Galani et al. Activity of Plazomicin against carbapenemase producers Material and Methods Clinical isolates collected from January 2008 to November 2010, were studied and only one isolate per patient was accepted. Identiﬁcation and MIC determinations were performed using an automated system (BD Phoenix automated microbiology system; BD Diagnostic Systems, Sparks, MD, USA). MICs of plazomicin (0.25–32 mg/ml), tobramycin (0.25– 32 mg/ml), and fosfomycin (16–512 mg/ml) were determined by the agar dilution method follow- ing the Committee on Antimicrobial European Susceptibility Testing (EUCAST) guidelines (www. eucast.org), whereas those of doripenem and tigecy- cline were determined using E-test (AB Biodisk, Solna, Sweden), in accordance with the manufac- turer’s instructions. Plazomicin was supplied by Achaogen, Inc. Tobramycin and fosfomycin were purchased from Sigma-Aldrich (St Louis, MO, USA). Agar medium in which fosfomycin MICs were tested was supplemented with 25 mg/ml of glucose-6-phosphate (Sigma-Aldrich). E. coli ATCC 25922 and Pseudomonas aeruginosa ATCC 27853 were used as control strains. Results were interpreted in accordance with the EUCAST guidelines (www. eucast.org). All isolates were screened for MBL and class A carbapenemase production with EDTA–meropenem and meropenem–boronic acid disc synergy tests,6 res- pectively. The presence of KPC and VIM genes was conﬁrmed by PCR with speciﬁc primers.6 ESBL pro- duction was tested with the CLSI ESBL conﬁrmatory test7 and with a modiﬁed test using clavulanate in Table 1 In vitro activity of plazomicin and comparators against 300 MDR enterobacterial isolates Breakpoints (S, R) Range (mg/ml) Susceptibility rate (%) (0.25 to 4 (8 to .32 (2 to .8 0.5 to .32 (1 to .8 (1 to .8 0.032 to .32 (4/4 to .64/4 (0.5 to .2 (16 to .512 (1 to .2 0.125 to 16 (0.5 to 4 (8 to .32 (2 to .8 0.5 to .32 (1 to .8 (1 to .8 0.032 to .32 (4/4 to .64/4 (0.5 to .2 (16 to .512 (1 to .2 0.125 to 16 (0.25 to 2 ((8 to .32 (2 to .8 1 to .32 (1 to .8 (1 to .8 0.032 to .32 (4/4 to .64/4 (0.5 to .2 (16–256 (1 to 2 0.25 to 16 (0.5 to 2 (8 to .32 (2 to .8 1 to .32 (1 to .8 (1 to .8 0.032 to .32 (4/4 to .64/4 (0.5 to .2 (16 to 256 (1 to .2 0.125 to 8 MIC50 1 32 4 32 .8 .8 8 .64/4 .2 (16 (1 2 1 32 4 32 .8 .8 8 .64/4 .2 (16 (1 2 1 (8 8 32 (1 (1 0.5 .64/4 .2 (16 (1 1 1 16 2 32 .8 .8 32 .64/4 2 32 (1 2 MIC90 2 .32 .8 .32 .8 .8 .32 .64/4 .2 128 .2 4 2 .32 .8 .32 .8 .8 .32 .64/4 .2 256 .2 4 2 .32 .8 .32 .8 .8 16 .64/4 .2 32 (1 2 1 .32 4 32 .8 .8 .32 .64/4 .2 128 (1 4 Microorganism All Klebsiella pneumoniae Escherichia coli Enterobacter spp Antimicrobial agent Plazomicin Amikacin Gentamicin Tobramycin Imipenem Meropenem Doripenem Piperacillin-Tazobactam Ciprofloxacin Fosfomycin w/G6P Colistin Tigecycline Plazomicin Amikacin Gentamicin Tobramycin Imipenem Meropenem Doripenem Piperacillin to Tazobactam Ciprofloxacin Fosfomycin w/G6P Colistin Tigecycline Plazomicin Amikacin Gentamicin Tobramycin Imipenem Meropenem Doripenem Piperacillin-Tazobactam Ciprofloxacin Fosfomycin w/G6P Colistin Tigecycline Plazomicin Amikacin Gentamicin Tobramycin Imipenem Meropenem Doripenem Piperacillin-Tazobactam Ciprofloxacin Fosfomycin w/G6P Colistin Tigecycline (8, .16 (2, .4 (2, .4 (2, .8 (2, .8 (1, .4 (8, .16 (0.5, .1 (32, .32 (2, .2 (1, .2 (8, .16 (2, .4 (2, .4 ((2, .8 (2, .8 (1, .4 (8, .16 (0.5, .1 (32, .32 (2, .2 (1, .2 (8, .16 (2, .4 (2, .4 (2, .8 (2, .8 (1, .4 (8, .16 (0.5, .1 (32, .32 (2, .2 (1, .2 (8, .16 ((2, .4 (2, .4 (2, .8 (2, .8 (1, .4 (8, .16 (0.5, .1 (32, .32 (2, .2 (1, .2 192 Journal of Chemotherapy 2012 VOL. 24 NO. 4 17.7 37.3 6.7 24.7 30.3 18.3 3.7 10.0 56.0 77.7 32.0 10.8 34.0 3.7 21.6 23.2 12.9 0.4 4.6 53.5 73.0 25.7 54.5 30.3 21.2 54.4 78.8 60.6 30.3 30.3 84.8 100 69.7 34.6 76.9 15.3 15.4 34.6 15.4 0.0 34.6 42.3 92.3 42.3