DETERMINING POST-PASTEURIZATION CONTAMINATION BY A SURFACE PLATE METHOD1

Post-pasteurization contamination constitutes a major problem for quality control and regulatory sanitarians in the market milk industry. The bacteria of most concern are gram-negative, aerobic, resistant to surface active agents, catalase-positive, and grow rapidly on the surface of solid media. Knowledge of these characteristics was utilized to provide the basis for a surface plating method to determine their numbers. Bacteria in this group account for most growth during low temperature storage and at warm temperatures. Results with the surface plate method were available in 16 to 20 hr. Preliminary data showed the test to be useful in indicating a lapse in proper pasteurization, cleaning, and/or sanitization.