The luciferin-luciferase bioluminescence method was used to estimate the amount of adenosine triphosphate (ATP) in microorganisms including 15 species of Gram-negative bacteria, 7 of Gram-positive bacteria, and one yeast. A LUMAC Biocounter M2500 was used. The correlation between relative light units (RLU) and ATP in saline solution and nutrient broth was 1.00. The amount of ATP (pico-gram) in all tested strains was calculated by using the standard curve of the saline solution for the serial dilutions of the cultures in nutrient broth. After 24hr cultures, a linear relationship was obtained between amount of ATP and number of viable propagules of Escherichia coli ATCC 11775. The lowest detection level for E. coli cells was 3.5×103 CFU/ml. The average amount of ATP in Gram-negative bacteria, Gram-positive bacteria, and yeast (Candida albicans) was 1.43, 12.48, and 212.81 fg/cell, respectively, the ATP level in C. albicans being about hundred times higher than the amount in most Gram-negative bacteria. The amount of ATP in Gram-positive bacteria, both rods and cocci, was ten times higher than that in Gram-negative bacteria. However, the amount of ATP in the spore of Bacillus species was very low. The findings suggest that the bioluminescenceis a rapid and useful method for estimating the number of micoorganisms, but the flora of the samples must be identified before using the bioluminescence method.
Heat resistance of Clostridium botulinum types A and B spores on the beef surface subjected to dry heat in an electric oven were examined. The standard heat resistance (D121°C and z value) of the spores in 0.067 M phosphate buffer (pH 7.0) were 0.63 min and 10.7°C for types A, and 0.24 min and 9.4°C for types B, respectively. Surface temperature of beef cubes was measured in oven at 270°C.The temperature reached to 100°C for 25 min and maintained until 40 min. Then, it began to rise again and reached to 130°C for 60 min. Types A and B spores inoculated on the surface of raw beef cubes (105 CFU/cm2) were subjected to dry heat at 250, 270 and 300°C. However there was no difference in the decreasing tendency of the numbers of both types A and B spores among heating temperature. Also these numbers gradually decreased with heating time and were below 10 CFU/cm2 within 40 min. D values of both spores on each heating temperature were 8.3-11.1 min. Beef cubes were heated at 270°C with 1, 3 or 5% (w/w) salt on their surface and incubated at 30°C for a month. The production of toxin in cubes were restricted by hard heat treatment and high salt concentration. This effect was more sensitive for types B spores.
A total of 292 imported and domestic bottled mineral waters (90 brands) obtained from consumers and retailers were examined for microbial foreign matters. Fungal and bacterial foreign matters were found in 45 samples (20 brands) and 14 samples (10 brands), respectively. The genus Penicillium was found at the highest frequency among the fungi, followed by Acremonium, Cladosporium. In some brands, several fungal species were found. The products containing the fungal foreign matters were much less contaminated by bacteria, compared with those containing bacterial foreign matters.