Influence of In-Vivo Endotoxin Liberation on Anti-Anaerobic Antimicrobial Efficacy

Abstract

The ability of cefoxitin, clindamycin, imipenem, meropenem, metronidazole and piperacillin-tazobactam to cause Gram-negative anaerobic bacteria to release endotoxin and the influence of such liberated endotoxin on antibiotic efficacy were investigated in In-Vivo experiments in animal models. Experimental infections in various animal models (mice, hamster and infant rats) with cultures of wild and reference strains of Bacteroides fragilis group and Fusobacterium spp. were carried out by injecting these animals with different inocula (10⁶, 10⁷ and 10⁸ cfu/ml) of the bacterial suspension. Appropriate doses of the test antibiotics were then injected and the plasma lipopolysaccharide (endotoxin) release measured by the Limulus Amoebocyte Lysate (LAL) Assay. Evidence of worsening of the outcome of the infections post-therapy was assessed, including histopathological changes in the internal organs. Infection with generalized septicemia was established with F. nuclea-tum in the mice and hamster models while with the B. fragilis group, infections only led to intra-abdominal abscess formation. Plasma endotoxin release was higher in animals infected with F. nucleatum than B. fragilis and was unrelated to the bacterial inoculum. Imipenem, meropenem and cefoxitin, in that order, induced the highest levels of endotoxin activities in the animal model, particularly following F. nucleatum infection. Histological examination of the internal organs of various animals showed variation in the pattern of histopathological changes; grades 3-4 inflammatory changes in the liver were observed in the Fusobacterium-infected animals that were treated with the car-bapenems and cefoxitin. Therapy with the other antibiotics did not exacerbate anaerobic sepsis. In this study, bacteremia did not lead to massive endotoxin release and antibiotic therapy appeared not to have negatively influenced the outcome of most of the Gram-negative anaerobic infections, except for infections caused by Fusobacterium spp. However, it is conceivable that if the gastrointestinal tract is the source of the endotoxin in patients with systemic inflammatory response syndrome, then the obligate anaerobes like Bacteroides and Fusobacterium species, which are members of the gut flora, may play a major role in the unfavorable outcome of antibiotic therapy in some of these infections.