Studies on haemolytic activity of important fish and human pathogenic bacteria using fish blood

Abstract

Haemolysis is one of the striking features for the detection of the pathogenicity of the bacterial pathogens and has gained importance in the fish disease diagnostics. Haemolysis may be due to the presence of certain lytic enzymes which acts on the blood agar leading to lysis of red blood cells. In this study, fish blood was preferred instead of sheep, horse or rabbit to confirm and evaluate its performance as an alternate source as supplement for the preparation of blood agar for haemolysis test. Blood agar plates were prepared by supplementing 5 per cent freshly collected fish blood to the basal medium and haemolytic activity against the fish and human pathogens was carried out. The reference strains used in this study were viz., Edwardsiella tarda, Aeromonas hydrophila, Enterobacter cloacae, Pseudomonas aeruginosa, Escherichia coli, Staphylococcus aureus, Vibrio cholerae, Salmonella paratyphii, Overnight grown cultures , were serially diluted and twenty-five microliter was spot inoculated onto freshly prepared fish blood agar plates in duplicates. Bacterial cultures showing haemolytic activity were observed after 48 h of incubation at 28 degree celsius and zone of haemolysis was measured. Results observed during this study were compared with haemolytic activity of same cultures on human blood. Both human blood and fish blood showed similar beta haemolytic activity for all pathogens but E. cloacae did not show haemolysis on fish blood. The average diameter of haemolysis zone recorded in FB was 180, 280, 0,220, 250, 140, 200, 220 and in HB is 130, 150, 140, 230, 170, 180, 150, 170 after 48 h respectively for E. tarda, A. hydrophila, E. cloacae, P. aeruginosa, E. coli, S. aureus, V. cholerae and S. paratyphii. In conclusion, beta- haemolytic activity observed better in FB plates when compared to HB plates and therefore, fish blood can be used as an alternative to sheep blood for haemolytic studies of fish pathogens.