Table 1.

Antimicrobial susceptibilities, the presence of OprD,mexR mutations, and AmpC β-lactamase activity of P. aeruginosa isolates

Groupa and isolate no.MICb (μg/ml) of:Presence of OprDMutations inmexR genecAmpC enzyme activityd (U/mg of protein)PCRRibotypee
IPMMEMCARPIPCAZATMAMKCIPTET
PAO110.564421<20.250.5
Group 1
 531616>2566416646432170,1261871
 591616>256328326432170,1261552
 6016162563216646432170,126842
 Median1616>25648164864321
Group 2
 682128323226416<0.5353
 438464411160.25<0.5114
 4684>25641240.06<0.5285
 5144128324451216<0.5126416
 581646442481<0.5126277
 77168643216880.130.5247
 153882561648256160.5126478
 Median841281644161<0.5
Group 3
 4588>256256161651216<0.51261316
 73168128256321651216<0.5126992
 7488>2562563232512160.51261032
 7588256128161612816<0.5126722
 81168256128321620.250.51261186
 156161625625632165123211261559
 Median128256256321651216<0.5
Group 4
 1162>256256321616486313
 5164>256>256321616281262,1053
 9164>25625632864241262,7083
 1084>256256323232285,4363
 11164>256256328160.581263,5603
 52816>2562563232320.2512854910
 7616864256321620.125<0.53349
 79168>256>2566432816321263,0609
 80882561281681288<0.51261806
 82161625612832168160.59479
 8316812864321632160.520911
 Median168>25625632161628
Group 5
 420.50.525632441610.5+5312
 5712>256>256328161616+1261,42213
 7211>25625664326412864+1268114
 7810.256442440.125<0.5+23
 15110.5128648451216<0.5+162
 Median10.5256648416160.5
Group 6
 4168>25632>25612816160.5NDh3
 41816128256161651216126NDOXA-10f1
 448425632324322<0.5126ND15
 71162>25632256161280.0632NDOXA-1016
 8588>256>25632166432126NDPSEg17
 152882562563216256160.5126NDOXA-102
 1548162561283216>51216512126NDOXA-102
 1551616256256321625616512126NDOXA-102
 157168>256>25616425616126NDPSE17
 15888>256>25616812816126NDPSE9
 159846412816440.50.5NDOXA-109
 160162>256256168324126NDPSE18
  • a The isolates which belonged to each group had the following characteristics: group 1, OprD loss, MexAB-OprM overexpression (+), AmpC β-lactamase production (+); group 2, OprD loss, group 3, OprD loss, AmpC production 2- to 5-fold higher than PAO1; group 4, OprD loss, AmpC production >5-fold higher than PAO1; group 5, OprD (+); group 6, OprD loss, production of secondary β-lactamases.

  • b IPM, imipenem; MEM, meropenem; CAR, carbenicillin; PIP, piperacillin; CAZ, ceftazidime; ATM, aztreonam; AMK, amikacin; CIP, ciprofloxacin; TET, tetracycline.

  • c 70, The amino acid substitution of Arg (CGG) for Gln (CAG) at amino acid 70; 126, Val (GAG) → Glu (GTG) change at amino acid 126.

  • d 1 U = 1 nmol of nitrocefin hydrolyzed/min at 37°C and at pH 7.0. The β-Lactamase activity of PAO1 was 35 U/mg of protein.

  • e Genomic DNAs of the isolates were restricted by PvuII.

  • f pI value of 6.1 on IEF and positive in OXA-10-specific PCR.

  • g pI value of 5.6 on IEF and positive in PSE-specific PCR.

  • h ND, not done.