Clonal occurrences of multidrug-resistant Gram-negative bacilli: report from the Meropenem Yearly Susceptibility Test Information Collection Surveillance Program in the United States (2004)

The Meropenem Yearly Susceptibility Test Information Collection Program is a global, longitudinal resistance surveillance network of more than 100 medical centers worldwide monitoring the susceptibility of bacterial pathogens to carbapenems and other broad-spectrum agents. Between 1999 and 2004, a total of 10–16 US medical centers referred up to 200 nonduplicate isolates from clinical infections to a central processing laboratory. Over this 6-year period, the antimicrobial activity of 12 broad-spectrum agents was assessed against 15 990 bacterial isolates using Clinical and Laboratory Standards Institute (formerly the National Committee for Clinical Laboratory Standards) reference methods. Analysis of the MIC results by year within organism species and/or organism groups revealed a continued decrease in fluoroquinolone susceptibility (ciprofloxacin and levofloxacin), especially among indole-positive Proteae (−22.1%), Escherichia coli (−17.0%), Enterobacter species (−10.0%), and Proteus mirabilis (−7.6%) isolates. Antibiogram analysis of strains demonstrating multidrug resistance from the same institutions were further characterized by automated ribotyping and pulsed-field gel electrophoresis to determine clonality. In 2004, a total of 165 selected multidrug-resistant (MDR) strains produced 64 different ribotypes with the largest representing 31 Escherichia coli isolates from 6 medical centers. Other clusters were also identified within single medical centers among Enterobacter cloacae (6 strains), Providencia stuartii (5 strains), and Morganella morganii (4 strains). A significant clonal outbreak encompassing 40 Acinetobacter baumannii isolates from 3 centers in a single endemic region was identified in 1999 and has persisted through 2004. Continued surveillance of these broad-spectrum antimicrobial agents against MDR pathogens appears warranted to monitor the incidence and spread of resistant clones causing serious infections. Possible emergence of resistance mechanisms via clonal dissemination proves to be among the principle threats that compromise carbapenem therapy, where meropenem maintains the broadest spectrum of coverage.