An evaluation of residual contamination by Clostridium botulinum in a trout farm following an outbreak of botulism in the fish stock

Abstract

Abstract Following an outbreak of botulism in the fish stock of a British trout farm in 1980, a survey of the residual contamination of the farm was carried out. Commencing in November 1980, the farm was examined monthly for one year after the disease had been eliminated. A nearby unaffected farm was examined as a control. Examination of pond muds showed that the affected farm remained contaminated throughout the year, counts of Clostridium botulinum type E ranging from 1‐800/g compared with counts at the control farm of 0.1‐0.7/g. Both C. botulinum types B and E were found in the control farm, either singly or together in individual samples of pond mud. Fish taken from the affected farm in May and August of 1981 showed a 77.1 % (s.e. ±7.7) contamination by type E. Examination of the environs of the affected farm yielded C. botulinum in 36 of 60 samples of mud and soil using enrichment culture techniques. Clostridium botulinum type E predominated in muds, occurring in 26 of 28 samples taken from the waters supplying and by‐passing the farm. In contrast, of the 32 soil samples tested from around the farm, eight yielded type B whereas only three contained type E.