The
meropenem yearly Susceptibility Test Information Collection (MYSTIC) programme is a global, longitudinal resistance surveillance network that monitors the activity of
meropenem and compares its activity with other broadspectrum
antimicrobial agents. We now report the antimicrobial efficacy of
meropenem compared to other broad-spectrum agents within the selective Gram-negative pathogen groups from two Croatian Hospitals investigated between 2002-2007. A total of 1510 Gram-negative pathogens were tested and the minimum-inhibitory concentrations (MICs) were determined by broth microdilution method according to CLSI.There was no resistance to either
imipenem or
meropenem observed for Escherichia coli, Klebsiella pneumoniae and Proteus mirabilis in both medical centers. High resistance rates of K. pneumoniae to
ceftazidime (18%),
cefepime (17%) and
gentamicin (39%) are raising concern. Acinetobacter baumannii turned out to be the most resistant Gram-negative bacteria with 81% resistant to
ceftazidime, 73% to
cefepime, 69% to
gentamicin and 71% to
ciprofloxacin. Almost 20% of Pseudomonas aeruginosa strains were resistant to
imipenem, 13% to
meropenem, 69% to
gentamicin and 38% to
ciprofloxacin.The prevalence of extended-spectrum
beta-lactamases (ESBLs) in E. coli was 10% and in K. pneumoniae 49%. PCR and sequencing of the amplicons revealed the presence of SHV-5 in nine E. coli strains and additional
tem-1 beta-lactamase five strains. Five K. pneumoniae strains were positive for bla(SHV-5 )gene. Eight ESBL positive Enterobacter spp. strains were found to produce tem and CtX-m
beta-lactamases. Plasmid-mediated
AmpC beta-lactamases were not found among K. pneumoniae, E. coli and Enterobacter spp. Three A. baumannii strains from Zagreb University Center were identified by multiplex PCR as OXA-58 like producers. Six A. baumannii strains from Split University Center were found to possess an ISAba1 insertion sequence upstream of bla(OXA-51 )gene. According to our results
meropenem remains an appropriate
antibiotic for the treatment of severe
infections caused by Gram-negative bacteria. These data indicate that despite continued use of
meropenem,
carbapenem resistance is not increasing among species tested, except for A. Baumannii, in the two study hospitals and suggest that clinicians can still administer
carbapenems as a reliable and effective choice in managing serious
nosocomial infections.