Takanori Takahashi

Airborne Fungal Colony-Forming Units in Outdoor and Indoor Environments in Yokohama, Japan

The fungal concentration and flora in indoor and outdoor air in Yokohama, Japan were analyzed with a Reuter centrifugal air sampler and dichloran 18% glycerol agar (DG18), and compared with the levels assessed with potato dextrose agar (PDA). The number of fungal colony-forming units (CFU) in outdoor air was < 13–2750/m3; Cladosporium spp. predominated, followed by Alternaria spp. and Penicillium spp. The fungal concentration in outdoor air peaked in September. The concentrations of fungi in outdoor air (n = 288) were significantly correlated with the maximum temperature of the day, minimum temperature of the day, average temperature of the day, average velocity of wind of the day, average temperature of the month, average relative humidity of the month and precipitation of the month. In indoor air, the fungal CFU was < 13–3750/m3. Cladosporium spp. predominated, followed by the xerophilic fungi such as the Aspergillus restrictus group, Wallemia sebi, the A. glaucus group, and Penicillium spp. The fungal concentration in indoor air peaked in October. The concentrations of fungi in indoor air (n = 288) were significantly correlated with the indoor temperature, indoor relative humidity and the outdoor climatic factors mentioned above, except for the average velocity of wind of the day.

Modification of Sorbitol MacConkey Medium Containing Cefixime and Tellurite for Isolation of Escherichia coli O157:H7 from Radish Sprouts

ABSTRACT A modified version of sorbitol MacConkey medium containing cefixime and tellurite (CT-SMAC medium) was produced by adding salicin and 4-methylumbelliferyl-β-d-galactopyranoside to CT-SMAC medium; this medium was designated CT-SSMAC medium and was used to isolate Escherichia coli O157:H7 from radish sprouts. Of 101 non-E. coli bacteria isolated from radish sprouts that produced colorless colonies similar to colonies of E. coliO157:H7 grown on CT-SMAC medium, 92 (91%) formed colonies that were red to pink or were β-galactosidase negative and colorless on CT-SSMAC medium. On the other hand, colonies of E. coliO157:H7 strains were colorless and β-galactosidase positive on CT-SSMAC medium. Our results suggest that CT-SSMAC medium is more selective than CT-SMAC medium for isolating E. coliO157:H7.

Evaluation of sorbitol-salicin MacConkey medium containing cefixime and tellurite (CT-SSMAC medium) for isolation of Escherichia coli O157:H7 from raw vegetables.

The utility of CT-SSMAC medium (sorbitol-salicin MacConkey medium containing cefixime and tellurite) for the isolation of Escherichia coli O157:H7 from raw vegetables was investigated. The colonies of all E. coli O157:H7 and O157:NM strains tested were colorless and beta-galactosidase-positive on CT-SSMAC medium. Furthermore, the number of colorless colonies on the CT-SSMAC medium was less than that on the sorbitol MacConkey medium containing cefixime and tellurite (CT-SMAC medium) from several raw vegetable samples. All colorless colonies grown on CT-SSMAC medium from raw vegetable samples were beta-galactosidase-negative. These findings suggest that the CT-SSMAC medium is useful for the isolation of E. coli O157:H7 from raw vegetable samples.

Occurrence of clostridia in glass bottled foods

Forty-one marketed samples of imported and domestic glass bottled foods were tested for clostridia contamination. It was detected in nine (22%) samples. Clostridia were isolated from fish sauce (Nam pla, Nuoc-mam), dressing, mustard, hot and sour soup mix (Tom Yum), mysids boiled down in soy, and salmon flakes. The origin of all clostridia positive samples was Asia. Clostridium botulinum and C. perfringens were not detected. The frequency of occurrence was higher by enrichment broth culture detection methods than by agar plate or pouch methods. These findings suggest that the number of bacteria in most of these clostridia positive food samples is very low, and the use of enrichment methods for detection of clostridia is essential.

Influence of butyric and lactic acids on the β-glucuronidase activity of Clostridium perfringens

T. FUJISAWA, K. AIKAWA, T. TAKAHASHI, S. YAMAI, K. WATANABE, Y. KUBOTA AND M. MIYAOKA. 2001. The β‐glucuronidase activity of intact cells of Clostridium perfringens was not influenced by the presence of either 0·09 or 0·19% lactic or butyric acids. In contrast, the enhanced enzyme activity of intact cells due to sodium deoxycholate was significantly decreased by the presence of these acids. These results suggest the possibility that the development of cancer due to the intake of a high fat diet may be inhibited by the presence of organic acids produced by intestinal bacteria.

Influence of sodium chloride on the β‐glucuronidase activity of Clostridium perfringens and Escherichia coli

While the β‐glucuronidase activity of intact cells of Clostridium perfringens was higher in 0·95% sodium chloride (NaCl) than that in 0, 0·1 or 0·5%, that of Escherichia coli was higher in 0·1% NaCl than that in 0, 0·5 or 0·95% NaCl in 0·1 mol l−1 KH2PO4. However, the enzyme activity of both species of intact cells was higher in buffer containing 16 mEq sodium, 134 mEq potassium and 16 mEq chloride per litre than in that containing 146 mEq sodium, 13 mEq potassium and 146 mEq chloride. These findings suggest that bacterial cells are affected by the presence of NaCl and that the effect of NaCl on the activity of bacterial β‐glucuronidase may differ by location in the large intestine.

Distribution and characteristics of aflatoxin-producingAspergillus flavus in the soil in Kanagawa Prefecture, Central Japan

In Kanagawa Prefecture, located in central Japan, aflatoxin-producingAspergillus flavus was isolated in 4 (2.5%) of 160 field soil samples. In the 4 fields, whose soil contained aflatoxin-producingA. flavus, the annual average temperature of the sampling sites of the soil ranged from 13.8 to 15.1°C. Of all the isolated strains of aflatoxin-producingA. flavus, 4 strains, isolated from a single soil sample, produced large amounts of aflatoxin B1 and B2 when incubated in coconut agar, peanut agar, peanuts or trilaurin-added rice, although they did not produce aflatoxin when incubated in rice, yeast extract-sucrose broth or sucrose-low salts broth.

Contamination of Commercial Corn Flour with Aflatoxins and Citrinin

In March 1980, mycotoxin-contaminated corn flour for sale in Tokyo was found for the first time by the mycotoxin examiner group of the Tokyo Metropolitan Research Laboratory of Public Health. After extensive investigation, it was ascertained that the corn flour was contaminated with a mixture of aflatoxins and citrinin. This flour was processed from imported corn by a corn mill company located in Kanagawa Prefecture. The Kanagawa Prefectural Public Health Laboratory therefore undertook an official mycotoxin survey of raw materials and finished products of corn which had been stocked at the corn mill company, checked for the presence of mycotoxins-producing molds in the milling process and finally carried out the sterilization of all equipment at the mill company. The results of a follow-up survey and the effect of the sterilization are reported in this paper.All 3 samples of marketed corn flour, produced on various dates by U Company, were contaminated with aflatoxins (6.75-50.0ppb of B1) and citrinin (13-22ppb).All samples of raw-material corn obtained from U Company were contaminated with aflatoxins (3.50-41.5ppb of B1), and 2 out of 3 samples tested were contaminated with citrinin (1.3-14ppb).All 3 samples of finished-product corn flour from the same source were contaminated with aflatoxins (40.8-76.5ppb of B1) and citrinin (9-56ppb).On the other hand, no aflatoxins or citrinin were detected in any marketed corn flour, raw-material corn or finished-product corn flour derived from N Company.Waste flour, “flour meal”, from U Company was found to be highly contaminated with aflatoxins (410ppb of B1) and citrinin (133ppb). From this waste flour, large numbers of Aspergillus flavus and Penicillium citrinum were isolated and the production of aflatoxins (0.283-37.0μg/g of B1), and citrinin (1, 300-4, 850μg/g) was chemically detected in 50% of the A. flavus strains and 100% of the P. citrinum strains examined, respectively.Since contamination of the millhouse equipment with A. flavus was discovered, all equipment was cleaned mechanically and sterilized by washing with a 1% solution of sodium hypochlorite.Even after the sterilization, A. flavus contamination in the impact mill system was still observed, so the impact mill was disassembled and re-sterilized by burning in addition to washing with the sodium hypochlorite solution.After the re-sterilization, no molds were isolated from any part of the impact mill.