Occurrence and expression of virulence-related properties by environmental halophilic Vibrio spp. in in vitro and in vivo systems

Pathogenicity of non-O1/ O139 Vibrio cholerae and its induced immune response in Macrobrachium rosenbergii

Outbreaks of mass mortalities occurred in Macrobrachium rosenbergii farms in Gaoyou county, Jiangsu Province of China. The bacterial isolates from M. rosenbergii exhibited the same phenotypic traits and biochemical characteristics, and were identified as non-O1/O139 Vibrio cholerae according to biochemical characteristics and molecular identification. In challenge test, M. rosenbergii infected with non-O1/O139 V. cholerae GXFL1-4 developed similar pathological signs to the naturally diseased prawns, and LD₅₀ of the strain to M. rosenbergii was 4.5 × 10⁶ CFU/mL at 96 h post-infection. Histopathological analysis revealed that hepatopancreas and intestines of diseased M. rosenbergii exhibited obvious inflammatory responses to non-O1/O139 V. cholerae infection. Detection virulence factors of the strain GXFL1-4 showed that the bacteria produced caseinase, lipase, amylase, lecithinase and hemolysin, and carried toxR, hlyA, ompW, ompU, hap, rtxA and rtxC virulence related genes, supporting the strong virulence to M. rosenbergii. Additionally, the immune related gene expression in M. rosenbergii evaluated by qRT-PCR analysis showed that HSP70, Crustin, Lysozyme, TRL1, ALF1, Lectin, Peroxinectin, proPO and SOD immune related genes were significantly up-regulated at 6 and 12 h after infection with GXFL1-4. The results of our study suggested that non-O1/O139 V. cholerae was an etiological element in the mass mortalities of M. rosenbergii and this study provided preliminary insights into the diversity in the immune response of M. rosenbergii to the bacterial invasion.

Prevalence of Biofilm Formation and Wide Distribution of Virulence Associated Genes among Vibrio spp. Strains Isolated from the Monastir Lagoon, Tunisia

In the current study, 65 Vibrio spp. were isolated from the Monastir lagoon water, were characterized phenotypically and genotypically. In addition, we looked for the presence of three Vibrio parahaemolyticus virulence genes (tlh, trh and tdh) and ten Vibrio cholerae virulence genes (ctxA, vpi, zot, ace, toxR, toxT, tosS, toxRS, tcpA and cpP). We also investigated the antibiotic susceptibilities and the adherence ability of the identified strains to abiotic material and to biotic surfaces. The cytotoxicity activity against HeLa and Vero cell lines were also carried out for all tested strains. All Vibrio isolates were identified to the species level and produced several hydrolytic exoenzymes. The results also revealed that all strains were expressing high rates of resistance to tested antibiotics. The minimum inhibitory concentration (MIC) values showed that tetracycline and chloramphenicol were the most effective antibiotics against the tested bacteria. Vibrio alginolyticus and V. cholerae species were the most adhesive strains to both biotic and abiotic surfaces. Besides, V. alginolyticus isolates has the high levels of recombination of genes encoding V. cholerae and V. parahaemolyticus virulence factors. In vitro cytotoxic activities of several Vibrio extracellular product were also observed among HeLa and Vero cells.

Chemical composition and antibiofilm activity of Petroselinum crispum and Ocimum basilicum essential oils against Vibrio spp. strains

In this study, we evaluated the antibacterial activity of parsley and basilic essential oils tested against Vibrio strains and their abilities to inhibit and eradicate the mature biofilm using the XTT assay. Petroselinum crispum essential oil was characterized by 1,3,8-p-menthatriene (24.2%), β-phellandrene (22.8%), apiol (13.2%), myristicin (12.6%) and terpinolene (10.3%) as a major constituents. While, in the basilic oil, linalool (42.1%), (E)-methylcinnamate (16.9%) and 1-8 cineole (7.6%) were the main ones. These two essential oils exhibit high anti-Vibrio spp. activity with varying magnitudes. All microorganisms were strongly affected indicating an appreciable antimicrobial potential of basilic with a diameter of inhibition zones growth ranging from 8.67 to 23.33 mm and MIC and MBC values ranging from (0.023-0.047 mg/ml) and (>3->24 mg/ml), respectively. The two essential oils can inhibit and eradicate the mature biofilm formed on polystyrene surface even at low concentrations, with high magnitude for Ocimum basilicum essential oil. This study gives a better insight into the anti-Vibrio activity of parsley and basilc oils and the possibility of their use to prevent and eradicate contamination of sea products by these strains.

Assessment of adhesion, invasion and cytotoxicity potential of oral Staphylococcus aureus strains

The oral cavity is regarded as a relevant site for Staphylococcus aureus colonization. However, characterization of virulence mechanisms of oral S. aureus remains to be uncovered. In this study, twenty one S. aureus strains isolated from the oral cavity of Tunisian patients were screened for adherence, invasion and cytotoxicity against HeLa cells. In addition, the presence of adhesins (icaA, icaD, can, fnbA and fnbB) and α-hemolysin (hla) genes in each strain was achieved by polymerase chain reaction (PCR). Our finding revealed that oral S. aureus strains were able to adhere and invade epithelial cells, with variable degrees (P < 0.05). Moreover they exhibited either low (23.8%) or moderate (76.2%) cytotoxic effects. In addition 76.2% of strains were icaA and icaD positive and 90.5% harbor both the fnbA and the fnbB gene. While the cna gene was detected in 12 strains (57.2%). Furthermore, the hla gene encoding the α-toxin was found in 52.4% of the isolates. All these virulence factors give to S. aureus the right qualities to become a redoubtable pathogen associated to oral infections.

Comparative study on the antibiotic susceptibility and plasmid profiles of Vibrio alginolyticus strains isolated from four Tunisian marine biotopes

The antibiotic resistance patterns and the plasmids profiles of the predominant etiological agent responsible for vibriosis in Tunisia, V. alginolyticus were studied to contribute to control their spread in some Mediterranean aquaculture farms and seawater. The sixty-nine V. alginolyticus strains isolated from different marine Tunisian biotopes (bathing waters, aquaculture and conchylicole farms and a river connected to the seawater during the cold seasons) were multi-drug resistant with high resistance rate to ampicillin, kanamycin, doxycyclin, erythromycin, imipinem, and nalidixic acid. The multiple resistance index ranged from 0.3 to 0.7 for the isolates of Khenis, from 0.5 to 0.8 for those of Menzel Jmil, from 0.5 to 0.75 (Hergla) and from 0.3 to 0.7 for the isolates of Oued Soltane. The high value of antibiotic resistance index was recorded for the V. alginolyticus population isolated from the fish farm in Hergla (ARI = 0.672) followed by the population isolated from the conchylicole station of Menzel Jmil (ARI = 0.645). The results obtained by the MIC tests confirmed the resistance of the V. alginolyticus to ampicillin, erythromycin, kanamycin, cefotaxime, streptomycin and trimethoprim. Plasmids were found in 79.48 % of the strains analyzed and 30 different plasmid profiles were observed. The strains had a high difference in the size of plasmids varying between 0.5 and 45 kb. Our study reveals that the antibiotic-resistant bacteria are widespread in the aquaculture and conchylicole farm relatively to others strains isolated from seawater.

Selection and identification of non-pathogenic bacteria isolated from fermented pickles with antagonistic properties against two shrimp pathogens

In this study, potential probiotic strains were isolated from fermented pickles based on antagonistic activity against two shrimp pathogens (Vibrio harveyi and Vibrio parahaemolyticus). Two strains L10 and G1 were identified by biochemical tests, followed by16S ribosomal RNA gene sequence analysis as Bacillus subtilis, and characterized by PCR amplification of repetitive bacterial DNA elements (Rep-PCR). Subsequently, B. subtilis L10 and G1 strains were tested for antibacterial activity under different physical conditions, including culture medium, salinity, pH and temperature using the agar well diffusion assay. Among the different culture media, LB broth was the most suitable medium for antibacterial production. Both strains showed the highest level of antibacterial activity against two pathogens at 30 °C and 1.0% NaCl. Under the pH conditions, strain G1 showed the greatest activity against V. harveyi at pH 7.3–8.0 and against V. parahaemolyticus at pH 6.0–8.0, whereas strain L10 showed the greatest activity against two pathogens at pH 7.3. The cell-free supernatants of both strains were treated with four different enzymes in order to characterize the antibacterial substances against V. harveyi. The result showed considerable reduction of antibacterial activity for both strains, indicating the proteinaceous nature of the antibacterial substances. A wide range of tolerance to NaCl, pH and temperature was also recorded for both strains. In addition, both strains showed no virulence effect in juvenile shrimp Litopenaeus vannamei. On the basis of these results and safety of strains to L. vannamei, they may be considered for future challenge experiments in shrimp as a very promising alternative to the use of antibiotics.

Development of a polymerase chain reaction (PCR) test for the detection of virulent forms of Vibrio parahaemolyticus

Vibrio parahaemolyticus is a marine bacterium and some strains cause gastroenteritis in humans. Clinical isolates are thought to possess virulence factors that are absent from the majority of environmental isolates. Use of randomly amplified polymorphic DNA (RAPD)-PCR produced a unique 600 bp amplicon (band Y) in the majority of clinical isolates and rarely in environmental isolates tested. The DNA from band Y was cloned and sequenced and found to code for an outer membrane protein (OMP). Two polymerase chain reaction (PCR) primers were designed to specifically amplify a 200 bp unique sequence from presumptive virulent strains (PCR-OMP). The virulence of 23 clinical and 32 environmental isolates was assessed in cytotoxicity tests by treatment of Caco-2 cells with extracellular products (ECPs). All but two of the clinical isolates (91%) were positive for the 200 bp PCR-OMP and their ECPs produced a significantly higher (p < 0.05) lactate dehydrogenase (LDH) release (mean 72.88%) than the ECPs of environmental isolates (mean 15.3%) with the exception of one environmental isolate that produced the 200 bp amplicon. A positive 200 bp PCR-OMP is strongly correlated with virulence, as determined by the cytotoxicity assay, and identified virulent forms better than current PCR tests for tdh, trh or T3SS2.

Prevalence of listeria, Aeromonas, and Vibrio species in fish used for human consumption in Turkey

A total of 78 raw retail fish samples from 30 freshwater and 48 marine fish were examined for the presence of Listeria, Aeromonas, and Vibrio species. The overall incidence of Listeria spp. was 30% in freshwater samples and 10.4% in marine fish samples. Listeria monocytogenes (44.5%) was the most commonly isolated species in freshwater fish, and Listeria murrayi (83.5%) was the most commonly isolated species in marine fish samples. Motile aeromonads were more common in marine fish samples (93.7%) than in freshwater fish samples (10%). Vibrio alginolyticus, Vibrio fluvialis, and Vibrio damsela were isolated only in marine fish samples, representing 40.9, 38.6, and 36.3% of Vibrio isolates, respectively. In freshwater and marine fish, the highest incidences of Listeria and Aeromonas were found in skin samples; the highest incidence of Vibrio in marine fish was found in gill samples. The location of Listeria spp. and L. monocytogenes in a fish was significantly different among freshwater fish. A high incidence of these bacterial pathogens was found in the brown trout (Salmo trutta) and horse mackerel (Trachurus trachurus). Handling of contaminated fish, cross-contamination, or eating raw fish might pose a health hazard, especially in immunosuppressed individuals, elderly people, and children. This study highlights the importance of bacterial pathogens in fish intended for human consumption, but more study is needed.

Survival of Vibrio alginolyticus in seawater and retention of virulence of its starved cells

The aim of this study was to evaluate the survival responses of four strains of Vibrio alginolyticus in seawater under starvation conditions. We used microcosms containing sterilised seawater and incubated at ambient temperature (22-25 degrees C). V. alginolyticus maintained its culturability for at least nine months. Long-term-starved cells showed an absence or a decrease in their enzymatic activities. Resuscitation assays of viable but non-culturable (VBNC) cells were conducted and the recovery of these cells was achieved after the addition of nutrients. Amplified 16S ribosomal DNA (rDNA) restriction analysis (ARDRA) was used to confirm that the same strain of V. alginolyticus persisted in all microcosms during a long period of time. Starved cells maintained their infectivity for gilt head sea bream (Sparus aurata) and sea bass (Dicentrachus labrax) as determined by intraperitoneal challenges.