Clostridium botulinum is an anaerobic, spore-forming, gram-positive bacterium, recognized as an etiological agent of the foodborne disease, botulism. Based on the neurotoxins produced, the organism is classified into 7 serotypes (A-G) and a number of subtypes [1,2]. C. botulinum is also divided into four metabolic groups based on physiological and serological characteristics – Group I (A and all proteolytic B and F), Group II (E and non-proteolytic B and F), Group III (type C and D) and Group IV (type G). Among these, C. botulinum types belonging to group I and II (A, B, E and F) are the cause of most cases of botulinum outbreaks in humans. Food-borne botulism is an intoxication brought about by the intake of preformed toxin in food [3,4]; 30 ng of neurotoxin is sufficient to cause illness and even death [5,6]. Hence the organism has been noted as significant hazard in food safety.

Fish contamination with C. botulinum is a worldwide problem. C. botulinum occurrence in fish and outbreaks of food poisoning have been studied extensively worldwide [[7], [8], [9]]. Non-proteolytic C. botulinum is a psychrotrophic organism which is capable of growth at 3 °C [10,11]. Many botulism outbreaks have been detected due to the intake of smoked, undercooked, stale or fermented fish, uncooked fish and also of seal and whale meat [12,13]. Recently, the increasing use of various processing technologies such as vacuum packaging and modified atmosphere packaging (MAP) to improve the shelf life of fishery products has generated concerns about the potential health risk for end consumers by non-proteolytic C. botulinum [14,15] since the anoxic conditions and low temperature in the packs are beneficial for the growth of C. botulinum. Production of toxin by C. botulinum types A-E in shrimp and mullet tissue homogenates, incubated at 4 oC and 30 oC under vacuum for 6 weeks has been reported [16]. McSharry et al. [17] reported the presence of C. botulinum in vacuum-packaged beef stored under both aerobic and anaerobic conditions at temperatures of 2 °C and 20 °C, highlighting the potential of the pathogen to persist across varying storage environments. In China, Min et al. [18] reported botulinum types A, B, and E outbreaks associated with vacuum-packaged fishery products. Pace et al. [19] surveyed 858 freshly smoked white fish chubs from fish smoking plants of the Milwaukee area and C. botulinum type B (3) and type E (7) were detected in ten samples. Hyytia et al. [20] reported C. botulinum type E in 5 % of 214 vacuum packed pickled rainbow trout, cold smoked rainbow trout, hot smoked white fish and rainbow trout and 3 % of the 123-air packed hot smoked vendace, Baltic herring and river lamprey fish products from retail markets in Finland. Tavakoli et al. [21] reported C. botulinum types E (2), B (1) and A (1) in 3.06 % of the 63 salted smoked fish samples from Iran.

Prevalence studies in different geographical areas have shown that C. botulinum type E is the most predominant type in temperate aquatic ecosystems and fish [22]. Type E has been incriminated in the majority of the botulism outbreaks associated with the intake of fish and fish products [18,23,24]. Outbreaks of type E botulism linked with consumption of fermented fish dishes were reported from North America, Europe, Asia [11,23] and Egypt [24]. A botulism outbreak was reported in Gujarat, India due to the consumption of an improperly stored Sevu, a deep-fried snack made of gram flour, contaminated with C. butyricum producing type E toxin and 34 school children were affected [25]. This was the first report of a suspected food borne botulism outbreak in India. Even a single case of botulism represents a public health emergency which might herald a larger outbreak. There are limited reports of botulism in India, because consumption of raw food material is very low., although it is important for the food industry to monitor and prevent growth of C. botulinum in products as the consequences of the intoxication are serious. The demand for convenience foods is increasing, and the fact that it is either consumed raw or under-cooked, or needs only minimal preparation time using a low amount of preservatives means that their consumption may pose a risk of foodborne botulism. Although C. botulinum has been reported in fish and fish products from India, no attempt was made to study whether this food safety hazard is prevalent in food products sold in major cities in India. As most of the convenience foods are ready to eat, it is necessary to screen the foods for the presence of C. botulinum. Hence, a study was undertaken to investigate the prevalence of C. botulinum types in various food products including convenience products which are sold in retail outlets and supermarkets in India.