Streptococcus iniae in aquaculture: a review of pathogenesis, virulence, and antibiotic resistance.

One of the main challenges in aquaculture is pathogenic bacterial control. Streptococcus iniae stands out for its ability to cause high mortality rates in populations of commercially important fish populations and its recent recognition as an emerging zoonotic pathogen. The rise in identifying over 80 strains some displaying antibiotic resistance coupled with the emerging occurrence of infections in marine mammal species and wild fish underscores the urgent need of understanding pathogenesis, virulence and drug resistance mechanisms of this bacterium. This understanding is crucial to ensure effective control strategies. In this context, the present review conducts a bibliometric analysis to examine research trends related to S. iniae, extending into the mechanisms of infection, virulence, drug resistance and control strategies, whose relevance is highlighted on vaccines and probiotics to strengthen the host immune system. Despite the advances in this field, the need for developing more efficient identification methods is evident, since they constitute the basis for accurate diagnosis and treatment.

Evaluating the efficacy of endolysins and membrane permeabilizers against Vibrio parahaemolyticus in marine conditions.

Endolysins have garnered significant attention as a potential alternative to antibiotics in aquaculture, mainly for combating Vibrio spp., Gram-negative pathogens responsible for infectious outbreaks. However, endolysin effectiveness against Gram-negative bacteria is limited due to the outer membrane's poor permeability. The combat against marine pathogens poses an additional challenge of finding endolysins that retain their activity in high ionic strength conditions. Thus, this study aimed to demonstrate that certain endolysins retain muralytic activity in seawater and also evaluated outer membrane permeabilizers as endolysin adjuvants. The effectiveness of KZ144 and LysPA26 endolysins, along with EDTA and oregano essential oil, was evaluated against Vibrio parahaemolyticus ATCC-17802 in natural seawater. Results revealed the muralytic activity of both endolysins in seawater. However, the endolysins appeared to counteract the permeabilizers' effect during the initial bactericidal assays. Further investigations revealed that the observed effect was not antagonistic. After the permeabilizer action, V. parahaemolyticus likely used endolysins as a growth substrate. Endolysins may not play an indifferent role if they fail to exert a bactericidal effect. Instead, they can serve as a substrate for fast-growing bacteria, such as V. parahaemolyticus, increasing bacterial density. It should be considered a potential drawback of endolysins' proteinaceous nature as bactericidal agents.

Depth effect on the prokaryotic community assemblage associated with sponges from different rocky reefs.

Background: Sponge microbiomes are essential for the function and survival of their host and produce biologically active metabolites, therefore, they are ideal candidates for ecological, pharmacologic and clinical research. Next-generation sequencing (NGS) has revealed that many factors, including the environment and host, determine the composition and structure of these symbiotic communities but the controls of this variation are not well described. This study assessed the microbial communities associated with two marine sponges of the genera Aplysina (Nardo, 1834) and Ircinia (Nardo, 1833) in rocky reefs from Punta Arena de la Ventana (Gulf of California) and Pichilingue (La Paz Bay) in the coast of Baja California Sur, México to determine the relative importance of environment and host in structuring the microbiome of sponges. Methods: Specimens of Aplysina sp were collected by scuba diving at 10 m and 2 m; Ircinia sp samples were collected at 2 m. DNA of sponge-associated prokaryotes was extracted from 1 cm3 of tissue, purified and sent for 16S amplicon sequencing. Primer trimmed pair-ended microbial 16S rDNA gene sequences were merged using Ribosomal Database Project (RDP) Paired-end Reads Assembler. Chao1, Shannon and Simpson (alpha) biodiversity indices were estimated, as well permutational analysis of variance (PERMANOVA), and Bray-Curtis distances. Results: The most abundant phyla differed between hosts. Those phyla were: Proteobacteria, Acidobacteria, Cyanobacteria, Chloroflexi, Actinobacteria, Bacteroidetes, and Planctomycetes. In Ircinia sp the dominant phylum was Acidobacteria. Depth was the main factor influencing the microbial community, as analysis of similarities (ANOSIM) showed a significant difference between the microbial communities from different depths. Conclusion: Microbial diversity analysis showed that depth was more important than host in structuring the Aplysina sp and Ircinia sp microbiome. This observation contrast with previous reports that the sponge microbiome is highly host specific.

Natural genetic transformation of Vibrio parahaemolyticus via pVA1 plasmid acquisition as a potential mechanism causing AHPND.

Vibrio parahaemolyticus is the causative bacterium of acute hepatopancreatic necrosis disease (AHPND) in white shrimp Litopenaeus vannamei. This bacterium secretes protein toxins whose genes are encoded in an auto-transmissible plasmid called pVA1. The presence of this plasmid in V. parahaemolyticus is determinant for disease development. Its propagation is not only linked to bacterial colonisation capacity but also to horizontal gene transfer mechanisms. Nevertheless, the active uptake of plasmid, which is known as natural genetic transformation (NGT), has not yet been proposed as a possible acquisition mechanism of the pVA1 plasmid among Vibrio species. Previous studies suggest that some Vibrio species have the ability to undergo NGT in the presence of chitin. Therefore, the objective of this study was to evaluate the induction of NGT mediated by chitin in V. parahaemolyticus (ATCC-17802) through its ability to incorporate and express the pVA1 plasmid. The results showed that a reference strain that does not initially contain the plasmid can incorporate the plasmid under the appropriate transformation conditions, and cause mortality in white shrimp similar to that observed for pathogenic strains isolated from infectious outbreaks. Given the management and conditions of a shrimp farm with large amounts of chitinous exoskeletons, it is feasible that NGT could be a possible acquisition mechanism of plasmid pVA1 among Vibrio species, turning a non-causative strain of V. parahaemolyticus into a causative strain. With this study, we have expanded the knowledge of the pathogenesis process mediated by NGT and the understanding of the possible propagation mechanisms of emerging diseases in the aquaculture sector.