Variations in virulence of three (3) Escherichia coli serotypes confirmed in experimental mammary gland infections

Abstract

An experiment was conducted to confirm the pathogenicity of three (3) serotypes of Escherichia coli (E. coli 037, 02a and 109) in mammary glands of experimental cows (cow 105, 107 and 102 respectively). Pathogenicity of
the E. coli which is a measure of virulence was observed to vary in the cows. Following inoculation bacterial number peak at 160,000 CFU/ml, 7,6000,000 CFU/ml and 3,600 CFU/ml respectively. Also milk somatic cell count (SCC) were observed to peak at 15,000 x 103 cell/ml, 58,700 x 103 cell/ml and 360 x 103 cells/ml respectively. The time taken for maximum bacterial number and somatic cell count to reach varied. There was leukemia with relative neutropenia in all cases. Typical responses included fever, painful inflammation of glands and gradual weakness of the experimental cows. Time to peak rectal temperature, also varies. The control quarter of teat of each cow infused with 1.0ml of saline showed little or no response. Milk SCC never exceeded 100,000 cells/ml in the control quarter. Systemic effects were little and cows appeared normal externally. E. Coli serotypes varied in virulence with the degree of variation highly
determined by the organism tried.