Phagocytic function of equine neutrophils exposed to Mycoplasma felis in vitro and in vivo.

This study investigates the effect of bacterium Mycoplasma felis on the killing activity of neutrophils, white blood cells, in horses. The researchers found no reduction in the bactericidal function of neutrophils after exposure to the pathogen, indicating that M. felis does not impair the bactericidal activity nor predispose horses to bacterial pleuritis.

Sample Preparation and Bactericidal Assay Development

• Neutrophils, a type of white blood cell, were isolated from the peripheral blood of adult horses (group 1). These cells were then purified using a density gradient of polyvinylpyrrolidone-coated silica gel, a substance used to separate different components of a mixture.
• A bactericidal assay, a test measure designed to determine the potency of an antibacterial agent, was developed. The test bacteria used was an equine skin isolate of Staphylococcus epidermidis. This target bacterium was mixed with fresh equine serum, a component of blood, to encourage opsonization, a process that makes an organism more susceptible to degradation by white blood cells.
• Significant killing of the bacteria by the neutrophils was observed after 60 or 120 minutes of incubation.

Investigation into the Effect of Mycoplasma felis

• The researchers found no reduction in the bactericidal activity of the neutrophils after incubation with a virulent strain of Mycoplasma felis, a bacterium normally associated with respiratory disorders in cats, for either 30 or 60 minutes.
• The function of neutrophils from horses suffering from M. felis-induced pleuritis (group 2) was similar to those from sham-inoculated control horses (group 3).

Role of Equine Serum and Antibodies

• The number of viable M. felis organisms significantly decreased in the presence of fresh equine serum and horse-specific antibodies. However, heat-inactivated serum, which would contain no active antibodies, did not have this effect, indicating the important role of these antibodies in bacterial killing.
• It was found that horse neutrophils were not phagocytizing – or consuming and destroying – M. felis. This seems to indicate that M. felis does not impact the bactericidal activity of horse neutrophils and thus does not predispose horses to developing bacterial pleuritis.