title: In vitro activity of tigecycline and comparators against carbapenem-susceptible and resistant Acinetobacter baumannii clinical isolates in Italy.
abstract: BACKGROUND
  In a recent multi-centre Italian survey (2003-2004), conducted in 45 laboratories throughout Italy with the aim of monitoring microorganisms responsible for severe infections and their antibiotic resistance, Acinetobacter baumannii was isolated from various wards of 9 hospitals as one of the most frequent pathogens. One hundred and seven clinically significant strains of A. baumannii isolates were included in this study to determine the in vitro activity of tigecycline and comparator agents.
  
  
  METHODS
  Tests for the susceptibility to antibiotics were performed by the broth microdilution method as recommended by CLSI guidelines. The following antibiotics were tested: aztreonam, piperacillin/tazobactam, ampicillin/sulbactam, ceftazidime, cefepime, imipenem, meropenem tetracycline, doxycycline, tigecycline, gentamicin, amikacin, ciprofloxacin, colistin, and trimethoprim/sulphametoxazole. The PCR assay was used to determine the presence of OXA, VIM, or IMP genes in the carbapenem resistant strains.
  
  
  RESULTS
  A. baumannii showed widespread resistance to ceftazidime, ciprofloxacin and aztreonam in more than 90% of the strains; resistance to imipenem and meropenem was 50 and 59% respectively, amikacin and gentamicin were both active against about 30% of the strains and colistin about 99%, with only one strain resistant. By comparison with tetracyclines, tigecycline and doxycycline showed a higher activity. In particular, tigecycline showed a MIC90 value of 2 mg/L and our strains displayed a unimodal distribution of susceptibility being indistinctly active against carbapenem-susceptible and resistant strains, these latter possessed OXA-type variant enzymes.
  
  
  CONCLUSIONS
  In conclusion, tigecycline had a good activity against the MDR A. baumannii strains while maintaining the same MIC(90) of 2 mg/L against the carbapenem-resistant strains.
authors.affiliation: Department of Microbiological and Gynaecological Sciences, University of Catania, Italy.
authors.forename: Maria Lina
authors.initials: ML
authors.lastname: Mezzatesta
authors.forename: Giusi
authors.initials: G
authors.lastname: Trovato
authors.forename: Floriana
authors.initials: F
authors.lastname: Gona
authors.forename: Vito Mar
authors.initials: VM
authors.lastname: Nicolosi
authors.forename: Daria
authors.initials: D
authors.lastname: Nicolosi
authors.forename: Alessandra
authors.initials: A
authors.lastname: Carattoli
authors.forename: Giovanni
authors.initials: G
authors.lastname: Fadda
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Nicoletti
authors.forename: Stefania
authors.initials: S
authors.lastname: Stefani
mesh_terms: D000151:Acinetobacter Infections / Q000382:microbiology*; D040981:Acinetobacter baumannii / Q000187:drug effects* / Q000302:isolation & purification; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics; D015780:Carbapenems / Q000494:pharmacology*; D004269:DNA, Bacterial / Q000235:genetics; D024881:Drug Resistance, Bacterial; D006801:Humans; D007558:Italy; D008826:Microbial Sensitivity Tests; D008911:Minocycline / Q000031:analogs & derivatives* / Q000494:pharmacology; D016133:Polymerase Chain Reaction / Q000379:methods; D000078304:Tigecycline; D001618:beta-Lactamases / Q000235:genetics
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D015780:Carbapenems; D004269:DNA, Bacterial; D000078304:Tigecycline; D001618:beta-Lactamases; D008911:Minocycline