Susceptibility of Escherichia coli Isolated from Intramammary Infections to Phagocytosis by Bovine Neutrophils

¹ Department of Dairy Science, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster 44691
² Department of Dairy Science, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster 44691
³ Department of Veterinary Science, The Pennsylvania State University, University Park 16802

Thirteen Escherichia coli isolated from naturally occurring IMI were tested for susceptibility to phagocytosis by bovine blood neutrophils. Isolates were opsonized in pooled serum collected from nine healthy lactating cows. Bacteria isolated from IMI first diagnosed within 3 d after calving were more resistant to phagocytosis than were isolates from IMI originating during either the first half of the dry period or later during lactation. Duration of the IMI was negatively correlated with both phagocytic index and percentage of neutrophils phagocytizing within bacterial isolates from IMI originating at calving and during lactation. Phagocytosis was independent of duration of IMI within isolates from IMI originating during the first half of the dry period. Susceptibility to in vitro phagocytosis by neutrophils was not related to O antigen serotype, encapsulation, or growth in dry cow secretion.

Key Words: Escherichia coli • phagocytosis

Submitted on June 3, 1992
Accepted on July 27, 1992

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