Vibrio ordalii antimicrobial susceptibility testing—Modified culture conditions required and laboratory-specific epidemiological cut-off values

Advances in Vibrio-related infection management: an integrated technology approach for aquaculture and human health

Vibrio species pose significant threats worldwide, causing mortalities in aquaculture and infections in humans. Global warming and the emergence of worldwide strains of Vibrio diseases are increasing day by day. Control of Vibrio species requires effective monitoring, diagnosis, and treatment strategies at the global scale. Despite current efforts based on chemical, biological, and mechanical means, Vibrio control management faces limitations due to complicated implementation processes. This review explores the intricacies and challenges of Vibrio-related diseases, including accurate and cost-effective diagnosis and effective control. The global burden due to emerging Vibrio species further complicates management strategies. We propose an innovative integrated technology model that harnesses cutting-edge technologies to address these obstacles. The proposed model incorporates advanced tools, such as biosensing technologies, the Internet of Things (IoT), remote sensing devices, cloud computing, and machine learning. This model offers invaluable insights and supports better decision-making by integrating real-time ecological data and biological phenotype signatures. A major advantage of our approach lies in leveraging cloud-based analytics programs, efficiently extracting meaningful information from vast and complex datasets. Collaborating with data and clinical professionals ensures logical and customized solutions tailored to each unique situation. Aquaculture biotechnology that prioritizes sustainability may have a large impact on human health and the seafood industry. Our review underscores the importance of adopting this model, revolutionizing the prognosis and management of Vibrio-related infections, even under complex circumstances. Furthermore, this model has promising implications for aquaculture and public health, addressing the United Nations Sustainable Development Goals and their development agenda.

Tentative Epidemiological Cut-Off Values and Distribution of Resistance Genes in Aquatic Pseudomonas Species Isolated from Rainbow Trout

Epidemiological cut-off value (ECV) analysis for commonly used antimicrobials in aquaculture have not been established for many aquatic pathogens, including Pseudomonas. This study was the first to examine the categorization of 92 aquatic Pseudomonas isolates by calculating seven antimicrobials ECVs using two analytical methods: normalized resistance interpretation and ECOFFinder. Pseudomonas spp. isolates had decreased sensitivity to all antimicrobials examined except for doxycycline and ciprofloxacin. The PCR analysis of the 91 isolates of Pseudomonas spp. detected the tetracycline genes are predominant with the count of 41 genes, including tetA, tetC, tetD, tetM, tetS and tetH, following sulfonamide genes are in 21 isolates including sul1 and sul2, floR gene in 15 isolates and ermA gene in three isolates. Our findings provide an understanding of the antimicrobial categorization of Pseudomonas species, which are significant groups, subgroups, and species for aquaculture due to insufficiently defined breakpoints or cut-off values reported in CLSI and/or EUCAST.

Proposed protocol for performing MIC testing to determine the antimicrobial susceptibility of Renibacterium salmoninarum in Chilean salmon farms

Surveillance of antibiotic resistance is of paramount importance for animal welfare and production. Despite aquaculture being a main source of animal protein, studies on antibiotic susceptibility in fish pathogens are scarce. Renibacterium salmoninarum, the aetiological agent of bacterial kidney disease (BKD), is one of the most common bacterial pathogens affecting salmon farming. In this work, we present an analysis of susceptibility patterns using determinations of minimum inhibitory concentration (MIC) for 65 field isolates, which were collected over seven years (2013-2019) from Atlantic salmon (Salmo salar) and coho salmon (Oncorhynchus kisutch) farms across southern Chile. The MIC protocol described by the Clinical Laboratory Standards Institute (CLSI) was used, but with microdilution instead of macrodilution and eight instead of four days of incubation. Two laboratories independently conducted analyses to provide data on the epidemiological cut-off values for R. salmoninarum to florfenicol, oxytetracycline and erythromycin. By using two calculation methods, our results provide evidence for an evolving subpopulation of non-wild-type isolates for the macrolide erythromycin, which is consistent with the respective treatment frequencies prescribed against BKD. Contrasting with what was expected, R. salmoninarum isolates were most susceptible to florfenicol and oxytetracycline, both of which are widely used antibiotics currently used in the Chilean salmon industry. The presented findings can serve as a reference for national or international antibiotic surveillance programmes, for both MIC interpretation and to identify emerging resistance to the conventional drugs used in BKD management. Finally, our results indicate that an 8-day incubation period for establishing MIC values of R. salmoninarum should be considered in a future revision of the CLSI guidelines.

Current Status of the Use of Antibiotics and the Antimicrobial Resistance in the Chilean Salmon Farms

The Chilean salmon industry has undergone a rapid development making the country the world's second largest producer of farmed salmon, but this growth has been accompanied by an intensive use of antibiotics. This overuse has become so significant that Chilean salmon aquaculture currently has one of the highest rates of antibiotic consumption per ton of harvested fish in the world. This review has focused on discussing use of antibiotics and current status of scientific knowledge regarding to incidence of antimicrobial resistance and associated genes in the Chilean salmonid farms. Over recent years there has been a consistent increase in the amount of antimicrobials used by Chilean salmonid farms, from 143.2 tons in 2010 to 382.5 tons in 2016. During 2016, Chilean companies utilized approximately 0.53 kg of antibiotics per ton of harvested salmon, 363.4 tons (95%) were used in marine farms, and 19.1 tons (5%) in freshwater farms dedicated to smolt production. Florfenicol and oxytetracycline were by far the most frequently used antibiotics during 2016 (82.5 and 16.8%, respectively), mainly being used to treat Piscirickettsia salmonis, currently considered the main bacterial threat to this industry. However, the increasing development of this industry in Chile, as well as the intensive use of antimicrobials, has not been accompanied by the necessary scientific research needed to understand the impact of the intensive use of antibiotics in this industry. Over the last two decades several studies assessing antimicrobial resistance and the resistome in the freshwater and marine environment impacted by salmon farming have been conducted, but information on the ecological and environmental consequences of antibiotic use in fish farming is still scarce. In addition, studies reporting the antimicrobial susceptibility of bacterial pathogens, mainly P. salmonis, have been developed, but a high number of these studies were aimed at setting their epidemiological cut-off values. In conclusion, further studies are urgently required, mainly focused on understanding the evolution and epidemiology of resistance genes in Chilean salmonid farming, and to investigate the feasibility of a link between these genes among bacteria from salmonid farms and human and fish pathogens.

Current Status of the Use of Antibiotics and the Antimicrobial Resistance in the Chilean Salmon Farms

The Chilean salmon industry has undergone a rapid development making the country the world's second largest producer of farmed salmon, but this growth has been accompanied by an intensive use of antibiotics. This overuse has become so significant that Chilean salmon aquaculture currently has one of the highest rates of antibiotic consumption per ton of harvested fish in the world. This review has focused on discussing use of antibiotics and current status of scientific knowledge regarding to incidence of antimicrobial resistance and associated genes in the Chilean salmonid farms. Over recent years there has been a consistent increase in the amount of antimicrobials used by Chilean salmonid farms, from 143.2 tons in 2010 to 382.5 tons in 2016. During 2016, Chilean companies utilized approximately 0.53 kg of antibiotics per ton of harvested salmon, 363.4 tons (95%) were used in marine farms, and 19.1 tons (5%) in freshwater farms dedicated to smolt production. Florfenicol and oxytetracycline were by far the most frequently used antibiotics during 2016 (82.5 and 16.8%, respectively), mainly being used to treat Piscirickettsia salmonis, currently considered the main bacterial threat to this industry. However, the increasing development of this industry in Chile, as well as the intensive use of antimicrobials, has not been accompanied by the necessary scientific research needed to understand the impact of the intensive use of antibiotics in this industry. Over the last two decades several studies assessing antimicrobial resistance and the resistome in the freshwater and marine environment impacted by salmon farming have been conducted, but information on the ecological and environmental consequences of antibiotic use in fish farming is still scarce. In addition, studies reporting the antimicrobial susceptibility of bacterial pathogens, mainly P. salmonis, have been developed, but a high number of these studies were aimed at setting their epidemiological cut-off values. In conclusion, further studies are urgently required, mainly focused on understanding the evolution and epidemiology of resistance genes in Chilean salmonid farming, and to investigate the feasibility of a link between these genes among bacteria from salmonid farms and human and fish pathogens.

Survival behaviour and virulence of the fish pathogen Vibrio ordalii in seawater microcosms

Vibrio ordalii, the causative agent of atypical vibriosis, is a Gram-negative, motile, rod-shaped bacterium that severely affects the salmonid aquaculture industry. V. ordalii has been biochemically, antigenically and genetically characterized. However, studies on the survival behaviour of this bacterium in aquatic environments are scarce, and there is no information regarding its disease transmission and infectious abilities outside of the fish host or regarding water as a possible reservoir. The present study investigated the survival behaviour of V. ordalii Vo-LM-06 and Vo-LM-18 in sterile and non-sterile seawater microcosms. After a year in sterile seawater without nutrients, 1% of both V. ordalii strains survived (~10(3) colony-forming units ml(-1)), and long-term maintenance did not affect bacterial biochemical or genetic properties. Additionally, V. ordalii maintained for 60 d in sterile seawater remained infective in rainbow trout Oncorhynchus mykiss. However, after 2 d of natural seawater exposure, this bacterium became non-culturable, indicating that autochthonous microbiota may play an important role in survival. Recuperation assays that added fresh medium to non-sterile microcosms did not favour V. ordalii recovery on solid media. Our results contribute towards a better understanding of V. ordalii survival behaviour in seawater ecosystems.

Iron assimilation and siderophore production by Vibrio ordalii strains isolated from diseased Atlantic salmon Salmo salar in Chile

Vibrio ordalii is the causative agent of vibriosis in several cultured salmonid species worldwide. Despite its impact on aquaculture, relatively little information is available about its virulence factors. The present study demonstrates for the first time that V. ordalii possesses different systems of iron acquisition, one involving siderophore synthesis and another one that uses direct binding of heme to use iron. Using 6 strains of V. ordalii from Atlantic salmon Salmo salar and the V. ordalii type strain, we could demonstrate that all strains could grow in presence of the chelating agent 2,2'-dipyridyl and produced siderophores in solid and liquid media. Cross-feeding assays among V. ordalii strains evidenced variability in the siderophores produced. Bioassays and PCR data suggest that V. ordalii could produce a siderophore with a structure similar to piscibactin, although the production of a second siderophore in certain strains cannot be discarded. Furthermore, all strains were able to use hemin and hemoglobin as the only iron sources, although the cell yield was higher when using hemoglobin. A hemin-binding assay indicated the presence of constitutive heme-binding molecules at the cell surface of V. ordalii. Virulence tests using rainbow trout as a model of infection revealed a clear relationship between iron-uptake ability and pathogenicity in V. ordalii.

Cell-surface properties of Vibrio ordalii strains isolated from Atlantic salmon Salmo salar in Chilean farms

Vibrio ordalii is the causative agent of atypical vibriosis and has the potential to cause severe losses in salmonid aquaculture, but the factors determining its virulence have not yet been elucidated. In this work, cell-surface-related properties of the isolates responsible for outbreaks in Atlantic salmon were investigated. We also briefly examined whether pathogenicity against fish varied for V. ordalii strains with differing cell-surface properties. Hydrocarbon adhesions indicated the hydrophobic character of V. ordalii, although only 4 of 18 isolates induced haemagglutination in Atlantic salmon erythrocytes. A minority of the studied isolates (6 of 18) and the type strain ATCC 33509T produced low-grade biofilm formation on polyethylene surface after 2 h post-inoculation (hpi), but no strains were slime producers. Interestingly, V. ordalii isolates showed wide differences in hydrophobicity. Therefore, we chose 3 V. ordalii isolates (Vo-LM-03, Vo-LM-18 and Vo-LM-16) as representative of each hydrophobicity group (strongly hydrophobic, relatively hydrophobic and quasi-hydrophilic, respectively) and ATCC 33509T was used in the pathogenicity studies. All tested V. ordalii strains except the type strain resisted the killing activity of Atlantic salmon mucus and serum, and could proliferate in these components. Moreover, all V. ordalii isolates adhered to SHK-1 cells, causing damage to fish cell membrane permeability after 16 hpi. Virulence testing using rainbow trout revealed that isolate Vo-LM-18 was more virulent than isolates Vo-LM-03 and Vo-LM-16, indicating some relationship between haemagglutination and virulence, but not with hydrophobicity.

PCR protocol for detection of Vibrio ordalii by amplification of the vohB (hemolysin) gene

Vibrio ordalii is the causative agent of atypical vibriosis and has the potential to cause severe losses in salmonid aquaculture. To prevent and control outbreaks, a rapid, reproducible, sensitive, and effective diagnostic method is needed. We evaluated a new conventional polymerase chain reaction (PCR) and real-time PCR (qPCR) protocol using a primer set (VohB_Fw-VohB_Rv) designed to amplify a 112 bp fragment flanking the vohB gene (coding for hemolysin production), against 24 V. ordalii strains isolated from different fish species, the V. ordalii type strain, and 42 representative related and unrelated bacterial species. The primer set was species-specific, recognizing all V. ordalii strains evaluated, with no cross-reaction with the other bacterial species. A sensitivity of 103 copies of the vohB gene was obtained with a standard curve. When the VohB_Fw-VohB_Rv qPCR protocol was applied to Atlantic salmon seeded tissues (kidney, liver, spleen, and muscle), the detection limit ranged from 5.27 × 102 to 4.13 × 103 V. ordalii CFU ml-1, i.e. 62 to 145 copies of the vohB gene, using the previously calculated standard curve. The conventional PCR also detected V. ordalii, but the total reaction time was 1 h longer. When the qPCR protocol was applied to naturally infected cage-cultured Atlantic salmon samples, 5 of 8 fish tested positive for V. ordalii, but only one of them was diagnosed as positive by direct cultivation on agar. We conclude that the PCR protocol evaluated is fast, specific, and sensitive enough to detect V. ordalii in infected tissues and is an important tool for secure diagnosis of atypical vibriosis, and is therefore helpful for the control of the disease through the prompt detection within fish populations.