Enhancement of experimental bacteremia and endocarditis caused by dysgonic fermenter (DF-2) bacterium after treatment with methylprednisolone and after splenectomy

Abstract

The dysgonic fermenter-2 bacterium is a newly recognized fastidious gram-negative bacillus that causes bacteremia and sometimes endocarditis in immunocompromised persons after they are bitten by dogs. To develop an experimental model of this infection, we placed polyethylene catheters across the aortic valves of New Zealand white rabbits, which were inoculated intravenously the next day with dysgonic fermenter-2 bacteria. After 1 week, the rabbits were killed and the endocardial vegetations were homogenized for quantitative culture. Large inocula (1.3 x 1010 to 2.1 x 1010 viable bacteria) were required to produce infected vegetations. All infected rabbits had negative blood cultures at the time of autopsy and most developed serum agglutinins against dysgonic fermenter-2 bacteria. Three daily injections of methylprednisolone (30 mg/kg), starting the day before inoculation, significantly increased the incidence of endocarditis and the number of bacteria per gram of infected vegetation (P < 0.05). Treatment with methylprednisolone prolonged the initial bacteremia and caused significant increases in the numbers of bacteria per gram of blood, spleen, and liver compared with those of untreated controls (P < 0.05). Rabbits that had previously undergone splenectomy showed prolongation of the initial bacteremia but no significant increase in the incidence of infected vegetations. These results showed that the dysgonic fermenter-2 bacterium is a pathogen that causes endocarditis in rabbits but that it requires a large inoculum and produces blood culture-negative infections. Treatment with methylprednisolone enhances infection by prolonging the initial bacteremia and probably by diminishing bactericidal activity in the vegetations.

Septicaemia with a dysgonic fermenter-2 (DF-2) bacterium in a compromised host

“…The organism, therefore, seems to b e an oppor tunistic pathogen. In accordance with th ese observations in humans, experimental DF-2 infection in rabbits ap pears to be enhanced by administration o f m ethylprednisolone (14). O ur patient suffered from chronic lymphocy tic leukaem ia with hypogammaglobulinaemia and had un dergone splenectomy three years earlier.…”

Inactivation of human coagulation factor X by a protease of the pathogen Capnocytophaga canimorsus

“…Unfortunately, the investigation of virulence factors has been hampered by the lack of animal models permitting the investigation of pathogenesis in vivo . Rabbits , mice and hamsters (unpublished data) clear bacteria completely. In vitro , in human plasma, Cc DPP7 was effective in the nanogram range, and 10 7 bacteria mL −1 sufficed to affect thrombin generation.…”

A Case of Capnocytophaga Canimorsus Meningitis in Immunocompetent Host: A Zoonotic Agent in the Lombardian Alpes in Italy

“…C. canimorsus is catalase positive, and by degrading hydrogen peroxide in phagocytic vacuoles, this enzyme could allow the bacteria to survive within phagocytes. Furthermore, is resistant to killing by serum complement [6,7]. For that reason, it escapes the eff ects of the human host immune system.…”