Abstract
The aim of this study was to determine the characteristics of carbapenem-resistant Pseudomonas aeruginosa (P. aeruginosa) strains and 5-year changes in resistance in a tertiary university hospital. The study included 90 and 101 randomly selected P. aeruginosa strains serotyped in 2003 and 2008, respectively. The standardized disk diffusion test and E-test were used to determine resistance to antibiotics. P. aeruginosa strains were considered to have high-level resistance if a minimum inhibitory concentration (MIC) for imipenem or meropenem was >32 µg/mL. To identify serogroups, sera containing specific antibodies against O group antigens of P. aeruginosa were used. P. aeruginosa isolates resistant to imipenem or/and meropenem were screened for metallo-β-lactamase (MBL) production by using the MBL E-test. Comparison of the changes in resistance of P. aeruginosa strains to carbapenems within the 5-year period revealed that the level of resistance to imipenem increased. In 2003, 53.3% of P. aeruginosa strains were found to be highly resistant to imipenem, while in 2008, this percentage increased to 87.8% (P=0.01). The prevalence of MBL-producing strains increased from 15.8% in 2003 to 61.9% in 2008 (P<0.001). In 2003 and 2008, carbapenem-resistant P. aeruginosa strains were more often resistant to ciprofloxacin and gentamicin than carbapenem-sensitive strains. In 2008, carbapenem-resistant strains additionally were more often resistant to ceftazidime, cefepime, aztreonam, piperacillin, and amikacin than carbapenem-sensitive strains. MBL-producing P. aeruginosa strains belonged more often to the O:11 serogroup than MBL-non-producing strains (51.7% vs. 34.3%, P<0.05). A greater percentage of non-MBL-producing strains had low MICs against ciprofloxacin and amikacin as compared with MBL-producing strains. The results of our study emphasize the need to restrict the spread of O:11 serogroup P. aeruginosa strains and usage of carbapenems to treat infections with P. aeruginosa in the intensive care units of our hospital.
Highlights
It has been proved that early appropriate antimicrobial therapy in patients with nosocomial infections may have a major impact on mortality, length of stay, emergence of resistant strains, and overall health care costs
The results of our study emphasize the need to restrict the spread of O:11 serogroup P. aeruginosa strains and usage of carbapenems to treat infections with P. aeruginosa in the intensive care units of our hospital
All P. aeruginosa strains were screened for resistance to carbapenems (IMP and MEM) by the routine disk diffusion test with antibiotic-containing disks (BBL, USA) according to the Clinical and Laboratory Standards Institute (CLSI) recommendations [9]
Summary
It has been proved that early appropriate antimicrobial therapy in patients with nosocomial infections may have a major impact on mortality, length of stay, emergence of resistant strains, and overall health care costs. Other mechanisms of the resistance of P. aeruginosa strains to carbapenems, such as the production of AmpC, extended-spectrum β-lactamases, or Toho1-type β-lactamases, can be involved as well, but the overall rates of morbidity and mortality among patients infected with MBL-producing strains are high [7]. The prevalence of carbapenem-resistant P. aeruginosa strains in the tertiary hospital of our university has increased from 10% to 40% (data not published) Such a high rate prompted us to study the characteristics of carbapenem-resistant P. aeruginosa strains and 5-year changes in resistance at our hospital and to present the guidelines in the future in order to decrease such a resistance
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