Antibiogram and heavy metal resistance of pathogenic bacteria isolated from moribund cage cultured silver catfish (Pangasius sutchi) and red hybrid tilapia (Tilapia sp.)

Exploring the potential of black fungus, Auricularia auricula, as a feed additive in African catfish, Clarias gariepinus, farming

This study explores the beneficial effects of Auricularia auricula (AA) as a feed additive in promoting growth, digestive enzyme activities, antioxidative responses, heat tolerance, and disease resistance against Edwardsiella tarda in African catfish (Clarias gariepinus) farming. The application of feed additives is a hot topic in recent aquaculture studies aimed at promoting the growth and health of aquaculture species. After 8 weeks of feeding trial, the results of the present study revealed that fish-fed AA diets performed significantly better (p < 0.05) compared to the control group in growth performances, including final weight, weight gain, and specific growth rate. The highest performances were observed in the fish-fed AA at 3 and 4 %. A similar trend was also observed in the values of feed conversion ratio, hepatosomatic index, and visceral somatic index, with the lowest values (p < 0.05) in the fish-fed AA at 3 and 4 %. AA diets enhanced the activities of all tested digestive enzymes (amylase, protease, and lipase) significantly (p < 0.05), with the highest activities in the fish-fed AA at 3 and 4 %. Meanwhile, fish-fed AA diets exhibited significantly higher (p < 0.05) catalase, superoxide dismutase, and glutathione peroxidase activities both before and after heat stress, with the highest activities in the fish that received AA at 3 and 4 %. Furthermore, AA diets stimulated disease resistance in African catfish, with the fish-fed AA at 4 % performing the highest cumulative survival rate (73.3 ± 5.77 %) post-infection with E. tarda in African catfish. The findings of the current study suggest that AA has huge potential as a feed additive in African catfish farming.

Antibiotic and heavy metal resistance of Aeromonas hydrophila and Edwardsiella tarda isolated from red hybrid tilapia (Oreochromis spp.) coinfected with motile aeromonas septicemia and edwardsiellosis

AIM

The aim of this study is to identify antibiogram and heavy metal resistance pattern of Aeromonas hydrophila and Edwardsiella tarda isolated from red hybrid tilapia (Oreochromis spp.) coinfected with motile aeromonas septicemia and edwardsiellosis in four commercial fish farms.

MATERIALS AND METHODS

A. hydrophila and E. tarda were isolated using glutamate starch phenol red and xylose lysine deoxycholate (Merck, Germany) as a selective medium, respectively. All the suspected bacterial colonies were identified using conventional biochemical tests and commercial identification kit (BBL Crystal, USA). Susceptibility testing of present bacterial isolates to 16 types of antibiotics (nalidixic acid, oxolinic acid, compound sulfonamides, doxycycline, tetracycline, novobiocin, chloramphenicol, kanamycin, sulfamethoxazole, flumequine, erythromycin, ampicillin, spiramycin, oxytetracycline, amoxicillin, and fosfomycin) and four types of heavy metals (mercury, chromium, copper, and zinc) were carried out using disk diffusion and two-fold agar dilution method, respectively.

RESULTS

Three hundred isolates of A. hydrophila and E. tarda were successfully identified by biochemical tests. Antibiotic susceptibility testing results showed that 42.2% of the bacterial isolates were sensitive to compound sulfonamides, sulfamethoxazole, flumequine, oxytetracycline, doxycycline, and oxolinic acid. On the other hand, 41.6% of these isolates were resistant to novobiocin, ampicillin, spiramycin, and chloramphenicol, which resulted for multiple antibiotic resistance index values 0.416. Among tested heavy metals, bacterial isolates exhibited resistant pattern of Zn2+ > Cr6+ > Cu2+ > Hg2+.

CONCLUSION

Results from this study indicated that A. hydrophila and E. tarda isolated from coinfected farmed red hybrid tilapia were multi-resistant to antibiotics and heavy metals. These resistant profiles could be useful information to fish farmers to avoid unnecessary use of antimicrobial products in the health management of farmed red hybrid tilapia.

Peperomia pellucida leaf extract as immunostimulator in controlling motile aeromonad septicemia due to Aeromonas hydrophila in red hybrid tilapia, Oreochromis spp. farming

Aim:

This study was revealed the potential of Peperomia pellucida leaf extract as an immunostimulator agent in controlling motile aeromonad septicemia due to Aeromonas hydrophila in red hybrid tilapia, Oreochromis sp.

Materials and Methods:

In the present study, minimum inhibitory concentration (MIC) of P. pellucida leaf extract against A. hydrophila was determined through two-fold microbroth dilution method. The plant extract was screening for its active compound using a gas chromatograph mass spectrometer, and the effectiveness of P. pellucida leaf extract as an immunostimulator agent was evaluated. The experimental fish were fed with medicated feed at three different concentrations (25 mg/kg, PP-25; 50 mg/kg, PP-50; and 100 mg/kg, PP-100) of P. pellucida leaf extract for 1 week before they were intraperitoneally exposed to A. hydrophila. Enzyme-linked immunosorbent assay was carried out to determine the value of antibody response to A. hydrophila in fish from a group of fish that received medicated feed, and the percentage of total cumulative mortality of the experimental fish were observed at the end of the experiment.

Results:

The results showed that the major bioactive compound is phytol (40%), and the MIC value was 31.5 mg/L. The value of antibody response to A. hydrophila in fish from a group of fish which received medicated feed (PP-25, 0.128±0.014 optical density [OD]; PP-50, 0.132±0.003 OD; and PP-100, 0.171±0.02 OD) was found significantly higher (p<0.05) compared to fish did not receive medicated feed (0.00 OD). Whereas, percentage cumulative mortality of fish from all groups of fish received medicated feed (PP-25, 18.0±3.2%; PP-50, 18.2±2.8%; and PP-100, 17.7±1.8%) were found significantly lower (p<0.05) compared to a group of fish did not receive medicated feed (83.2±1.4%).

Conclusion:

The findings of the present study indicated the huge potential of P. pellucida leaf extract as natural immunostimulator agent for aquaculture uses.

Foodborne agents associated with the consumption of aquaculture catfish

In the Food, Conservation, and Energy Act (Farm Bill) of 2008, Congress amended the Federal Meat Inspection Act to provide that catfish be inspected by the U.S. Department of Agriculture's Food Safety and Inspection Service (FSIS). As part of the development of its inspection program, the FSIS conducted an assessment of the food safety risk associated with consuming farm-raised catfish. To thoroughly identify hazards for consideration in the risk assessment, the scientific literature was surveyed for all potential agents that have been linked to illness associated with farm-raised catfish consumption. A review of microbial hazards suggested that Salmonella is the foodborne pathogen most likely to be associated with catfish, but the impact of other pathogens remains unclear. This review also summarizes the current data available on chemical residues in catfish, including pesticides and heavy metals, and any regulatory levels that have been established for these compounds. The current usage of veterinary drugs in aquaculture also is outlined, including information on unapproved usage of drugs in catfish.

Bacteria associated with wild mud crab (Scylla serrata) from Setiu Wetland, Malaysia with emphasis on antibiotic resistances

A study was carried out to investigate the presence of bacteria flora in wild mud crab (Scylla serrata) from Setiu Wetland as well as their antibiotic resistances. A total of 91 bacterial isolates consisting of 12 bacterial species were successfully isolated from mud crab. Oxolinic acid was found to be effective against all the bacterial isolates whilst the highest percentage of antibiotic resistance was shown by lincomycin (94.5%) followed by ampicillin (90.1%), amoxicillin (86.8%) and oleandomycin (78.0%). The study is very useful to evaluate the safety of mud crab for human consumption based on wild mud crab-associated bacteria as well as their antibiotic resistances.