MYSTIC (Meropenem Yearly Susceptibility Test Information Collection) results from the Americas: resistance implications in the treatment of serious infections

The Meropenem Yearly Susceptibility Test information Collection (MYSTIC) programme aims to provide in vitro surveillance data for geographically diverse institutions where meropenem is available for use. The in vitro activity of meropenem and eight comparator antimicrobial agents against 2340 significant pathogens obtained in 1999 was assessed and compared in 14 study centres in Brazil, Mexico and the USA. Isolates were further characterized for production of extended-spectrum beta-lactamases (ESBLs), AmpC beta-lactamases and carbapenemases. Carbapenems demonstrated their broad spectrum and potency, inhibiting greater than or equal to 95% of all isolates irrespective of the geographical region or centre type. The overall order of activity of the nine agents tested against all pathogens in 1999 was meropenem (96%) > imipenem (95%) > cefepime (92%) > gentamicin (89%) > piperacillin/tazobactam (88%)> ceftazidime = tobramycin (86%)> cefotaxime (84%) > ciprofloxacin (83%). Thus far, the results from the Americas indicate that meropenem has excellent potency and spectrum of activity despite being prescribed for the treatment of seriously ill patients. In contrast, other ESBLs, fluoroquinolones and aminoglycosides have lost activity in many institutions as a result of the selection of strains producing ESBLs or having AmpC and other resistance determinants. Carbapenem resistance was observed rarely and at a prevalence similar to those reported in earlier studies. Carbapenems appear to be a continuing reliable option for the treatment of serious nosocomial infection.