Original article / research
Biofilm Formation and Colistin Susceptibility of Clinical Isolates of Acinetobacter Species in a Tertiary Care Hospital of Nepal
Dr. Birendra Raj Tiwari,
Saint James School of Medicine, Albert Lake Drive, The Quarter, Anguilla.
E-mail: tiwari.birendra58@g mail.com
Introduction: Acinetobacter species are a major cause of hospital acquired infections worldwide with remarkable level of resistance to various classes of antibiotics. This study was conducted to evaluate Minimum Inhibitory Concentration (MIC) activity of colistin against biofilm forming and MDR Acinetobacter species isolated from hospitalized patients by E-test.
Aim: The aim of this study was to evaluate the MIC of colistin against biofilm forming, Multi Drug Resistant (MDR) Acinetobacter species by E-test in a tertiary care hospital of Kathmandu.
Materials and Methods: Isolation and identification of Acinetobacter species was done by standard methods. Biofilms were developed using 96-well microtiter plates in Tryptic Soy Broth (TSB). Optical Density (OD) was measured at 570 nm after washing, fixation and staining. Antibiotic susceptibility test was performed by Kirby-Bauer disk diffusion method. Carbapenem resistance and Metallo B-Lactamase (MBL) production were tested by Modified Hodge Test (MHT) and Imipenem-EDTA combined disk method respectively. MIC was determined by E-test against colistin.
Results: Out of 573 bacterial isolates the number of Acinetobacter species was 73 (12.7%) and among them 72 (99%) were biofilm producers having significant relationship to multi drug resistance (p=0.01). All isolates were resistant to cephalosporins; 65 isolates (89%) were carbapenem resistant, 61 isolates (93.8%) gave positive MHT, 36 (56%) of total carbapenem resistant Acinetobacter isolates revealed positive for MBL, 72 (99%) of isolates were found sensitive to colistin by disc diffusion method whereas only 68 (93.1%) by MIC testing.
Conclusion: Acinetobacter clinical isolates have a strong ability to produce biofilm. Carbapenemases and MBL were also observed in this study. Only colistin and polymyxin B were effective against higher numbers of isolates, however, 5 (6.9%) of the isolates were found resistant as detected by MIC testing and indicated reduced susceptibility to colistin.
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