Effect of reduced water activity on vegetative growth of cells and on germination of endospores of Sporolactobacillus.
Growth of vegetative cells and germination of endospores of Sporolactobacillus at reduced water activity (aw) values were studied with NaCl and glycerol as humectants, and compared with Bacillus cereus and Clostridium sporogenes. With NaCl the highest aw for complete inhibition of both growth of vegetative cells and germinated spores of Sporolactobacillus was 0.955. With glycerol, growth of vegetative cells was completely inhibited at 0.905 as compared to 0.880 for vegetative growth resulting from germinated endospores. The mechanism of this phenomenon cannot be explained yet. NaCl appeared to have a toxic effect, in addition to inhibition by reduced aw per se.
Selective method for the isolation of Sporolactobacillus from food and environment sources.
A detection procedure was developed in which a modified Lactobacilli MRS medium was used to enrich for Sporolactobacillus from a variety of foods, feed soil and environmental samples. Each sample was rinsed with 50 ml of a modified Lactobacilli MRS broth containing 1.0% (w/v) alpha-methyl glucoside 0.1% (w/v) potassium sorbate, 0.00224% (w/v) bromocresol green indicator, adjusted to pH 5.5 with acetic acid and incubated at 37 degrees C for 7 d under 5% CO2. Volumes of 2 ml from each sample were heat shocked at 80 degrees C for 5 min and 0.1 ml spread onto plates of Lactobacilli MRS agar (Difco), pH 5.5 and APT agar (BBL), pH 5.5. Plates were incubated for 5 d and suspect colonies were tested for catalase production, benzidine reaction, nitrate reduction, motility and Gram stain reaction. This method was demonstrated to be selective for Sporolactobacillus.
Human exposure to methylmercury from crayfish (Procambarus clarkii) in China
Methylmercury (MeHg) accumulation in aquatic food raises global concerns about human exposure to MeHg. Crayfish is the world’s third largest farmed crustacean species and a favorite aquatic food in many countries. However, human health hazard due to MeHg exposure via crayfish consumption is unclear, partly because appropriate survey data are lacking. We report on mercury concentrations and speciation in edible tail muscle of crayfish collected from restaurants in 23 Chinese cities. On average, MeHg constituted 99.1 % of mercury in tail muscle, and MeHg concentrations were comparable with those reported for fish in China. Variation in MeHg concentrations was not attributable to broad geographic region (i.e., provinces) or tail length. For different populations, potential health risk (characterized by hazard quotient or HQ) of MeHg exposure through crayfish consumption depended largely on crayfish consumption rates. In particular, a health hazard (HQ > 1) was found for high-rate consumers (i.e., 95 %ile or higher) in some cities in the middle and lower reaches of the Yangtze River (MLYR), during the peak consumption season. Our results suggest that more attention should be paid to dietary MeHg intake via crayfish consumption in China, particularly for communities with high consumption in MLYR.