Assessment of Gill Pathological Responses in Yellowfin Sea Bream (Acanthopagrus Latus) Under Aeromonas Hydrophila Exposure

Bacterial diseases in cultured fish are considered the main problem with aquaculture system in Iran. The gills are multifunctional organs responsible for respiration, osmoregulation, nitrogenous waste excretion, and acid-base balance. Moreover, they are very sensitive to water contamination. Aeromonas hydrophila (A. hydrophila) is an opportunist pathogen responsible for a wide range of diseases in different species of fish. The gill histological alterations were used to assess the effects of A. hydrophila exposure on yellowfin sea bream, Acanthopagrus latus (A. latus). In this regard, 90 A. latus were exposed to the concentrations of A. hydrophila (103 and 106 CFU/ml) for three weeks. The most histopathological alterations in the gill of the exposed fish included hypertrophy and hyperplasia of the epithelial cells, lamellar fusion, club shaping of gill lamellae, lifting of the epithelium and edema of lamellae with large sub-epithelial space, blood congestion, and hypertrophy and hyperplasia of the mucosal cells. The histopathological alterations were observed in the gill of fish exposed to higher levels of A. hydrophila (106 CFU/ml) consisted of aneurysm and hemorrhage with blood congestion. According to the obtained results of this study, A. hydrophila could cause severe histopathological changes in the gill of A. latus and decrease gas change capability in yellowfin sea bream. Furthermore, the findings of the present study suggested that histopathological changes of the gill provide helpful information about the environmental conditions and as particular biomarkers may help the evaluation of fish general health.

Purification and optimization of production conditions of a marine-derived antibiotic and ultra-structural study on the effect of this antibiotic against MRSA

OBJECTIVES

In this study we have attempted to partially purify, characterize and optimize the fermentation condition for the antimicrobial compound production with anti-MRSA (Methicillin Resistant Staphylococcus aureus) activity produced by Pseudoalteromonas piscicida PG-02 bacterium, isolated from the Persian Gulf, and finally understand the morphological changes in MRSA due to this antibiotic.

MATERIALS AND METHODS

Optimization process of antibacterial compound production was studied based on the sources of carbon and nitrogen, optimum temperature, optimum pH and optimum incubation time. The purification of intended antibiotic was done using TLC and also thermostability and enzymatic stability treatment was studied. Ultrastructural study on the effect of intended antibacterial compound on MRSA was done using a Transmission Electron Microscopy (TEM).

RESULTS

The optimized bioprocess conditions for the maximum production were at temperature 28 degrees C, pH 7, NaCI 0.5% (w/v), 96 hrs (incubation time), glucose and tryptone as carbon source and nitrogen source, respectively. The antibacterial component showed thermal sensitivity but it was sensitive to proteinase K, so this compound may have proteinaceous nature. The results of sonication revealed that this compound is accumulated in both intra- and extra-cellular locations. TEM pictures showed disorganization of cytoplasmic membrane upon the extract treatment comparing to control so, it can be said that this antibacterial compound can be considered as a bactericidal agent against MRSA.

CONCLUSION

On the basis of obtained results, this bacterium can be regarded as a valuable strain for discovery of new weapon as bactericidal agent in fighting against multi-drug resistant bacteria especially MRSA.