engleski

Results from Meropenem Yearly Susceptibility testing Information (MYSTIC) Programme: Reports from two Croatian hospitals

Meropenem Yearly Susceptibility test Information Collection (Mystic) Programme is a global, longitudinal resistance surveillance network that monitors the activity of meropenem and compares the activity with other broad-spectrum antimicrobial agents, only in selected medical centers that are actively prescribing meropenem. We now report the four years period results (2002- 2005) for the antimicrobial potency of meropenem compared to other broad-spectrum agents within the selective pathogen groups from the two Croatian Hospitals. The 2 hospitals (Clinical Hospital Center Zagreb and University Hospital Split) participating in the MYSTIC Programme are located in different geographical regions of Croatia. The study protocol outlines that 100 aerobic Gram- negative and 100 aerobic Gram-positive isolates from serious infections in hospitalised patients be submitted to the central monitoring laboratory. Isolates from species with known intrinsic resistance mechanisms to carbapenems were excluded (oxacillin-resistant staphylococci, Enterococcus faecium and Stenotrophomonas maltophilia). Organisms were identified by standard biochemical tests. All gram-negative isolates and staphylococci were stored in ctab cultures whereas streptococci were kept in lyquid nitrogen. The minimum-inhibitory concentrations (MIC) were determined by broth microdilution method according to NCCLS. MICs were determined for meropenem, imipenem, ceftazidime alone and combined with clavulanic acid, cefepime, piperacillin/tazobactam, gentamicin and ciprofloxacin. An inoculum equivalent to the turbidity of the 0.5 Mc Farland was prepared, diluted to approximate 5x105 CFU/ml and then dispensed into the wells of 96 well microtiter plates. Microtiter plates were incubated at 37°C in ambient air for 18-24 h. All interpretations of susceptibility were based on NCCLS criteria. Extended-spectrum beta-lactamases (ESBLs) were detected among E. coli and K. pneumoniae strains by double-disk synergy method. Metallo-beta- lactamases (Mbls) were detected by E test Mbl test. Quality control was performed with ATCC strains of Escherichia coli ATCC 25922, P. aeruginosa ATCC 27853, Staphylococcus aureus ATCC 29213 and Enterococcus faecalis ATCC 29212. The concentrations of antibiotics which inhibited 50 and 90% of the strains (MIC50 and MIC90) and the percentage of resistant were calculated. The results from two hospitals were compared Results There was no resistance to either imipenem or meropenem observed for E. coli, K. pneumoniae and P. mirabilis in both medical centers. E. coli strains from Split were more resistant to ceftazidime (8%) and cefepime (4%) than those from Zagreb (1%, and 0.7%, 2% respectively) whereas isolates from Zagreb were more resistant to ciprofloxacin (7%) and gentamicin (13%) compared to those from Split (2% and 12% respectively). There was a higher percentage of resistance among K. pneumoniae isolates in comparison to E. coli from both centers to ceftazidime (28% from Zagreb and 44% from Split) and to cefepime (14% from Zagreb and 20% from Split). Genamicin and ciprofloxacin were also less active against K. pneumoniae from both centers (28% strains resistant to gentamicin from Zagreb and 37% from Split, 10% of the strains resistant to ciprofloxacin from Zagreb and 8% from Split). P. mirabilis strains were sensitive to to all beta- lactam agens, but there was 23% of the strains from Zagreb resistant to gentamicin and 9.8% to ciprofloxacin. Meropenem was the most potent agent against A. baumannii and P. aeruginosa strains from both centers. There was a high percentage of A. baumanii strains from Split resistant to all beta-lactam agents (above 80%). More P. aeruginosa strains from Zagreb were resistant to gentamicin (63%) and ciprofloxacin (52%) compared to those from Split (35% and 27% respectively). Imipenem shoed best activity against Gram-positive cocci from both centers (Staphylococcus aureus and Enterococcus faecalis). According to our results meropenem remains the antibiotic of choice for the treatment of severe infections caused by Gram- negative bacteria. No resistance to this agent was observed so far among E. coli, K. pneumoniae and P. mirabilis. Resistance to carbapenems observed in some P. aeruginosa strains could be due to production of metallo-beta-lactamases which are already detected in some of our strains (unpublished data), alterations in outer membrane proteins and efflux. Carbapenem resistance found in A. baumannii isolates from Split could be explained by production of oxacillinases (unpublished data). Imipenem was superior in vitro to meropenem against gram-positive bacteria. In principle, isolates from Split were more resistant to most antibiotics tested, which could be attributable to the antibiotic policy of the hospital.

MYSTIC; resistance; beta-lactamases; meropenem

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