title: A 5-year Surveillance Study on Antimicrobial Resistance of Acinetobacter baumannii Clinical Isolates from a Tertiary Greek Hospital.
abstract: BACKGROUND
  Acinetobacter baumannii has emerged as a major cause of nosocomial outbreaks. It is particularly associated with nosocomial pneumonia and bloodstream infections in immunocompromised and debilitated patients with serious underlying pathologies. Over the last two decades, a remarkable rise in the rates of multidrug resistance to most antimicrobial agents that are active against A. baumannii has been noted worldwide. We evaluated the rates of antimicrobial resistance and changes in resistance over a 5-year period (2010-2014) in A. baumannii strains isolated from hospitalized patients in a tertiary Greek hospital.
  
  
  METHODS
  Identification of A. baumannii was performed by standard biochemical methods and the Vitek 2 automated system, which was also used for susceptibility testing against 18 antibiotics: ampicillin/sulbactam, ticarcillin, ticarcillin/clavulanic acid, piperacillin, piperacillin/tazobactam, cefotaxime, ceftazidime, cefepime, imipenem, meropenem, gentamicin, amikacin, tobramycin, ciprofloxacin, tetracycline, tigecycline, trimethoprim/sulfamethoxazole, and colistin. Interpretation of susceptibility results was based on the Clinical and Laboratory Standards Institute criteria, except for tigecycline, for which the Food and Drug Administration breakpoints were applied. Multidrug resistance was defined as resistance to ≥3 classes of antimicrobial agents.
  
  
  RESULTS
  Overall 914 clinical isolates of A. baumannii were recovered from the intensive care unit (ICU) (n = 493), and medical (n = 252) and surgical (n = 169) wards. Only 4.9% of these isolates were fully susceptible to the antimicrobials tested, while 92.89% of them were multidrug resistant (MDR), i.e., resistant to ≥3 classes of antibiotics. ICU isolates were the most resistant followed by isolates from surgical and medical wards. The most effective antimicrobial agents were, in descending order: colistin, amikacin, trimethoprim/sulfamethoxazole, tigecycline, and tobramycin. Nevertheless, with the exception of colistin, no antibiotic was associated with a susceptibility rate >40% for the entire study period. The most common phenotype showed resistance against ampicillin/sulbactam, cephalosporins, carbapenems, aminoglycosides, ciprofloxacin, and tigecycline. An extremely concerning increase in colistin-resistant isolates (7.9%) was noted in 2014, the most recent study year.
  
  
  CONCLUSIONS
  The vast majority of A. baumannii clinical isolates in our hospital are MDR. The remaining therapeutic options for critically ill patients who suffer from MDR A. baumannii infections are severely limited, with A. baumannii beginning to develop resistance even against colistin. Scrupulous application of infection control practices should be implemented in every hospital unit. Lastly, given the lack of available therapeutic options for MDR A. baumannii infections, well-controlled clinical trials of combinations of existing antibiotics are clearly needed.
authors.affiliation: Department of Clinical Microbiology, University Hospital of Heraklion, Crete, Greece. sofiamaraki@in.gr.
authors.forename: Sofia
authors.identifier: http://orcid.org/0000-0002-8553-0849
authors.initials: S
authors.lastname: Maraki
authors.affiliation: Department of Pediatrics, Democritus University of Thrace Faculty of Medicine and University General District Hospital of Evros, Alexandroupolis, Thrace, Greece.
authors.forename: Elpis
authors.identifier: http://orcid.org/0000-0001-7837-9733
authors.initials: E
authors.lastname: Mantadakis
authors.affiliation: University of Crete Medical School, Heraklion, Greece.
authors.forename: Viktoria Eirini
authors.identifier: http://orcid.org/0000-0002-9373-1800
authors.initials: VE
authors.lastname: Mavromanolaki
authors.affiliation: Department of Internal Medicine, Infectious Diseases Unit, University of Crete Medical School, Heraklion, Crete, Greece.
authors.forename: Diamantis P
authors.identifier: http://orcid.org/0000-0001-7603-2592
authors.initials: DP
authors.lastname: Kofteridis
authors.affiliation: Department of Internal Medicine, Infectious Diseases Unit, University of Crete Medical School, Heraklion, Crete, Greece.
authors.forename: George
authors.identifier: http://orcid.org/0000-0001-5857-9703
authors.initials: G
authors.lastname: Samonis
keywords: Acinetobacter baumannii; Antimicrobial susceptibilities; Colistin; Multidrug resistance; Tigecycline