Differentiation of Clostridium perfringens from Related Clostridia in Iron Milk Medium

Abstract

The stormy fermentation reaction of Clostridium perfringens in iron milk medium was compared to that of several C. perfringens-like strains. These clostridia, C. barati, C. perenne, C. absonum, and C. paraperfringens are very similar to C. perfringens on the basis of certain biochemical reactions and, consequently, are often difficult to distinguish from C. perfringens. Furthermore, these related clostridia may also be present in foods. Results of this study demonstrate that after 18 h of incubation at 45°C, only C. perfringens gave a positive reaction in iron milk with inocula as low as 22 cells/g. Some of the other strains began to show only gas production at 18 h. After 24 to 42 h some strains gave positive results and after 72 h all were positive. Enumeration of C. perfringens from food samples in iron milk medium by a 3-tube most probable number (MPN) technique gave similar results to enumeration by plate count using Shahidi-Ferguson Perfringens (SFP) agar. Furthermore, a rapid positive response occurred after only 2 and 3 h incubation of iron milk inoculated with 108 and 107 cells/ml, respectively. The high selectivity, ease of identification and rapid growth of C. perfringens in iron milk make the iron milk MPN procedure a valuable assay for accurate enumeration and differentiation of C. perfringens from related Clostridia in food products.