Use Of Antibiotics In Aquaculture Research Articles

Synergistic Combination of Biodegradable Peptide Polymer and Curcumin as Promising Antibiotic Substitution in Aquaculture to Alleviate the Global Challenge of Antimicrobial Resistance

Comprehensive SummaryThe massive use of antibiotics in aquaculture and resulted antibacterial resistance problem urgently need antibiotic substitutions. Herein, we report a promising substitution of aquaculture antibiotics using a synergistic combination of biodegradable peptide polymers and curcumin, a natural compound from plant. The synergistic combination shows strong antibacterial activity against V. fluvialis and some other common bacteria in aquaculture. The membrane‐damaging antibacterial mechanism echoes our finding that the synergistic combination will not induce bacteria to develop resistance after continuous use. The synergistic combination also displays effective cure on V. fluvialis‐infected zebrafish. The biodegradability of the peptide polymer enables the combination to lose antibacterial activity and will not cause selective pressure on bacterial in the environment. Our study indicates potential application of synergistic composition, biodegradable peptide polymer and curcumin, as promising antibiotic substitution in aquaculture, which represents a promising strategy to address the global challenge of antimicrobial resistance.

Insights into the Vibrio Genus: A One Health Perspective from Host Adaptability and Antibiotic Resistance to In Silico Identification of Drug Targets.

The genus Vibrio comprises an important group of ubiquitous bacteria of marine systems with a high infectious capacity for humans and fish, which can lead to death or cause economic losses in aquaculture. However, little is known about the evolutionary process that led to the adaptation and colonization of humans and also about the consequences of the uncontrollable use of antibiotics in aquaculture. Here, comparative genomics analysis and functional gene annotation showed that the species more related to humans presented a significantly higher amount of proteins associated with colonization processes, such as transcriptional factors, signal transduction mechanisms, and iron uptake. In comparison, those aquaculture-associated species possess a much higher amount of resistance-associated genes, as with those of the tetracycline class. Finally, through subtractive genomics, we propose seven new drug targets such as: UMP Kinase, required to catalyze the phosphorylation of UMP into UDP, essential for the survival of bacteria of this genus; and, new natural molecules, which have demonstrated high affinity for the active sites of these targets. These data also suggest that the species most adaptable to fish and humans have a distinct natural evolution and probably undergo changes due to anthropogenic action in aquaculture or indiscriminate/irregular use of antibiotics.

Antibiotics usage practices in aquaculture in Bangladesh and their associated factors

BackgroundIrrational and inappropriate use of antibiotics in aquaculture can contribute to the development of antibiotic resistance. ObjectivesIn this study, we aimed to assess antibiotic usage in inland and coastal fish farms in Bangladesh and identify factors associated with this practice. MethodsWe conducted a cross-sectional study to collect antibiotic usage information from 672 fish farmers in Bangladesh. The frequency of use, the types of antibiotics, the purpose of usage, and antibiotic prescribing practices were estimated. Adjusted odds ratios (aOR) were calculated to measure the association between antibiotic usage and factors related to the characteristics of the farms and farmers using multivariable logistic regression models. ResultsTwenty-two farms reported using antibiotics in the last 24 h preceding the interview (3%, 95% CI: 2–5%); 36 farms (5%, 95% CI: 4–7%) in the last 72 h, 141 farms (21%, 95% CI: 18–24%) in the last 14 days, and 478 farms (71%, 68–75%) reported antibiotic usage at least once since the start of their production cycle. Antibiotics usage in the last 14 days preceding the interviews was higher in freshwater fish farms (98%) than in brackish water farms (2%). Oxytetracycline, ciprofloxacin, and amoxicillin were the most frequently used antibiotics. Most of the antibiotics were reported to be used for both therapeutic and prophylactic purposes (71%, 95% CI: 63–78%). Antibiotics used within the last 14 days were mainly advised by feed dealers or drug sellers (51%, 95% CI: 43–60%), followed by farmers themselves (31%, 95% CI: 23–38%) and local service providers (18%, 95% CI, 12–25%). Fish farms having history of antibiotic use within the last 14 days preceding interviews was significantly associated with illness in fish (aOR 1.98, 95% CI:1.21–3.29) compared to farms with healthy fish and fishes cultured in ponds (aOR 9.34, 95% CI: 3.69–23.62) compared to enclosure cultures. ConclusionsImprovement of fish health through better farming practices and changes in feed dealers' and farmers' attitudes towards self-prescription of antibiotic without veterinarian diagnostics may help to reduce the levels of antibiotic usage and thus contribute to mitigating antimicrobial resistance.

Prevalence of Antibiotic Resistance Bacteria in Aquaculture Sources in Johor, Malaysia Prevalence of Antibiotic Resistance

The intensive use of antibiotics in aquaculture results in the proliferation of antibiotic. In this study, antibiotic resistant bacteria from six different aquaculture sources (pond of Fisheries Research Institute (FRI), and rivers of Kukup, Pulai, Pendas Laut, Sungai Melayu and Kong Kong) were isolated. These isolates were tested for antibiotic resistance against seven antibiotics via the disc diffusion method. Finally, phenotypic and genotypic identification via 16S rRNA sequencing and phylogenetic analysis were carried out. The results show that 58 out of 118 bacterial isolates are resistant to multiple antibiotics. The highest isolate resistance was observed towards rifampicin (89.66%), followed by ampicillin (79.31%) and sulfafurazole (67.24%). The isolates with multiple antibiotic resistant (MAR) index values with more than 20% were subjected to 16S rRNA gene sequencing. The majority of the bacterial strains exhibit multiple antibiotic resistance, indicating that they were isolated from highly contaminated sources based on the tested water qualities profiles, which showed the high level of turbidity and total dissolved solid (TDS) in most sampling sites with the high number of MAR bacteria obtained.Keywords: Antibiotic resistance, Multiple antibiotic resistance, Aquaculture sources,MAR index value, 16S rRNA gene sequencing

Antibiotic application may raise the potential of methylmercury accumulation in fish

Mercury (Hg) biotransformation can significantly affect the Hg speciation and bioaccumulation in fish, where gut microbiota play an important role in this process. Antibiotics have been extensively used in aquaculture and can affect gut microbial structure. However, the influence of antibiotics on Hg biotransformation in fish has not been thoroughly understood. The present study investigated the effects of antibiotic (florfenicol) application on gut microbiota and subsequent impacts on Hg biotransformation and bioaccumulation in tilapia (Oreochromis mossambicus). The results showed that the florfenicol treatment did not affect IHg accumulation in the IHg-exposed fish or the MeHg accumulation in the MeHg-exposed fish. However, methylation was significantly weakened (from 0.015% d−1 to 0.005% d−1) and demethylation was completely terminated (from 0.046% d−1 to non-observable level) in the florfenicol-treated fish as compared to the control fish. This can be ascribed to the major shift in the richness of microbial methylators/demethylators in fish gut. Furthermore, florfenicol disturbed the homeostasis of gut microbiome and enhanced the growth of opportunistic pathogens. Our results strongly suggested that antibiotic application significantly altered the gut microbial community, thereby increasing the potential of MeHg accumulation by fish. This study highlights the importance of appropriate use of antibiotics in aquaculture as well as decreasing the environmental risks of Hg contamination in fish.

Autogenous vaccines in aquaculture: Tool to combat resistance of bacteria to antibiotics?

New technological progress and increased demands for fish as a source of animal protein are driving significant growth of aquaculture production. Intensification of production increases the severity and frequency of infectious disease outbreaks, and so requires significant effort to prevent and control disease. Because of the global crisis of bacterial resistance to antibiotics, the use of antibiotics in aquaculture is increasingly subjected to strict control and regulatory measures, leading to potential misuse. The lack of availability of approved veterinary medical products for use in aquaculture, combined with the risk of drug resistance development and antibiotic residues in fish flesh or water, support the development of preventive actions, including vaccines. However, the diversity of species and aquaculture production methods, including epidemiological units and their links, results in economic challenges for commercial vaccine development and authorization. As a possible response to the increasing demand for less antibiotic use in fish farms, and to the expenses associated with novel veterinary product development, there is a need for increased use of safe and effective autogenous vaccines in aquaculture. Regulatory processes for autogenous vaccine production, approval and application should recognize the specificities of epidemiological units and their links in aquatic animal production facilities. The joint efforts of regulatory authorities, producers, and veterinary services to follow veterinary biosecurity principles, including risk analysis, surveillance, and selection/prioritization of pathogens, are essential to provide maximum safety and efficacy of autogenous vaccines as disease prevention and control tools within larger areas, such as compartments and zones, and allow for reductions in antibiotic use.

Reduction of Antibiotic-Resistant Bacterial Counts in a Mangrove-Riverine System in Capiz, Philippines - Preliminary Data

The anthropogenic impact of effluents and indiscriminate use of antibiotics in aquaculture promotes the emergence and proliferation of antibiotic resistant (ABR) bacteria. Comparative total bacterial and ABR counts were determined from 3 locations of the Cadimahan river of Capiz province, Philippines. The upstream station showed lower total bacterial but higher ABR counts, which is the inverse of the downstream station which showed higher total bacterial but lower ABR counts. The ABR counts accounted for 0.0173%, 0.0043% and 0.0002% of the total bacterial counts for upstream, midstream, and downstream, respectively, showing a strong inverse correlation of -0.84 in the Pearson correlation coefficient. This result suggests a remediating effect potentially mediated by microbial dynamics in the Mangrove-riverine system.

Susceptibility to Bismuth(III) of Aquaculture Bacterial Pathogens: Effectiveness of Bismuth-Deferiprone Therapy against Vibrio anguillarum Infection in Fish.

Bismuth is a heavy metal with antibacterial properties that has a long history of medicinal use. The results reported here suggest that bismuth(III) (chelated with deferiprone) could be used in aquaculture systems to treat bacterial disease outbreaks, greatly reducing antibiotic use. We tested bismuth susceptibility in a collection of aquaculture bacterial pathogens. In the presence of bismuth concentrations ranging from 1.3 to 13 µM, most bacteria started showing a drastic decrease in their growth ability, although with high inter- and intraspecific variability. The minimal inhibitory concentrations of bismuth ranged from 13 to more than 780 µM, depending on bacterial species and strain. The results of in vivo assays suggest that low concentrations of bismuth could be especially effective to treat vibriosis caused by Vibrio anguillarum, since bismuth greatly reduced mortality in experimentally infected fish without any observable side effects. A bismuth therapy, alone or combined with other antimicrobials, could contribute to reduce the use of antibiotics in aquaculture.

Research trends of aqua medicines, drugs and chemicals (AMDC) in Bangladesh: the last decade's (2011-2020) story to tell

Aquaculture medicines, drugs, and chemicals or simply AMDC, are critical in protecting aquaculture farmers from disease in farmed animals and economic losses. The AMDC is now a well-established industry in Bangladesh, and each year, new products that benefit farmers are launched. This review examined published research information on AMDC over the last decade (2011-2020) and discovered that 41 research publications from various parts of Bangladesh were published, citing the names of 1484 AMDC products. It was discovered that 19 generic antibiotics are well established and widely used in different regions' aquaculture, including shrimp aquaculture. Although some researchers expressed concern about the use of antibiotics in aquaculture, they believe that with proper withdrawal periods and the application of small doses, farmers may avoid economic losses. However, the pathway of the antibiotic introduction in aquaculture setup in Bangladesh was unknown to the researchers, through this review, we revealed the pathway of antibiotics introduction in aquaculture. Additionally, this review revealed that various AMDC products, including oxygen suppliers, growth promoter supplements, disinfectants, raw chemicals, probiotics, pond preparation and management AMDC, and toxic gas removal AMDC, are readily available in various markets throughout Bangladesh. The observation implied that research on the efficacy of various AMDC products in Bangladesh's agro-ecological zones could be conducted, which would aid researchers in deciphering the true nature of AMDC in sub-tropical climates. Asian J. Med. Biol. Res. 2021, 7 (2), 90-106

Antibiotic-Resistant Bacteria in Aquaculture and Climate Change: A Challenge for Health in the Mediterranean Area.

Aquaculture is the productive activity that will play a crucial role in the challenges of the millennium, such as the need for proteins that support humans and the respect for the environment. Aquaculture is an important economic activity in the Mediterranean basin. A great impact is presented, however, by aquaculture practices as they involve the use of antibiotics for treatment and prophylaxis. As a consequence of the use of antibiotics in aquaculture, antibiotic resistance is induced in the surrounding bacteria in the column water, sediment, and fish-associated bacterial strains. Through horizontal gene transfer, bacteria can diffuse antibiotic-resistance genes and mobile resistance genes further spreading genetic determinants. Once triggered, antibiotic resistance easily spreads among aquatic microbial communities and, from there, can reach human pathogenic bacteria, making vain the use of antibiotics for human health. Climate change claims a significant role in this context, as rising temperatures can affect cell physiology in bacteria in the same way as antibiotics, causing antibiotic resistance to begin with. The Mediterranean Sea represents a ‘hot spot’ in terms of climate change and aspects of antibiotic resistance in aquaculture in this area can be significantly amplified, thus increasing threats to human health. Practices must be adopted to counteract negative impacts on human health, with a reduction in the use of antibiotics as a pivotal point. In the meantime, it is necessary to act against climate change by reducing anthropogenic impacts, for example by reducing CO2 emissions into the atmosphere. The One Health type approach, which involves the intervention of different skills, such as veterinary, ecology, and medicine in compliance with the principles of sustainability, is necessary and strongly recommended to face these important challenges for human and animal health, and for environmental safety in the Mediterranean area.

Effect of dietary inactivated Lactobacillus plantarum on growth performance, antioxidative capacity, and intestinal integrity of black sea bream (Acanthopagrus schlegelii) fingerlings.

Probiotic supplementation in fish feed is becoming popular as a viable alternative to curb the indiscriminate use of antibiotics in aquaculture. The effect of inactivated Lactobacillus plantarum on growth performance and health related indices of black sea bream (Acanthopagrus schlegelii) fingerlings was studied, using different concentrations of a commercial inactivated L. plantarum product (Immuno-LP20): D1 (control, 0 mg/kg), D2 (100 mg/kg), D3 (200 mg/kg), D4 (400 mg/kg), D5 (800 mg/kg), and D6 (1600 mg/kg). After an eight-week feeding trial during which the diets were fed to triplicate groups of fish (initial weight: 1.58 ± 0.05 g), D2, D3, and D4 produced fish with significantly higher growth parameters than the control fish (P < 0.05), whilst all fish fed the diets with L. plantarum had significantly improved feed utilization parameters than the control group. Serum total protein content, and lysozyme activity significantly increased in fish fed D4 than the control fish, whilst complement 4 content was higher in fish fed almost all the inactivated probiotic diets (except D5) than the control fish. Serum superoxide dismutase activity was significantly higher in fish fed all the Immuno-LP20 diets except D2, and liver glutathione peroxidase activity in D2, D3, and D4 fish were significantly higher than in the control fish. Intestinal structure was also significantly improved in fish fed the Immuno-LP20 diets. According to these results, using inactivated L. plantarum as dietary supplement could be beneficial in the production of black sea bream at an optimum inclusion rate similar to 100 mg/kg ≤ 400 mg/kg Immuno-LP20.

NKL-24: A novel antimicrobial peptide derived from zebrafish NK-lysin that inhibits bacterial growth and enhances resistance against Vibrio parahaemolyticus infection in Yesso scallop, Patinopecten yessoensis

The extensive use of antibiotics in aquaculture has resulted in the prevalence of antibiotic-resistant bacteria and, consequently, new antibacterial strategies or drugs with clear modes of action are urgently needed. Antimicrobial peptides (AMPs) are currently widely considered as alternatives to antibiotics in the treatment of infections in aquatic animals. In this study, we aimed to evaluate the effects of NKL-24, a truncated peptide derived from zebrafish NK-lysin, against Yesso scallop (Patinopecten yessoensis) pathogen, Vibrio parahaemolyticus. The results showed that NKL-24 had a potent antibacterial effect against V. parahaemolyticus via a membrane active cell-killing mechanism. The in vitro study showed that sub-lethal levels of NKL-24 obviously reduced bacterial swimming ability and downregulated the transcription of the selected genes associated with V. parahaemolyticus virulence. Studies on NKL-24 biosafety in hemocytes and in Yesso scallop have shown no adverse effects from this peptide. Bacteria challenge test results demonstrated that NKL-24 significantly decreased the mortality and inhibited bacterial growth in the scallop infected with V. parahaemolyticus, while further in vivo examination revealed that NKL-24 could enhance non-specific immune parameters. Moreover, NKL-24 was capable of modulating a series of V. parahaemolyticus-responsive genes in the scallop. These results suggest the protective action of NKL-24 against V. parahaemolyticus and the potential of this peptide as a promising candidate for aquaculture applications.

Antibiotic-induced alterations and repopulation dynamics of yellowtail kingfish microbiota

BackgroundThe use of antibiotics in aquaculture is a common infection treatment and is increasing in some sectors and jurisdictions. While antibiotic treatment can negatively shift gut bacterial communities, recovery and examination of these communities in fish of commercial importance is not well documented. Examining the impacts of antibiotics on farmed fish microbiota is fundamental for improving our understanding and management of healthy farmed fish. This work assessed yellowtail kingfish (Seriola lalandi) skin and gut bacterial communities after an oral antibiotic combination therapy in poor performing fish that displayed signs of enteritis over an 18-day period. In an attempt to promote improved bacterial re-establishment after antibiotic treatment, faecal microbiota transplantation (FMT) was also administered via gavage or in the surrounding seawater, and its affect was evaluated over 15 days post-delivery.ResultsAntibiotic treatment greatly perturbed the global gut bacterial communities of poor-performing fish – an effect that lasted for up to 18 days post treatment. This perturbation was marked by a significant decrease in species diversity and evenness, as well as a concomitant increase in particular taxa like an uncultured Mycoplasmataceae sp., which persisted and dominated antibiotic-treated fish for the entire 18-day period. The skin-associated bacterial communities were also perturbed by the antibiotic treatment, notably within the first 3 days; however, this was unlike the gut, as skin microbiota appeared to shift towards a more ‘normal’ (though disparate) state after 5 days post antibiotic treatment. FMT was only able to modulate the impacts of antibiotics in some individuals for a short time period, as the magnitude of change varied substantially between individuals. Some fish maintained certain transplanted gut taxa (i.e. present in the FMT inoculum; namely various Aliivibrio related ASVs) at Day 2 post FMT, although these were lost by Day 8 post FMT.ConclusionAs we observed notable, prolonged perturbations induced by antibiotics on the gut bacterial assemblages, further work is required to better understand the processes/dynamics of their re-establishment following antibiotic exposure. In this regard, procedures like FMT represent a novel approach for promoting improved microbial recovery, although their efficacy and the factors that support their success requires further investigation.

The Isolation of Antimicrobial Resistant Aeromonas spp. from Aquaculture Samples and their Susceptibility to Medicinal Plant Extracts

Aeromonas spp, ubiquitous in both terrestrial and aquatic environments are becoming renowned as enteric pathogens of serious public health concern as they have a number of virulence and resistant determinants that are linked to both human and aquatic diseases due to consistent and incorrect use of antibiotics in aquaculture. The effect of crude aqueous and ethanol extracts of some medicinal plants on antimicrobial resistant Aeromonas spp. isolated from aquaculture water and fish samples was studied. Two hundred and forty (240) Aeromonas isolates, made up of 168 Aeromonas hydrophila and 72 Aeromonas salmonicida, were recovered from aquaculture water and fish gill samples collected from different commercial fish ponds using selective media. The isolates were assessed for their antibiotic susceptibility against ten (10) conventional antibiotics using the Kirby-Bauer technique. Extracts from three medicinal plants, Vernonia amygdalina, Ocimum gratissimum and Garcinia kola were also analyzed for their antimicrobial effects on the isolates that were resistant to the conventional antibiotics. Aeromonas hydrophila isolates expressed the highest resistant rates of 100%, 78.6% and 70.8% to aztreonam, cefotaxime and neomysin respectively, and the A. salmonicida isolates also had a similar trend of high resistant rates of 100%, 87.5% and 77.8% to aztreonam, neomysin and cefotaxime respectively. Antimicrobial resistant analyses with the plant extracts showed 100% inhibition of the isolates at 100 mg/ml for both aqueous and ethanol extracts. Phytochemical screening identified the presence of certain phytochemicals like alkaloids, saponins, tannins, flavonoids, steroids and glycosides which could have accounted for the antimicrobial effects of the plant extracts under study. It can be inferred then, that extracts from Vernonia amygdalina, Ocimum gratissimum and Garcinia kola can inhibit resistant aquaculture Aeromonas isolates and so can present an alternative source of antimicrobials in the effort to combat the increasing incidence of antimicrobial resistance in aquaculture.

Unravelling the menace: detection of antimicrobial resistance in aquaculture.

One of the major problems to be addressed in aquaculture is the prominence of antimicrobial resistance (AMR). The occurrence of bacterial infections in cultured fishes promotes the continuous use of antibiotics in aquaculture, which results in the selection of proliferated antibiotic-resistant bacteria and increases the possibility of transfer to the whole environment through horizontal gene transfer. Hence, the accurate cultivation-dependent and cultivation-independent detection methods are very much crucial for the immediate and proper management of this menace. Antimicrobial resistance determinants carrying mobile genetic transfer elements such as transposons, plasmids, integrons and gene cassettes need to be specifically analysed through molecular detection techniques. The susceptibility of microbes to antibiotics should be tested at regular intervals along with various biochemical assays and conjugation studies so as to determine the extent of spread of AMR. Advanced omic-based and bioinformatic tools can also be incorporated for understanding of genetic diversity. The present review focuses on different detection methods to unearth the complexity of AMR in aquaculture. This monitoring helps the authorities to curb the use of antibiotics, commencement of appropriate management measures and adequate substitute strategies in aquaculture. The long battle of AMR could be overcome by the sincere implementation of One Health approach. SIGNIFICANCE AND IMPACT OF THE STUDY: The use of antibiotics and increased antimicrobial resistance (AMR) are of major concerns in aquaculture industry. This could result in global health risks through direct consumption of cultured fishes and dissemination of AMR to natural environment through horizontal gene transfer. Hence, timely detection of the antimicrobial-resistant pathogens and continuous monitoring programmes are inevitable. Advanced microbiological, molecular biological and omic-based tools can unravel the menace to a great extent. This will help the authorities to curb the use of antibiotics and implement appropriate management measures to overcome the threat.

Bioprospecting of an Indigeneous Bacillus thuringiensis Strain G5-8-3T02 for Shrimp Culture System

Aim: An indigenous Bacillus thuringiensis strain G5-8-3T02 earlier isolated from healthy shrimp intestine and established to safeguard Penaeus monodon from Vibrio mimicus infection was assessed as a potential candidate bacterium for drug enhancement for shrimp culture systems.&#x0D; Methodology: Optimal temperature, pH and salinity for growth and antibacterial activity of Bacillus thuringiensis against Vibrio mimicus were determined. The effects of enzymes (pepsin, catalase, lipase and α- amylase), pH (2-9), heat (37°C – 121°C) and surfactants (Sodium dodecyl sulphate and Tween 80) on antibacterial activity were also evaluated. Cell growth and antibacterial activity were monitored daily for 5 days via spectrophotometric method at 600 nm and agar well diffusion assay respectively. The metabolite extracted with methanol was analyzed for bioactive compounds using Gas Chromatography-Mass Spectrometry (GC-MS).&#x0D; Results: The optimum temperature, pH and salinity for growth and metabolite production were 35°C, pH 6-7 and 10-15 ppt. respectively. The crude extract did not totally lose its activity when treated with enzymes, various pH values, heat and surfactants. The quantitative composition of the metabolite revealed 15 bioactive compounds. The main compound produced was 2, 6, 10-Trimethyltridecane with peak area of 14.58%.&#x0D; Conclusion: The non-pathogenic, antagonistic, indigenous Bacillus thuringiensis strain G5-8-3T02 could be engaged in the management of vibriosis in shrimp culture since the use of antibiotics in aquaculture for disease control yields objectionable effects. The identified bioactive compounds might be valuable for drug development for shrimp culture system.

In vitro antimicrobial effect of various commercial essential oils and their chemical constituents on Aeromonas salmonicida subsp. salmonicida.

This study aimed to evaluate in vitro efficacy of essential oils (EOs) and their compounds (EOCs) alone or in combination against Aeromonas salmonicida subsp. salmonicida, the causative agent of furunculosis in salmonid fish. Antimicrobial activity of 13 EOs and 16 EOCs was investigated for four A. salmonicida subsp. salmonicida strains using broth microdilution. The checkerboard assay was used to evaluate a putative synergy between the most efficient EOs and EOCs against the tested strains. Cinnamon bark, oregano, clove, and thyme oils and their major compounds cinnamaldehyde, eugenol, carvacrol and thymol showed the lower minimum inhibitory concentration and minimum bactericidal concentration values. The association of cinnamaldehyde and eugenol (V/V: 30%/70%) showed a synergistic activity against three tested strains. The combinations of cinnamon with oregano, clove or thyme EOs showed a neutral or additive activity against all the tested strains. Cinnamon, oregano, clove and thyme oils and their major phytochemical compounds showed strong activities against A. salmonicida subsp. salmonicida strains. To reduce the use of antibiotics in aquaculture, phytochemicals such as cinnamaldehyde and eugenol can be tested alone or in combination in in vivo studies as functional feed alternatives.

Occurrence, virulence gene and antimicrobial susceptibility profiles of Arcobacter sp. isolated from catla (Catla catla) in India.

In the present study, a total of 100 catla (Catla catla-major South Asian carp, local name botcha) collected from local fish markets and aquaculture ponds were subjected for isolation and characterization of Arcobacter sp. In all, 21 Arcobacter sp. were isolated, of which 18 (85·7%) were Arcobacter butzleri and three (14%) were A. cryoaerophilus as identified by multiplex PCR. All 18 A. butzleri isolates were positive for mviN, ciaB and tlyA virulence genes, three of A. cryoaerophilus isolates carried mviN gene and none of the isolates were positive for cadF, irgA, cj1349, hecA and hecB genes. All isolates (n=21) were resistant to penicillin (100%). Meanwhile, 71·43, 23·81, 23·81, 14·29 and 9·52% of the isolates showed resistance towards vancomycin, nalidixic acid, erythromycin, cefixime and kanamycin, respectively. Multidrug resistance was observed in 23·81% of the Arcobacter sp. isolates and none of the isolates were positive for any of the extended spectrum beta-lactamases either by phenotypic or by molecular identification genes (blaOXA , blaSHV , blaTEM , blaCTX-M1 , blaCTX-M2 and blaCTX-M9 groups). The results emphasize the need to implement specific control procedures to reduce the use of antibiotics in aquaculture particularly the ones which are very important in human medicine. SIGNIFICANCE AND IMPACT OF THE STUDY: Arcobacter species are emerging food- and water-borne human pathogens. In this study, Arcobacter butzleri was predominant in fish compared to A. cryoaerohilus and A. skirrowii. Higher incidence of arcobacters in fish market samples suggests cross contamination and unhygienic handling of fish in markets. Virulence genes profile and antibiotics resistance of the Arcobacter sp. isolated in current study indicate pathogenic potential of Arcobacter sp. to humans. Occurrence of multidrug-resistant Arcobacter sp. in fish is a major concern in food safety. To our knowledge, this is the first report of Arcobacter sp. from freshwater fish, catla (Catla catla) in India.

Antibacterial Susceptibility Pattern of Bacteria Isolated from Retail Fish in Okada, Edo State Nigeria

This study aimed at the microbiological analysis of retail frozen and smoked fish in Okada Edo state Nigeria. Four different retail fish samples were collected from different point of sale in Okada market. Two fresh iced and smoked samples respectively were used for the study. After sub culturing prepared samples into appropriate media, 38 bacterial isolates were obtained from primary culture plates and characterized using standard microbiological methods. Antimicrobial susceptibility tests were performed on the isolates using the Kirby-Bauer disc diffusion method. All the isolates obtained were Gram positive cocci bacteria and had a probable identity of Streptococcus sp, Staphylococcus sp and Coagulase negative Staphylococcus sp. The fresh fish samples had a minimum viable count of 1.7x 106 cfu/g and a maximum count of 4x 106 cfu/g while the smoked fish samples had a minimum viable count of 1.8x 106 cfu/g and a maximum count of 8.5x 106 cfu/g. Results from this study shows that the samples do not meet the acceptable limit (5x 105 cfu/g) of the International Commission of Microbiological Specification for Food (ICMSF). The antibiotic susceptibility test showed the presence of antibiotic resistant organisms among the retail fish samples. The detection of high viable counts of bacteria isolates beyond acceptable limits and their antibiotic resistance pattern elucidates the need for continuous monitoring of retail sea foods in the environment. Prudent use of antibiotics in aquaculture should be promoted to avoid the public health impact caused by antibiotic resistance transferred from retail sea foods to humans.

The Use of Selected Bacteria and Yeasts to Control Vibrio spp. in Live Food.

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.