Comparıson of dısc dıffusıon, e test and broth mıcrodılutıon methods for the determınatıon of resıstance to tıgecyclın, colıstın and polymyxın b by multıple resıstant Acinetobacter baumanıı ısolates

Hospital infections are one of the most important health-care problems because of their high morbidty and mortality, increased length of hospital stay and the high cost of therapyIn recent years, Acinetobacter species are the most frequently isolated nosocomial agents which are detected, especially in intensity care unitsNowadays, the increasing resistance to antimicrobials which are used for treatment of infections caused by Acinetobacter baumannii species has become an important health problem in Turkey like the rest of the worldThe increase in both the frequency of infections caused by Acinetobacter baumannii and in its antimicrobial resistance made it necessary to investigate new treatment options and new drugs. The development of the resistance, maked it necessary to search and improve old (e.g. polymyxins) and new antibiotics (e.g. tigecyclins). The importance of the polypeptide structured antibiotic colistin (polymyxin-E) has been increasing once more, because of the development of multiple resistance phenotypes in Gram negative bacteria. However, in our country, the number of studies that have investigated the activity of these antibiotics are limited. The new semisynthetic tetracycline, tigecyclin, is a promising drug for the treatment of infections caused by multiple resistant Gram negative bacteria including, A. baumanniiThis study was conducted on 200 Acinetobacter species which are isolated from various clinical samples sent to the Microbiolgy Laboratory of the Gaziantep Universty of Research Hospital between September 2006 and April 2008. Identification of bacteria are made by using of conventional microbiological methods and automatized identification system for bacteria (Vitek 2, bioMerieux, FranceThe in-vitro drug susceptibility of bacteria to antibiotics was determined by disc diffusion method under the guidelines of Clinical and Laboratory Standards Institute (CLSI). Susceptibilities of colistin, tigecyclin and polymyxin B to 95 multiple resistance Acinetobacter species were tested with E test and broth microdilution methods. It is found that all of isolates were sensitive to colistin, 90 (94.7%) of them were sensitive to polymxin and 83 (87.3%) of them sensitive to tigecyclin by disc diffusion method. All of the isolates (100%) were sensitive to colistin,90 (97.4%) of them were sensitive to polymyxin and 72 (75.7%) of them were sensitive to tigecycline by E test method. All of the isolates were sensitive to colistin, 90 (97.4%) of them were sensitive to polymyxin and 86 (90.5%) of them were sensitive to tigecycline by broth microdilution methodWhen we compared E test and broth microdilution methods, it was observed that their results were more concordant to each other than disc diffusion method. Activity of colistin, polymyxin B and tigecyclin to Acinetobacter species was found to be quite high.Key Words: Acinetobacter, Colistin, Polymyxin B, Tigecycline.