Pathogenicity of capsulate and non-capsulate members of Bacteroides fragilis and B. melaninogenicus groups in mixed infection with Escherichia coli and Streptococcus pyogenes.

Abstract

Summary.The relationships between capsulate and non-capsulate Bacteroidesfragilis strains and Escherichia coli, and between capsulate and non-capsulate strains of the B. melaninogenicus group and Streptococcus pyogenes, were studied in a subcutaneous abscess model in mice. Selective antimicrobial agents directed against either aerobic or anaerobic bacteria were used alone or in combination to explore the effect of eradication of one component of the mixed infection. Single agent therapy effective against both aerobic and anaerobic flora was also employed. Single therapy of mixed infection directed at the elimination of only one organism ( S . pyogenes, E. coli or Bacteroides sp.) caused significant reductions in the numbers of sensitive organisms and also smaller yet significant decreases in the numbers of insensitive organisms. However, the abscesses were not eliminated after such therapy. Combination therapy or use of a single agent (cefoxitin) directed against the aerobic and anaerobic components of the infection was more effective. Non-capsulate Bacteroides spp. became capsulate after passage in mice mixed with either S . pyogenes or E. coli. Therapy directed at the elimination of S . pyogenes and E. coli did not prevent the emergence of capsulate Bacteroides spp. These data demonstrate the synergy between all members of the B. fragilis group and E . coli and between the B . melaninogenicus group and S . pyogenes, and reiterate the need to direct antimicrobial therapy at the eradication of the aerobic and anaerobic components of mixed infections. IntroductionMembers of the Bacteroides fragilis group mixed with Escherichia coli are often isolated from intraabdominal infections (Brook, 1988), while members of the B. melaninogenicus group and Streptococcus pyogenes are frequently isolated from orofacial and respiratory infections (Brook, 198 1). Although the virulence of capsulate strains of B. fragilis is well established (Onderdonk et al., 1977; Brook et al., 1984a, b) the pathogenicity of other members of the B. fragilis and B. melaninogenicus groups requires further investigation.We have previously demonstrated the ability of "helper" organisms to assist in the emergence of capsulate Bacteroides spp. in vivo (Brook et al., 1983,

Effect of virulent anaerobes on the outcome of peritoneal dialysis associated peritonitis

“…A reduction in the levels of immunoglobulin G and G3 has been noted in peritoneal dialysis effluents in comparison with serum, and the concentrations of these crucial opsonizing agents are related inversely to the frequency of peritonitis. 15 Anaerobes can deplete or bind opsonins that bind to aerobes, thus preventing their oposonization; Other important factors that impair host defence mechanisms are low pH and high osmolality of peritoneal dialysis fluid, both can impair polymorph nuclear leukocyte function and antibiotic efficacy and anaerobes suppress the activity of those polymorph nuclear leukocytes, macrophages, and lymphocytes. Bacteroides fragilis can also interact with peritoneal macrophages inducing procoagulant activity and fibrin deposition that impairs clearance of the infecting organisms.…”

In Vivo Efficacy of Humanized Ceftaroline Fosamil-Avibactam Exposures in a Polymicrobial Infection Model

“…However, it is important to note that the total bacterial load of each infection is substantially greater than those of most other infections used in murine models, as each inoculum consisted of up to three organisms with 10 7 CFU of each bacterium. Furthermore, a synergistic relationship between B. fragilis and Gram-negative aerobic organisms, such as Enterobacteriaceae, has been previously described which has been shown to increase mortality and overall bacterial growth (16,17). This relationship and the rapid increase in bacterial growth can make it more difficult to treat these infections than to treat single-organism infections.…”

Bacteroides infections in children

“…26 The emergence of capsule production in polymicrobial infection may explain the predominance of B. fragilis in chronic infection.…”