Rapid and Visual Detection of Vibrio parahaemolyticus in Aquatic Foods Using blaCARB-17 Gene-Based Loop-Mediated Isothermal Amplification with Lateral Flow Dipstick (LAMP-LFD).

Vibrio parahaemolyticus is recognized as one of the most important foodborne pathogens responsible for gastroenteritis in humans. The blaCARB-17 gene is an intrinsic ß-lactamase gene and a novel species-specific genetic marker of V. parahaemolyticus. In this study, a loop-mediated isothermal amplification (LAMP) assay combined with a lateral flow dipstick (LFD) was developed targeting this blaCARB-17 gene. The specificity of LAMP-LFD was ascertained by detecting V. parahaemolyticus ATCC 17802 and seven other non-V. parahaemolyticus strains. Finally, the practicability of LAMP-LFD was confirmed by detection with V. parahaemolyticus-contaminated samples and natural food samples. The results showed that the optimized reaction parameters of LAMP are as follows: 2.4 mmol/l Mg2+, 0.96 mmol/l dNTPs, 4.8 U Bst DNA polymerase, and an 8:1 ratio of inner primer to outer primer, at 63°C for 40 min. The optimized reaction time of the LFD assay is 60 min. Cross-reactivity analysis with the seven non-V. parahaemolyticus strains showed that LAMP-LFD was exclusively specific for V. parahaemolyticus. The detection limit of LAMP-LFD for V. parahaemolyticus genomic DNA was 2.1 × 10-4 ng/µl, corresponding to 630 fg/reaction and displaying a sensitivity that is 100-fold higher than that of conventional PCR. LAMP-LFD in a spiking study revealed a detection limit of approximately 6 CFU/ml, which was similar with conventional PCR. The developed LAMP-LFD specifically identified the 10 V. parahaemolyticus isolates from 30 seafood samples, suggesting that this LAMP-LFD may be a suitable diagnostic method for detecting V. parahaemolyticus in aquatic foods.

[Preparation and characterization of monoclonal antibodies specific for CjaA protein of Campylobacter jejuni].

AIM: Expression, purification of Campylobacter jejuni CjaA protein and development of monoclonal antibodies (mAbs) against this protein. METHODS: The C. jejuni cjaA gene was amplified and inserted into the expression plasmids, pGEX-6p-1 and pET30a (+). The purified rGST-CjaA protein was used as an immunogen in 8-week-old BALB/c mice, and injected subcutaneously. The purified rHis-CjaA protein used as a detecting antigen for screening mAbs against CjaA was prepared. The specificity of mAbs was characterized by Dot-ELISA and Western blot assays. RESULTS: The recombinant expression plasmids, pGEX-6p-1-cjaA and pET30a(+)-cjaA were obtained. The sizes of the recombinant proteins, rGST-CjaA and rHis-CjaA, were consistent with their predicted size. Specific reaction was found between CjaA positive serum and expressed protein by Western blot assay, confirming its identification as a Campylobacter jejuni immunogen. Three hybridoma cell lines, designated 2B6, 3C2 and 4F11, secreting mAbs against CjaA were obtained. Their immunoglobulin subclasses were all IgG1. The ELISA titers of the ascites fluid were 1:1×10(5);, 1:2×10(5); and 1:4×10(5);, respectively. Western blot analysis confirmed that the three mAbs reacted with the rHis-CjaA fusion protein but not the His tag. The Dot-ELISA results demonstrated that the three mAbs only with CjaA and not the tags for the expression vectors. CONCLUSION: The successful preparation of three mAbs specific for the CjaA protein lays the foundation for further study regarding the biological characteristics of CjaA and the pathogenesis of C. jejuni.