Changes in Pathogen Number during Preservation of Milk Derived from Mastitic Dairy Cows

Abstract

Pathogens are sometimes undetected in mastitic milk after cultivation. It was found that several innate immune components such as antimicrobial peptides exist in milk and that their concentration increases in mastitic milk. Therefore, we hypothesized that pathogen in milk is killed by innate immune components during preservation of milk. The present experiment was undertaken to con rm this hypothesis. Milk was collected from mastitic udders (somatic cell count > 300,000 cells/ml) of dairy cows in the southern region of Japan. After preservation of milk at room temperature for 0, 0.5, 1, 2, 3, 4 and 5 h, milk was put on media and cultured for 18 to 48 h to count formed colony. Streptococci was detected in 40% of milk and 10% of them contained Streptococcus uberis. Coliform and Staphylococcus aureus were observed in less than 20% and 10% of milk, respectively. Coagulase negative Staphylococci, Yeast-like fungus and Corynebacterium bovis were also detected in less than 10% of milk. The number of Staphylococcus aureus in milk has not changed signi cantly during 5-h cultivation. The number of Streptococcus uberis in milk decreased slightly compared with that at 0 h, but there was no signi cant difference. In the milk with Coliform, number ratio was signi cantly decreased to under 50% at 4 h compared with that at 0 h. Number ratio was signi cantly decreased at only 0.5 h of culture in milk with Coagulase negative Staphylococci, Yeast-like fungus, Corynebacterium bovis and their ratio further declined at 5 h of culture to under 20% in Coagulase negative Staphylococci or 10% in Yeast-like fungus and Corynebacterium bovis. These results suggest that pathogenic microbes in high-somatic cell count milk decreased during preservation at room temperature. Therefore, reduction of microbes from the time of collection to examination should be taken into consideration to evaluate milk contamination.