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Title: NILE TILAPIA, OREOCHROMIS NILOTICUS, BLOOD AGAR AND THE CULTURE OF FISH BACTERIAL PATHOGENS

Author
item Pasnik, David
item Evans, Joyce
item Klesius, Phillip

Submitted to: European Association of Fish Pathologists
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/7/2005
Publication Date: 9/25/2005
Citation: Pasnik, D.J., Evans, J.J., Klesius, P.H. 2005. Nile tilapia, oreochromis niloticus, blood agar and the culture of fish bacterial pathogens. Bulletin of the European Association of Fish Pathologists. 25(5):218-224.

Interpretive Summary: Blood agar plates are regularly used for the culture and subsequent isolation of bacterial pathogens of fish, and most studies have utilized mammalian blood agar plates for this purpose. Few studies have used blood agar made from fish or aquatic animal blood to culture piscine pathogens, while some have used fish serum to supplement culture media for parasite culture. Several studies have noted differences in bacterial activity when fish pathogens are grown on a variety of mammalian blood agar. The question remains whether fish blood agar (FBA) could confer advantages over mammalian blood agar when culturing and characterizing piscine bacterial pathogens. In this study, we evaluated four bacterial species, the '-haemolytic Streptococcus iniae and Acinetobacter calcoaceticus and the non-haemolytic Staphylococcus epidermis and Edwardsiella tarda, previously isolated from fish. These isolates were cultured using blood agar made with fish blood or sheep blood, and the relative growth, colony morphology, and haemolytic activity on each type of agar was compared. Bacteria counts and colony morphology were not significantly different between the same isolates cultured on FBA or SBA. Only the zones of haemolysis of S. iniae were significantly smaller on FBA than on the SBA. Therefore, the use of FBA is an adequate alternative to SBA for the culture of fish pathogens.

Technical Abstract: Fish blood agar (FBA) was made using blood from Nile tilapia, Oreochromis niloticus. Four bacterial isolates from fish, the '-haemolytic Streptococcus iniae and Acinetobacter calcoaceticus and the non-haemolytic Staphylococcus epidermis and Edwardsiella tarda, were plated on FBA and sheep blood agar (SBA) to examine differences between bacteria counts, colony morphology, and haemolytic activity. Bacteria counts and colony morphology were not significantly different between the same isolates cultured on FBA or SBA. Only the zones of haemolysis of S. iniae were significantly smaller on FBA than on the SBA. Therefore, the use of FBA is an adequate alternative to SBA for the culture of fish pathogens.