title: Invitro Activities of Polymyxins and Rifampicin against Carbapenem ResistantAcinetobacter baumanniiat a Tertiary Care Hospital from South India.
abstract: BACKGROUND
  Acinetobacter baumannii(A.baumannii) is rapidly emerging as a potent organism causing a multitude of nosocomial infections. The organism also carries various resistance mechanisms to antibiotics, making treatment more difficult. Very few choices are left, asA.baumanniistrains have begun to develop resistance against cephalosporins, aminoglycosides and even carbapenems.
  
  
  OBJECTIVE
  To examine the sensitivity pattern of three older antibiotics namely colistin, polymyxin B and rifampicin against carbapenem resistantA.baumanniiby disk diffusion method and the sensitivity of colistin alone by Minimum Inhibitory Concentration (MIC) determination by VITEK automated system.
  
  
  METHODS
  Hundred clinical isolates of carbapenem resistantA. baumanniiwere tested for sensitivity to colistin, polymyxin B and rifampicin by Kirby-Bauer disk diffusion method. They were also tested for sensitivity to colistin by VITEK 2C (biomérieux) automated microbial identification system. The zone diameters and Minimum Inhibitory Concentration values for the above two methods, respectively were observed and analysed. All the Antibiotic Susceptibility Tests were done according to the CLSI guidelines.
  
  
  RESULTS
  By Kirby-Bauer disk diffusion method, 78% of the carbapenem resistant strains were found to be sensitive, 12% intermediate sensitive and 10% resistant to colistin. All the isolates were sensitive to polymyxin B and 80% were resistant to rifampicin. By the VITEK automated system, 99% of the isolates were sensitive to colistin (more in number than by disk diffusion method).
  
  
  CONCLUSIONS
  Polymyxins (colistin - polymyxin E and polymyxin B) are the next choice for multidrug resistant serious nosocomial infections like those ofA. baumannii, till newer antibiotics are discovered to treat such infections. Rifampicin resistance was found to be very high and hence, is not advised for monotherapy.
authors: Associate Professor, Department of Microbiology, Government Medical College & ESIC Hospital , Coimbatore, Tamil Nadu, India .
authors: Dheepa
authors: D
authors: Muthusamy
authors: Student, PSG Institute of Medical Sciences & Research , Peelamedu, Coimbatore, Tamil Nadu, India .
authors: S
authors: S
authors: Sudhishnaa
authors: Professor and Head, Department of Microbiology, PSG Institute of Medical Sciences & Research , Peelamedu, Coimbatore, Tamil Nadu, India .
authors: Appalaraju
authors: A
authors: Boppe
keywords: Carbapenemase; Disk diffusion test; Nosocomial infections