• Jacqueline Buijs, Anthonius S M Dofferhoff, Johan W Mouton, and Jos W M van der Meer.
• Department of Medical Microbiology and Infectious Diseases, Canisius-Wilhelmina Hospital, Nijmegen, The Netherlands. j.buijs@atriummc.nl/jacqbuijs@hotmail.com
• J. Antimicrob. Chemother. 2007 May 1;59(5):926-33.

ObjectivesInitial antibiotic treatment of severe infections can lead to clinical deterioration due to sudden endotoxin release and concomitant exaggerated inflammatory response. Antibiotic-induced morphological changes may contribute to this phenomenon. High-dose ceftazidime, which inhibits penicillin-binding protein (PBP)-1 in Gram-negative bacteria, causes quick bacteriolysis and low endotoxin release. Low-dose ceftazidime leads to PBP-3 inhibition, which causes bacterial filament formation, associated with high endotoxin releases. PBP-2-specific antibiotics induce spheroplasts, again associated with low endotoxin release. We hypothesized that antibiotic type, concentration and regimen influence bacterial morphology, endotoxin levels and inflammatory response.MethodsNeutropenic mice with Escherichia coli or Pseudomonas aeruginosa sepsis were treated with ceftazidime or meropenem 10-320 mg/kg as an intravenous bolus or as continuous tail vein infusions of 0.1 mL/h. Four hours later, bacterial counts, morphology, plasma endotoxin, pro-inflammatory cytokines [tumour necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6)] and antibiotic concentrations were measured.ResultsContinuous infusion of 80 mg/kg ceftazidime was the lowest dose preventing filaments in E. coli infections. Bolus treatment resulted in filament formation, irrespective of the dose. During continuous treatment, IL-6 and TNF-alpha concentrations were higher compared with bolus treatment and controls for both antibiotics and both strains. A clear relationship between cfu counts in muscle and circulating IL-6 was shown (r=- 0.579, P=0.007), suggesting that plasma IL-6 is a valuable indicator of bacterial killing at the infection site.ConclusionsOur findings show that not PBP affinity but the method of antibiotic administration is crucial during initial treatment of severe infections.

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