Comparative activity of meropenem in US medical centers (2007): initiating the 2nd decade of MYSTIC program surveillance

Since 1997, the Meropenem Yearly Susceptibility Test Information Collection (MYSTIC) Program has monitored the antimicrobial activity of broad-spectrum agents against pathogens from hospitalized patients. In the United States, 2894 isolates were submitted in 2007 from 15 sites, including 1392 Enterobacteriaceae, 643 nonfermentative Gram-negative bacilli, and 829 Gram-positive cocci. All isolates were tested by broth microdilution methods. Meropenem (MIC90 range, 0.12–2 μg/mL) exhibited the lowest resistance rates (1.9–2.4%) against Enterobacteriaceae, and fluoroquinolones had the highest rates of resistance (17.3–18.3%). KPC carbapenemases, usually found in Klebsiella pneumoniae, were also detected in Citrobacter freundii, Enterobacter spp., and Escherichia coli. Confirmed extended-spectrum β-lactamase–producing isolate rates for E. coli, Klebsiella spp., and Proteus mirabilis isolates were 6.0%, 12.0%, and 0.0%, respectively. Meropenem remained active against Gram-positive pathogens such as staphylococci (methicillin-susceptible; MIC90, 0.12–0.25 μg/mL), Streptococcus pneumoniae (MIC90, 0.5 μg/mL), and β-hemolytic and viridans group streptococci (MIC90 range, 0.06–0.25 μg/mL). These US MYSTIC Program results demonstrate the continued emergence of novel β-lactamases and multidrug-resistant bacterial phenotypes necessitating monitoring of carbapenem activities against Enterobacteriaceae species as well as nonfermentative bacilli.