Changes in the Natural Microflora During Incubation of Fresh and Processed Human Milks

Abstract

Seven pooled human milks, each from at least 6 different breast-feeding mothers (4 weeks post-partum) were studied for microbial population and flora changes during storage at 37degreeC. Coagulase-negative Staphylococcus spp. constituted a considerable part (39-100%) of the microflora in 6 of 7 pools of fresh milk, with coryneform bacteria, Lactobacillus , Micrococcus and Streptococcus spp. isolated less frequently. Storage of raw milk for 8 h caused a shift in flora favoring the Lactobacillus spp. After 24 h, coagulase-negative Staphylococcus were dominant in 4 of 7 pools, coryneform bacteria in 2 of 7, and Lactobacillus and Micrococcus spp. each in 1 of 7 pools. Low levels of bacteria were detected in 2 of 7 pasteurized pools, consisting of Staphylococcus spp. or yeasts. Freezing of the milk before storage at 37degreeC had little effect on the aerobic plate counts.