Influence of Escherichia coli and Arcanobacterium pyogenes isolated from bovine puerperal uteri on phenotypic and functional properties of neutrophils

Abstract

When cows develop endometritis after birth, Escherichia coli and Arcanobacterium pyogenes are usually the most prominent bacteria present in bovine uterine lochial secretions. A. pyogenes alone is rarely found in the course of a disturbed puerperium. This was confirmed in this study, since average and high-grade uterine contaminations were always associated with the presence of both bacteria. The contamination grade was positively correlated with uterine polymorphonuclear granulocyte (PMN) numbers and negatively correlated with blood PMN numbers. Whether E. coli and A. pyogenes affect the phenotype and function of bovine PMN in a similar or differential way was subject to in vitro studies. PMN were tested in the presence of washed bacterial fragments or culture supernatants taken as a source for soluble and/or secreted bacterial products. Fragments and soluble products differed only quantitatively in their effects on PMN. Usually, long-time exposure (24 h) of PMN to fragments induced the strongest effects. Accelerated death of granulocytes was only moderately induced by both E. coli and A. pyogenes products. Both E. coli and A. pyogenes products induced the enhanced expression of a membrane molecule detected by mAb IL-A110 and of CD11b. Expression of other surface structures remained largely unchanged (MHC class I, CD11c). Functional parameters of PMN (phagocytosis; generation of reactive oxygen species, ROS; antibody-independent cellular cytotoxicity, AICC) generally declined after pre-incubation for 24 h with products of E. coli or A. pyogenes. Interestingly, soluble products of A. pyogenes stimulated the phagocytosis of PMN. However, co-incubation with E. coli products abrogated this stimulatory effect. The results supply evidence for similar modes of action of the gram-negative E. coli and the gram-positive A. pyogenes on bovine PMN. Alterations in PMN function and phenotype are mainly triggered by direct contact between bacterial fragments and PMN. Inhibition experiments with polymyxin B demonstrated that E. coli-mediated effects were not solely due to the action of lipopolysaccharide. The dominant functional depression of neutrophils by E. coli products strengthens the suggestion that the earlier appearance of E. coli in the uterus may support the co-infection of this organ by A. pyogenes at later times.