The kinetics of inflammation and phagocytosis during bovine mastitis induced by Streptococcus agalactiae bearing the protein X

Abstract

The protein X of Streptococcus agalactiae is a surface antigen borne by a high proportion of strains isolated from bovine mastitis. We have tested the capacity of two strains of X-bearing Streptococcus agalactiae to induce mastitis in dairy cows. The reference X-strain (411.07) produced an intramammary infection with local clinical signs in the three inoculated quarters. Another X-bearing strain (443.31) of bovine origin produced infection in all 11 quarters inoculated with only 25 or 85 colony-forming units. In naive cows, strain 433.31 induced less exudation of plasma into the milk, shedding of bacteria, macroscopic alteration, and a lower somatic cell count (SCC) than did the reference strain. Only one quarter spontaneously eliminated the infection before antibiotic treatment 9 days after inoculation. The serum of all the cows contained naturally acquired or induced antibodies to the challenge strain (443.31) and possessed opsonic activity. Before inflammation occurred, the milk was almost devoid of antibody or opsonic activities. The early phase of infection was characterized by rapid multiplication of streptococci in the milk, followed by a sharp drop in bacterial counts concomitant with the onset of inflammation. Three cows immunized with protein X displayed higher SCC and bactericidal activity in milk from the inoculated quarter at the onset of inflammation than non-immunized cows. Two of the three immunized cows underwent an early and transient febrile episode and eliminated the infection.

Mobilization of neutrophils and defense of the bovine mammary gland

“…The shortening of the lag period following the traversing of the teat canal by bacteria could change the outcome of the infection, lessening the severity of clinical mastitis or augmenting the proportion of bacteriological cures. There are several observations supporting this assumption, obtained by immunisation with S. aureus, E. coli or S. agalactiae [16,19,44]. These observations reinforce the recognized importance of the swift and intense recruitment of PMN following the entry of bacteria in the lumen of the gland [58], and is an incentive for studying the mechanisms behind the mobilization of PMN to the mammary gland.…”

“…Immunization of cows with killed E. coli, or with a purified surface antigen of S. agalactiae, is followed by an increase of PMN influx in response to intramammary challenge with the corresponding pathogen, as compared to the response in unimmunized control cows. This stronger mobilization of PMN corresponded to lower bacterial counts in milk and to increased bacteriological cures [16,44].…”

“…This is true of the infections by mycoplasma [120], staphylococci [19,121], streptococci [16] or E. coli [44]. A simple protein antigen like the egg albumin, which does not cause by itself any inflammatory reaction in naïve animals, induce an intense recruitment of PMN when it is introduced at a dose of a few µg through the teat canal of cows immunized beforehand by the subcutaneous route [42].…”

“…In practice, less than 100 colony-forming units (cfu) are enough, and the size of the inoculum seems to primarily modulate the duration of the lag period preceding the inflammatory response, not the severity of the disease: increasing the inoculum, in the range of 10 to 100 000 (cfu) of mastitis pathogens such as Escherichia coli or Staphylococcus aureus, essentially shortens the lag period before infection manifests itself. Once they have penetrated the gland, bacteria multiply in the milk and reach concentrations between 10 4 and 10 6 cfu·mL -1 before they elicit inflammation [14][15][16]. The growth of E. coli seems to be unrestricted in the milk in the first few hours after inoculation, with the in vivo doubling time close to 20 min.…”

Virulence factors involved in the pathogenesis of bovine intramammary infections due to Staphylococcus aureus

“…With a similar experiment in the guinea-pig, De Cueninck has shown that this phenomenon could be transferred by peritoneal cells but not by serum from immunised animals to control animals. 135 Similarly, Rainard et al 136 have recently immunised cows with purified protein X, a surface antigen of Str. agalactiae.…”