Presence of less heavily encapsulated Klebsiella pneumoniae capsular type 1 in semen of healthy stallions and cervical swabs of mares suffering from metritis and comparison of virulence between heavily and less heavily encapsulated strains.

Abstract

Less heavily encapsulated Klebsiella pneumoniae (K.pneumoniae) strains of capsular type 1, which were different from ordinary heavily encapsulated strains, were isolated from semen of healthy stallions and from cervical swabs of mares suffering from metritis. Less heavily encapsulated strains possessed capsules ranging 1.3-2.2μm in transverse diameter, which were obviously smaller than those of heavily encapsulated strains, which possessed capsules more than 3.0μm in diameter. Of the 5 strains of K.pneumoniae capsular type 1 isolated from the semen of healthy stallions, 1 (20.0%) was heavily encapsulated and the remaining 4 (80.0%) were less heavily encapsulated, while of the 83 strains of K.pneumoniae capsular type 1 from the cervical swabs of mares suffering from metritis, 76 (91.6%) were heavily encapsulated and only 7 (8.4%) were less heavily encapsulated. Less heavily encapsulated strains showed low (semen-origin strains, LD50 was 10 to 10 CFU) or intermediate (cervical swab-origin strain, LD50 was 10 CFU) virulence for mice and were easily phagocytized by equine and murine polymorphonuclear leukocytes (PMNL), while heavily encapsulated strains showed high virulence (LD50 was 102 to 104 CFU) for mice and were protected from phagocytosis by the equine and murine PMNL.