Comparison of Different Methods to Identify tdh-Positive Pathogenic Vibrio parahaemolyticus Isolates

Performance evaluation of a rapid immunochromatographic test kit in detecting bovine mastitis-causing streptococci

Mastitis causes significant economic losses to the dairy industry due to decreased milk production in infected cows. Identification of mastitis-causing pathogens, such as streptococci, is necessary for selecting an effective antibiotic for treating mastitis. Although bacterial cultivation is widely used for pathogen identification, it requires more than 24 hr to complete. Contrarily, Lateral flow assays are simple, rapid, and inexpensive testing procedures. In this study, the effectiveness of an immunochromatographic test kit for detecting streptococci in milk samples from cows with clinical mastitis was evaluated as an alternative to bacterial cultivation. The performance of the immunochromatographic test kit for detecting mastitis-causing pathogens was compared with that of bacterial cultivation and real-time quantitative polymerase chain reaction (qPCR). The sensitivity and specificity of the immunochromatographic test kit were 0.800 and 0.875, respectively, compared with bacterial cultivation. Additionally, the κ statistic values of the immunochromatographic test kit was 0.667, indicating substantial agreement with the results of bacterial cultivation. Statistically, sensitivity and specificity of the immunochromatographic kit and real-time qPCR did not differ significantly; thus, the immunochromatographic test kit detected mastitis-causing streptococci as effectively as real-time qPCR. Therefore, the immunochromatographic kit is a rapid, inexpensive, and simple method for detecting streptococci and contributes to the timely selection of appropriate antibiotics for treatment and promotes early recovery from mastitis.

Development and evaluation of a sensitive recombinase aided amplification assay for rapid detection of Vibrio parahaemolyticus

Vibrio parahaemolyticus (V. parahaemolyticus) is a widely distributed pathogen in the coastal areas, which causes food poisoning and leads to gastroenteritis and sepsis. Therefore, developing a simple, sensitive, and rapid detection method for V. parahaemolyticus is a major concern globally. This study established a sensitive and rapid technique based on recombinase aided amplification (RAA) to detect V. parahaemolyticus. The RAA reaction was carried out successfully at 39 °C within 30 min. The sensitivity of the RAA assay was 10¹ copies/μL using the recombinant plasmid and 10^-3 ng/μL using the V. parahaemolyticus strain. In addition, RAA directly detected 7 × 10³ CFU/mL of simulated fecal samples and 0.1 CFU/mL after enrichment for 4 h. The sensitivity and specificity of the RAA assay using fecal and fish samples were 100% similar to that of the real-time PCR. We conclude that the RAA assay is an ideal screening method for detecting V. parahaemolyticus due to its rapidity, high accuracy, and simplicity in operation.

Genome sequencing and functional annotation of Bacillus sp. strain BS-Z15 isolated from cotton rhizosphere soil having antagonistic activity against Verticillium dahliae

In the present study, antagonistic activity of bacterial strain BS-Z15, was evaluated against Verticillium dahlia. The fermented broth of BS-Z15 inhibited the growth of Verticillium dahliae. The genome of strain BS-Z15 had a total size of 4,068,702 base pairs and contained 4318 genes, of which 4196 are coding sequences and 122 are non-coding RNA. Among these genes, nine genomic islands, 86 tRNAs, 13 sRNAs, and one prophage was determined. With the help of annotation databases, most unigene functions were identified. At the same time, genomic comparison between BS-Z15 and 12 Bacillus members showed that the genes of BS-Z15 were closely related to the Bacillus group, and were conserved between the two groups, including most of the genes associated with fungal antagonism. BS-Z15 contains genes involved in a variety of antagonistic mechanisms, including genes encoding or synthesizing mycosubtilin, chitinases (but not CHIA and CHIB), glycoside hydrolases, iron nutrients, and antibiosis. However, it only contained the complete mycosubtilin- and bacilibactin-related operators in the reported main antifungal gene cluster of B. subtilis. Mycosubtilin and bacilibactin may be the main active antifungal substance. Besides, some genes could encode products related to biofilm production, which may be related to the colonization ability of the strain in plant rhizospheres. The complete genome of B. subtilis BS-Z15 provided new insights into the potential metabolites it produces related to its biocontrol activity.

Comparison on the Growth Variability of Vibrio parahaemolyticus Coupled With Strain Sources and Genotypes Analyses in Simulated Gastric Digestion Fluids

Vibrio parahaemolyticus is a food-borne pathogen that causes pathogenic symptoms such as diarrhea and abdominal pain. Currently no studies have shown that either pathogenic and non-pathogenic V. parahaemolyticus possess growth heterogeneity in a human environment, such as in gastric and intestinal fluids. The tlh gene is present in both pathogenic and non-pathogenic V. parahaemolyticus strains, while the tdh and trh genes are only present in pathogenic strains. This study firstly applied simulated human gastric fluids to explore growth variability of 50 strains of V. parahaemolyticus at 37°C. The bacterial growth curves were fitted by primary modified Gompertz model, and the maximum growth rate (μ_max), lag time (LT), and their CV values were calculated to compare the stress response of pathogenic and non-pathogenic V. parahaemolyticus to simulated human gastric fluids. Results showed that the simulated human gastric fluids treatment significantly increased the μ_max of pathogenic strains and shortened the lag time, while decreased the μ_max of non-pathogenic strains and prolonged the lag time. Meanwhile, the CV values of genotypes (tlh⁺/tdh⁺/trh^–) evidently increased, showing that the pathogenic genotype (tlh⁺/tdh⁺/trh^–) strains had strong activity to simulated gastric fluids. All of the results indicated that the V. parahaemolyticus strains exhibited a great stress-resistant variability and growth heterogeneity to the simulated gastric fluids, which provides a novel insight to unlock the efficient control of pathogenic V. parahaemolyticus.

The ability of Lactobacillus rhamnosus to bind patulin and its application in apple juice

The purpose of this study was to evaluate the ability of Lactobacillus rhamnosus to bind patulin (PAT) in the buffer solution and apple juice. The binding of L. rhamnosus to PAT was reversible, which improved the stability of the bacterial complex. The ability to bind PAT can be enhanced with the inactivation of the strain by high temperature and acid treatment. Acid-treated bacteria had the highest PAT binding rate of 72.73±1.05%. The binding rates of acid and high temperature (121 °C) treatments were increased by 21.37% and 19.15%, respectively. L. rhamnosus showed the best detoxification ability to PAT at 37 °C, where the binding rate reached 50.9±1.03%. When the dose of inactivated bacteria powder was 0.02 g ml−1, the minimum concentration of PAT in apple juice was 0.37 µg ml−1. The addition of the L. rhamnosus inactivated powder did not affect the quality of the juice product and effectively bound the PAT in apple juice.

Rapid subtyping of pathogenic and nonpathogenic Vibrio parahaemolyticus by fourier transform infrared spectroscopy with chemometric analysis

Vibrio parahaemolyticus which naturally inhabits marine and estuarine environment represents pathogenic strains (virulence genes tdh or trh positive) and non-pathogenic strains (virulence genes negative). In this study, a rapid method for subtyping pathogenic and non-pathogenic V. parahaemolyticus was established using fourier transform infrared (FTIR) spectroscopy with chemometric analysis. This method targeted three strains of genotypes of V. parahaemolyticus including tdh positive, trh positive and virulence gene-negative (nonpathogenic) V. parahaemolyticus. The FTIR absorption spectra between 1800 and 900 cm^-1 highlighted the most distinctive variations and were the most useful for characterizing the three bacteria. The successful differentiation and identification of the three bacteria could be accomplished in less than 1 h by FTIR using principal component analysis (PCA), or another cluster model of hierarchical cluster analysis (HCA). The method was verified by analyzing spiked V. parahaemolyticus fish samples. Furthermore, all of ten clinical isolates of V. parahaemolyticus were identified as tdh-positive, none of the clinical isolates were trh-positive, and all of ten environmental isolates were identified as non-pathogenic by the subtyping method, which were confirmed by PCR assays. All data demonstrated that the newly established subtyping method by FTIR is practical, time-saving, labor-saving, specific and cost-effective, especially suitable for the basic laboratories of CDC and port quarantine departments to perform suiveillance and epidemiological traceability of pathogenic V. parahaemolyticus.