Density gradient centrifugation (DGC) is useful for the separation of living microbial cells from food samples that are not filterable. After DGC, however, careful operation is necessary to collect each density layer. For a simple and reproducible collection after DGC, we have developed a seamless operation system composed of a 5-needle unit, a microchannel plate, and a microflow controller, and named this a density slicer system. Two types of 5-needle units were devised and both showed nearly the same performance. Reproducible results with the automatic operation system could be demonstrated using an Escherichia coli cell suspension.
We evaluated the antiviral activity of a chlorine dioxide gas solution (CD) and sodium hypochlorite (SH) against feline calicivirus, human influenza virus, measles virus, canine distemper virus, human herpesvirus, human adenovirus, canine adenovirus and canine parvovirus. CD at concentrations ranging from 1 to 100 ppm produced potent antiviral activity, inactivating ≥ 99.9% of the viruses with a 15 sec treatment for sensitization. The antiviral activity of CD was approximately10 times higher than that of SH.
To identify the pathogenic fungi present in bathrooms, the growth of fungi collected from the drains of bathrooms was studied at various temperatures and compared with that of fungi from kitchen sink drains. Only a small number of fungi from bathrooms and sinks grew on media incubated at 37°C, at which temperature the fungal count was about 1/600 of that at 25°C. Although hot water is used more frequently in bathrooms than in sinks, the fungal counts at 37°C were similar for bathrooms and sinks. Five species of fungus that can grow at 37°C and were found to grow prolifically in bathrooms were identified using DNA and morphological analysis. In both bathrooms and sinks, Exophiala dermatitidis was predominant in culture at 37°C. Moreover, E. dermatitidis grew at 40°C and used surfactant as a nutrient. Thermotolerant fungi appear to inhabit bathrooms and all residential water appliances.
To investigate the adaptability to higher temperatures of Antarctic microorganisms persisting in low temperature conditions for a long time, Antarctic lake samples were incubated in several selection media at 25°C and 30°C. The microorganisms did not grow at 30°C; however, some of them grew at 25°C, indicating that the bacteria in Antarctic have the ability to grow at a wide range of temperatures. Total DNA was extracted from these microorganisms and amplified using the bacteria-universal primers. The amplified fragments were cloned, and randomly selected 48 clones were sequenced. The sequenced clones showed high similarity to the α-subdivision of the Proteobacteria with specific affinity to the genus Agrobacterium, Caulobacter and Brevundimonas, the ß-subdivision of Proteobacteria with specific affinity to the genus Cupriavidus, and Bacillus of the phylum Firmicutes. These results showed the presence of universal genera, suggesting that the bacteria in the Antarctic lake were not specific to this environment.
We analyzed and compared the bacterial communities in ayu-narezushi (narezushi made using the sweetfish) produced by two different manufacturers in Mie Prefecture, Japan, with the 16S ribosomal RNA gene clone library method. The bacterial diversity of ayu-narezushi 1 (Library 1) was higher than that of ayu-narezushi 2 (Library 2). The predominant lactic acid bacteria were Lactobacillus fuchuensis, Lactococcus piscium, and Leuconostoc gelidum in Library 1 and Lactobacillus sakei in Library 2, suggesting that these species play important roles in the fermentation of the 2 samples of ayu-narezushi. The results of LIBSHUFF indicated a significant difference between 2 libraries (P = 0.001).
Fourteen laboratories with expertise in Salmonella detection in food joined in a collaborative study. The laboratories performed qualitative analyses of ground pork samples using the proposed detection method. Salmonella Typhimurium (hydrogen sulfide-producing strain) and Salmonella Senftenberg (hydrogen sulfide-nonproducing strain) were used for inoculation. Three levels of Salmonella contamination were used for the study (0, 1-10, and 11-100 cfu/25 g). We evaluated the presence of Salmonella in each sample and the serological O group. Unmarked samples delivered to the laboratories were accurately judged to be inoculated or not inoculated with Salmonella at a 99.8% (419/420) detection rate in this collaborative study. The proposed method is suitable as a standard method to detect Salmonella in food.