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Abstract
SUMMARY
The present study was planned to investigate streptococcosis in cultured and wild African catfish (Clarias gareipinus), where 20 bacterial isolates of Streptococcus were detected and identified as Streptococcus faecalis.
Streptococcus faeclis characterized by Gram positive cocci arranged in short chain and non motile. It grow on blood agar as small, dull grayish white, round with complete entire edges and slightly raised colonies. The isolates were positive for O/F glucose test, aeculin hydrolysis, growth at 6.5% NaCl, growth at 25 and 45oC but not at 10oC and produce acid only from sorbitol, mannitol, glucose and sucrose but not from arabinose and lactose while negative for cytochrome oxidase, catalase, Indole, citrare utilization, gelatin and starch hydrolysis.
Three types of vaccines corresponding to the types of vaccination methods were performed from Streptococcus Faecalis:
1. Wet- packed whole cells bacterin for oral vaccination. The bacterin was added to the feed at level of 5 mg/gm minced meat for 15 days.
2. Inactivated brain heart infusion broth culture for immersion vaccination. The fish were immersed in the bacterin broth diluted with the aquarium water in ratio of 1:1 to give a concentration of 2 mg bacterial cells/ml for 3 minutes.
3. Inactivated washed bacterial cells emulsified in normal saline in ratio 1:1 and were used for injection vaccination by I/P inoculation of 0.1 ml per fish.
All methods of vaccination produced resistance to fish against Streptococcus faecalis infection.
The resistance to Streptococcus faecalis infection is nearly the same in three methods of vaccination at 30 days post – vaccination. The oral and injection methods resulted in 90% protection and 88.8 % relative percent survival while immersion method resulted in 80 % protection and 77.7 % RPS compared 90 % mortality in control group.