FIG 2.

Assessment of phenotypic adaptation. Enterobacter cloacae (MDA 166) showed a sustained 4-fold increase in MIC from passage 4 to 20. To determine whether the increase in MIC was due to induced resistance or phenotypic adaptation, the organism cultured in passage 20 was then exposed to Mueller-Hinton broth (MHB) without antimicrobial agents (no exposure to MIN, RIF, and CHX) and passaged for an additional 7 passages. MICs to MIN, RIF, and CHX were determined after each additional passage. After 3 passages without antimicrobial agents, the MIC returned to 2, indicating a phenotpyic adaptation to survival when exposed to MIN, RIF, and CHX.