JAC 49/2 pp. 331-335

Two parameters are commonly used for the evaluation of antibiotic efficacy in animal models: bacterial counts in tissue fluids and survival rate. The second parameter is easy to assess and seems more relevant from the clinical perspective; a curative dose is used as a reliable end-point for showing subtle differences in antibiotic behaviour. Reduction in bacterial counts provides information on bactericidal activity in vivo; nevertheless, in vitro inocula and an inocula reduction rate equivalent to those in vivo have never been established and reduction in bacterial count may not be related to animal survival. Bacterial virulence is the minimal bacterial mass capable of producing injury to a given host and can be defined as the competence of an infectious agent to produce pathological effects, as indicated by case fatality rates and/or the ability to invade the host. This study explores the modification by -lactam therapy of the bacteraemic profile (representative of ability to invade the host) produced by a bacterial mass (representative of virulence) and its relationship with mortality rates (representative of competence to produce pathological effects). A serotype 6 penicillin-resistant isolate of Streptococcus pneumoniae was used as infecting strain, as this is one of the most frequently isolated serotypes in bacteraemia and respiratorytract infections in Spain. Materials and methods