Date of Award:


Document Type:


Degree Name:

Master of Science (MS)


Nutrition, Dietetics, and Food Sciences

Department name when degree awarded

Bacteriology and Public Health

Committee Chair(s)

Gary H. Richardson


Gary H. Richardson


C. Anthon Ernstrom


Paul B. Carter


The metachromatic agar-diffusion test of Lachica, Hoeprich, and Genigeorgis (1971) was modified by adding 17 ml of the agar medium to a 100 by 15 mm plastic petri dish, using 5 µl samples and 3 mm wells. The test detected 0.5 ng/ml of thermonuclease in 3 hr at 37 C. This was equivalent to 106 to 10 7 cells/ml of Staphylococcus aureus strains 196 E, 14458, and 19095 grown in Brain Heart Infusion (BHI) broth. The test sensitivity was decreased ten fold in raw and pasteurized milk.

One-half gram of cheese was dissolved in 4.5 ml of 0.1 M sodium citrate for quantitative studies. When staphylococcal (>8 x 10 /ml) contaminated raw milk was pasteurized and made into cheese, more thermonuclease activity/ml was noted in the curd than whey. During prolonged storage at 4 C, thermonuclease activity decreased in raw and pasteurized milk and laboratory made cheese.

Bacillus subtilus, Streptococcus faecalis var liquefaciens, Streptococcus thermophilus, and Streptococcus cremoris strain ML8 reduced thermonuclease activity during growth incubation in BHI broth. Thermonuclease was detected directly in staphylococcal contaminated 7 laboratory aged cheese (>10 /gm) without prior purification, concentration, or extraction procedures.