PMC3020613_01
Susceptibility testing of Enterobacter cloacae to carbapenems. Both methods had ill-defined zones of inhibition with inner colonies growing up to the disks or the E-test strips, respectively.
03-0096-F1.jpg
PMC3020613_01_03-0096-F1.jpg
F1
By both disk diffusion and E-test methods (AB Biodisk, Solna, Sweden), the zones of inhibition around the imipenem, meropenem, and ertapenem disks were indistinct, with inner colonies extending up to the disk or the highest concentration on the E-test strip (MIC >32 mug/mL) and were interpreted as resistant (Figure 1).
Effect of addition of clavulanic acid (10 muL of 1,000 mug/mL) to the zones of inhibition of the three carbapenem disks. Top row (left to right): imipenem, meropenem, and ertapenem disks without clavulanic acid. Bottom row (left to right): imipenem, meropenem, and ertapenem disks with clavulanic acid.
03-0096-F2.jpg
PMC3020613_01_03-0096-F2.jpg
F2
Addition of 10 muL of 1,000 mug/mL clavulanic acid to the imipenem, meropenem, and ertapenem disks resulted in clearly defined and enlarged zones of inhibition and loss of the inner colonies (Figure 2).
Analytical isoelectric focusing (IEF) of serially diluted broth induced enzymes. The isoelectric points (pIs) of the two prominent bands midway and at the bottom of the gel are 6.9 and >9.0. Lanes 1-3: uninduced enzyme serially diluted 1:1, 1:2, and 1:4. Lanes 4-6: enzyme induced with 8 mug/mL of cefoxitin serially diluted 1:1, 1:2, and 1:4. Lanes 7-9: enzyme induced with 4 mug/mL of imipenem serially diluted 1:1, 1:2 and 1:4. Lane 10: NOR-1 control, induced with 16 mug/mL of cefoxitin.
03-0096-F3.jpg
PMC3020613_01_03-0096-F3.jpg
F3
AmpC and the pI 6.9 carbapenem-hydrolyzing enzyme, as visualized in Figure 3. A cefoxitin-induced preparation of E. cloacae NOR-1 (that produces NmcA) was included as a control strain for IEF.