Submitted to: Veterinary Record
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/10/1998
Publication Date: N/A
Interpretive Summary: Researchers in the Immunology and Disease Resistance Laboratory, USDA, Beltsville have discovered a breakdown in the cows immune system which may make more easily get clinical mastitis after becoming infected with Escherichia coli. They have found that receptors, called L-selectin, on the cell surface of white blood cells start to disappear once cows become infected. These receptors act as docking ports so that white blood cells can become attached to and move along the wall of blood vessels. These enables the white blood cells to quickly move through the walls of blood vessels when an infection is present. Without these receptors a delay in their movement to the site of the infection occurs. Thus the white blood cells cannot perform their professional role of seeking out and destroying the invading bacteria. Thus, an infection or mastitis occurs.
Technical Abstract: Bacterial clearance, L-selectin adhesion receptor expression and neutrophil recruitment during experimentally induced Escherichia coli mastitis were investigated. Acute mastitis was induced by injection of 104 cfu E. coli into both left quarters of twelve clinically healthy lactating cows, 2 to 6 weeks after parturition. Half the cows were treated intravenously 10 hours after infection, and subcutaneously 30 hours after infection with enrofloxacin. In both groups, bacterial count, milk serum albumin, milk somatic cell count, circulating leukocyte count and L-selectin expression on neutrophils were determined. Both groups responded to challenge with udder inflammation and fever. Treatment with enrofloxacin affected the elimination rate of bacteria at hours +14, +18, +24, +48, and +72 after challenge, but not the bacteriological cure rate (5 out of 6 for treated and 3 out of 6 for nontreated cows). The drop in L-selectin expression found following challenge didn't differ between groups throughout the study. No effect of treatment was found on SCC. Based on these findings, it is concluded that the number of bacteria in milk is not correlated with L-selectin expression on circulating PMN during experimentally induced E. coli mastitis.