Pathogenicity and antibiotic sensitivity pattern of Salmonella species isolated from pond-reared Clarias gariepinus (Burchell,1822)

Abstract

Salmonella species has been isolated from fish ponds, and two different clinical cases of Salmonella infections were reported in tropical fishes. It therefore becomes important to investigate the occurrence of Salmonella in farmed Clarias gariepinus, and evaluate fish and public health significance.

Bacteria isolated on Salmonella-Shigella agar from blood and upper intestinal tract of 50 C gariepinus juveniles were biochemically characterised and those identified as Salmonella sp were evaluated for antibiotic sensitivity using the disc diffusion method. Two groups, A and B of C. gariepinus juveniles were each divided into 4 subgroups of 10 fish. Three subgroups in A and B were experimentally infected via oral and intraperitoneal route respectively with 1.2 x 106, 1.2 x 107 and 1.2 x 108 cfu of Salmonella. The forth subgroup is the control. Daily observation was made for clinical signs, lesions and mortality for 14 days.

Biochemical tests confirmed 72% and 32% occurrence of Salmonella sp in the intestinal tract and the blood of sampled fish respectively. Antibiotic resistance frequency of 100% (augmentin, ceftriazone and nitrofurantoin), 89% (gentamicin and amoxycilin), 78% (cotrimoxazole and tetracycline), 33% (ofloxacin) and 11% (ciprofloxacin and pefloxacin) was observed. The multiple antibiotic resistance indices of the observed isolates ranged from 0.5 to 0.9. No clinical signs, lesions or mortality was observed in experimentally infected fish.

Farmed Clarias gariepinus may be a reservoir for Salmonella sp probably acquired from faecal contamination of pond water, or consumption of contaminated feed. Risk of Salmonella infection to consumers and producers may be high, with serious public and animal health significance. Multi-drug antibiotic resistance is an indication of misuse of antibiotic in our society. There is the danger of possible spread of multi-drug resistant Salmonella sp, and choice of drug for treatment of Salmonella infection in man and livestock may be limited.

Keywords: Isolation, Salmonella sp, Experimental infection, Antibiotic sensitivity