[Objective] To observe the distribution of major pathogenic bacteria of cow mastitis in milk in vitro.[Method] The Staphylococcus aureus and Escherichia coli(E.coli) were added into the milk.After standing for 8,12 and 24 h at 4 °C,the milk were divided into upper,middle and lower three equal parts.The bacterial counts distributed in the three parts of milk were respectively determined by plating colony-counting method.[Result] The counts of these two pathogenic bacteria in upper milk were higher than that in middle and lower milk significantly(P < 0.001),and no significant difference was found between middle milk and lower milk.[Conclusion] The pathogenic bacteria of cow mastitis can float with fat droplet in milk and then invade into the deeper tissue of mammary gland.
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