Fraser broth and HCLA (Hemolytic ceftazidime lithium chloride agar) were evaluated for the recovery of Listeria spp. and L. monocytogens. Fraser broth required 10¹-10⁵ CFU/ml Listeria spp.for the development of a black color at 35°C for 24 hr. The efficacy of Fraser broth 24 hr incubation transfer from EB and EB 48 hr incubation was not different regardless of injury by testing experimentally contaminated, milk and cheese. Out of 301 naturally contaminated meats and meat environmental swabs tested, Fraser broth gave a false-positive rate of 16.0% and a false-negative rate of 1.6% for 24 hr incubation. However false-negative samples were blackend by 48 hr. 100% (50/50) of L. monocytogenes colonies on HCLA were easily distinguished by narrow zone of β-hemolysis from the samples inoculated L. monocytogenes and L. innocua simultaneously for 24 hr incubation. HCLA recovered L. monocytogenes in 100% of 139 meats and meat environmental naturally contaminated samples without false-positives or false-negatives for 24 hr incubation. When use in combination with Fraser broth and HCLA, The judgement for Listeria-free is obtained by 3 days. And the presence of L. monocytogenes is known for 3-4 days.

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The effects of a portable air circulation system with installed ventilator and HEPA (high efficiency particulate air) filters on airborne microorganisms in the packaging area (packaging areas A and B) of two daily food plants were examined.
The bacterial counts at packaging areas A and B were 0.269-0.533 and 0.041-0.577 cfuper L of air, respectively, and after operation of the air circulation system, the counts were reduced to 0.056-0.132 and 0.026-0.028 cfu per L of air, respectively. The fungal counts at packaging areas A and B were 0.087-0.201 and 0.047-0.444 cfu per L of air, respectively, and after operation, the counts were reduced to 0.016-0.029 and 0.022-0.058 cfu per L of air, respectively. The microbial population at packaging area B tended to increase in the afternoon before operation of the air circulation system.
No significant differences were found among the effectiveness of the air circulation system for controlling airborne microorganisms pollution at each sampling point at packaging areas A and B.
The predominant constituents of airborne bacteria isolated from packaging area B consisted of 23.7% Staphylococcus sp., 20.1% Micrococcus sp. and 13.6% Bacillus sp., and after operation of the air circulation system, this composition was essentially unchanged. Throughout this research period, Listeria sp. was not detected.

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When food-poisoning occurs, the source of the foodstuff has been determined by manually comparing the prevalence of patients with and without certain foods, using chi-square test. The increase in the rate of patients with food-poisoning and in the sources of foodstuff suggest that the development of a simpler method of more quickly and accurately analysing potential sources is required.
We developed software for estimating the source of foodstuffs from a master-table using a questionnaire to determine whether a subject is a patient, and whether he has consumed the foodstuff or not. The data are then analyzed by statistical methods on a personal computer . The software is sufficient to analyze foodstuffs during large scale food-poisoning using a combination of chi-square test, Fisher's exact test and t-test. Statistical expertise is not required to operate the software and anyone can determine the source of food-poisoning . Thus, this software may facilitate the investigation of the source when food-poisoning occurs.

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Using whole eggs inoculated with 10⁶/ml of Salmonella Enteritidis (SE), bavarois was experimentally prepared according to the formula and procedure used at a senior's house where a large SE outbreak occurred in 1989. In this procedure, the whole egg was heated to 55.6°C, and the decrease in SE number was small. Bavarois, custard cream and ice cream mix were prepared according to the formulas in text books, inoculated with 10⁵/ml of SE and heated at 58°C, 63°C and 68°C for 3.5 min each. The number of SE decreased to 10⁴/ml level by heating at 53°C for 3.5 min, to less than 10/ml by heating at 68°C for 3.5min, but was positlve in a 25g sample of bavarois and custard cream. By heating at 68°C for 3.5mm which is recommended by the Ministry of Hyglene and Welfare to final users of liquid eggs, SE bacame negatlve in a 25g sample of these three kinds of cakes.
The pH values of four experimentally prepared cakes were roughly 7.0, and the water activities were higher than 0.95 where salmonellas can grow well. Especially the water activity of bavarols made with the recipe at the senior's house was very high. When these four cakes were inoculated with 10²/g of SE and stored at 30°C after completing cooking and cooling to room temperature, SE grew in all the cakes. Especially the SE inoculated into the bavarois prepared according to senior's house formula grew rapidly. When these cakes were stored at 10°C, the growth of SE was very slow in all the experimentally prepared cakes.

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