title: Characteristics of carbapenem-resistant Pseudomonas aeruginosa strains in patients with ventilator-associated pneumonia in intensive care units.
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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Laboratory Medicine, Medical Academy, Lithuanian University of Health Sciences, Eivenių 2, 50028 Kaunas, Lithuania. astravitka@hotmail.com
authors.forename: Astra
authors.initials: A
authors.lastname: Vitkauskienė
authors.forename: Erika
authors.initials: E
authors.lastname: Skrodenienė
authors.forename: Asta
authors.initials: A
authors.lastname: Dambrauskienė
authors.forename: Giedrė
authors.initials: G
authors.lastname: Bakšytė
authors.forename: Andrius
authors.initials: A
authors.lastname: Macas
authors.forename: Raimundas
authors.initials: R
authors.lastname: Sakalauskas
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D015780:Carbapenems / Q000494:pharmacology*; D003428:Cross Infection / Q000382:microbiology*; D024881:Drug Resistance, Bacterial; D006801:Humans; D007362:Intensive Care Units; D008097:Lithuania; D053717:Pneumonia, Ventilator-Associated / Q000382:microbiology*; D011552:Pseudomonas Infections / Q000382:microbiology*; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000302:isolation & purification
chemical_list: D000900:Anti-Bacterial Agents; D015780:Carbapenems