Functional characterization of Vibrio alginolyticus T3SS regulator ExsA and evaluation of its mutant as a live attenuated vaccine candidate in zebrafish (Danio rerio) model

Vibrio alginolyticus, a Gram-negative bacterium, is an opportunistic pathogen of both marine animals and humans, resulting in significant losses in the aquaculture industry. Type III secretion system (T3SS) is a crucial virulence mechanism of V. alginolyticus. In this study, the T3SS regulatory gene exsA, which was cloned from V. alginolyticus wild-type strain HY9901, is 861 bp encoding a protein of 286 amino acids. The ΔexsA was constructed by homologous recombination and Overlap-PCR. Although there was no difference in growth between HY9901 and ΔexsA, the ΔexsA exhibited significantly decreased extracellular protease activity and biofilm formation. Besides, the ΔexsA showed a weakened swarming phenotype and an ~100-fold decrease in virulence to zebrafish. Antibiotic susceptibility testing showed the HY9901ΔexsA was more sensitive to kanamycin, minocycline, tetracycline, gentamicin, doxycycline and neomycin. Compared to HY9901 there were 541 up-regulated genes and 663 down-regulated genes in ΔexsA, screened by transcriptome sequencing. qRT-PCR and β-galactosidase reporter assays were used to analyze the transcription levels of hop gene revealing that exsA gene could facilitate the expression of hop gene. Finally, Danio rerio, vaccinated with ΔexsA through intramuscular injection, induced a relative percent survival (RPS) value of 66.7% after challenging with HY9901 wild type strain. qRT-PCR assays showed that vaccination with ΔexsA increased the expression of immune-related genes, including GATA-1, IL6, IgM, and TNF-α in zebrafish. In summary, these results demonstrate the importance of exsA in V. alginolyticus and provide a basis for further investigations into the virulence and infection mechanism.

Pseudomonas aeruginosa Type III Secretion System Virulotypes and Their Association with Clinical Features of Cystic Fibrosis Patients

Purpose

Pseudomonas aeruginosa appears as the main pathogen in cystic fibrosis (CF) involved in recurrent pneumonia and pulmonary exacerbations. The type III secretion system (T3SS) is one of its main determinants of virulence and is associated with poor clinical progression and increased mortality. This study determined the relationship of clinical features of patients with CF and P. aeruginosa T3SS virulotypes.

Materials and Methods

From January 2018 to March 2019, P. aeruginosa were isolated from sputum and/or oropharyngeal swabs. T3SS markers (exoS, exoU, exoT and exoY) were detected by PCR. Clinical severity according to Shwachman-Kulckycki score and spirometry data were associated with T3SS virulotypes.

Results

A total of 49 patients had positive cultures for P. aeruginosa. T3SS virulence-related markers were detected as follows: exoS 97.9% (n=48), exoU 63.2% (n=31), exoT 95.9% (n=47) and exoY 97.9% (n=48). The prevalence of exoS⁺/exoU⁺ virulotype was higher than previously reported in CF settings, being detected in 61.2% of the evaluated isolates, present in 70% of intermittent infections and with a significantly higher frequency in cases of exacerbations. The presence of exoU in chronic infection was not associated with poor clinical results. In chronic infections, the exoS⁺/exoU⁻ virulotype prevailed (77.8%) and was associated to worse clinical results according to the Shwachman-Kulckycki score and spirometric.

Conclusion

Our findings revealed a high prevalence of the atypical exoS⁺/exoU⁺ virulotype among P. aeruginosa isolates from patients with CF, which was associated with intermittent infection and early clinical alterations, while the exoS⁺/exoU⁻ virulotype was associated with chronic infection and worse clinical results. Finally, the presented data highlight the relevance of T3SS virulence markers in the clinical progression and disease severity in CF patients.

A T3SS Regulator Mutant of Vibrio alginolyticus Affects Antibiotic Susceptibilities and Provides Significant Protection to Danio rerio as a Live Attenuated Vaccine

Vibrio alginolyticus is a major cause of Vibriosis in farmed marine aquatic animals and has caused large economic losses to the Asian aquaculture industry in recent years. Therefore, it is necessary to control V. alginolyticus effectively. The virulence mechanism of V. alginolyticus, the Type III secretion system (T3SS), is closely related to its pathogenicity. In this study, the T3SS gene tyeA was cloned from V. alginolyticus wild-type strain HY9901 and the results showed that the deduced amino acid sequence of V. alginolyticus tyeA shared 75–83% homology with other Vibrio spp. The mutant strain HY9901ΔtyeA was constructed by Overlap-PCR and homologous recombination techniques. The HY9901ΔtyeA mutant exhibited an attenuated swarming phenotype and an ~40-fold reduction in virulence to zebrafish. However, the HY9901ΔtyeA mutant showed no difference in growth, biofilm formation and ECPase activity. Antibiotic susceptibility test was observed that wild and mutant strains were extremely susceptible to Amikacin, Minocycline, Gentamicin, Cefperazone; and resistant to oxacillin, clindamycin, ceftazidime. In contrast wild strains are sensitive to tetracycline, chloramphenicol, kanamycin, doxycycline, while mutant strains are resistant to them. qRT-PCR was employed to analyze the transcription levels of T3SS-related genes, the results showed that compared with HY9901 wild type, ΔtyeA had increased expression of vscL, vscK, vscO, vopS, vopN, vscN, and hop. Following vaccination with the mutant strain, zebrafish had significantly higher survival than controls following infection with the wild-type HY9901 (71.2% relative percent survival; RPS). Analysis of immune gene expression by qPCR showed that vaccination with HY9901ΔtyeA increased the expression of IgM, IL-1β, IL-6, and TNF-α in zebrafish. This study provides evidence of protective efficacy of a live attenuated vaccine targeting the T3SS of V. alginolyticus which may be facilitated by up-regulated pro-inflammatory and immunoglobulin-related genes.

A compound isolated from Alpinia officinarum Hance. inhibits swarming motility of Pseudomonas aeruginosa and down regulates virulence genes

AIM

The study was aimed at purifying the active principle from Alpinia officinarum rhizomes responsible for inhibition of swarming motility of Pseudomonas aeruginosa and analysing the mechanism of action.

METHODS AND RESULTS

The active compound from methanol extract of A. officinarum was purified by silica gel column chromatography followed by elution from Amberlite resin. The compound 1-(3,5-dihydroxyphenyl)-2-(methylamino)ethan-1-one, inhibited swarming motility at 12·5 µg ml^-1 . This inhibition was independent of rhamnolipid production. Real-time PCR analysis showed significant down-regulation of virulence-associated genes including T3SS exoS, exoT and flagella master regulator fleQ.

CONCLUSIONS

The compound from A. officinarum inhibited swarming motility and significantly down-regulated the expression of type III secretory system effector genes exoS and exoT and flagellar master regulator fleQ genes.

SIGNIFICANCE AND IMPACT OF THE STUDY

The study identifies a potent swarming inhibitory compound from the common medicinal plant A. officinarum and reinstates the potential of plant-derived compounds in tackling virulence properties of pathogenic bacteria.