Applicability of Heat-Stable Deoxyribonuclease Assay for Assessment of Staphylococcal Growth and the Likely Presence of Enterotoxin in Cheese

A Simple Sensitive Method for Determining Staphylococcal Thermonuclease in Cheese

“…aureus in cheese, when only nuclease concentrations of 2 1 ng/g were considered positive results. This was concluded using essentially the thermonuclease determination method described by Cords & Tatini (1973). In the current study, the maximum zone diameter obtained with control cheese was 6.88 mm (including well diameter).…”

“…The minimum detectable levels of purified thermonuclease reported previously were 300 ng/ml in Tris buffer (Cords & Tatini 1973), 5 ng/ml in brain heart infusion broth (Lachica et al 197 1) and 10 ng/ml in Tris buffer containing 0.1% bovine serum albumin in our laboratory (Ibrahim & Baldock 1981). In the present study, 0.5 ng/ml could be detected.…”

“…The extraction, concentration and assay method described by Cords & Tatini (1973) was used with two modifications. The total diameter of the pink zone and well were measured (three or four readings per well), using a stereoscopic zoom microscope (Olympus) with transmitted illumination, fitted with a calibrated eye-piece micrometer.…”

“…aureus, and, unlike Staph. aureus cells, has a marked resistance to extensive heating, storage and biological activity of other micro-organisms (Chesbro & Auborn 1967;Cords & Tatini 1973;Ibrahim & Baldock 1981).…”

“…A number of methods have been proposed for the determination of thermonuclease in foods (Chesbro & Auborn 1967;Lachica et al 1972~;Cords & Tatini 1973;Koupal & Deibel 1978;van Schouwenburg-van Foeken et al 1978). These methods either lacked sensitivity or were laborious, cumbersome and time-consuming.…”