[Microbiological causes of antibiotic therapy failure in respiratory tract infections].

This article reviews the most important aspects of antibiotic treatment failure in respiratory tract infection which may occur with empirical as well as under target antibiotic therapy. Potential risk factors leading or predisposing to treatment failure exist in hospital acquired infections which cover polymicrobial aetiology with high multidrug resistance bacteria, changed conditions of pharmacokinetic and pharmacodynamic (PK/PD) parameters of antibiotics, bioavailability, drug interactions and inactivation. Microbial determinants of treatment failure includes bacterial physiology in laboratory cultures and inside the host, inadequate drug choice, lack of knowledge of PK/PD parameters with insufficient antibiotic level in target tissue. Differences between microbial in vitro tests and clinical outcome can be caused by varied CFU concentration, growing phase, nutritional, pH and redox conditions. Many factors of treatment failure are focused on bacterial biofilm structure and phenomenon of small-colony variants (SCVs) which both display reduced susceptibility to antimicrobial agents protected by matrix feature, enhanced production of PIA and by slow multiplication of biofilm forming cells.