In this study, we dealt with the air-borne microorganisms at the A, B, and C plants in April and July 1978.
1. Colony numbers of air-borne bacteria, yeasts, and molds were estimated by the exposure of nutrient or potato dextrose agar plates (9cm) for 15 minutes and successive incubation of the plates for 48 hours at 30°C and 37°C. At the A, B, and C plants, the average counts of the bacteria were 62.00, 26.79, and 52.96/plate in April, and 50.50, 39.72, and 49.10/plate in July. The average counts of yeasts and molds were 46.62 (17.86), 18.30 (8.09), and 27.21 (11.21) in April, and 12.92 (19.36), 17.98 (16.56), and 16.71 (15.36) in July.
2. Colony numbers of Staphylococcus aureus were determined similarly by using mannitol salt agar plates. The time of exposure was 30 minutes and the plates were incubated for 48 hours at 30°C. The typical isolates from each plate were identified by Bergey's manual (8th ed.). The average counts of Sta. aureus detected at the A, B, and C plants were 0.56, 0.26, and 2.06/plate in April, and 1.32, 2.09, and 1.79/plate in July respectively.
3. Colony numbers of coliform bacteria were determined by using desoxycholate agar plates. The duration of exposur was 60 minutes, and then, the plates were incubated for 24 hours at 37°C. Isolates from desoxycholate agar plates were identified as coliform bacteria by a complete test according to the methodology of the food hygiene law in Japan. The average counts of coliform bacteria at the A, B, and C plants were 0.34, 0.21, and 2.41/plate in April, and 2.50, 4.21, and 5.73/plate in July respectively.
These facts suggest that it is important to give careful attention to the air-borne microorganisms at the processing plants.