Inhibitory effects of sucrose palmitic acid ester on the germination-to-outgrowth process of Clostridium perfringens SM101 spores

As a commercially available esterified compound derived from sucrose and palmitoyl acids, sucrose ester palmitic acid (SEPA) has been used as an emulsifier in food processing. It possesses antibacterial activity against vegetative and spore-forming bacteria, including Clostridium, Moorella, Bacillus, and Geobacillus species, prompting the food industry to use it as a food additive to achieve a desirable shelf life; however, the precise mechanism by which the compound affects the physiological processes of bacteria and how it inhibits bacterial growth remains unclear. In this study, we focused on the inhibitory effect of SEPA on the germination-to-outgrowth process of Clostridium perfringens SM101 spores, a strain widely used as a model of C. perfringens. When the isolated spores were exposed to ≧ 20 μg/ml of SEPA on brain heart infusion agar, bacterial colony formation was completely inhibited. Time-resolved phase-contrast microscopy was employed to visualize the effect of SEPA on the entire regrowth process of SM101 spores. SEPA did not affect the "germination stage," where each spore changes its optical density from phase-bright to phase-dark. In contrast, the presence of SEPA completely blocked the "outgrowth stage," in which the newly synthesized vegetative cell body emerges from the cracked spore shell. The results demonstrate that SEPA inhibits the revival process of the spores of a pathogenic strain of C. perfringens and that the site of its action is the "outgrowth stage" and not the "germination stage," as evidenced by single- cell analysis.