Bacteraemia and seeding of capsulate Bacteroides spp. and anaerobic cocci.

Abstract

The effect of capsulation on the ability of Bacteroides fragilis, B. asaccharolyticus and anaerobic gram-positive cocci to induce bacteraemia and seeding to various organs was investigated. The test species were injected into mice subcutaneously alone, or mixed with other aerobic or facultative organisms. Capsulate anaerobes were isolated more frequently from the blood, spleen, liver, and kidneys of infected animals than were non-capsulate organisms. After injection of single anaerobic strains, capsulate organisms were recovered from 163 (39%) of 420 animals; non-capsulate anaerobes were recovered from only 14 (3%) of 420 animals. After injection of B. fragilis mixed with aerobic or facultative organisms, the capsulate B. fragilis strain was isolated more often and for longer periods than the non-capsulate strain. Capsulate B. fragilis was also recovered more often 5 days after injection with other organisms, than when injected alone. These data demonstrate that capsulate Bacteroides spp. and anaerobic gram-positive cocci are more virulent than non-capsulate strains in single and mixed infections.