Soft-agar-coated filter method for early detection of viable and thermostable direct hemolysin (TDH)- or TDH-related hemolysin-producing Vibrio parahaemolyticus in seafood

Sensitive colorimetric immunoassay of Vibrio parahaemolyticus based on specific nonapeptide probe screening from a phage display library conjugated with MnO2 nanosheets with peroxidase-like activity

Pathogen detection continues to receive significant attention due to the harmful effects of pathogens on public health. Herein, specific nonapeptide-fusion proteins pVIII (pVIII fusion) were isolated from phage VQTVQIGSD (designated by the sequence of a fused foreign peptide), which was specifically screened from the f8/9 landscape phage library against Vibrio parahaemolyticus (V. parahaemolyticus) in a high-throughput way. The as-prepared V. parahaemolyticus-specific recognition element is cheaper and more available than antibodies. Further, a highly sensitive colorimetric immunoassay for V. parahaemolyticus was established using pVIII fusion as capture probes coupled with protein-templated MnO₂ nanosheets (NSs) as signal probes. In the presence of a target bacterium, V. parahaemolyticus, a sandwich-type complex of pVIII fusion-V. parahaemolyticus-MnO₂ NS@pVIII fusion was formed through specific recognition of pVIII fusion and V. parahaemolyticus. The signal probes (MnO₂ NSs) could catalyze the reaction of 3,3',5,5'-tetramethylbenzidine and H₂O₂ to generate a colorimetric change. The proposed V. parahaemolyticus detection method demonstrated a wide detection range (20-10⁴ colony-forming units (CFU) mL^-1), low limit of detection (15 CFU mL^-1), excellent selectivity, and high reliability for real marine samples, showing potential application in marine microbiological detection and control.

The pathogenesis, detection, and prevention of Vibrio parahaemolyticus

Vibrio parahaemolyticus, a Gram-negative motile bacterium that inhabits marine and estuarine environments throughout the world, is a major food-borne pathogen that causes life-threatening diseases in humans after the consumption of raw or undercooked seafood. The global occurrence of V. parahaemolyticus accentuates the importance of investigating its virulence factors and their effects on the human host. This review describes the virulence factors of V. parahaemolyticus reported to date, including hemolysin, urease, two type III secretion systems and two type VI secretion systems, which both cause both cytotoxicity in cultured cells and enterotoxicity in animal models. We describe various types of detection methods, based on virulence factors, that are used for quantitative detection of V. parahaemolyticus in seafood. We also discuss some useful preventive measures and therapeutic strategies for the diseases mediated by V. parahaemolyticus, which can reduce, to some extent, the damage to humans and aquatic animals attributable to V. parahaemolyticus. This review extends our understanding of the pathogenic mechanisms of V. parahaemolyticus mediated by virulence factors and the diseases it causes in its human host. It should provide new insights for the diagnosis, treatment, and prevention of V. parahaemolyticus infection.

A new biphasic test for the detection of Helicobacter pylori in gastric biopsies

The objective of this study was to create a biphasic cultural method for the detection of Helicobacter pylori in gastric biopsy specimens. The biphasic systems were made by using a urea agar slant with overlaying broth in a single vessel. Initially, three different liquid media including brain-heart infusion broth, Brucella broth, and Bolton broth were tested for their ability to support the growth of H. pylori. Bolton broth with 10% defibrinated horse blood demonstrated a significant increase in the numbers of H. pylori (p<0.05). The result showed that positive urease was used to concentrate viable H. pylori cells where the numbers of bacteria were 10(5)cfu. In addition, the reliable incubation time was at least 36h. In total, 55 biopsies were comparatively studied using commercial rapid urease test and PCR. Seven samples (12.72%) were positive with H. pylori by the biphasic test. With the CLOtest, 6 (10.91%) samples were positive. In conclusion, the Hp biphasic test achieved more positive samples than did the commercial rapid urease test.

Multi-Probe-Fluorescence in situ Hybridization for the Rapid Enumeration of Viable Vibrio parahaemolyticus

A one-step multi-probe FISH method of detecting viable Vibrio parahaemolyticus was developed. Three candidate regions, corresponding to Helix 440+441, Helix 588, and Helix 1241 in 16S rRNA, were selected for detection, the thermodynamic parameters (ΔG(overall)) of the probes were optimized, and VP437, VP612 and VP1253, whose fluorescence were 1.7 to 11.3 times that of ΔG(overall)-unadjusted sequences, were designed. The addition of competitive oligonucleotides to reactions with VP612 and VP1253 strengthened the specificity of the probes. The three probes were labeled with FITC, TAMRA, and Cy5, respectively, and using a mixture of the probes and six competitive oligonucleotides, one-step FISH was applied to the species-specific detection of V. parahaemolyticus including epidemic strains of O3:K6 and O4:K68 serotypes. V. alginolyticus, V. rotiferianus, and V. campbellii were not detected in the reaction. Microcolonies (30-80 μm in diameter) of V. parahaemolyticus were observed within 6 hours at 37°C on seawater agar plates in both fresh and heat-damaged V. parahaemolyticus. Viable bacterial counts based on the proposed method were significantly different from those measured with typical vibrio selective media (CHROMagar Vibrio and TCBS).

The development of loop-mediated isothermal amplification combined with lateral flow dipstick for detection of Vibrio parahaemolyticus

AIMS

The current study was aimed to develop a loop-mediated isothermal amplification (LAMP) combined with amplicon detection by chromatographic lateral flow dipstick (LFD) assay for rapid and specific detection of Vibrio parahaemolyticus.

METHODS AND RESULTS

Biotinylated LAMP amplicons were produced by a set of four designed primers that recognized specifically the V. parahaemolyticus thermolabile haemolysin (tlh) gene followed by hybridization with an FITC-labelled probe and LFD detection. The optimized time and temperature conditions for the LAMP assay were 90 min at 65 °C. The LAMP-LFD method accurately identified 28 isolates of V. parahaemolyticus but did not detect 24 non-parahaemolyticus Vibrio isolates and 35 non-Vibrio bacterial isolates. The sensitivity of LAMP-LFD for V. parahaemolyticus detection in pure cultures was 120 CFU ml⁻¹. In the case of spiked shrimp samples without enrichment, the detection limit for V. parahaemolyticus was 1·8 x 10³ CFU g⁻¹ or equivalent to 3 CFU per reaction while that of conventional PCR was 30 CFU per reaction.

CONCLUSIONS

The established LAMP-LFD assay targeting tlh gene was specific, rapid and sensitive for identification of V. parahaemolyticus.

SIGNIFICANCE AND IMPACT OF THE STUDY

The developed LAMP-LFD assay provided a valuable tool for detection of V. parahaemolyticus and can be used effectively for identification of V. parahaemolyticus in contaminated food sample.

Enhancement of viable Campylobacter detection by chemotactic stimuli

The effects of chemotactic stimuli on motility ability of viable Campylobacter to pass through a 0.45 microm pore size filter in viscous condition were investigated. Reference strains including C. jejuni ATCC 33291, C. coli MUMT 18407, C. lari ATCC 43675, and C. upsaliensis DMST 19055 were used. The initial numbers of artificially-inoculated viable cells per g of chicken meat were approximately 10 to 10(4). Constituents of mucin plus bile (1:1), varieties of amino acids, and sodium salts were added into a soft-agar-coated membrane filter and incubated at both 37 degrees C and 42 degrees C for 24h. The drop plate method was used to determine numbers of viable Campylobacter at 6, 12, 18, and 24h. After 6h, constituents of mucin plus bile at the concentrations of 1, 5, and 10% demonstrated significant increases in numbers of viable cells (p<0.05). The numbers of the organisms at 42 degrees C were higher than those at 37 degrees C. In contrast, no significant difference in cell numbers was observed by adding amino acids or sodium salts. In addition, the role of starvation on chemotactic responses was also studied. Starved cells showed lower chemotactic response than non-starved cells. This method permitted rapid detection of viable thermophilic Campylobacter.

New Biotype of Vibrio cholerae O1 from Clinical Isolates in Surabaya

A surveillance of new pathogenic variants of Vibrio cholerae O1 strains was initiated to identify the emerge and spread throughout Surabaya. Findings from seven years (1994–2000) and from years 2008 until now by using a two-fold surveillance strategy was pursued involving 1) hospital-based case recognition, and 2) environment samples. Rectal swabs and environment samples were transported to ITD-UNAIR, Surabaya for culture and isolates were characterized by serotypic identification and arbitrarily primed PCR fingerprints revealed a group of strains with similar fingerprint patterns that are distinct from those of the current El Tor epidemic strain. These strains have been analyzed by in vitro technique and the group has been denominated the Surabaya-Indonesian variant of V. cholerae O1.

Sensitive and rapid detection of cholera toxin-producing Vibrio cholerae using a loop-mediated isothermal amplification

Background

Vibrio cholerae is widely acknowledged as one of the most important waterborne pathogen causing gastrointestinal disorders. Cholera toxin (CT) is a major virulence determinant of V. cholerae. Detection of CT-producing V. cholerae using conventional culture-, biochemical- and immunological-based assays is time-consuming and laborious, requiring more than three days. Thus, we developed a novel and highly specific loop-mediated isothermal amplification (LAMP) assay for the sensitive and rapid detection of cholera toxin (CT)-producing Vibrio cholerae.

Results

The assay provided markedly more sensitive and rapid detection of CT-producing V. cholerae strains than conventional biochemical and PCR assays. The assay correctly identified 34 CT-producing V. cholerae strains, but did not detect 13 CT non-producing V. cholerae and 53 non-V. cholerae strains. Sensitivity of the LAMP assay for direct detection of CT-producing V. cholerae in spiked human feces was 7.8 × 10² CFU per g (1.4 CFU per reaction). The sensitivity of the LAMP assay was 10-fold more sensitive than that of the conventional PCR assay. The LAMP assay for detection of CT-producing V. cholerae required less than 35 min with a single colony on thiosulfate citrate bile salt sucrose (TCBS) agar and 70 min with human feces from the beginning of DNA extraction to final determination.

Conclusion

The LAMP assay is a sensitive, rapid and simple tool for the detection of CT-producing V. cholerae and will be useful in facilitating the early diagnosis of human V. cholerae infection.