Contamination by Listeria of frozen red salmon and smoked salmon was investigated. Although none of the 60 samples of frozen red salmon were contaminated with Listeria, 23 out of 76 smoked salmon samples (30.3%) were contaminated. L. monocytogenes was detected in 12 of the positive samples. Other species identified were L. welshimeri, L. innocua and L. seeligeri. The serotypes of isolated L. monocytogenes were 1/2a, 1/2b, 1/2c, 3a, 3b and 4b. The end product of smoked salmon was stored in an aerobic or an anaerobic package at 2°C and 10°C to experimentally trace the behavior of L. monocytogenes. In samples stored at 2°C the initial count of 102/g increased to 104∼105/g in 10 days and to 108/g in 20 days. In samples stored at 10°C, the number increased to 107∼108/g in 5 days. The growth was somewhat inhibited in anaerobic conditions when compared to aerobic conditions. In samples stored at -20°C for 6 months, the initial count of 104∼105/g showed a decrease in the order of one in either raw or smoked salmon.
Production of a factor causing vacuoles in HEp-2 culture cells by Bacillus cereus No. 55 was examined in a semi-synthetic medium containing ammonium sulfate as a sole nitrogen source (AYPS medium). Although the vacuolation activity in the culture supernatant was low after cultivation of B. cereus in the medium, the activity was increased by supplementation of glucose to the medium. However, the activity did not increase by the supplement of galactose and lactose to the medium. The activity of the factor increased with an increase in the cell concentration of B. cereus when it was cultured with shaking in AYPS medium supplemented with 0.5% glucose. In the medium with 0.1% glucose, the cell concentration reached the highest level at 8 hr, but the activity was the highest at 48 hr. In both media the rate of sporulation was above 65% after a 48hr cultivation with shaking. By contrast, the rate of sporulation was very low (4-15%) without shaking. The activity was first detected at 24 hr and increased until 48 hr to the same level as that in the culture with shaking. For purification of the vacuolation factor, salting out with ammonium sulfate, n-butanol extraction, solubilization with methanol and thin-layer chromatography (TLC) on silicagel 60 were effective. After fractionation by the TLC, the vacuolation activity was detected in five fractions.
Lecithinase-positive clostridia including Clostridium perfringens isolated from feces of nine healthy adults each fed lactulose (3 g/day for 2 wk) or lactosucrose (2 g/day for 1 wk) were examined. Before the consumption of lactulose or lactosucrose, lecithinase-positive clostridia in fecal specimens were detected in 9/9 (mean 3.9 × 105/g) and 8/9 (4.5 × 105/g) specimens, respectively. On consumption of lactulose or lactosucrose, they were detected in 4/9 (4.2 × 103/g after 2 wk) or 6/9 (2.9 × 104/g after 1 wk) specimens, respectively. Clostridia isolated from 18 fecal specimens before consumption were identified as C. perfringens (102-108/g) from 17/18 specimens, C. sordellii (103-105/g) and C. baratii (102/g) from 2 specimens each, and C. bifermentans (103/g) from 1 specimen, but only C. perfringens from 4/9 (102-105/g) and 6/9 (102-107/g) specimens on lactulose and lactosucrose consumption, respectively.
The microflora and metabolic products between the cecum and feces of rats were compared. The microflora of the cecum was similar to that of the feces. However the metabolic products greatly differed between the cecum contents and feces. The pH value was higher and the amounts of short-chain fatty acids (SCFA) and ammonia were larger in the cecum contents than in the feces. Particularly concerning the SCFA, the level of acetic acid, propionic acid and butyric acid were significantly higher in the cecum contents, and the latter were not found in the feces.
The effects of Lactobacillus isolated from funazushi (salted and fermented crusian carp) on the fecal microflora and metabolic products were studied in rats. Mixed cultures containing the following viable cell levels per day of Lactobacillus were administered in rats: L. alimentarius, 108; L. plantarum, 1010; L. sake, 1010; L. sanfrancisco, 1010; and L. kefir, 1010. On days 7 and 14 of lactobacilli administration, the number of fecal Lactobacillus tended to increase, while Enterobacteriaceae and Staphylococcus significantly decreased (p<0.05). The concentration of fecal ammonia and short-chain fatty acids, and the fecal pH values did not change markedly during lactobacilli administration. The amount of daily fecal evacuation significantly increased (p<0.05) during the test period.
The antimicrobial activity of mustard extract, which has allyl isothiocyanate as the major pungent component, against Escherichia coli, Vibrio parahaemolyticus, Salmonella Typhimurium and Staphylococcus aureus, typical food poisoning bacteria in Japan, was examined by gaseous contact. The mustard extract preparation and each nutrient agar plate spread with the test bacteria were put in a lunch box made from polystyrene, which was then incubated at 30°C. The vapor concentration of allyl isothiocyanate in the container rose to about 180 ppm after one hour and since gradually decreased to about 30 ppm after 24 hrs. The growth of each bacteria was tested at 3, 6, 9 and 24 hrs after start of incubation by counting the number of colonies formed on each selective agar media with samples prepared from the nutrient agar with the aid of a stomacher. A bacteriostatic effect was observed against E. coli, S. Typhimurium and S. aureus 9 hrs after start of incubation and a bactericidal effect was observed against V. parahaemolyticus.