title: Antimicrobial susceptibility patterns of multidrug-resistant Pseudomonas aeruginosa and Acinetobacter baumannii against carbapenems, colistin, and tigecycline.
abstract: OBJECTIVE
  To examine susceptibility of Pseudomonas aeruginosa (P. aeruginosa) and Acinetobacter baumannii (A. baumannii ) against carbapenems along with colistin and tigecycline as alternative therapeutic options.
  
  
  METHODS
  A total of 117 strains of multidrug-resistant (MDR) non-fermenting Gram negative bacteria isolated  from non-duplicate samples were collected consecutively. We included one sample from each patient (84 isolates of A. baumannii and 33 isolates of P. aeruginosa  isolated from patients seen at King Khalid University Hospital, Riyadh, Saudi Arabia, from June to December 2010). Isolates were identified by the MicroScan WalkAway 96 Plus system. The minimum inhibitory concentrations (MICs) were determined by E-test following the Clinical and Laboratory Standards Institute breakpoint recommendations.
  
  
  RESULTS
  Most A. baumannii strains were resistant to imipenem (90.5%), meropenem (90.5%), and doripenem (77.4%). Whereas, a higher percentage of P. aeruginosa was resistant to imipenem (90.9%), and meropenem (81.8%), only 39.4% were resistant to doripenem. Colistin had excellent activity against both A. baumannii (100%) and P. aeruginosa (93.9%), while 89.3% of A. baumannii strains were susceptible to tigecycline.
  
  
  CONCLUSIONS
  Among the carbapenems, doripenem was found to be the most potent antimicrobial agent against P. aeruginosa, whereas colistin proved to be an effective alternative antimicrobial agent for treatment of A. baumannii or P. aeruginosa. Tigecycline remains the best therapeutic option for MDR A. baumannii.
authors: Department of Pathology/Microbiology, College of Medicine, King Khalid University Hospital, King Saud University, PO Box 2925, Riyadh 11461, Kingdom of Saudi Arabia. ali.somily@gmail.com
authors: Ali M
authors: AM
authors: Somily
authors: Muhammad M
authors: MM
authors: Absar
authors: Muhammad Z
authors: MZ
authors: Arshad
authors: Abdulkarim I
authors: AI
authors: Al Aska
authors: Zahid A
authors: ZA
authors: Shakoor
authors: Amal J
authors: AJ
authors: Fatani
authors: Yunus M
authors: YM
authors: Siddiqui
authors: Thomas S
authors: TS
authors: Murray
mesh_terms: D040981:Acinetobacter baumannii / Q000187:drug effects*; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D015780:Carbapenems / Q000494:pharmacology; D003091:Colistin / Q000494:pharmacology; D024901:Drug Resistance, Multiple, Bacterial; D008826:Microbial Sensitivity Tests; D008911:Minocycline / Q000031:analogs & derivatives / Q000494:pharmacology; D011550:Pseudomonas aeruginosa / Q000187:drug effects*; D000078304:Tigecycline
chemical_list: D000900:Anti-Bacterial Agents; D015780:Carbapenems; D000078304:Tigecycline; D008911:Minocycline; D003091:Colistin