BACTERIOLOGICAL TESTING OF MILK FOR REGULATORY PURPOSES–USEFULNESS OF CURRENT PROCEDURES AND RECOMMENDATIONS FOR CHANGE

Abstract

While routine bacteriological tests afford virtually no protection against milk-borne disease, they should reflect insanitary production conditions. Mounting evidence suggests that current tests are doing an indifferent job here. No single test can furnish an adequate picture. we need to reflect the presence of psychrotrophs, thermodurics, mastitis organisms, lactic acid bacteria, etc. Psychrotrophs, the most important group in refrigerated milk, come mainly from dirty udders and equipment. These deserve major attention. Usefulness of the Standard Plate Count in reflecting their presence would be enhanced by an incubation temperature lower than 32 C. The psychrotrophic count at 7 C for 10 days has obvious limitations. These can be minimized by suggested modifications. Preliminary Incubation (P. I.) at 13 C for 18 hr indirectly reflects psychrotrophs, which multiply rapidly under these conditions. Other procedures suggested include the cytochrome oxidase test, Water Agar test, catalase production, nitrate reduction at 30 C, and a test for sodium desoxycholate-tolerant bacteria. For the detection of thermodurics, a simple nitrate-formate reduction test following P. I. at 22 C for 16 hr has been proposed. Extensive collaborative testing in various areas should precede the adoption of new methods and standards, while a suitable incentive to producers can greatly encourage sanitary milk production.