[Bacterial resistance to antibiotics: biologic and ecologic aspects].

After a short introduction on bacterial resistance to the antibiotics and on the importance of the problem of emergence of the resistant strains, the mechanisms responsible are discussed. There are three major ways by which bacteria resist beta-lactam antibiotics; these include: altered outer membrane permeability, production of beta-lactamase and diminished affinity of the PbPs. Production of beta-lactamase is by far the most frequently encountered; for this reason there has been a major effort in the past 20 year to design new beta-lactam antibiotics, but on the other side bacteria elaborate constantly new strategies against new antibiotics. Moreover the use of antibacterial agents over the past half century has elicited a widespread deployment of genes for resistance in population of bacteria throughout the world and is conditioning the evolution of microbes.