Antibiotic-induced endotoxin release is organism-dependent in experimental Gram-negative sepsis

Abstract

The majority of in vitro and animal experiments that have been performed to assess antibiotic-induced endotoxin release (AIER) have employed a single test isolate, usually Escherichia coli. To determine the influence of microorganism type on AIER and interleukin-6 (IL-6) response, CF-1 mice were made septic following a 12-15% total body surface area nonlethal burn and subeschar challenge (LD90) with Klebsiella pneumoniae K2 (∼103 cfu), Proteus mirabilis 4552 (∼101 cfu) and Pseudomonas aeruginosa SBI-N (∼102 cfu). Three intraperitoneal (i.p.) doses, given every 4 h, of ceftazidime (TAZ, 200 mg/kg), imipenem (IMI, 100 mg/kg), ciprofloxacin (CIP, 25 mg/kg) and gentamicin (GEN, 25 mg/kg) were administered post burn and infection beginning when mice were septic with organ dysfunction. Free endotoxin concentrations were significantly ( P < 0.001) higher following all antibiotics for treatment of K. pneumoniae as compared to Ps. aeruginosa (intermediate) and P. mirabilis infections. Differential AIER was highest for TAZ and IMI, intermediate for CIP and lowest for GEN, for the treatment of K. pneumoniae and Ps. aeruginosa infections. There was a strong positive correlation between endotoxin release and IL-6 production for K. pneumoniae-treated animals, however increased endotoxin levels for Pseudomonas were accompanied by decreases in IL-6 levels. For P. mirabilis infection endotoxin levels were comparatively low, but highest for GEN and IMI. However, corresponding IL-6 levels increased only 3.2-fold for IMI and actually decreased by 50% for GEN following the first dose. Interestingly, CIP resulted in only modest endotoxin release and TAZ caused no appreciable release, however IL-6 concentrations dramatically increased 39.9-fold (TAZ) and 32.6-fold (CIP). This suggests that other pro-inflammatory mediators released from the bacterium, and not endotoxin, were more important determinants in the overall host response to antibiotic exposure. In conclusion, these data provide supportive evidence that absolute and differential AIER and production of IL-6 is organism-dependent in experimental Gram-negative sepsis. As a result, general conclusions concerning differential AIER for infection caused by E. coli or K. pneumoniae cannot necessarily be extrapolated to other species of Gram-negative bacilli. Furthermore, these study results strongly indicate that the microorganism and other pertinent pro-inflammatory factors (i.e. exotoxins, proteases), must be taken into account in the study design and data analysis of any experimental or clinical trial that is conducted to determine the significance of differential AIER.