 wastewater samples, and the results were compared with those obtained for conventional PCR, multiplex PCR, and culture isolation. Isolates were identified by multiplex PCR and restriction fragment length polymorphism analysis of PCR-amplified DNA fragment, and typed by randomly amplified polymorphic DNA. Arcobacter sp. was detected in 25 of the 26 chicken carcasses (96%) and in 4 of the 10 liver samples (40%) by real-time PCR. Twenty-five chicken samples were positive also by conventional PCR, but in most of them the detection was only possible after 48-h enrichment. Arcobacter butzleri was the most frequently detected species. Twenty-four Arcobacter isolates were obtained from chicken samples, where A. butzleri is the only identified species. All the wastewater samples (100%) were positive for Arcobacter sp. by real-time PCR without enrichment. A. butzleri and Arcobacter cryaerophilus were detected by multiplex PCR. Fifteen samples were found to be positive by culture. Thirty-six isolates were obtained; all of them were identified as A. butzleri by multiplex PCR. However, by PCR-restriction fragment length polymorphism, 34 were identified as A. butzleri, 1 as A. cryaerophilus, and another 1 as Arcobacter skirrowii. A great genetic heterogeneity was observed by randomly amplified polymorphic DNA-PCR profiling. The real-time PCR assay developed in this work showed better detection levels than conventional PCR, together with shorter times of testing samples. Therefore, it could be used as a rapid and accurate instrument for monitoring Arcobacter contamination levels in food and water samples.

Enhanced enrichment and detection of thermotolerant Campylobacter species from water using the Portable Microbe Enrichment Unit and real-time PCR

An enhanced enrichment using the Portable Microbe Enrichment Unit (PMEU) with the microaerobic bubbling of broths was applied for the detection of thermotolerant Campylobacter species from water. This PMEU enrichment was compared with the conventional static enrichment of the international standard ISO 17995:2005. In addition, Campylobacter detection after enrichment using a real-time PCR detection was compared with colony counts. The tests with stressed Campylobacter jejuni cells in drinking water indicated that the PMEU enrichment yielded a significantly higher number of Campylobacter cells in the Bolton broth compared with the conventional static incubation. Application of the real-time PCR technique shortened the Campylobacter detection time. This combination of method modifications can be used for Campylobacter detection from water and adds methodological repertoire for the rapid survey and management of waterborne outbreaks.

Direct detection and identification of Arcobacter species by multiplex PCR in chicken and wastewater samples from Spain

Twenty-two chicken livers, 10 chicken carcasses, and 15 wastewater samples were processed and analyzed for Arcobacter by PCR and traditional culture methods. Samples were enriched for 24 and 48 h, incubated at 30 degrees C under aerobic conditions, and streaked on blood selective media. To determine the best isolation conditions, 20 samples also were processed under microaerophilic conditions at 37 degrees C. Simple and multiplex PCR assays were used directly with enrichment broths and isolated strains. Seventeen Arcobacter strains were isolated from chicken samples, and A. butzleri was the only Arcobacter species identified. The direct PCR assay revealed that 29 of the 32 chicken samples were contaminated with Arcobacter. A. butzleri was the most frequently detected species, although Arcobacter cryaerophilus also was present in some of the samples and Arcobacter skirrowii occasionally was detected. All the wastewater samples were positive by PCR assay for Arcobacter after 24 h of enrichment. A. butzleri and A. cryaerophilus were detected with the multiplex PCR assay. Fourteen Arcobacter strains were isolated from 10 of the 15 water samples analyzed; 7 were identified as A. butzleri and the remaining 7 were A. cryaerophilus. Both for chicken and water samples, Arcobacter detection rate for PCR amplification was higher than for culture isolation. These results indicate the high prevalence of Arcobacter in chicken and wastewater and the inadequacy of available cultural methods for its detection. The species-specific multiplex PCR assay is a rapid method for assessing Arcobacter contamination in chicken and wastewater samples and is a viable alternative to biochemical identification of isolated strains.

Campylobacter in waterfowl and aquatic environments: incidence and methods of detection

Campylobacters are emerging as one of the most significant causes of human infections worldwide, and the role that waterfowl and the aquatic environment have in the spread of disease is beginning to be elucidated. On a world scale campylobacters are possibly the major cause of gastrointestinal infections. Campylobacters are common commensals in the intestinal tract of many species of wild birds, including waterfowl. They are also widely distributed in aquatic environments where their origins may include waterfowl as well as sewage effluents and agricultural runoff. Campylobacters have marked seasonal trends. In temperate aquatic environments they peak during winter, whereas spring-summer is the peak period for human infection. Campylobacter species may survive, and remain potentially pathogenic, for long periods in aquatic environments. The utility of bacterial fecal indicators in predicting the presence of campylobacters in natural waters is questionable. Viable but nonculturable Campylobacter cells may occur, but whether they have any role in the generation of outbreaks of campylobacteriosis is unclear. The routine detection of Campylobacter spp. in avian feces and environmental waters largely relies on conventional culture methods, while the recognition of a particular species or strain is based on serotyping and increasingly on molecular methods. Thus, PCR combined with selective enrichment enhances the detection of campylobacters in water and feces, while DNA sequencing facilitates recognition of particular species and strains.

Evaluation of the use of PCR and reverse transcriptase PCR for detection of pathogenic bacteria in biosolids from anaerobic digestors and aerobic composters

A PCR-based method and a reverse transcriptase PCR (RT-PCR)-based method were developed for the detection of pathogenic bacteria in organic waste, using Salmonella spp., Listeria monocytogenes, Yersinia enterocolitica, and Staphylococcus aureus as model organisms. In seeded organic waste samples, detection limits of less than 10 cells per g of organic waste were achieved after one-step enrichment of bacteria, isolation, and purification of DNA or RNA before PCR or RT-PCR amplification. To test the reproducibility and reliability of the newly developed methods, 46 unseeded samples were collected from diverse aerobic (composting) facilities and anaerobic digestors and analyzed by both culture-based classical and newly developed PCR-based procedures. No false-positive but some false-negative results were generated by the PCR- or RT-PCR-based methods after one-step enrichment when compared to the classical detection methods. The results indicated that the level of activity of the tested bacteria in unseeded samples was very low compared to that of freshly inoculated cells, preventing samples from reaching the cell density required for PCR-based detection after one-step enrichment. However, for Salmonella spp., a distinct PCR product could be obtained for all 22 nonamended samples that tested positive for Salmonella spp. by the classical detection procedure when a selective two-step enrichment (20 h in peptone water at 37 degrees C and 24 h in Rappaport Vassiliadis medium at 43 degrees C) was performed prior to nucleic acid extraction and PCR. Hence, the classical procedure was shortened, since cell plating and further differentiation of isolated colonies can be omitted, substituted for by highly sensitive and reliable detection based on nucleic acid extraction and PCR. Similarly, 2 of the 22 samples in which Salmonella spp. were detected also tested positive for Listeria monocytogenes according to a two-step enrichment procedure followed by PCR, compared to 3 samples that tested positive when classical isolation procedures were followed. The study shows that selective two-step enrichment is useful when very low numbers of bacterial pathogens must be detected in organic waste materials, such as biosolids. There were no false-positive results derived from DNA of dead cells in the waste sample, suggesting that it is not necessary to perform RT-PCR analyses when PCR is combined with selective enrichment. Large numbers of added nontarget bacteria did not affect detection of Salmonella spp., L. monocytogenes, and Y. enterocolitica but increased the detection limit of Staphylococcus aureus from <10 to 10(4) CFU/g of organic waste. Overall, the detection methods developed using seeded organic waste samples from one waste treatment facility (WTF) needed to be modified for satisfactory detection of pathogens in samples from other WTFs, emphasizing the need for extensive field testing of laboratory-derived PCR protocols. A survey of 13 WTFs in Germany revealed that all facilities complied with the German Biowaste Ordinance, which mandates that the end product after anaerobic digestion or aerobic composting be free of Salmonella In addition, all biosolids were free of L. monocytogenes, Staphylococcus aureus, and Y. enterocolitica, as evidenced by both classical and PCR-based detection methods.

Rapid detection of Campylobacter jejuni in chicken rinse water by melting-peak analysis of amplicons in real-time polymerase chain reaction

Five DNA extraction protocols for the detection of Campylobacter spp. by polymerase chain reaction (PCR) were compared. A method involving Triton X-100 produced template DNA of sufficient quality to allow the detection of Campylobacter jejuni at levels of 100 CFU/ml in pure culture. Primers were designed on the basis of the cadF gene sequence. With a SYBR Green I real-time PCR assay, these primers amplified only sequences present in C. jejuni to produce a product with a melting temperature of 81.5 degrees C. None of the strains of Campylobacter coli, Campylobacter lari, or Campylobacter fetus tested produced this product during the PCR assay. Other noncampylobacter species tested were shown not to possess the cadF sequence. The real-time PCR combined with a rapid, simple Triton X-100 DNA extraction protocol made it possible to detect < 10 CFU of C. jejuni per ml of chicken rinse within 14 h.

Specific detection of Arcobacter and Campylobacter strains in water and sewage by PCR and fluorescent in situ hybridization

The aim of this study was to evaluate PCR and fluorescent in situ hybridization (FISH) techniques for detecting Arcobacter and Campylobacter strains in river water and wastewater samples. Both 16S and 23S rRNA sequence data were used to design specific primers and oligonucleotide probes for PCR and FISH analyses, respectively. In order to assess the suitability of the methods, the assays were performed on naturally and artificially contaminated samples and compared with the isolation of cells on selective media. The detection range of PCR and FISH assays varied between 1 cell/ml (after enrichment) to 10(3) cells/ml (without enrichment). According to our results, both rRNA-based techniques have the potential to be used as quick and sensitive methods for detection of campylobacters in environmental samples.

Detection of Campylobacter jejuni strains in the water lines of a commercial broiler house and their relationship to the strains that colonized the chickens

Campylobacter jejuni is frequently present in the intestinal tract of commercial broiler chickens, and their drinking water has been proposed to be an initial source of bacteria for newly hatched chicks. We studied three sequential commercial broiler flocks raised in a house from which we had cultured C. jejuni from the nipple waters prior to placement of the first flock. Campylobacter cells were detected by immunofluorescence in the biofilm of the drinking nipples during the weeks when the flock was colonized with C. jejuni but not during weeks when the birds were negative. Campylobacter jejuni was isolated from the drinking water during the growth of the first flock and was present in the birds from all three flocks. Randomly amplified polymorphic DNA (RAPD)-polymerase chain reaction (PCR) typing with primer OPA11 indicated that seven distinct strains were present within the broiler house. One strain found in drinking water was similar to a strain found in birds in the second flock; however, RAPD-PCR with primer HLW85 showed that the strains were not identical. These results suggest that although the watering system is a potential source of C. jejuni in broiler flocks, the waterborne strain in this study was not detected in the birds.

Detection of Campylobacter jejuni and Campylobacter coli in environmental waters by PCR enzyme-linked immunosorbent assay

A PCR enzyme-linked immunosorbent assay (ELISA) assay was applied to the detection of Campylobacter jejuni and Campylobacter coli in environmental water samples after enrichment culture. Bacterial cells were concentrated from 69 environmental water samples by using filtration, and the filtrates were cultured in Campylobacter blood-free broth. After enrichment culture, DNA was extracted from the samples by using a rapid-boiling method, and the DNA extracts were used as a template in a PCR ELISA assay. A total of 51 samples were positive by either PCR ELISA or culture; of these, 43 were found to be positive by PCR ELISA and 43 were found to be positive by culture. Overall, including positive and negative results, 59 samples were concordant in both methods. Several samples were positive in the PCR ELISA assay but were culture negative; therefore, this assay may be able to detect sublethally damaged or viable nonculturable forms of campylobacters. The method is rapid and sensitive, and it significantly reduces the time needed for the detection of these important pathogens by 2 to 3 days.

Detection of Campylobacter jejuni in poultry samples using an enzyme-linked immunoassay coupled with an enzyme electrode

An enzyme-linked immunoassay coupled with a tyrosinase modified enzyme electrode was used for rapid detection of Campylobacter jejuni. The immunomagnetic separation (IMS) method was investigated to achieve optimal isolation of C. jejuni cells. Eight types of beads with three different sizes and function groups were coated with anti-C. jejuni to isolate C. jejuni from the sample solution. Bead size and coating methods were found to be major factors that influenced the capture efficacy. Streptavidin-labeled beads (2.8 microm) provided the greatest capture ability. Three blocking reagents were tested to minimize non-specific binding. Bovine serum albumin (BSA) showed the best blocking capability. Two IMS formats were tested. Competitive immunoassay cut the detection time to 1.5 h, but the detection limit was relatively high (10(6) CFU/ml). This system was evaluated using C. jejuni pure culture and poultry samples inoculated with C. jejuni. This detection method for C. jejuni could be completed within 2.5 h and had a detection limit of 2.1 x 10(4) CFU/ml. No significant difference was found between pure culture samples and poultry samples (P>0.01). A linear relationship was found between C. jejuni cell numbers and the peak current ratio in a range of 10(2)-10(7) CFU/ml (R(2)=0.94).

Molecular detection of Campylobacter spp. in drinking, recreational and environmental water supplies

A molecular detection assay was performed on 207 samples of drinking, recreational and environmental waters collected in Northern Ireland. The water sources which were PCR positive for Campylobacter spp. included 2/91 (2.2%) drinking water from domestic household taps, 5/57 (8.8%) swimming pool water, 1/23 (4.3%) lake water and 1/1 water from a jacuzzi. Extracted DNA from all water samples was amplified employing a sequence-specific PCR assay based on a 206 bp conserved region of the flagellin A-flagellin B (flaA/flaB) loci for Campylobacter jejuni, C. coli and C. lari. Given the physiological and cultural fragile nature of these species, no waters were cultured using conventional methods due to concern for reversion to non-culturability from time of collection to laboratory analysis. As this genus has been demonstrated to form a 'viable but non-culturable' (VBNC) form, failure to culture organisms conventionally from water does not necessarily equate to a negative result, hence molecular detection assays, especially those which can demonstrate cell viability, may be useful in helping to elucidate potential epidemiological sources and reservoirs of this organism, especially where water is suspected as being the vehicle of transmission.

Direct detection of thermotolerant campylobacters in chicken products by PCR and in situ hybridization

We have evaluated the use of PCR and fluorescent in situ hybridization (FISH) techniques for the detection of thermotolerant campylobacters in naturally contaminated chicken products. 16S rRNA sequence data was used to design two specific primers and an oligonucleotide probe for PCR and FISH analyses, respectively. The PCR protocol amplified a 439-bp fragment corresponding to a portion of specific 16S RNA gene from thermotolerant campylobacters. The detection range of the PCR assay varied between 10 cells (after enrichment) to 10(2) cells per mL (without enrichment). FISH probes were able to identify thermotolerant Campylobacter species in 'spiked' and 'unspiked' naturally contaminated samples. PCR and FISH were performed on naturally contaminated samples and compared with the isolation of cells on selective media. The in situ hybridization technique was less sensitive than PCR, although its sensitivity of detection was increased considerably after 22 h of enrichment. These results confirm the usefulness of 16S rRNA-based techniques for the direct detection of campylobacters in food samples.

Detection of small numbers of Campylobacter jejuni and Campylobacter coli cells in environmental water, sewage, and food samples by a seminested PCR assay

A rapid and sensitive assay was developed for detection of small numbers of Campylobacter jejuni and Campylobacter coli cells in environmental water, sewage, and food samples. Water and sewage samples were filtered, and the filters were enriched overnight in a nonselective medium. The enrichment cultures were prepared for PCR by a rapid and simple procedure consisting of centrifugation, proteinase K treatment, and boiling. A seminested PCR based on specific amplification of the intergenic sequence between the two Campylobacter flagellin genes, flaA and flaB, was performed, and the PCR products were visualized by agarose gel electrophoresis. The assay allowed us to detect 3 to 15 CFU of C. jejuni per 100 ml in water samples containing a background flora consisting of up to 8, 700 heterotrophic organisms per ml and 10,000 CFU of coliform bacteria per 100 ml. Dilution of the enriched cultures 1:10 with sterile broth prior to the PCR was sometimes necessary to obtain positive results. The assay was also conducted with food samples analyzed with or without overnight enrichment. As few as </=3 CFU per g of food could be detected with samples subjected to overnight enrichment, while variable results were obtained for samples analyzed without prior enrichment. This rapid and sensitive nested PCR assay provides a useful tool for specific detection of C. jejuni or C. coli in drinking water, as well as environmental water, sewage, and food samples containing high levels of background organisms.

A reverse transcriptase polymerase chain reaction assay for the detection of thermophilic Campylobacter spp

A novel method was developed for the detection of thermophilic enteropathogenic campylobacters based on the detection of mRNA using the reverse transcriptase polymerase chain reaction (RT-PCR). The RNA extraction method, DNase treatment and RT-PCR assay were shown to be specific for mRNA. The assay is specific for the thermophilic campylobacters Campylobacter jejuni, Campylobacter coli and Campylobacter upsaliensis and restriction fragment length polymorphism (RFLP) analysis of the 256 bp amplified product with the restriction endonucleases Alu I, Dde I and Dra I revealed distinct species specific patterns. The assay was applied to the detection of C. jejuni cells killed by heating at 72 degreesC for 5 min and mRNA was detected by RT-PCR immediately after heat killing but became undetectable within 4 h when the cells were held at 37 degreesC. The assay therefore can differentiate between viable and dead cells of C. jejuni.

Rapid PCR with nested primers for direct detection of Campylobacter jejuni in chicken washes

Rapid detection of Campylobacter jejuni by PCR directly from foods, without prior growth steps, would be beneficial for the poultry industry. We have previously reported a PCR assay that allows detection of this bacterium after 48 h growth on Campy cefex agar. We have now developed a more rapid nested PCR assay that specifically detects C. jejuni in chicken washes that have not undergone any lengthy growth steps prior to PCR. For the nested reaction, an external set of primers, C-1 and C-4, are used for 24 cycles. At this time, 1 microl of the PCR product is removed and added to a second reaction. The second PCR assay is run with C-1 and an internal primer, C-2, for 24 cycles. A single band on a 4% NuSieve agarose gel at 122 bp was apparent with C. jejuni cells at a sensitivity of 10(2) cfu ml-1. With this method chicken carcasses can be washed and C. jejuni identified all within 1 day. We detected C. jejuni in approximately 80% of four groups of chickens using this method. The identifications have been confirmed by standard microbiological techniques.

Microtitre plate hybridization system for detection of thermophilic Campylobacter rRNA

A microtitre plate nucleic acid probe hybridization system was developed for the detection of ribosomal RNA from thermophilic Campylobacter (Camp. jejuni, Camp. coli, Camp. lari and Camp. upsaliensis). A specific DNA probe obtained by amplification of 23S rRNA sequences using the polymerase chain reaction technique was immobilized on a microtitre plate, and used for hybridization with target 23S rRNA from cell lysates. The RNA-DNA hybrids thus formed in the wells were detected by an immunoenzymatic assay using a monoclonal antiRNA-DNA hybrid antibody. The sensitivity of this system was 2.7 x 10(4) cells ml(-1). This simple, sensitive and inexpensive hybridization and immunoenzymatic assay system should facilitate the detection of Campylobacter in food and clinical samples.

Microtitre plate riboprobe system for detection of ultrasonicated Campylobacter jejuni genomic DNA

Microtitre plate nucleic acid probe hybridization systems were developed for the detection of thermophilic Campylobacter and Campylobacter jejuni. Specific RNA probes obtained by in vitro transcription of DNA templates synthesized by polymerase chain reaction using two sets of specific primers incorporating bacteriophage T7 promoter sequences were immobilized on a microtitre plate. The hybridizations were carried out on samples of genomic DNA sheared by ultrasonication. Optimum conditions for the ultrasonic treatment were determined in order to obtain the highest degree of hybridization with immobilized RNA probe. Finally, detection of RNA-DNA hybrids in the wells was accomplished by an immunoenzymatic assay using a monoclonal anti-RNA-DNA hybrid antibody. This rapid, simple hybridization and immunoenzymatic assay system will facilitate the detection of Campylobacter in foods and clinical samples.

Ribotypes and AP-PCR fingerprints of thermophilic campylobacters from marine recreational waters

Thirty-two strains of thermophilic campylobacters isolated from marine recreational water and seven reference strains were biotyped and analysed by chromosomal DNA HaeIII ribopatterns and AP-PCR profiles based on a random 10-mer primer (5'-CAA TCG CCG T-3'). The majority of seawater isolates (90%) were Campylobacter coli, and three strains were Camp. jejuni. Southern blot hybridization analysis showed differences between the strains, and in a numerical analysis three main clusters were formed at the 45% similarity level, that corresponded to Camp. jejuni subsp. jejuni, Camp. coli, and a combination of Camp. coli and Camp. jejuni subsp. doylei. AP-PCR profiles also differentiated between the species but were less discriminatory than ribotyping because six strains (17%) could not be typed by this method. Numerical analysis gave four main clusters at the 45% similarity level, corresponding to Camp. jejuni subsp. jejuni, Camp. coli (two clusters) and Camp. lari. The study shows that strains within each species are diverse genomically. Both molecular methods were highly discriminatory, although some strains with identical ribotypes could be distinguished by AP-PCR, and they are valuable new alternatives to traditional typing in epidemiological studies of environmental campylobacters.