Evaluation of a Novel Dry Sheet Culture Method for Rapid Enumeration of Total Aerobic Count in Foods

Abstract

A novel dry sheet culture method (Sanita-kun ACplus; SkACp) for rapid enumeration of total viable count has been developed. This rehydrated plate system comprises an adhesive sheet, nonwoven fabric coated with nutrients, and two types of water absorption polymers. In addition, SkACp facilitates methods for both rapid count (rapid mode: 24-h incubation) and accurate enumeration (standard mode: 48-h incubation) because it not only contains conventional 2,3,5-triphenyltetrazolium chloride but also contains two kinds of new tetrazolium salts for rapid and accurate enumeration of total aerobic count. When SkACp was assessed with 91 microorganisms, 87 strains (95.6%), excluding lactic acid and psychrotrophic bacteria, formed red-colored colonies within 24 h, whereas all microorganisms tested formed colonies within 48 h. The SkACp method, with both 24 and 48 h of incubation, was compared with plate count agar (PCA) and 3M Petrifilm AC (PAC) by using 107 naturally contaminated foods. For all foods tested (n = 107), the linear correlation coefficients of 48-h counts on SkACp compared with PCA and PAC were 0.98 and 0.75, respectively, while the 24-h counts on SkACp compared with PCA and PAC were 0.77 and 0.96, respectively. For foods tested, excluding yogurt and lactic beverages ( n = 101), the linear correlation coefficients of 48-h counts on SkACp compared with PCA and PAC were 0.98 and 0.96, respectively, while the 24-h counts on SkACp compared with PCA and PAC were 0.96 and 0.95, respectively. These results demonstrated that SkACp (48 h) is a useful alternative for the enumeration of the total aerobic count for all foods, whereas SkACp (24 h) was also an effective method for rapid enumeration in foods, excluding yogurt and lactic beverages.