Abstract

Streptococcosis causes economic losses due to the high mortality in Nile tilapia (Oreochromis niloticus). The present study was carried out to detect the streptococci by PCR and chemical analysis in cultured tilapia fish. A total of 100 cultured tilapia fishes and 20 water samples were collected from 4 different fish farms at different locations in Kafr El-sheikh Governorate for bacteriological and chemical analysis. The results of water quality parameters examination revealed that the mean values of pH, dissolved oxygen, unionized ammonia, and nitrite were 8.2 ± 0.73, 7.44 ± 0.54 parts per million (ppm), 0.05 ± 0.008 ppm, and 0.00 ppm, respectively. All water quality parameters except for ammonia were within the permissible limit. The bacterial isolation results revealed 38 % positive samples for Streptococcus species isolated from tilapia fishes and 40 % were positive for Streptococcus species isolated from water samples. Of those 38 positive fish samples, 25 (65.78%) were Enterococcus faecalis, 15 (39.47%) were Streptococcus pyogenes, 6 (15.78%) were Enterococcus faecium, 5 (13.15 %) were Streptococcus agalactiae, and 3 (7.89 %) were Streptococcus iniae. On the other hand, from 8 positive farms water samples, 7 (87.5%) were Enterococcus faecalis, 2 (25%) were Streptococcus pyogenes , 2 (25%) were Enterococcus faecium, 3 (37.5%) were Streptococcus agalactiae, and 1 (12.5%) was Streptococcus iniae . Using mPCR to identify Streptococcus for some fish and water isolates, 6 Enterococcus faecalis with 310 base per (bp) were detected while 3 Streptococcus agalactiae with 153 bp and 2 Enterococcus faecium at 215 bp were detected. However, the mPCR from Streptococcus species directly from organs from fish and water samples revealed that 5 Enterococcus faecalis were detected at 310 bp while 2 Streptococcus agalactiae was identified at 153 bp. The biochemical results indicated that the infected fish with the streptococcal species had reduced total protein, albumin, and globulin in the blood serum while total cholesterol, urea, creatinine levels, and AST, ALT, GPX, CAT, SOD activities significantly increased, compared to non- infected fish.