Detection of Campylobacter jejuni and Campylobacter coli in foods by enrichment culture and polymerase chain reaction enzyme-linked immunosorbent assay

Review of paper-based microfluidic analytical devices for in-field testing of pathogens

Pathogens cause various infectious diseases and high morbidity and mortality which is a global public health threat. The highly sensitive and specific detection is of significant importance for the effective treatment and intervention to minimise the impact. However, conventional detection methods including culture and molecular method gravely depend on expensive equipment and well-trained skilled personnel, limiting in the laboratory. It remains challenging to adapt in resource-limiting areas, e.g., low and middle-income countries (LMICs). To this end, low-cost, rapid, and sensitive detection tools with the capability of field testing e.g., a portable device for identification and quantification of pathogens, has attracted increasing attentions. Recently, paper-based microfluidic analytical devices (μPADs) have shown a promising tool for rapid and on-site diagnosis, providing a cost-effective and sensitive analytical approach for pathogens detection. The fast turn-round data collection may also contribute to better understanding of the risks and insights on mitigation method. In this paper, critical developments of μPADs for in-field detection of pathogens both for clinical diagnostics and environmental surveillance are reviewed. The future development, and challenges of μPADs for rapid and onsite detection of pathogens are discussed, including using the cross-disciplinary development with, emerging techniques such as deep learning and Internet of Things (IoT).

Risk factors for campylobacteriosis in Australia: outcomes of a 2018-2019 case-control study

BACKGROUND

We aimed to identify risk factors for sporadic campylobacteriosis in Australia, and to compare these for Campylobacter jejuni and Campylobacter coli infections.

METHODS

In a multi-jurisdictional case-control study, we recruited culture-confirmed cases of campylobacteriosis reported to state and territory health departments from February 2018 through October 2019. We recruited controls from notified influenza cases in the previous 12 months that were frequency matched to cases by age group, sex, and location. Campylobacter isolates were confirmed to species level by public health laboratories using molecular methods. We conducted backward stepwise multivariable logistic regression to identify significant risk factors.

RESULTS

We recruited 571 cases of campylobacteriosis (422 C. jejuni and 84 C. coli) and 586 controls. Important risk factors for campylobacteriosis included eating undercooked chicken (adjusted odds ratio [aOR] 70, 95% CI 13-1296) or cooked chicken (aOR 1.7, 95% CI 1.1-2.8), owning a pet dog aged < 6 months (aOR 6.4, 95% CI 3.4-12), and the regular use of proton-pump inhibitors in the 4 weeks prior to illness (aOR 2.8, 95% CI 1.9-4.3). Risk factors remained similar when analysed specifically for C. jejuni infection. Unique risks for C. coli infection included eating chicken pâté (aOR 6.1, 95% CI 1.5-25) and delicatessen meats (aOR 1.8, 95% CI 1.0-3.3). Eating any chicken carried a high population attributable fraction for campylobacteriosis of 42% (95% CI 13-68), while the attributable fraction for proton-pump inhibitors was 13% (95% CI 8.3-18) and owning a pet dog aged < 6 months was 9.6% (95% CI 6.5-13). The population attributable fractions for these variables were similar when analysed by campylobacter species. Eating delicatessen meats was attributed to 31% (95% CI 0.0-54) of cases for C. coli and eating chicken pâté was attributed to 6.0% (95% CI 0.0-11).

CONCLUSIONS

The main risk factor for campylobacteriosis in Australia is consumption of chicken meat. However, contact with young pet dogs may also be an important source of infection. Proton-pump inhibitors are likely to increase vulnerability to infection.

Aptamer-based approaches for the detection of waterborne pathogens

Waterborne ailments pose a serious threat to public health and are a huge economic burden. Lack of hygiene in drinking and recreational water is the chief source of microbial pathogens in developing countries. Poor water quality and sanitation account for more than 3.4 million deaths a year worldwide. This has urged authorities and researchers to explore different avenues of pathogen detection. There is a growing demand for rapid and reliable sensor technologies, in particular those that can detect in situ and perform in harsh conditions. Some of the major waterborne pathogens include Vibrio cholerae, Leptospira interrogans, Campylobacter jejuni, Shigella spp., enterotoxigenic Escherichia coli, Clostridium difficile, Cryptosporidium parvum, Entamoeba histolytica, and Hepatitis A virus. While conventional methods of pathogen detection like serodiagnosis and microbiological methods have been superseded by nucleic acid amplification methods, there is still potential for improvement. This review provides an insight into aptamers and their utility in the form of aptasensors. It discusses how aptamer-based approaches have emerged as a novel strategy and its advantages over more resource-intensive and complex biochemical approaches.

Diarrheal illness and prosthetic joint infection caused by Campylobacter coli following consumption of undercooked chicken wings

Campylobacter species are common causes of diarrheal illness following consumption of contaminated food or unpasteurized dairy products, but subsequent dissemination and joint space infections are rare. We describe a patient who consumed undercooked chicken wings, with subsequent development of a febrile gastrointestinal illness marked by copious, watery stool output. This was followed by acute onset of pain and inability to bear weight on his right hip and leg where he had undergone prior arthroplasty. Synovial fluid cultures revealed Campylobacter coli, identified utilizing matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The patient made a full recovery following hip joint space debridement with prosthesis retention, coupled with sequential intravenous and oral ciprofloxacin therapy. This case highlights both the potential for prosthetic joint infection with Campylobacter coli following diarrheal illness, as well as challenges in reducing Campylobacter contamination within commercially distributed chicken wings.

Comparison of 2 types of broths and 3 selective agars for the detection of Campylobacter species in whole-chicken carcass-rinse samples

In this study, we compared the effectiveness of 2 types of Bolton broths and 3 selective media for isolating Campylobacter spp. from naturally contaminated whole-chicken carcass-rinse samples. One hundred chickens were rinsed with buffered peptone water, and the rinses were added to 2× Bolton broth (with or without blood supplementation). The samples were incubated and then streaked onto Preston agar, modified cefoperazone charcoal deoxycholate agar (mCCDA), and Campy-Cefex agar, which was followed by incubation under microaerobic conditions. No statistical differences were observed (P > 0.05) in isolation rate and selectivity between the 2 types of Bolton broths. Among the 3 selective agars, Preston agar yielded a significantly (P < 0.05) better isolation rate and selectivity. The Campy-Cefex agar, which is recommended by many food authorities for its high quantitative detection ability, showed extensive contamination with competing microorganisms and exhibited the lowest isolation rate and selectivity.

Prevalence of Campylobacter and Salmonella in raw chicken on retail sale in the republic of Ireland

To assess the current risks to consumers from Campylobacter and Salmonella in raw chicken products sold in the Republic of Ireland, a retail survey was undertaken to define their prevalence. Samples (n = 510) were analyzed using protocols based on ISO 10272-1:2006 and ISO 6579:2002. Processor codes on pack labels showed that 67% of samples were produced in the Republic of Ireland and 25% in the United Kingdom. Salmonella was present in 5.1% of samples, but the eight serovars found caused less than 7% of human salmonellosis reported in the Republic of Ireland. The results suggest that on-farm controls to limit Salmonella infection of broilers have been successful and that in Ireland raw chicken is not a significant cause of salmonellosis in humans. The overall prevalence of Campylobacter spp. was 84.3%. Isolation by the ISO method found 52.7% of samples to be positive, but overgrowth by contaminants was frequently evident. Therefore, in addition to enrichment, an homogenized sample was plated directly onto modified charcoal cefoperazone deoxycholate agar, and this detected a further 31.6%. Speciation of isolates (n = 426) determined that 67% were Campylobacter jejuni and 32% were Campylobacter coli. These species are the most common cause of campylobacteriosis in man. The results indicate that there is a need for poultry producers to introduce interventions to minimize the exposure of consumers in the Republic of Ireland to Campylobacter spp., as has been successfully done for Salmonella.

Dual enlargement of gold nanoparticles: from mechanism to scanometric detection of pathogenic bacteria

A mechanism of dual enlargement of gold nanoparticles (AuNPs) comprising two steps is described. In the first step, the AuNPs are enlarged by depositing Au atoms on their crystalline faces. In this process, the particles are not only enlarged but they are also observed to multiply: new Au nuclei are formed by the budding and division of the enlarged particles. In the second step, a silver enhancement is subsequently performed by the deposition of silver atoms on the enlarged and newly formed AuNPs to generate bimetallic Au@Ag core-shell structures. The dual nanocatalysis greatly enhances the electron density of the nanostructures, leading to a stronger intensity for colorimetric discrimination as well as better sensitivity for quantitative measurement. Based on this, a simple scanometric assay for the on-slide detection of the food-born pathogen Campylobacter jejuni is developed. After capturing the target bacteria, gold-tagged immunoprobes are added to create a signal on a solid substrate. The signal is then amplified by the dual enlargement process, resulting in a strong color intensity that can easily be recognized by the unaided eye, or measured by an inexpensive flatbed scanner. In this paper, dual nanocatalysis is reported for the first time. It provides a valuable mechanistic insight into the development of a simple and cost-effective detection format.

Prevalence of Campylobacter spp. in raw retail poultry on sale in Northern Ireland

A year-long survey of fresh, retail poultry products on sale in Northern Ireland was undertaken to define the prevalence of Campylobacter spp. by using protocols based on ISO (standard) 10272-1:2006. Incubation at 37 and 42 degrees C was undertaken to increase the diversity of isolates obtained. Overall, 652 isolates were identified as Campylobacter spp. by using PCR and amplified fragment length polymorphic typing. Phenotyping wrongly identified 21% of isolates. Prevalences of Campylobacter found were chicken, 91% (n = 336); turkey, 56% (n = 77); and duck, 100% (n = 17). Prevalence rates for chicken produced in Northern Ireland, Scotland, England, and Wales were similar, with a mean value of 91%. The prevalences in product from the latter two countries were much higher than were found in two United Kingdom-wide surveys of chicken. The incubation temperature did not affect the relative proportions of the species isolated (P > 0.05). Campylobacter jejuni composed 64.6% of isolates, Campylobacter coli, 27.4%, and Campylobacter lari, 1%. Most cases of human campylobacteriosis are caused by C. jejuni and C. coli. The overall Campylobacter prevalence results are consistent with Northern Ireland surveys undertaken since 2000, and indicate that United Kingdom strategies to control Campylobacter in chicken have not had a significant effecton the prevalence of this pathogen in retail products on sale in Northern Ireland.

Development of a surface plasmon resonance biosensor for the identification of Campylobacter jejuni

The purpose of this study was to develop a biosensor based on surface plasmon resonance (SPR) for the rapid identification of C. jejuni in broiler samples. We examined the specificity and sensitivity of commercial antibodies against C. jejuni with six Campylobacter strains and six non-Campylobacter bacterial strains. Antigen-antibody interactions were studied using enzyme-linked immunosorbent assay (ELISA) and a commercially available SPR biosensor platform (Spreeta). Campylobacter cells killed with 0.5% formalin had significant lower antibody reactivity when compared to live cells, or cells inactivated with 0.5% thimerosal or heat (70 degrees C for 3 min) using ELISA. The SPR biosensor showed a good sensitivity with commercial antibodies against C. jejuni at 10(3) CFU/ml and a low cross reactivity with Salmonella serotype typhimurium. The sensitivity of the SPR was similar when testing spiked broiler meat samples. However, research is still needed to reduce the high background observed when sampling meat products.

Detection of Campylobacter jejuni and Campylobacter coli in chicken meat samples by real-time nucleic acid sequence-based amplification with molecular beacons

A nucleic acid sequence-based amplification (NASBA) assay based on molecular beacons was used for real-time detection of Campylobacter jejuni and Campylobacter coli in samples of chicken meat. A set of specific primers and beacon probe were designed to target the 16S rRNA of both species. The real-time NASBA protocol including the RNA isolation was valid for both of the cell suspensions in buffered saline and the artificially contaminated chicken meat samples. The presence of rRNA could be correlated with cellular viability, following inactivation of the bacteria by heating, in inoculated chicken meat samples but not in RNase-free cell suspensions.

A LightCycler real-time PCR hybridization probe assay for detecting food-borne thermophilic Campylobacter

In a previous study, we reported the performance of a PCR assay amplifying 287-bp of the 16S rRNA gene of thermo-tolerant Campylobacter (C. jejuni, C. lari, C. coli) through an international ring-trial involving 12 participating laboratories. Based on the validated set of primers, a LightCycler real-time PCR assay (LC-PCR), which used fluorescent hybridization probes was developed. The test incorporated an internal amplification control co-amplified with the 16S rRNA gene of Campylobacter to monitor potential PCR inhibitors and ensure successful amplifications. The specificity study involving 39 Campylobacter and nine strains of other species indicated that the LC-PCR test was highly specific, giving cross-reactivity with only one strain of C. upsaliensis (CCUG19559). The sensitivity of the LC-PCR assay, evaluated in 32 spiked poultry-rinse or pork carcass-swab samples, was determined at 10CFU/ml carcass-rinse. The prevalence of samples positive for thermo-tolerant Campylobacter was 58.8% in 68 naturally contaminated poultry rinse samples tested by LC-PCR and the data were in good concordance with those of bacteriological method. The Ct values of the three replicates obtained for each sample tested in three different runs demonstrate that the LC-PCR was highly reproducible and afford a powerful tool for rapid detection of the thermo-tolerant Campylobacter strains.

A robotic DNA purification protocol and real-time PCR for the detection of Campylobacter jejuni in foods

Primers designed to amplify a Campylobacter jejuni cadF gene sequence were used in an SYBR Green I real-time PCR assay as an alternative to conventional bacteriological methods for the rapid detection of C. jejuni in foods. Twenty-five grams of chicken skin (breast and thigh) was contaminated by adding approximately 1, 10, or 50 CFU of C. jejuni ATCC 35560. Twenty-five grams of pork and 25-ml aliquots of milk were also inoculated with 1 and 10 CFU of the pathogen. The samples were incubated in Bolton broth for different periods at 37 and 42 degrees C under microaerophilic conditions. Using a commercial robotic DNA purification system, DNA was extracted and purified from 1-ml aliquots of the enrichment cultures before and after centrifugation of the 250-ml enrichment broth at 15,900 x g for 10 min at 4 degrees C. The DNA was used as the template in a real-time PCR assay. C. jejuni was detected after 12 h of enrichment from samples inoculated with about 50 CFU/25-g sample. After centrifugation, an enrichment step of 8 h was sufficient to allow detection of pathogen in samples inoculated with 10 CFU/25 g. However, 24 h of enrichment was necessary to detect pathogen in samples inoculated with approximately 1 CFU/25 g. The real-time PCR protocol developed in this study significantly reduced the detection time of C. jejuni in foods.

Detection of Campylobacter jejuni in naturally contaminated chicken skin by melting peak analysis of amplicons in real-time PCR

Contamination of poultry by Campylobacter spp. is a significant source of human diarrheal diseases. Traditional methods currently used to detect Campylobacter in foods are time-consuming and labor-intensive. In this study, primers designed for the Campylobacter jejuni cadF gene sequence were used in a SYBR Green I real-time PCR assay as an alternative to a conventional bacteriological method for the rapid detection of C. jejuni from poultry. Twelve portions of chicken purchased from two local grocery stores and 39 portions obtained from a commercial processing plant were examined. Samples of the skin were enriched in Bolton broth at 37 degrees C for 3 h and then at 42 degrees C for 9, 21, or 45 h under microaerobic conditions. DNA was extracted from 1-ml aliquots of the enrichment cultures using 1% Triton X-100. The DNA was used as the template in a real-time polymerase chain reaction (PCR) assay. After 24 h of enrichment, C. jejuni was isolated from 13 samples and all of the positive cultures were also detected by the real-time PCR procedure. C. jejuni was detected by both methods from samples artificially contaminated with 1 or 10 CFU of C. jejuni per 10 g, after 24 h of enrichment. The real-time PCR method was found to be sensitive and specific. It significantly reduced the time required for the detection of C. jejuni in poultry following enrichment of samples.

Prevalences and transmission routes of Campylobacter spp. strains within multiple pig farms

In this work, faecal samples were collected from 15 pig farms to determine the Campylobacter prevalences at different times during the rearing period and to visualize the exchange of strains among the pig population by genotyping specific isolates. All isolated strains were identified as C. coli. Whereas no Campylobacter were detectable in the faeces of piglets at the day of birth, the Campylobacter incidence rose within days to 32.8%. After transfer to the nursery unit the prevalence increased to 56.6%. Approximately two-thirds of the pigs remained C. coli shedders in the fattening unit. In contrast to most farms, one farm expressed a very low Campylobacter incidence during the whole rearing period. Amplified fragment length polymorphism (AFLP) analysis was performed on all C. coli isolates of one farm. Clonal strains were identified from the brood sows and their offsprings or neighbouring piglets. After moving to the nursery unit, new genotypes appeared in that pig group but the original C. coli strains largely remained within that group. C. coli genotypes, identified during the fattening period, replaced the previously isolated genotypes. Transportation to the abattoir had no significant influence on the shedding rate of C. coli. The detection rate before transportation was 79.1% and decreased slightly to 78.2% (n=330). Additionally, eleven of 1474 environmental samples from different sources of the pig farms were positive for C. coli. This study demonstrates the importance of pigs as a reservoir for C. coli. Maternal C. coli strains are the primary source of infection but non-related genotypes from different sources appear during the rearing period and these latter strains constitute largely the final C. coli flora.

Comparison of three methods for detecting Campylobacter spp. in chilled or frozen meat

There is a demand from the meat industry as well as from public health authorities for a simple and rapid detection method for thermophilic Campylobacter spp. from food. Hence, we compared different isolation procedures for their usefulness for this purpose. Bolton enrichment medium without blood, incubated statically in stomacher bags in microaerophilic atmosphere, detected more samples positive for thermophilic Campylobacter spp. than did Preston enrichment broth in bottles with small headspace and tight caps, incubated in aerobic atmosphere. Use of an automated antigen detection system to identify enrichment cultures positive for Campylobacter spp. was as sensitive as selective agars, and reduced the detection time by 24 h. Campylobacter spp. were recovered from 18.4% of the 461 samples tested. The prevalence was highest in refrigerated poultry meat (52% of the 80 samples tested) and poultry offal (41% of the 44 samples tested).

Further Characterization ofCampylobacterIsolated from U.S. Dairy Cows

The objective of the present study was to compare polymerase chain reaction (PCR) identification with ribotype results and to use pulsed field electrophoresis (PFGE) to correlate genotypic patterns with antibiotic resistance of Campylobacter isolated from lactating dairy cows in the United States. Thirty isolates were studied. Twenty-seven of the isolates were identified by PCR as Campylobacter jejuni and three were identified as Campylobacter coli. Genotypic patterns of 15 isolates were determined by PFGE, and although isolates originated from geographically separated regions of the United States, some were genotypically identical. In contrast to their genetic similarity, antibiotic sensitivity patterns differed within some genotypes. Under the conditions of our study, we concluded that ribotyping is not as discriminatory as PCR for speciation, and that a phenotypic trait such as antimicrobial resistance cannot always be predicted within the same genotype.

Campylobacter spp. in New Zealand raw sheep liver and human campylobacteriosis cases

Sheep liver samples were tested for the presence and numbers of Campylobacter jejuni and C. coli during both spring and autumn. Over the same period, isolates were obtained from human clinical cases from the same geographical area as where the food samples were purchased. A subset of the C. jejuni isolates was typed by both Penner serotyping and pulsed field gel electrophoresis using the restriction enzyme SmaI, to estimate the proportion of liver isolate types that were also isolated from human cases of campylobacteriosis. Of the 272 liver samples tested, 180 (66.2%) contained Campylobacter. Most of the positive samples contained <3 MPN/g of the organism, and only 12 (6.7%) were contaminated at a level exceeding 100 MPN/g. A total of 180 C. jejuni isolates were obtained from sheep liver and another 200 from human faeces. Of these, 212 isolates were randomly selected for typing, half from raw liver and half from human faeces. More than half (61.1%) of the 106 C. jejuni isolates from liver were of subtypes that were also isolated from human cases. While the C. jejuni present in sheep liver were mostly of subtypes also isolated from human cases, the significance of this food as a vehicle of human campylobacteriosis needs to be examined further in respect to other factors such as dose-response information, consumption data, frequency of undercooking and cross contamination.

A review of conventional detection and enumeration methods for pathogenic bacteria in food

With continued development of novel molecular-based technologies for rapid, high-throughput detection of foodborne pathogenic bacteria, the future of conventional microbiological methods such as viable cell enumeration, selective isolation of bacteria on commercial media, and immunoassays seems tenuous. In fact, a number of unique approaches and variations on existing techniques are currently on the market or are being implemented that offer ease of use, reliability, and low cost compared with molecular tools. Approaches that enhance recovery of sublethally injured bacteria, differentiation among species using fluorogenics or chromogenics, dry plate culturing, differentiation among bacteria of interest using biochemical profiling, enumeration using impedence technology, techniques to confirm the presence of target pathogens using immunological methods, and bioluminescence applications for hygiene monitoring are summarized here and discussed in relation to their specific advantages or disadvantages when implemented in a food microbiology setting.Key words: food pathogen, detection, enumeration methods, food safety.

Infections related to the ingestion of seafood Part I: viral and bacterial infections

Foodborne diseases cause an estimated 76 million illnesses in the USA each year. Seafood is implicated in 10-19% of these illnesses. A causative agent can be traced in about 44% of seafood-related outbreaks, viruses accounting for around half of these illnesses. Although viruses are the most common cause of seafood-related infections, most hospitalisations and deaths are due to bacterial agents. A wide variety of viruses, bacteria, and parasites have been implicated in seafood-related outbreaks, which are reported worldwide. The factor most commonly associated with infection is consumption of raw or undercooked seafood. People with underlying disorders, particularly liver disease, are more susceptible to infection. The first part of this two-part review summarises the general incidence of seafood-related infections and discusses the common viral and bacterial causes of these infections. For each agent, the microbiology, epidemiology, mode of transmission, and treatment are discussed. In the May issue of the journal we will discuss parasites associated with seafood consumption, the safety of seafood, and the measures put in place in the USA to increase its safety.

Detection of Campylobacter and Shigella Species in Food Samples Using an Array Biosensor

Campylobacter and Shigella bacteria are common causes of food- and water-borne illness worldwide. There is a current need in food, medical, environmental, and military markets for a rapid and user-friendly method of detecting such pathogens. The array biosensor developed at the NRL encompasses these qualities. In this study, 25-min, sandwich immunoassays were developed for the detection of Campylobacter and Shigella species in both buffer and a variety of food and beverage samples. The limit of detection for Shigella dysenteriae in buffer and chicken carcass wash was 4.9 x 10(4) cfu mL(-)(1), whereas Campylobacter jejuni could be measured at concentrations as low as 9.7 x 10(2) cfu mL(-)(1). The limits of detection and dynamic range were found to vary depending on the sample matrix, but could be improved by running the sample over the waveguide surface for longer periods of time. Samples were run with no preconcentration or enrichment steps and little-to-no sample pretreatment prior to analysis.

Comparison of culture, polymerase chain reaction (PCR), TaqMan Salmonella, and Transia Card Salmonella assays for detection of Salmonella spp. in naturally-contaminated ground chicken, ground turkey, and ground beef

Four types of assays were evaluated for the detection of Salmonella spp. in retail ground chicken (86 packages), ground turkey (104 packages), and ground beef (54 packages). Two 25 g samples from each package were separately subjected to pre-enrichment in buffered peptone water for 20 h at 37 degrees C followed by enrichment in Rappaport Vassiliadis (RV) broth for 20 h at 42 degrees C. The RV enrichments were plated onto Rambach agar, Rainbow Agar Salmonella, and XLT4 agar, and were also tested by a PCR assay targeting the Salmonella invA gene, as well as by the TaqMan Salmonella PCR assay. Additionally, the RV enrichments were tested using the Transia Card Salmonella immunoassay. Results showed that 16.8, 24.0, 28.8, and 26.4% of turkey samples were positive for Salmonella spp. by culture, PCR, TaqMan PCR, and Transia Card Salmonella assays, respectively. Eighteen, 28.5, 35.5, and 34.9% of chicken samples were positive by culture, PCR, TaqMan PCR, and Transia Card Salmonella assays, respectively, and 6.5, 6.5, 6.5, and 18.5% of ground beef samples were positive by the four assays, respectively. Analysis of the data using the kappa statistic showed that there was substantial to excellent agreement between the PCR and TaqMan PCR assays and between the PCR and culture assays (kappa coefficients ranging from 0.67 to 0.87), while there was poor to fair agreement between the results of the Transia Card Salmonella assay and the other methods (kappa coefficients ranging from 0.28 to 0.32). Overall, results showed that the PCR-based assays were more sensitive than the culture method, and the culture and PCR-based assays were more specific than the immunoassay for detection of Salmonella in ground chicken, turkey, and beef due to the occurrence of false positive results using the immunoassay.

A real-time PCR assay for the detection of Campylobacter jejuni in foods after enrichment culture

A real-time PCR assay was developed for the quantitative detection of Campylobacter jejuni in foods after enrichment culture. The specificity of the assay for C. jejuni was demonstrated with a diverse range of Campylobacter species, related organisms, and unrelated genera. The assay had a linear range of quantification over six orders of magnitude, and the limit of detection was approximately 12 genome equivalents. The assay was used to detect C. jejuni in both naturally and artificially contaminated food samples. Ninety-seven foods, including raw poultry meat, offal, raw shellfish, and milk samples, were enriched in blood-free Campylobacter enrichment broth at 37 degrees C for 24 h, followed by 42 degrees C for 24 h. Enrichment cultures were subcultured to Campylobacter charcoal-cefoperazone-deoxycholate blood-free selective agar, and presumptive Campylobacter isolates were identified with phenotypic methods. DNA was extracted from enrichment cultures with a rapid lysis method and used as the template in the real-time PCR assay. A total of 66 samples were positive for C. jejuni by either method, with 57 samples positive for C. jejuni by subculture to selective agar medium and 63 samples positive in the real-time PCR assay. The results of both methods were concordant for 84 of the samples. The total time taken for detection from enrichment broth samples was approximately 3 h for the real-time PCR assay, with the results being available immediately at the end of PCR cycling, compared to 48 h for subculture to selective agar. This assay significantly reduces the total time taken for the detection of C. jejuni in foods and is an important model for other food-borne pathogens.