[Study of the virulence of coagulase-negative staphylococci in experimental infections].

The pathogenicity and virulence of 3 strains of Staphylococcus epidermidis, Staphylococcus haemolyticus and Staphylococcus saprophyticus, respectively were studied in BALB/c mice by intraperitoneal (ip) challenge using 4 bacterial suspensions of different colony forming units (CFU) of each strain. Strains were isolated from wound, blood, and urine of inpatients. On the base of the lethality rates, S. saprophyticus proved to be the most virulent (LD50 = 2.7-2.9 x 10(7) CFU/g body wt), while the S. epidermidis species was the least virulent (LD50 = 6-8 x 10(7) CFU/g body wt). The lethality rate of male mice was higher than that of the female ones at the same challenge bacterium concentration. Mice of higher body weight were generally more sensitive to a quality of bacteria calculated to 1 g of mice than the lighter mice. The 245 mice surviving the challenge were dissected at the 10th day of infection. Splenomegaly was found to be the most frequent macroscopic pathological alteration. There appeared kidney abscesses, liver abscesses, and rarely peritoneal abscess. The frequency of pathological findings were directly proportional to the amount of bacteria injected. The results indicate that clinical strains of coagulase-negative staphylococci (CNS) examined were pathogenic and virulent for BALB/c mice they are invasive after ip injection and can cause macroscopic pathological changes in parenchymal organs. Thus, ip CNS challenge in mice may be a model to imitate and study infections caused by CNS in human.