Table 2.

Sources of specimens, origins, and antibiotic profiles for 10 polymyxin B-resistant clinical isolates of A. baumannii

IsolateClinical sourceaOriginMIC (μg/ml)
COLbPXBbIMPcMEMcFEPcCAZcP/TcA/ScAMKcGENcTOBcCIPcT/ScDOXcMINcTIGc
C2BAL (XDR)dSpain6416>8>8>16>16>64>16>32>816>2>2>8>81
C4Blood (XDR)dU.S.3264>8>8>16>16>64>16>32>8>16>4>2>8>80.5
C5Pleural fluidU.S.16328>816>16>6488>81>4>2422
C8BloodU.S.3216488>16644≤4≤20.5>41222
C11BALIsrael8160.54>16>16648>32>8>16>4>2≤111
C12Blood (MDR)dU.S.1616>8>816>16>643216>8>16>4>2221
C13BALU.S.161648>16>16>64>168>816>4>221ND
C14WoundBrazil3280.518>16>6482≤20.5>4≤0.50.250.25ND
C15BloodFrance12864218>16≤0.5432>8>16>4≤0.5>84ND
C87VCT (MDR)dSpain6416>8>8>16>16>64<8>32>8>16>4>2ND0.50.5
  • a BAL, bronchoalveolar lavage; VCT, ventricular catheter tip.

  • b Colistin (COL) and polymyxin B (PXB) MICs were determined by the broth microdilution method according to the Clinical and Laboratory Standards Institute (CLSI; 2009).

  • c MICs were determined by the broth microdilution M07-A8 method (CLSI; 2009) using commercially prepared and validated panels (TREK Diagnostic Systems, OH) in CAMH broth to the following antibiotics: IMP, imipenem; MER, meropenem; FEP, cefepime; CAZ, ceftazidime; P/T, piperacillin-tazobactam; A/S, ampicillin-sulbactam; AMK, amikacin; GEN, gentamicin; TOB, tobramycin; CIP, ciprofloxacin; T/S, trimethoprim-sulfamethoxazole; DOX, doxycycline; MIN, minocycline; and TIG, tigecycline. ND, not done.

  • d The clinical isolates were classified according to their susceptibility to the antimicrobials listed above (excluding colistin/polymyxin B and tigecycline) as follows: multidrug resistant (MDR), resistant to at least 3 antimicrobial families (including carbapenems) and displaying variable susceptibility to the remaining agents, and extremely drug resistant (XDR), resistant to all the antibiotics listed (8). Susceptibility interpretations were performed according to the CLSI (2010) criteria, when available. Due to the lack of CLSI breakpoints for tigecycline in Acinetobacter, no susceptibility could be inferred. Antibiotic profiles were categorized as MDR or XDR.