MULTIPLEX PCR FOR DIRECT IDENTIFICATION OF THERMOPHILICCAMPYLOBACTER,C. JEJUNI,C. COLI,C. LARIANDC. UPSALIENSISAND SIMULTANEOUS DETECTION OFCDTBGENE

In Silico Analysis of the cadF Gene and Development of a Duplex Polymerase Chain Reaction for Species-Specific Identification of Campylobacter jejuni and Campylobacter coli

Background

Campylobacteriosis is a zoonotic infectious disease caused by Campylobacter jejuni and C. coli. The cadF gene is considered as a genus-specific gene while other genes are mainly used for discrimination at the species level.

Objectives

This study aimed to analyze the cadF gene and to develop a duplex PCR assay for simultaneous detection of C. coli and C. jejuni, the two commonly encountered species.

Materials and Methods

In silico analysis of the cadF gene was carried out by several software and available online tools. A duplex PCR optimized with specific primers was used for detection and differentiation of both species. To evaluate specificity and sensitivity of the test, a panel of different Campylobacter spp. together with several intestinal bacterial pathogens was tested. The limit of detection (LOD) of method was determined using serial dilutions of standard genomes.

Results

The analysis of the full size cadF gene indicated variations in this gene, which can be used to differentiate C. jejuni and C. coli. The duplex PCR designed in this study showed that it could simultaneously detect and differentiate both C. jejuni and C. coli with product sizes of 737 bp and 461 bp, respectively. This assay, with 100% specificity and sensitivity, had a limit of detection (LOD) of about 14 and 0.7 µg/mL for C. jejuni and C. coli, respectively.

Conclusions

In silico analysis of the cadF full-gene showed variations between the two species that can be used as a molecular target for differentiating C. jejuni and C. coli in a single-step duplex-PCR assay with high specificity and sensitivity.

Rapid Detection of Campylobacter jejuni, Campylobacter coli, and Campylobacter lari in Fresh Chicken Meat and By-Products in Bangkok, Thailand, Using Modified Multiplex PCR

A multiplex PCR assay for simultaneous detection and differentiation of Campylobacter jejuni, Campylobacter coli, and Campylobacter lari was developed and validated to assess the occurrence of these bacteria in fresh chicken meat and by-products in Bangkok, Thailand, by using a new combination of four previously published PCR primers for C. jejuni, C. coli, C. lari, and a universal 16S rDNA gene as an internal control. The specificity was determined by using 13 strains of other bacteria. With pure culture DNA, the detection limit was 0.017 ng/PCR for C. jejuni and C. coli and was 0.016 ng/PCR for C. lari. It can detect 10 CFU of C. jejuni, C. coli, and C. lari in 2 g of chicken meat within a 16-h enrichment time. Our multiplex PCR assay was applied for identification of Campylobacter spp. in 122 supermarket samples and 108 fresh market samples. Of the 230 samples evaluated by multiplex PCR, 54.0, 3.3, and 10.7% of supermarket samples were positive for C. jejuni, C. coli, and mixed C. jejuni and C. coli, respectively, and 56.5 and 33.3% of fresh market samples were positive for C. jejuni and mixed C. jejuni and C. coli, respectively. No sample was positive for C. lari. Fresh market samples had significantly higher C. jejuni and C. coli contamination than those from supermarkets (relative risk: 1.3; P = 0.0001). Compared with the culture method (a gold standard), the sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy of multiplex PCR were 97.7, 86.8, 96.1, 92.0, and 95.2%, respectively. No significant difference was observed between results from two methods (P = 0.55). Therefore, the established multiplex PCR was not only rapid and easy to perform but had a high sensitivity and specificity to distinguish between C. jejuni, C. coli, and C. lari, even in samples containing mixed contamination. Our study indicated that fresh chicken meat and by-products from fresh markets were significantly less hygienic than those from supermarkets.