Naraid Suanyuk

Roles of phagocytosis activating protein (PAP) in Aeromonas hydrophila infected Cyprinus carpio

Cyprinus carpio (koi) is one of the most popular ornamental fish. A major problem for C. carpio farming is bacterial infections especially by Aeromonas hydrophila. Previously studies had shown that the Phagocytosis Activating Protein (PAP) gene was involved in the innate immune response of animals. Therefore, we attempted to identify a role for the PAP gene in the immunology of C. carpio. The expression of the PAP was found in C. carpio whole blood and increased when the fish were stimulated by inactivated A. hydrophila. In addition, PAP-phMGFP DNA was injected as an immunostimulant. The survival rate and the phagocytic index were significantly increased in the A. hydrophila infected fish that received the PAP-phMGFP DNA immunostimulant. A chitosan-PAP-phMGFP nanoparticle was then developed and feeded into fish which infected with A. hydrophila. These fish had a significantly lower mortality rate than the control. Therefore, this research confirmed a key role for PAP in protection fish from bacterial infection and the chitosan-PAP-phMGFP nanoparticle could be a good prototype for fish immunostimulant in the future.

Serotype distribution and antimicrobial susceptibilities of Streptococcus agalactiae isolated from infected cultured tilapia (Oreochromis niloticus) in Thailand: Nine-year perspective.

Streptococcus agalactiae (group B Streptococcus, GBS) infection remains a major problem associated with high mortality of cultured tilapia worldwide. The present study reports the serotype distribution and antimicrobial susceptibilities of GBS isolated from infected tilapia cultured in Thailand. One hundred and forty-four GBS isolates were identified by biochemical, serological and molecular analyses. Of these 144 GBS isolates, 126 were serotype Ia and 18 were serotype III. Antimicrobial susceptibilities of the 144 GBS isolates were determined by the disc diffusion method. Most GBS isolates were susceptible to lincomycin, norfloxacin, oxytetracycline, ampicillin, erythromycin and chloramphenicol, but resistant to oxolinic acid, gentamicin, sulfamethoxazole and trimethoprim. However, 17 isolates displayed an oxytetracycline-resistant phenotype and harboured the tet(M) gene. The broth microdilution method was used to determine the minimal inhibitory concentrations (MICs) of 17 oxytetracycline-resistant GBS isolates, and then minimal bactericidal concentrations (MBCs) of these isolates were evaluated. Oxytetracyline-resistant isolates were found to be susceptible to ampicillin, lincomycin, norfloxacin, erythromycin and chloramphenicol, with the MIC and MBC ranging from ≤ 0.125 to 0.5 μg ml- 1 and ≤ 0.125 to 2 μg ml- 1, respectively. Moreover, all 17 oxytetracycline-resistant isolates demonstrated resistance to trimethoprim, oxolinic acid, gentamicin, sulfamethoxazole and oxytetracycline, with the MIC and MBC ranging from 16 to ≥ 128 μg ml- 1 and ≥ 128 μg ml- 1, respectively. These findings are useful information for antibiotic usage in fish aquaculture.

In vitro and in vivo assessments of Rhodomyrtus tomentosa leaf extract as an alternative anti-streptococcal agent in Nile tilapia (Oreochromis niloticus L.)

Purpose. Rhodomyrtustomentosa is a Thai medicinal plant that has been attracting attention for its remarkable antibacterial properties against Gram‐positive pathogenic bacteria. The purpose of this study was to evaluate the antibacterial properties of R. tomentosa leaf extract against Streptococcus agalactiae and Streptococcus iniae isolated from infected tilapia. Methodology. The anti‐streptococcal activity of R. tomentosa was determined using broth microdilution assays. Results. The extract demonstrated strong antibacterial activity against the fish pathogens, with minimum inhibitory concentrations (MICs) ranging from 7.8-62.5 &mgr;g ml−1. It was found to possess a dose‐dependent bacteriostatic effect on this organism. Scanning electron microscopy revealed irregular and long chains of swollen cells, as well as corkscrew shapes andincomplete separation of cell division of S. agalactiae cells following the treatment at sub‐MIC. Moreover, S. agalactiae cells pre‐treated with the extract became more sensitive to oxidative stress induced by H2O2 than the untreated cells. Based on the mortality of Nile tilapia after intraperitoneal infection of S. agalactiae at median lethal dose (LD50), the pre‐treated cells caused a significant (P<0.01) reduction in mortality of S. agalactiae‐infected Nile tilapia. Conclusion. The results suggested that R. tomentosa could be further developed as a simple and effective agent for the treatment of streptococcosis in Nile tilapia.

Spironucleosis in cultured red tilapia.

Tilapia culture has expanded rapidly worldwide, especially in Southeast Asia, including Thailand, Vietnam, Indonesia, India, Taiwan and China. Large-scale commercial culture of tilapia almost exclusively involves three species: Oreochromis niloticus , Oreochromis mossambicus and Oreochromis aureus , of which the Nile tilapia, O niloticus , is the most commonly farmed species. Infectious diseases pose constant and serious threats to fish that are intensively farmed under conditions of high population density, poor water quality and poor farm management. Currently, however, tilapia culture is most at risk from emerging viral and bacterial infections and novel parasitic diseases (Shoemaker and others 2000, Adeyemo and Agbede 2008). Diplomonad flagellate are commonly found in a wide variety of hosts, from mammals to fish. They can infect a wide range of fish species both fresh and marine water, across a broad geographic range from coldwater fish farms to tropical areas (Kent and others 1992, Poynton and others 1995, Koudela and others 1996, Sterud and others 1998). Red tilapia cultured in earthen ponds in Songkhla Province demonstrated some clinical abnormalities. Tilapia fingerlings showed distinct clinical signs: emaciation and multiple white nodules in muscle tissue. Although the infected fish swam normally, the distinct white nodules made them the subject of attack by healthy fish, and they ultimately died from the resultant wounds. Consequently, one hundred and fifty red tilapia, average weight 5–10 g were collected from earthen ponds in Angthong Province, and transported live to the Aquatic Animal Health Research Center, Prince of Songkla University, Had Yai, Thailand. Sampled fish were examined macroscopically and then anesthetised with 50 ppm quinaldine (Muench 1958). Subsequently, fish were dissected and gill, liver, kidney, gall bladder and intestine tissues were sampled for the …