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Studies on the Removal of Staphylococcus Aureus from Milk-Contact Surfaces by Ultrasonic Cleaning Methods

Department of Dairy Industry, Cornell University, Ithaca, New York

ABSTRACT

These studies are concerned with the removal of Phosphoras³²-labeled Staphylococcus aureus from milk-contact surfaces by ultrasonic cleaning procedures, and the growth of the residual organisms on these surfaces. The test organism was incorporated into the soil menstrua (a modified Ringer Solution and homogenized, pasteurized whole milk), dried down with the soils upon various milk-contact surfaces under highly reproducible conditions;, removed by ultrasonic irradiation treatments, and assayed by submersion in Staphylococcus (Agar) Medium No. 110, Bacto-Strip contact, plastic replica-embedding and staining, Geiger counting, and autoradiographic techniques.

The results indicate that, as in other cleaned-in-place (CIP) procedures, soil build-up can be a problem in ultrasonic cleaning if the initial soil deposits are not thoroughly removed. The rough surfaces show greater capacity for soil build-up. Type of surface roughness influences not only the degree of bacterial retention but also the pattern of subsequent growth of the residual organisms. The type of cleaning solution and time of ultrasonic irradiation of the cleaning bath exerted a definite influence on cleaning efficiency; however, specimen configuration in the cleaning bath and type of bacterial soil menstruum were of over-riding importance in the results achieved.

Under the conditions of testing utilized in these experiments, the radiological assaying procedures and the plastic replica-embedding and staining technique proved more accurate in determining bacterial residues on ultrasonically cleaned surfaces than macro-colony agar submersion counts and Bacto-Strip determinations.

¹ Present address: Robert A. Taft Sanitary Engineering Center, Cincinnati, Ohio.