Mechanisms of bacterial antibiotic resistance.

Infectious complications are major contributing factors to morbidity and mortality in the ICU setting. Organisms frequently encountered in the ICU include Pseudomonas aeruginosa, Staphylococcus aureus, Haemophilus influenzae (particularly in trauma victims), enterococci, Klebsiella pneumoniae, Enterobacter spp., Acinetobacter baumanii, Escherichia coli, and Stenotrophomonas (Xanthomonas) maltophilia. Antibiotics have played a major role in the treatment of infections caused by such bacterial pathogens. Organisms have responded to the antibiotic challenge, however, evolving and developing resistance to all available antimicrobial agents to a greater or lesser degree. Specific mechanisms of resistance include reductions in cell-wall membrane permeability, alterations of antimicrobial agent target sites, enzymatic inactivation of antibiotics, and development of bypass pathways around antimicrobial targets. This article describes, pathogen by pathogen, antimicrobial agents that are useful for the treatment of infection in the ICU setting and the mechanisms whereby bacteria have short-circuited our antimicrobial armamentarium.