Antimicrobial Susceptibility and Beta-Lactamase Production of Selected Gram-Negative Bacilli from Two Croatian Hospitals: MYSTIC Study Results

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 broad-spectrum 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 β-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 β-lactamases. Plasmid-mediated AmpC β-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 Gramnegative 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.