Emergence of Tigecycline Resistant Acinetobacter baumannii From an Intensive Care Unit (ICU) in Tehran

Background: Acinetobacter species, specially, Acinetobacter baumannii, is known, as an important opportunistic pathogen, with a variety of infections such as pneumonia, bacteraemia, meningitis, urinary tract, skin and soft tissue infections, associated with high mortality. High prevalence of multidrug resistance in A. baumannii, limits our therapeutic choices in the treatment of infections caused by this bacterium. Objectives: The current study aimed to determine in vitro activity of tigecycline and colistin against clinical isolates of MDR A. baumannii, from patients admitted in ICUs Tehran hospitals. Material and Methods: This study was conducted from March 2009 to November 2010, on a total of 91 Acinetobacter species isolated from clinical specimens in ICUs. All isolates were subjected to PCR to detect blaOXA-51-like gene that is unique to A. baumannii. The antimicrobial susceptibility for 13 different antibiotics was tested. Results: A. baumannii (blaOXA-51-like gene) was detected in 84 (92.30%) isolates. Resistance rates in A. baumannii, were found to be for Imipenem 50 (59.52%), Gentamicin 65 (77.38%), Ciprofloxacin 81 (96.42%), Amikacin 44 (52.38%), Cefotaxime 81 (96.42%), Cefepime 69 (82.14%), Ceftazidim 81 (96.42%), Meropenem 74 (88.09%), Trimethoprim - sulfamethoxazole 78 (92.85%), Aztreonam 82 (97.61%), Colistin and Polymyxin-B 0%. No interpretive criteria have been approved for tigecycline against Acinetobacter spp. so; the results were interpreted by the criteria recommended by Jones, and US FDA for Enterobacteriaceae. Resistance rates for tigecycline were 3 (3.57%) (Jones criteria) and 19 (22.61%) (FDA criteria). Conclusions: It is clear that new antimicrobials are needed to treat MDR A. baumannii. Polymyxins and tigecycline are among the few antibiotics available to treat infections with these bacteria but little was known about the antimicrobial activity of these agents. The Present study provided valuable information about the effects of the above mentioned drugs that can be used for health policy. It should be noted that there is a need for regular surveillance of bacterial resistance to these antimicrobial agents.