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Background Vibriosis cases in Northern European countries and countries bordering the Baltic Sea increased during heatwaves in 2014 and 2018. Aim We describe the epidemiology of vibriosis and the genetic diversity of Vibrio spp. isolates from Norway, Sweden, Denmark, Finland, Poland and Estonia in 2018, a year with an exceptionally warm summer. Methods In a retrospective study, we analysed demographics, geographical distribution, seasonality, causative species and severity of non-travel-related vibriosis cases in 2018. Data sources included surveillance systems, national laboratory notification databases and/or nationwide surveys to public health microbiology laboratories. Moreover, we performed whole genome sequencing and multilocus sequence typing of available isolates from 2014 to 2018 to map their genetic diversity. Results In 2018, we identified 445 non-travel-related vibriosis cases in the study countries, considerably more than the median of 126 cases between 2014 and 2017 (range: 87–272). The main reported mode of transmission was exposure to seawater. We observed a species-specific geographical disparity of vibriosis cases across the Nordic-Baltic region. Severe vibriosis was associated with infections caused by Vibrio vulnificus (adjOR: 17.2; 95% CI: 3.3–90.5) or Vibrio parahaemolyticus (adjOR: 2.1; 95% CI: 1.0–4.5), age ≥ 65 years (65–79 years: adjOR: 3.9; 95% CI: 1.7–8.7; ≥ 80 years: adjOR: 15.5; 95% CI: 4.4–54.3) or acquiring infections during summer (adjOR: 5.1; 95% CI: 2.4–10.9). Although phylogenetic analysis revealed diversity between Vibrio spp. isolates, two V. vulnificus clusters were identified. Conclusion Shared sentinel surveillance for vibriosis during summer may be valuable to monitor this emerging public health issue.

Vibrio harveyi is one of the major pathogens in aquaculture. To identify the key virulence factors affecting pathogenesis of V. harveyi towards fish, we conducted a field investigation for three representative fish farms infected with V. harveyi. Multilocus sequence typing (MLST) and whole-genome sequencing were conducted to delineate the phylogenetic relationship and genetic divergence of V. harveyi. A total of 25 V. harveyi strains were isolated from the diseased fish and groundwater and were subtyped into 12 sequence types by MLST. Five virulence genes, mshB, pilA, hutR, ureB, and ureG, were variably presented in the sequenced strains. The virulence gene profiles strongly correlated with the distinct pathogenicity of V. harveyi strains, with a strain harboring all five genes exhibiting the highest virulence towards fish. Phenotype assay confirmed that reduced virulence correlated with decreased motility and biofilm formation ability. Additionally, three types of type VI secretion system, namely T6SS1, T6SS2, and T6SS3, were identified in V. harveyi strains, which can be classified into six, four, and 12 subtypes, respectively. In conclusion, the results indicated that the virulence level of V. harveyi is mainly determined by the above virulence genes, which may play vital roles in environmental adaptation for V. harveyi.

Gram-negative marine bacterium Vibrio parahaemolyticus is an important aquatic pathogen and has been demonstrated to be the causative agent of acute hepatopancreatic necrotic disease (AHPND) in shrimp aquaculture. The AHPND-causing V. parahaemolyticus strains contain a pVA1 plasmid encoding the binary PirAVP and PirBVP toxins, are the primary virulence factor that mediates AHPND and mortality in shrimp. Since PirABVP toxins are secreted extracellularly, one can hypothesize that PirABVP toxins would aggravate vibriosis in the aquatic environment. To address this, in vivo and in vitro experiments were conducted. Germ-free Artemia franciscana were co-challenged with PirABVP toxins and 10 Vibrio spp. The in vivo results showed that PirABVP toxin interact synergistically with MM30 (a quorum sensing AI-2 deficient mutant) and V. alginolyticus AQ13-91, aggravating vibriosis. However, co-challenge by PirABVP toxins and V. campbellii LMG21363, V. parahaemolyticus CAIM170, V. proteolyticus LMG10942, and V. anguillarum NB10 worked antagonistically, increasing the survival of Artemia larvae. The in vitro results showed that the addition of PirABVP toxins significantly modulated the production of the virulence factors of studied Vibrio spp. Yet these in vitro results did not help to explain the in vivo results. Hence it appears that PirABVP toxins can aggravate vibriosis. However, the dynamics of interaction is strain dependent.

Vibrio species are a significant causative of mass mortality in mariculture worldwide, which can quickly accumulate in live food and transmit into the larval gut. With restrictions on the use of antibiotics in aquaculture, finding a proper solution to reduce the risk of Vibriosis is vital. This study aimed to evaluate the susceptibility of Vibrio harveyi, V. campbellii, V. anguillarum, and V. parahaemolyticus to twenty-six bacterial and yeast strains and use the beneficial ones to enrich live food (Branchiopod, Artemia franciscana, rotifer, Brachionus plicatilis and copepod, Tigriopus japonicus). Thus, a modified disk diffusion method was applied. After a susceptibility assay, the bacteria and yeast beneficial in suppressing the Vibrio species were labeled by fluorescent stain and used to measure the accumulation potential in different live foods. Also, the beneficial bacteria and yeast were used to enrich live foods, and then the count of loaded Vibrio was estimated after 5, 10, 15, and 20 h by the serial dilution method. From the total bacteria and yeast strains that were used, Candida parapsilosis, Pseudoalteromonas flavipulchra, Lactobacillus sakei, Bacillus natto, and B. amyloliquefaciens inhibited all four Vibrio species. The results of microbial labeling showed that L. sakei in Artemia, C. parapsilosis in rotifers, and V. harveyi in copepods had the highest accumulation rate. The results of the estimation of loaded Vibrio in different live foods also showed that the use of beneficial bacteria and yeast each significantly reduced the count of Vibrio. Application of bacteria and yeast to suppress pathogenic Vibrio maybe a sustainable method for preventing this pathogen from harmfully invading aquaculture and may also aid in reducing the chances of antibiotic resistance in pathogenic Vibrio.

We report the results from a mesocosm study investigating the interrelationship between microalgae and vibrios. The mesocosms were inoculated with plankton, plankton + sedi- ment, or sediment. We followed the diatom bloom and increases in the abundance of Vibrio spp. and V. parahaemolyticus in conjunction with several environmental variables in all mesocosms and at a reference site. The dominating diatom genera were also identified. Temperature, salinity, and pH were nearly invariant in the mesocosms and did not contribute to the results. The principal environ- mental variables that correlated to vibrio abundance were total bacterial plate counts, phosphorus and ammonia (positive relationship), and oxygen and silica (negative). Nitrate, total bacterial counts and chlorophyll a (chl a) did not correlate with vibrio growth. The highest diatom abundances were followed by increases in vibrios in all mesocosms. This was also observed in field sampling. Together, these results suggest that diatom blooms could support Vibrio spp. growth. V. parahaemolyticus was initially favoured by sediment. The contribution of V. parahaemolyticus to the total bacterial popula- tion was low, on average 0.5%, but constituted a rather high proportion of the vibrio population in the mesocosm systems, i.e. on average 18%. Some of the identified diatom genera, e.g. Chaetoceros and Skeletonema, were negatively correlated to vibrios, while Coscinodiscus was positively correlated. The results indicate that phytoplankton blooms, when recorded as high levels of chl a, should be used with caution as predictors for future vibrio epidemics, since the origin of the chl a might have a significant effect on vibrio abundance.

Discovering the means to control the increasing dissemination of pathogenic vibrios driven by recent climate change is challenged by the limited knowledge of the mechanisms in charge of Vibrio spp. persistence and spread in the time of global warming. To learn about physiological and gene expression patterns associated with the long-term persistence of V. harveyi at elevated temperatures, we studied adaptation of this marine bacterium in seawater microcosms at 30 degrees C which closely mimicked the upper limit of sea surface temperatures around the globe. We found that nearly 90% of cells lost their culturability and became partly damaged after two weeks, thus suggesting a negative impact of the combined action of elevated temperature and shortage of carbon on V. harveyi survival. Moreover, further gene expression analysis revealed that major adaptive mechanisms were poorly coordinated and apparently could not sustain cell fitness. On the other hand, elevated temperature and starvation promoted expression of many virulence genes, thus potentially reinforcing the pathogenicity of this organism. These findings suggest that the increase in disease outbreaks caused by V. harveyi under rising sea surface temperatures may not reflect higher cell fitness, but rather an increase in virulence enabling V. harveyi to escape from adverse environments to nutrient rich, host-pathogen associations. This work was supported by the Spanish Ministry of Economy and Competitiveness grant CGL2015-70929-R, Ikerbasque (Basque Foundation for Science) and pre-doctoral grants PRE-2013-1-901 (I.M.) from the Basque Government and PIF15/101 (E.O.) from the University of the Basque Country. A.E.-C. is funded by ISCIII of the MINECO (Ref: PT17/0009/0019) and cofinanced by FEDER.