Bacterium Edwardsiella Ictaluri Research Articles

AKTIVITAS ANTIBAKTERI EKSTRAK KAYU SECANG ( Caesalpinia sappan L.) TERHADAP BAKTERI Edwardsiella tarda DAN Edwardsiella ictaluri PATOGEN BUDIDAYA PERIKANAN

The disease caused by pathogenic bacteria is one of the main problems in aquaculture in the Jambi Province. One of the diseases that occurs in cultivated catfish is due to infection by bacteria Edwardsiella tarda and Edwardsiella ictaluri, which cause Edwardsiellosis with a mortality rate above 50%. The antibacterial properties of the sappanwood extract (Caesalpinia sappan, L.) can be used to overcome problems in aquaculture, while reducing the use of antibiotics that can have negative impacts. This research aims to explore the antibacterial potential of sappanwood extract (Caesalpinia sappan, L.), a local plant believed to possess strong antimicrobial activity. The study began with isolating bacteria from catfish that showing symptoms of the disease, identifying the test bacteria, followed by extracting sappanwood using 96% ethanol solvent. Subsequently, the antibacterial activity was tested using the disc diffusion method with extract concentrations of 1%, 5%, and 10%. The research results indicate that sappanwood extract at a concentration of 5% has a very strong ability to inhibit the growth of E. tarda and E. ictaluri bacteria. The inhibition zones produced show significant antibacterial activity equivalent to the antibiotic ciprofloxacin used as a positive control.

Influence of probiotic and prebiotic supplementation on intestinal microbiota and resistance to Edwardsiella ictaluri infection in channel catfish (Ictalurus punctatus) following florfenicol administration.

Enteric septicemia of catfish (ESC), caused by the gram-negative enteric bacteria Edwardsiella ictaluri, is a significant threat to catfish aquaculture in the southeastern United States. Antibiotic intervention can reduce mortality; however, antibiotic use results in an imbalance, or dysbiosis, of the gut microbiota, which may increase susceptibility of otherwise healthy fish to enteric infections. Herein, recovery of the intestinal microbiota and survivability of channel catfish in response to ESC challenge was evaluated following a 10-day course of florfenicol and subsequent probiotic or prebiotic supplementation. Following completion of florfenicol therapy, fish were transitioned to a basal diet or diets supplemented with a probiotic or prebiotic for the remainder of the study. Digesta was collected on Days 0, 4, 8 and 12, beginning on the first day after cessation of antibiotic treatment, and gut microbiota was characterized by Illumina sequencing of the 16S rRNA gene (V4 region). Remaining fish were challenged with E. ictaluri and monitored for 32 days post-challenge. Florfenicol administration resulted in dysbiosis characterized by inflated microbial diversity, which began to recover in terms of diversity and composition 4 days after cessation of florfenicol administration. Fish fed the probiotic diet had higher survival in response to ESC challenge than the prebiotic (p = .019) and negative control (p = .029) groups.

Synergistic infection of Edwardsiella ictaluri and Flavobacterium oreochromis in cage cultured tilapia (Oreochromis sp.).

Widespread distribution of a highly pathogenic Edwardsiella ictaluri strain in farmed tilapia in northern Vietnam has recently been reported. The subsequent investigation noticed a disease outbreak occurred at five nearby tilapia farms with floating cages, in which the clinical signs of both edwardsiellosis and columnaris diseases were observed on the same infected fish and caused 65% to 85% fish mortality. Naturally diseased fish (n = 109) were sampled from the five infected farms for bacterial identification and conducting challenge tests. The two bacteria Edwardsiella ictaluri and Flavobacterium oreochromis were identified by a combination of biochemical tests, PCR and 16SrRNA sequencing methods. Experimental challenge tests on Nile tilapia resulted in the median lethal dose (LD50 ) of E. ictaluri and F. oreochromis at 70 CFU/fish by intraperitoneal (i.p.) injection and 3.6 × 106 CFU/mL by immersion, respectively. The experimentally co-infected challenged fish exposed to LD50 doses resulted in 83% ± 6% mortality, with the infected fish exhibiting clinical signs of both edwardsiellosis and columnaris diseases, mimicking the naturally diseased fish. This finding suggests that the co-infection of E. ictaluri and F. oreochromis may interact in a synergistic manner, to enhance the overall severity of the infection and elevates the need for efficient methods to control both pathogens.

PENGUJIAN PENYAKIT KOMODITAS IKAN AIR TAWAR PADA LALU LINTAS DOMESTIK DI STASIUN KARANTINA IKAN JAMBI

Increased trade flows of international and domestic fishery coomodities in the opportunity to enter and spread Hama penyakit Ikan Karantina (HPIK) caused by pathogenic organism, namely bacteria, parasites, fungi, and viruses. This study aims to identify whether freshwater fish commodities in domestic traffic are infected with parasites, the bacteria Edwardsiella ictaluri, TiLV (Tilapia lake Virus) and the fungus Aphanomyces invadans at the Fish Quarantine Stasion, Quality Control and Safety of Fishery Products Jambi. Fish samples consist of 15 fish samples to be tranported. Based on results of the examinatoin of fish diseases, Parasite Examination there were 4 parasites with 3 types of parasites, namely 2 parasites of Dactylogyrus sp. On the gills of Tilapia and catfish. One (1) parasite Gyrodactylus sp. On fish slime Stripe 3, and 1 parasite Camallanus sp.in the intestines of betta fish; on bacterial examination of the 4 samples of fish examined, Edwardsiella ictaluri bacteria were nof found; on virus examination the result were negative for TiLV (Tilapia lake Virus); on examination of the fungus with the PCR method, negatif result were obtained for the fungus Aphanomyces invadans which is the cause of EUS (Epizootic Ulcerative Syndrome).

Evaluation of the immune responses against enteric septicemia and determination of immune markers for selective breeding of pangasius families (Pangasianodon hypophthalmus)

The immune response of two groups of selective breeding panagasius families: susceptible (or sensitive) (S) and resistant (R) family groups, including red blood cell count (RBC count), white blood cell count (WBC count), neutrophil (NEU), monocyte (MONO), lymphocyte (LYM), and melano-macrophage centers (MMCs) count in liver, kidney and spleen tissue and antibody titers (ABT) against the bacteria Edwardsiella ictaluriwere evaluated in this research. Fish were sampled at five truncated points after infection with the bacteria Edwardsiella ictaluri including before the challenge, 24, 48, 264, and 312 hpi. The immune response of the R group was more effective than that of the S group, showing: (1) RBC decreased less during the challenge; (2) WBC, NEU, MONO, LYM increased more rapidly, especially at the truncated point 24-48 hpi; (3) MMCs in liver, kidney, and spleen of the R group increased faster up to the truncated point 48 hpi while the S group increased more slowly and only up to the truncated point 24 hpi; (4) ABT were higher in all stages of the challenge. The research developed a multivariable logistic regression model with immune markers such as NEU, ABT and MMCs in the liver at the truncated point of 24-48 hpi to identify individuals which were resistant to Enteric Septicemia of Catfish (ESC), with sensitivity and specificity of 91.7, 95.0%, respectively.

Genetic analysis of resistance in Mekong striped catfish (Pangasianodon hypophthalmus) to bacillary necrosis caused by Edwardsiella ictaluri.

The aim of this study was to analyse four cohabitation challenge-test experiments with Mekong striped catfish (Pangasianodon hypophthalmus) against the bacterium Edwardsiella ictaluri. The data were genetically analysed per experiment by three models: 1) a cross-sectional linear model; 2) a cross-sectional threshold model; and 3) a linear survival model, at both 50% mortality (for models 1 and 2) and at the end of the test (for all three models). In two of the experiments (3 and 4) that were carried out in two replicated tanks, the predicted family effects (sum of sire, dam and common environmental effects) in each tank were correlated with the family survival in the other replicated tank (cross-validation). The heritability estimates of resistance to E. ictaluri infection were≤0.012 with the survival model, and up to 0.135 - 0.220 (50% survival) and 0.085 and 0.174 (endpoint survival) for the cross-sectional linear and threshold models, respectively. The challenge test should aim for an endpoint survival that ceases naturally at 50%. Then, genetic analysis should be carried out for survival at the endpoint (reflecting susceptibility) with a simple cross-sectional linear model.

Nursing stages of striped catfish (Pangasianodon hypophthalmus) in Vietnam: Pathogens, diseases and husbandry practices

This study describes the prevalence of common diseases and pathogens of Pangasianodon hypophthalmus in nursing farms in the Mekong delta, Vietnam, and identifies the preventive husbandry measures in use by these farms and their association with diseases. In a first study, farmers of 63 randomly selected nursing farms in An Giang, Can Tho, and Dong Thap provinces were interviewed using semi-structured questionnaires. Questions included topics on disease occurrence and application of husbandry measures in their last crop. The results showed that prevalence of bacillary necrosis of pangasius (BNP) was 75%, motile Aeromonas septicemia (MAS) 60%, parasitic disease 48%, saprolegniasis 19%, pale gill and liver syndrome 17%, tail rot 14%, and swollen swim bladder disease 3%. Eighty-eight percent of farmers had more than one of these diseases in their last crop. The duration of these crops are on average 2 months. Delaying the onset of feed training was significantly preventive for MAS (OR = 0.85, 0.75–0.95 95% CI) and BNP (OR = 0.88, 0.78–0.97), using iodine to disinfect water for BNP (OR = 0.23, 0.05–0.95), draining the pond sludge for parasitic disease (OR = 0.32, 0.10–0.97) and reducing time between filling the pond with water and stocking of fish for parasitic disease (OR of increasing time was 2.49, 1.13–6.40). Of all farmers interviewed, 43% used antibiotics preventively in fish food, but this practice was not significantly associated with lower disease prevalence. In a second study, fish from 48 randomly selected nursing ponds were sampled. Samples were randomly split to diagnose parasites (n = 443), common bacteria (n = 48 pools), or common fungi (n = 371). Prevalences of some pathogens were high, i.e. the parasite Trichodina, 48%, the bacteria Aeromonas hydrophila, causative for MAS, 23%, the bacteria Edwardsiella ictaluri, causative for BNP, 40%, the fungi Fusarium spp., causative for swollen swim bladder disease, 9.7%, and the fungi Aspergillus spp. 9.4%. The high prevalence of some of these diseases and pathogens is concerning, and shows that current preventive and mitigation measures need to be improved. The high number of crops with multiple diseases may indicate a reduced general resilience of the fish, which indicates that mitigation strategies would benefit from a comprehensive approach, instead of focused on single diseases or pathogens. Current preventive husbandry practices needs optimizing, but can play an important role in future mitigation strategies towards improved sustainability of striped catfish nursing farms.

Antibacterial activity of Anadendrum microstachyum and Selaginella plana against two pathogenic bacteria (Edwardsiella ictaluri and Streptococcus agalactiae) causing freshwater fish diseases

Aquatic plants are potential to use as antibacterial to control pathogens that cause disease in fish. The antibacterial activity of extracts of Anadendrum microstachyum and Selaginella plana were tested against Edwardsiella ictaluri and Streptococcus agalactiae using disc diffusion Kirby-Bauer method. Plant extracts of A. microstachyum and S. plana at concentration 0.2 g could inhibit E. ictaluri and S. agalactiae; therefore A. microstachyum and S. plana are potential be developed as antibacterial compounds to substitute the use of antibiotic in fish farming and as candidates new drug to prevent and control of diseases in aquaculture.

Virulent bacteriophage of Edwardsiella ictaluri isolated from kidney and liver of striped catfish Pangasianodon hypophthalmus in Vietnam.

Striped catfish Pangasianodon hypophthalmus farmed in the Mekong Delta, Vietnam, represents an important contribution to Vietnamese aquaculture exports. However, these fish are affected by frequent disease outbreaks across the entire region. One of the most common infections involves white spots in the internal organs, caused by the bacterium Edwardsiella ictaluri. In this study, a virulent phage specific to E. ictaluri, designated MK7, was isolated from striped catfish kidney and liver samples and characterized. Morphological analysis indicates probable placement in the family Myoviridae with a 65 nm icosahedral head and a 147 %%CONV_ERR%% 19 nm tail. A double-stranded DNA genome of approximately 34 kb was predicted by restriction fragment analysis following digestion with SmaI. The adsorption affinity (ka) of the MK7 phage was estimated as 1.6 %%CONV_ERR%% 10-8 ml CFU-1 min-1, and according to a 1-step growth curve, its latent period and burst size were ~45 min and ~55 phage particles per infected host cell, respectively. Of the 17 bacterial strains tested, MK7 only infected E. ictaluri, although other species of Edwardsiella were not tested. E. ictaluri was also challenged in vitro, in both broth and water from a striped catfish pond and was inactivated by MK7 for 15 h in broth and 51 h in pond water. Thus, initial characterization of phage MK7 indicates its potential utility as a biotherapeutic agent against E. ictaluri infection in striped catfish. This is the first report of a lytic phage specific to an important striped catfish pathogen.

Antibacterial Activity of Constituents from Mangosteen Garcinia mangostana Fruit Pericarp against Several Channel Catfish Pathogens.

Bacterial diseases cause major financial damage to the producers of Channel Catfish Ictalurus punctatus in the southeastern USA. The two most common bacterial diseases among pond-raised Channel Catfish are enteric septicemia of catfish, caused by the gram-negative bacterium Edwardsiella ictaluri, and columnaris disease, caused by the rod-shaped, gram-negative bacterium Flavobacterium columnare. Streptococcosis is another, less-common bacterial disease in catfish and is caused by the gram-positive coccus Streptococcus iniae. Catfish farmers typically rely on commercial antibiotics and other chemicals to prevent the economic damage from these diseases. Environmentally benign and efficacious alternatives to the currently used antibiotics and chemicals will tremendously help the catfish aquaculture industry. As part of our ongoing efforts in the search for such novel compounds, we investigated ethyl acetate and methanol extracts of mangosteen Garcinia mangostana fruit pericarp via bioassay-guided fractionation. Gamma-mangostin (γ-mangostin) was isolated and identified as the most promising active metabolite against F. columnare. One of the constituents in the mangosteen fruit pericarp, alpha-mangostin (α-mangostin), is the major xanthone; α-mangostin was found to be 10-fold less active than γ-mangostin when minimum inhibitory concentration values were compared.

First detection of Edwardsiella ictaluri (Proteobacteria: Enterobacteriaceae) in wild Australian catfish.

The bacterium Edwardsiella ictaluri is considered to be one of the most significant pathogens of farmed catfish in the United States of America and has also caused mortalities in farmed and wild fishes in many other parts of the world. E.ictaluri is not believed to be present in wild fish populations in Australia, although it has previously been detected in imported ornamental fishes held in quarantine facilities. In an attempt to confirm freedom from the bacterium in Australian native fishes, we undertook a risk-based survey of wild catfishes from 15 sites across northern Australia. E.ictaluri was detected by selective culturing, followed by DNA testing, in Wet Tropics tandan (Tandanus tropicanus) from the Tully River, at a prevalence of 0.40 (95% CI 0.21-0.61). The bacterium was not found in fishes sampled from any of the other 14 sites. This is the first report of E.ictaluri in wild fishes in Australia.

Molecular and functional characterization of liver X receptor in ayu, Plecoglossus altivelis: Regulator of inflammation and efferocytosis

Liver X receptors (LXR) are modulators of metabolic processes and inflammation in mammals as nuclear receptors. However, the precise function of LXR in teleosts remains unclear. Here, we characterized a LXR gene (PaLXR) from ayu, Plecoglossus altivelis. The PaLXR transcript was expressed widely in all tissues studied, and changes in expression were observed in tissues and monocytes/macrophages (MO/MΦ) upon infection with the bacterium Edwardsiella ictaluri. PaLXR activation decreased the mRNA expression of interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), and IL-10 upon E. ictaluri infection, while their expression was increased following the knockdown of PaLXR by siRNA. Moreover, E. ictaluri infection induced the apoptosis of ayu neutrophils and PaLXR activation enhanced the internalization of E. ictaluri-infected apoptotic neutrophils by MO/MΦ (efferocytosis), while PaLXR knockdown led to decreased efferocytosis. Furthermore, PaLXR activation inhibited intracellular bacterial survival during efferocytosis, while PaLXR knockdown enhanced survival. In conclusion, our results indicate that PaLXR plays a role in the modulation of innate immune responses in ayu MO/MФ.

양식 동자개(Pelteobagrus fulvidraco)의 Edwardsiella ictaluri 감염

We observed yellow catfish Pelteobagrus fulvidraco fingerlings cultured in land ponds in Korea swimming in a corkscrew spiral pattern while hanging head-up and tail-down at the water surface, before eventually dying. Externally, these fish displayed “hole in the head” disease, pale gills, and hemorrhages in the base of the pectoral and caudal fins; internally they had liver hemorrhages and kidney discoloration. The bacterium Edwardsiella ictaluri (YCK-01 and YCL-01) was identified in the kidneys and livers of diseased fish via phenotypic characteristics and PCR analysis using the ictaluri-specific primers IVS (an intervening sequence) and IRS (the inter-ribosomal spacer). Infectivity challenges by intraperitoneal and immersion routes showed that a representative bacterial strain (YCK) exhibited strong virulence to yellow catfish, with an LD₅₀ of 3.2×10⁴ CFU/fish and 2.5×10⁶ CFU/mL, respectively. This is the first report of E. ictaluri infection in yellow catfish from Korea.

Can immunostimulants efficiently replace antibiotic in striped catfish (Pangasianodon hypophthalmus) against bacterial infection by Edwardsiella ictaluri?

The present study was performed to determine the efficacy of lipopolysaccharide (LPS) and levamisole on immune response and disease resistance in striped catfish and to compare their respective efficiency with the one of an antibiotic treatment after infection of fish by the bacteria Edwardsiella ictaluri. Fish were divided into 3 groups and each group was injected with LPS (3 mg/kg fish), levamisole (5 mg/kg fish) or phosphate buffer saline as control. At day 21st post immunostimulant injection, fish were bled for assaying immunological variables and then challenged with E. ictaluri. Three days after bacterial infection, an antibiotic treatment was applied into fish subgroups and mortality was compared daily between antibiotic treated and untreated fish until 2 weeks post-challenge. LPS and levamisole significantly enhanced non-specific immune responses such as respiratory burst, lysozyme and complement activity in fish compared with control (p < 0.05). Respiratory burst and complement activity significantly increased in levamisole groups when compared with LPS groups while lysozyme activity did not differ significantly between immunostimulant treatments. Total immunoglobulins significantly increased in levamisole treatment compared with control. After challenge test, accumulated mortality was reduced significantly in both non-antibiotic and antibiotic subgroups of LPS and levamisole compared with control. Moreover, no differences of mortality were observed between fish treated with levamisole or LPS without antibiotics and control fish treated with antibiotics. These results support the possible replacement of antibiotics in striped catfish farming by immunostimulants such as levamisole and LPS.

Comparative susceptibility of Channel Catfish, Blue Catfish, and their hybrid cross to experimental challenge with Bolbophorus damnificus (Digenea: Bolbophoridae) cercariae.

The digenetic trematode Bolbophorus damnificus has been implicated in significant losses in catfish aquaculture since the late 1990s. The complex life cycle sequentially involves the American white pelican Pelecanus erythrorhynchos, the marsh rams horn snail Planorbella trivolvis, and Channel Catfish Ictalurus punctatus. Research supports anecdotal reports from the industry, suggesting that the hybrid of Channel Catfish×Blue Catfish I. furcatus is less susceptible to disease agents that have been historically prohibitive to Channel Catfish production, namely the gram-negative bacteria Edwardsiella ictaluri and Flavobacterium columnare, as well as the myxozoan parasite Henneguya ictaluri. This current research compared the susceptibility of Channel Catfish, Blue Catfish, and their hybrid cross to an experimental challenge by B. damnificus. Fish were exposed to 0, 100, 200, and 400 B. damnificus cercariae per fish, and the numbers of metacercariae per fish were determined 14 d postchallenge. Metacercariae were recovered from all challenged fish. There were no significant differences among fish groups challenged with the same dose, suggesting Channel and Blue Catfish and their hybrid are comparably susceptible to B. damnificus infection. As such, it is recommended that producers raising hybrid catfish remain diligent in controlling populations of the snail intermediate host to prevent production losses attributed to B. damnificus, especially when loafing pelicans have been observed at the aquaculture operation.

The effect of feeding diets containing deoxynivalenol contaminated corn on channel catfish (Ictalurus punctatus) challenged withEdwardsiella ictaluri

Channel catfish were fed practical corn-soybean meal diets for 10 weeks that contained various weighed amounts of ground, dried field corn contaminated with 20 mg deoxynivalenol (DON) kg−1. Weighed amounts of DON corn were blended with weighed amounts of ground, clean corn that contained no DON (0 mg kg−1) to yield five diets that had 0, 2.5, 5.0, 7.5 and 10.0 mg DON kg−1 of diet. Results show that catfish fed diets that contained DON for 7 weeks did not experience lower weight gains or poorer feed conversion ratios that were significantly (P > 0.05) different from control-fed fish. Mortality of catfish during the 21-day post-challenge period indicate that catfish fed diets containing DON-contaminated corn that provided at least 5.0 mg DON kg−1 of diet had significantly (P < 0.05) lower mortality than catfish fed the control diet or the diet that provided 2.5 mg DON kg−1 of diet. The presence of DON-contaminated corn in the experimental diets did not significantly (P > 0.05) alter fish body weight gains and appeared to provide a protective effect for channel catfish challenged with the pathogenic bacterium Edwardsiella ictaluri.

Enhanced susceptibility of channel catfish to the bacterium Edwardsiella ictaluri after parasitism by Ichthyophthirius multifiliis

Bacterium Edwardsiella ictaluri and parasite Ichthyophthirius multifiliis (Ich) are two common pathogens of cultured fish. The objective of this study was to evaluate the susceptibility of channel catfish Ictalurus punctatus to E. ictaluri and determine bacterial loads in different fish organs after parasitism by Ich. Fish received the following treatments: (1) infected by I. multifiliis at 5000theronts/fish and exposed to E. ictaluri; (2) infected by I. multifiliis alone; (3) exposed to E. ictaluri alone; and (4) non-infected control. E. ictaluri in fish organs were quantified by quantitative real-time polymerase chain reaction and reported as genome equivalents per mg of tissue (GEs/mg). The results demonstrated that the Ich-parasitized catfish showed significantly (P<0.05) higher mortality (91.7%) when exposed to E. ictaluri than non-parasitized fish (10%). The bacterial loads in fish infected by 5000theronts/fish ranged from 6497 to 163,898GEs/mg which was between 40 and 2000 fold higher than non-parasitized fish (49–141GEs/mg). Ich infection enhanced the susceptibility of channel catfish to bacterial invasion and increased fish mortality.

Replacement of fish meal in juvenile channel catfish, Ictalurus punctatus, diets using a yeast-derived protein source: the effects on weight gain, food conversion ratio, body composition and survival of catfish challenged with Edwardsiella ictaluri

We examined the effects of a yeast-derived protein source (NuPro®) as a replacement for menhaden fish meal on weight gain, specific growth rate (SGR), food conversion ratio (FCR), whole-body composition and disease resistance in juvenile channel catfish (9.9 ± 0.2 g fish−1). NuPro® replaced fish meal at six levels (0, 25, 50, 75, 100 and 125 g kg−1 diet). Catfish were sampled for whole-body composition and then challenged with the bacterium Edwardsiella ictaluri. Growth performance was negatively affected (P < 0.01) when NuPro® was added at 125 g kg−1 diet. The amount of whole-body fat decreased (P < 0.05) when NuPro® was added at 75 g kg−1 or more of the diet. Regardless of the amount of NuPro® added, survival after challenge with E. ictaluri was similar among treatments. Results indicate that up to 100 g kg−1 of NuPro® can be added without negatively affecting growth performance. The yeast-derived protein source used in this study is a sustainable protein alternative that could be used as a partial replacement for fish meal in juvenile channel catfish diets.

In Vitro Evaluation of the Antimicrobial Agent AquaFrin as a Bactericide and Selective Algicide for Use in Channel Catfish Aquaculture

AbstractProducers of pond‐raised channel catfish Ictalurus punctatus in the southeastern United States can experience huge economic losses due to enteric septicemia of catfish (ESC) and columnaris disease and to the presence of certain odor‐producing cyanobacteria in production ponds that result in “off‐flavor” channel catfish. AquaFrin (lauryl methyl pyrifrin), a product currently being evaluated for commercial use, belongs to a class of porphyrins that have been shown to be very effective as antibacterial agents. As a preliminary step to assess the potential use of AquaFrin as a therapeutant against ESC and columnaris, we used a rapid bioassay to evaluate AquaFrin for antibacterial activity against the Gram‐negative bacterium Edwardsiella ictaluri (etiological agent of ESC), two genotypes of the Gram‐negative bacterium Flavobacterium columnare (etiological agent of columnaris disease), and the representative Gram‐positive bacterium Staphylococcus aureus (American Type Culture Collection 29213) for comparison. In addition, we performed a bioassay‐directed evaluation of AquaFrin for selective toxicity toward the musty cyanobacterium Planktothrix perornata. AquaFrin was found to possess antibacterial activity toward all tested bacteria and yielded the following minimal inhibitory concentration results: 0.5 mg/L for F. columnare isolate ALM‐00‐173, 1.0 mg/L for F. columnare isolate BioMed, 0.1 mg/L for S. aureus, and 9.8 mg/L for E. ictaluri. The range of 96‐h 50% inhibition concentrations (0.07–0.2 mg/L) for AquaFrin toward P. perornata and the green alga Selenastrum capricornutum indicates strong potential for its use as a broad‐spectrum algicide.

Plant Natural Compounds with Antibacterial Activity towards Common Pathogens of Pond-Cultured Channel Catfish (Ictalurus punctatus)

The bacteria Edwardsiella ictaluri and Flavobacterium columnare cause enteric septicemia and columnaris disease, respectively, in channel catfish (Ictalurus punctatus). Natural therapeutants may provide an alternative to current management approaches used by producers. In this study, a rapid bioassay identified plant compounds as potential therapeutants. Chelerythrine chloride and ellagic acid were the most toxic toward E. ictaluri, with 24-h IC50 of 7.3 mg/L and 15.1 mg/L, respectively, and MIC of 2.1 mg/L and 6.5 mg/L, respectively. Chelerythrine chloride, ellagic acid, β-glycyrrhetinic acid, sorgoleone, and wogonin were the most toxic towards two genomovars of F. columnare, and wogonin had the strongest antibacterial activity (MIC = 0.3 mg/L).