[Multiresistant Gram-negative bacterial infections: Enterobacteria, Pseudomonas aeruginosa, Acinetobacter baumannii and other non-fermenting Gram-negative bacilli]

Multiresistant Gram-negative bacteria represent a major health problem worldwide. This is related to the severity of the infections they cause, the difficulties for empiric (even directed) treatment, the ease of multiresistance spread, and the absence of new antimicrobial agents active against this group of pathogens. Accordingly, antimicrobial therapy should be based on the results of susceptibility testing, and may require using antimicrobial combinations. The production of extended-spectrum beta-lactamases represents the most important current problem of resistance among enterobacteria; these organisms cause nosocomial infections, but can also be cultured from non-hospitalised patients. In our country, enterobacteria producing plasmid-mediated AmpC enzymes or most carbapenemases are still uncommon, at the moment. Enterobacteria expressing these types of beta-lactamases present high rates of resistance to aminoglycosides and quinolones, because plasmids coding for beta-lactamases also contain other genes involved in additional resistances and/or the selection of additional chromosomal mutations. Among multiresistant Gram-negative non-fermenting bacteria, the most clinically relevant organism is Pseudomonas aeruginosa, an organism with intrinsic resistance to multiple agents and with ability to capture acquired resistance mechanisms. Other organisms in the latter group include Acinetobacter baumannii, with increasing rates of resistance to antimicrobial agents, and to a lesser extent Stenotrophomonas maltophilia.