Development and spread of bacterial resistance to antimicrobial agents: Anoverview

Resistance to antimicrobial agents is emerging in a wide variety of nosocom ial and community-acquired pathogens. The emergence and spread of multiply resistant organisms represent the convergence of a variety of factors that include mutations in common resistance genes that extend their spectrum of activity, the exchange of genetic information among microorganisms, the evo lution of selective pressures in hospitals and communities that facilitate the development and spread of resistant organisms, the proliferation and sp read of multiply resistant clones of bacteria, and the inability of some la boratory testing methods to detect emerging resistance phenotypes. Twenty y ears ago, bacteria that were resistant to antimicrobial agents were easy to detect in the laboratory because the concentration of drug required to inh ibit their growth was usually quite high and distinctly different from that of susceptible strains. Newer mechanisms of resistance, however, often res ult in much more subtle shifts in bacterial population distributions. Perha ps the most difficult phenotypes to detect, as shown in several proficiency testing surveys, are decreased susceptibility to beta -lactams in pneumoco cci and decreased susceptibility to vancomycin in staphylococci. In summary , emerging resistance has required adaptations and modifications of laborat ory diagnostic techniques, empiric anti-infective therapy for such diseases as bacterial meningitis, and infection control measures in health care fac ilities of all kinds. Judicious use is imperative if we are to preserve our arsenal of antimicrobial agents into the next decade.