Anaerobic spore formers in commercial spices and ingredients for infant food

Abstract

Anaerobic spore-formers can cause food intoxication. Clostridium (Cl.) perfringens type-A strains are mainly involved. In addition to the original contamination of food, e.g., meat or milk, ingredients such as spices or meat extracts are the main source and low numbers of clostridia are present (i.e., up to 10(2) cells/g). At present, information about the quantitative ecology of clostridia is incomplete; therefore 115 commercial food products were investigated (spices: n = 70, meat extracts: n = 15, instant foods: n = 30). For the detection of low numbers of clostridia (less than 10(3)/g), the most probable number (MPN) technique was used. For the detection of higher numbers (greater than 10(3)/g) a cultivation method in solid media was developed. The mesophilic sulphite-reducing clostridia spores were detected by the pour-plating method with overlayer. Twenty-one of the 70 commercial spices, 7 of the 30 specimen of instant food and 12 of the 15 meat extracts were clostridia-positive. The low counts ranged between 3 X 10(0) and 10(3) cells/g, in most cases (2/3) in the range 10(1)/10(2)/g. Only in 6 cases were more than 10(3) clostridia/g detected. Most of those isolated were identified as Cl. perfringens (46 of 73 isolates). Only in meat extracts did clostridia species other than Cl. perfringens strains predominate. Three of the 23 Cl. perfringens strains proved to be heat-resistant. A hydrated meat extract originally contaminated with low numbers was tested in a pilot study for the enrichment of clostridia. This extract showed an increase of up to 10(7) cells/ml after a 24-h incubation period.(ABSTRACT TRUNCATED AT 250 WORDS)