In June 1996, the outbreak of waterborne cryptosporidiosis in Saitama prefecture, Japan caused prolonged diarrheal illness in more than 8, 000 people who drank tap water contaminated with Cryptosporidium parvum oocysts. The Ministry of Health and Welfare had to introduce a provisional determination method of Cryptosporidium consisting of an immunofluorescence assay and Nomarski differential interference contrast microscopy. For river water samples, however, this method cannot distinguish C. parvum from other C. parvum-like organisms such as free-living protozoan because of non-specific fluorescence and structural resemblance to C. parvum oocysts. In this study, the microstructure of C. parvum oocysts of a sample was directly observed using a low-vacuum scanning electron microscope (SEM). The sample used for observation river water to which concentrated C. parvum oocysts were previously added . The sample was filtered on a specimen stub, washed with distilled water, then frozen with liquid nitrogen. As a result of this method, C. parvum oocysts could be observed at a>2, 000×magnification and the fine microstructure such as oocyst-wall and four sporozoites could be seen at 10, 000×magnification. Therefore, these results were concluded that the low-vacuum SEM method is useful for discrimination and identification of C. parvum oocysts.
To investigate the effects of weather conditions on bacterial food poisoning, the relations of seven indices of weather, viz. maximal, minimal and mean air temperature, mean vapor pressure, minimum and mean relative humidity, and global solar radiation, to daily outbreaks of food poisoning from Vibrio parahaemolyticus, Staphylococcus and Salmonella in Tokyo were examined by multiple logistic regression analysis, during 1981-86 and 1987-91, respectively. By factor analysis, the seven weather indices were summarized into two factors, viz. temperature/vapor pressure, to which maximal, minimal and mean air temperature and mean vapor pressure were positively related, and humidity/solar radiation, to which minimal and mean humidity were positively related, while global solar radiation was negatively related. The outbreak of Vibrio parahaemolyticus food poisoning was positively related to minimal temperature three days before the outbreak for both of the time periods investigated (p<0.05, multiple logistic regression analysis). Similarly, the outbreak of Staphylococcus food poisoning was positively related to temperature/vapor pressue three days before the outbreak (p<0.05). However, none of the weather indices were significantly related to the outbreak of Salmonella food poisoning in either period (p>0.05). It is suggested that a high temperature/vapor pressure factor three days before outbreaks of Vibrio parahaemolyticus and Staphylococcus food poisoning had the most significant effect on the outbreaks of these two types of food poisoning.
One hundred and ninety strains of Escherichia coli were detected in edible oysters collected from ten oyster beds in the Seto-Inland Sea . These strains were used for the investigation of thermal resistance and for the growth protective effect of sodium pyruvate against heat shock. 1. When the cells were heated in Heart Infusion Broth Medium at 50°C for 24hr, 74 of 190 isolates were heat resistant. 2. When these 74 strains were heated in Heart Infusion Broth Medium at 80°C for 1min, 39 isolates of these 74 strains were heat resistant. 3. Thirty-five strains, which were resistant at 50°C for 24hr heating but were not resistant 80°C for 1 min heating, were used to determine the growth protecting effect of 1% pyruvate against heat resistance at 80°C for 1 min in Heart Infusion Broth Medium. Twentyfour strains (69%) showed the growth protecting effect of 1% pyruvate against the heat resistance at 80°C for 1 min in Heart Infusion Broth Medium.