Preliminary study on the isolation of Clostridium butyricum strains from natural sources in the UK and screening the isolates for presence of the type E botulinal toxin gene

Abstract

Clostridia such as Clostridium tyrobutyricum, C. pasteurianum and C. butyricum may cause spoilage problems in certain types of food, but they are not normally regarded as dangerous. However some strains of C. butyricum have acquired the type E botulinum neurotoxin gene and have caused both infant and classical botulism in Italy (1986), China (1994) and India (1996). This study was carried out to examine a range of samples from fresh vegetables to food and environmental samples in the UK and test their ability to produce type E botulinal neurotoxin (BoNT) by probing for the presence of the toxin gene. Samples were enriched in modified Bhat and Barker (MBB) broth which is a minimal medium with lactate and acetate as a source of carbon and energy. In addition selective antibiotics are present in the medium to favour the growth of C. butyricum. This was followed by plating out onto iron sulphite agar (ISA) for isolation of C. butyricum from food and environmental samples. A total of 978 samples were tested and 302 (31%) yielded presumptive C. butyricum isolates. The highest percentage of positives came from soil, potato skins, Swede skin, yoghurt and cream. No positive isolates were obtained from pate, garlic or spring greens. A sub-sample of isolates was examined for the presence of gene encoding the type E botulinum neurotoxin using PCR. Only one of the many existing PCR methods was successful and therefore used for screening C. butyricum isolates for the presence of the type E toxin gene. None of the 93 tested isolates were found to be toxigenic (type E botulinal neurotoxin).