Minoru Mori

Amino acid requirements for the growth and enterotoxin production by Staphylococcus aureus in chemically defined media

The production of enterotoxins A, B, and C by five strains of Staphylococcus aureus was studied in a series of defined media, each differing from the complete defined medium in the lack of one amino acid. Valine was required for growth; arginine and cystine for growth and enterotoxin production. Omission of individual amino acid affected in different ways the yields of the toxins produced.

Evaluation of Methods for the Isolation and Detection of Escherichia coli O157:H7 from Minced Beef

This study has evaluated enrichment and detection procedures for the isolation and detection of Escherichia coli O157:H7 inoculated into minced beef, i. e., 24hr enrichment in modified EC broth containing novobiocin (mEC+n) followed by plating onto sorbitol IPA bile salt agar (SIB), sorbitol MacConkey agar (SMAC), cefixime-tellurite SMAC (CT-SMAC) and Rainbow O157 agar, or immunomagnetic separation (IMS) followed by plating onto these four kind of media. The recovery of E. coli O157:H7 was greater on CT-SMAC than SMAC, SIB or Rainbow O157 Agar. The protocol using mEC+n incubated at 42°C, followed by IMS and inoculation onto CT-SMAC was the most succesful procedure. However, 24hr enrichment in mEC+n followed by CT-SMAC was almost as effective as the IMS method for the isolation of E. coli O157:H7.

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.