Salah Mesalhy Aly

Studies on Bacillus subtilis and Lactobacillus acidophilus, as potential probiotics, on the immune response and resistance of Tilapia nilotica (Oreochromis niloticus) to challenge infections

The probiotic activity of two bacteria (Bacillus subtilis and Lactobacillus acidophilus) was evaluated by its effect on the immune response of Nile tilapia (Oreochromis niloticus), beside its protective effect against challenge infections. Furthermore, their in-vitro inhibitory activity was evaluated. The in-vitro antimicrobial assay showed that Bacillus subtilis and Lactobacillus acidophilus inhibited the growth of A. hydrophila. The B. subtilis inhibited the development of P. fluorescens while L. acidophilus inhibited the growth of Strept. iniae. The B. subtilis and L. acidophilus proved harmless when injected in the O. niloticus. The feed, containing a mixture of B. subtilis and L. acidophilus or B. subtilis alone, showed significantly greater numbers of viable cells than feed containing L. acidophilus only after 1, 2, 3 and 4 weeks of storage at 4 degrees C and 25 degrees C. The survival rate and the body-weight gain were significantly increased in the fish given B. subtilis and L. acidophilus for one and two months after application. The hematocrit values showed a significant increase in the group that received the mixture of B. subtilis and L. acidophilus compared with the control group. The nitroblue tetrazolium (NBT) assay, neutrophil adherence and lysozyme activity, showed a significant increase in all the probiotic-treated groups after 1 and 2 months of feeding, when compared with the untreated control group. The serum bactericidal activity was high in the group that was given a mixture of the two bacteria. The relative level of protection (RLP) was significantly higher against A. hydrophila, in the bacterial mixture treated group and against P. fluorescens in the L. acidophilus treated group, after one month of the feeding trial. A significantly higher RLP, against A. hydrophila or P. fluorescens, was noticed after 2 months of the feeding trial in the group given a mixture of the two bacteria, and against Strept. iniae in the group fed a diet containing L. acidophilus.

Effect of garlic, black seed and Biogen as immunostimulants on the growth and survival of Nile tilapia, Oreochromis niloticus (Teleostei: Cichlidae), and their response to artificial infection with Pseudomonas fluorescens

Three dosage levels of black seed, garlic and commercial Biogen were administered for three months in summer and six months in winter to test their stimulation effect on growth, survival and response to challenge infection in Oreochromis niloticus. At the end of summer, no significant difference was observed in the growth performance of O. niloticus with most treatments, but the level of non-specific mortalities was reduced in all treatment groups compared to the control group. Significant changes were seen in nitroblue tetrazolium (NBT) values in groups treated with 1.0 and 3.0% garlic. Mortalities following challenge with Pseudomonas fluorescens were lower in the groups that received garlic compared to the other two treatments. At the end of winter a significant increase in body weight gain was seen in fish fed a 1% garlic-enriched diet. Significant changes were also noted in condition factor in fish fed with 2% garlic and 1.5% Biogen. Non-specific mortality was reduced in all groups that received immunostimulants, except Biogen. Immunostimulants improved the general health of the fish, enabling them to overcome stress due to cold during winter, thereby improving growth.

The role of ornamental goldfish Carassius auratus in transfer of some viruses and ectoparasites to cultured fish in Egypt: comparative ultrapathological studies

Goldfish, common carp and Nile tilapia were sampled between September 2002 and May 2003 to investigate lesions induced by viral diseases and ectoparasites. Goldfish exhibited neoplasms, Dermocystidium sp., Ichthyophthirius multifiliis (Ich), Trichodina reticulata, Lernaea cyprinacea and systemic infections. Neoplastic and systemic infections in goldfish were associated with viral infection. Oreochromis niloticus and Cyprinus carpio were mainly infested with several species of Trichodina and monogeneans. The presence of Dermocystidium sp. in carp, and viral particles in the liver and spleen of O. niloticus and C. carpio, was uncommon. Microscopically, intracytoplasmic inclusion bodies in the hepatic cells and lymphocytic infiltration in other internal organs of the three fish species were seen. Ultrastructural study showed enveloped viral particles in some cells in all fish species. The recorded parasitic infections were associated with degenerative, necrotic, inflammatory and proliferative changes in the skin and underlying muscles. Imported ornamental goldfish may be a source of infection to carp and native tilapia. Histopathology and transmission electron microscopy demonstrated the etiology and pathogenesis of infection and the preliminary diagnosis of viral infection, which is not common in Egypt. It is recommended that goldfish be excluded from edible-fish aquaculture ponds. Strict regulations regarding the transfer and quarantine of imported fish should be implemented.

Attenuated virulence of pigment-producing mutant of Aeromonas veronii bv. sobria in HeLa cells and Nile tilapia (Oreochromis niloticus)

Abstract Aeromonas species are potential water/foodborne pathogens, whereas Aeromonas veronii bv. sobria is one of the most virulent species to human and fish. Most current experimental evidence has publicized that suicide plasmid dependent IS1-element untargeted integration into A. veronii bv. sobria ATCC 9071T strain was recently used to generate brown pigment-producing and spontaneous pelleting (BP+SP+) mutant. Current study was conducted to compare virulence of wild-type ATCC 9071T strain and its BP+SP+ mutant with respect to cytotoxicity in HeLa cells and lethality in Nile tilapia. It was found that the cytotoxicity of wild-type ATCC 9071T strain to HeLa cells has reached 75% versus 50% for the cytotoxicity of BP+SP+ mutant. Further, the median lethal dose (LD50) of wild-type ATCC 9071T strain in Nile tilapia was 8.25 Log10 colony-forming units (CFU)/ml, compared to 9.16 Log10 CFU/ml for the LD50 of BP+SP+ mutant. Thus, current study supports the notion that non pigment-producing Aeromonas strains are more virulent than pigment-producing ones.