TABLE 3

MIC90s of rifampin, mupirocin, azithromycin, fusidic acid, meropenem, aztreonam, retapamulin, and clarithromycin in the presence or absence of SPR741 against clinical and MDR isolate panels

BacteriumAntibioticSPR741 concn (μg/ml)No. of strains includedaMIC (μg/ml)Potentiation factorb (MIC90)
MIC50MIC90Range
E. coliRifampin02516>1284–>128
2200.0160.060.004–8>2,048
Mupirocin025128>12832–>128
220120.5–32>64
Azithromycin02581281–>128
2200.12520.03–864
Fusidic acid025>128>128>128
2200.12520.25–8>64
Meropenem0250.01540.002–64
2190.01640.001–321
Aztreonam025161280.016–>128
2190.5160.004–648
Retapamulin0258164–16
2190.060.50.03–132
Clarithromycin02516328–>128
2190.25320.016–321
K. pneumoniaeRifampin025163216–>128
2254160.125–642
8240.520.0616
Mupirocin025128>12832–>128
22516640.5–32>2
8248321–32>4
Azithromycin02532>1284–128
225128>1284–>1281
824280.125–16>16
Fusidic acid025>128>128>128
225128>1284–>1281
82416641–64>2
Meropenem0254640.016–64
225161280.03–1280.5
8248320.03–1282
Aztreonam0251281280.125–128
2251281280.016–1281
8241281280.06–1281
Retapamulin0256412816–128
2254321–1284
824140.125–432
Clarithromycin02564>12832–>128
22516640.25–64>2
8241320.06–64>4
A. baumanniiRifampin017241–4
2160.030.060.016–0.12564
8100.0080.0160.002–0.03256
Mupirocin017>128>12864–>128
2166412816–128>2
81016322–32>8
Azithromycin017480.25–>128
2160.510.03–648
8100.50.50.03–0.516
Fusidic acid017128>12832–>128
216120.5–4>64
8100.250.50.125–1>256
Meropenem01741280.06–128
216180.06–1616
890.50.50.03–0.5256
Aztreonam017326416–64
2168162–164
810121–432
Retapamulin017641281–128
216180.25–816
890.540.5–432
Clarithromycin0178160.125–64
2160.1250.50.03–432
890.0310.016–116
  • a The growth of several strains in the panel was inhibited by 8 μg/ml SPR741, and so the number of strains included in the analysis under these conditions was reduced.

  • b Fold reduction in the MIC90 in the presence of SPR741 relative to the MIC90 in the absence of SPR741.