Development of novel visual detection methodology for Salmonella in meat using saltatory rolling circle amplification.

AIM: The aim of this study was to develop a saltatory rolling circle amplification (SRCA) assay for rapid, simple and visual detection of Salmonella in meat. METHODS AND RESULTS: Saltatory rolling circle amplification assay was established using simple PCR primers targeting the invA gene of Salmonella enterica. The specificity of the SRCA assay was determined using 28 Salmonella and 15 non-Salmonella strains. The analytical sensitivity of the developed SRCA, conventional and real-time PCR assays were 70 fg, 7 pg and 700 fg S. enterica DNA per tube, respectively. The limit of detection (LoD) of the SRCA assay was 40 CFU per gram of meat without enrichment and 4 CFU per gram after including 6 h brief enrichment step. The detection limits of 40 CFU per gram and 4 CFU per gram of meat were achieved within 165 min and 9 h, respectively (including DNA extraction). To assess the real-world relevance of the SRCA assay, it was used to screen Salmonella from the field pork samples (n = 82). The same samples were also tested with culture (ISO 6579: 2002) method, conventional and real-time PCR assays. Using the developed assay with 6-h enrichment step, it could give accurate results as that of the culture method. CONCLUSIONS: The results of this study showed that the SRCA assay is a rapid, simple, sophisticated equipment-free and user-friendly method for accurate detection of Salmonella in meat foods. To our information, this is the first study to deploy SRCA assay for screening foods for Salmonella. SIGNIFICANCE AND IMPACT OF THE STUDY: The developed SRCA assay is cost-effective, easy-to-perform and equipment-free; therefore, it has the potential to replace other molecular detection methods for regular screening of Salmonella in foods in field laboratories.

Prevalence of Campylobacter jejuni and Campylobacter coli in captive wildlife species of India.

Campylobacteriosis is an important zoonotic disease and the prevalence of Campylobacter is largely unknown in the wildlife of India. A total of 370 samples, comprising of 314 fresh faecal samples from apparently healthy captive wild animals and birds, 30 stool swabs from animal care takers and 26 samples of the animals' food and water were collected from G. B. Pant High Altitude Zoo, Nainital, Kanpur Zoo, Wildlife Park, IVRI and the Post Graduate Research Institute in Animal Sciences (PGRIAS), Chennai, Tamilnadu from August 2014 to May 2015. Samples were processed for cultural isolation, direct PCR and multiplex PCR for species confirmation. To decipher the genetic diversity, the 16S rRNA gene was amplified, sequenced and analyzed. Based on isolation, the overall occurrence rate of Campylobacter spp. was 0.8% (3/370), being 2.94% (3/102) for captive wild birds. Three Campylobacter jejuni were isolated from silver pheasants, lady amherest pheasants and saras cranes. Direct PCR assay showed the overall occurrence rate of Campylobacter spp. to be 4.77% (15/315), being 1.58% (2/126) for captive wild ruminants, 5.81% (5/86) for non-ruminants and 7.84% (8/102) for birds. All the isolates were identified as C. jejuni.