87 amostras de leite cru ou pré-aquecido, de conjunto, foram empregadas em estudos da correlação existente entre os tempos de redução da resazurina (segundo o método da “tríplice leitura”) e as contagens bacterianas em placas.Verificou-se que, de modo geral, quanto mais rápidas foram as mudanças produzidas no corante, mais elevados se mostraram os conteúdos bacterianos das amostras (enquadrados nos grupos <100.000, 100.001 a 500.000, 500.001 a 4.000.000 e >4.000.000 por ml). Não foi porém íntima a correlação observada.93 amostras individuais de leite cru com baixas contagens bacterianas (<100.000 por ml), foram empregadas para a verificação da influência, dos leucócitos sôbre a prova da resazurina.Constatou-se que os aumentos nos índices leucocitários(<500.000, 500.001 a 1.000.000, 1.000.001 a 2.000.000, 2.000.001 a 5.000.000 e >5.000.000 por ml) foram associados a bem definidos decréscimos no tempo de redução do corante.

87 samples of raw or pre-heated bulk milk, and 93 individual samples (stored less than 24 hours after milking), were subjected to the agar plate method and to the resazurin triple reading test. For distinguishing changes in resazurin that are due to bacteria from those due to leucocytes, microscopic observations were made.These studies showed that, in. general, the more rapidly the dye is decolorized, the higher the numbers of bacteria of bulk milk samples. However, there was no dose correlation between results obtained with the resazurin test (reduction times of <0.5, 1, 2, 3, and >3 hours), and with plate counts (<100.000, 100.001 — 500.000, 500.001 — 4.000.000, and >4.000.000 per ml).A microscopic study of the samples that feli into the lower plate count group (<100.000 per ml.) and however reduced the dye in 1 hour, showed that they contained a large number of leucocytes, ranging from 850.000 to 1.900.000 per ml.This sensitivity of the resazurin to “abnormal” milk, is regarded as advantageous. Since a testing method which grades milk on the basis of leucocyte, as well as bacterial content, furnishes a more comprehensive index of the true quality of the milk.Every one of individual samples showed low plate count (<100.000 per ml.). Thus, it was possible to verify the influence of leucocytes on the resazurin test.The authors found that increased leucocyte counts were associated with well — defined decreases in reduction time. Leucocyte counts between 500.001 and 1.000.000 per ml, had little effect 011 reduction. Counts 1.000.001 — 2.000.000, ha.d au appreciable effect 011 resazurin:29.4% of the samples, reduced resazurin to the Munseil 5 P 7/4 point in >3 hours; 23.5% in 3, 35.3% in 2, and 11.8% in 1 hour. Counts of>2.000.000, had a strong reducing effect on indicator. Thus, 9.6% of the samples with leucocytes C0UfltS between 2.000.001 and 5.000.000 per ml, reduced resazurin in 3 or >3 hours; 52.4% in 2, 28,5% in 1, and 9.5% in 0.5 hour. Of the samples with counts 5.O0O.OOO, 31.8% reduced the indicator in 0,5 hour; 45.5%, in 1 hour; and 22.7%, in 2 hours.Since resazurin is sensitive to reducing action of leucocytes (or substances associated there with), the triple reading test can be used for detecting “abnormal” milk (caused by mastitis, reeent calving, late lactation, etc.).