SUSCEPTIBILITY OF AGAR-ENTRAPPED ESCHERICHIA-COLI CULTURES TO CEFOTAXIME AS ASSESSED BY THE POTENTIOMETRIC MEASUREMENT OF LIPOIC ACID REDUCTION

We used an original potentiometric procedure to monitor the metabolic activity of biofilm-like structures and to assess their susceptibility to betalactam antibiotics. The reduction of exogeneous alpha-lipoic a cid to dihydrolipoic acid by planktonic and agar-entrapped bacteria, m etabolizing glucose, was followed by potential-time measurements using gold versus reference electrodes. Immobilized cultures displayed a lo wer susceptibility to cefotaxime than their free counterparts. The red ox potential-time courses showed that the gel matrix was more rapidly oxygen depleted than the free-cell culture medium. The depletion of bo th glucose and dissolved O2 inside the gel induced a breakdown in the reducing activity of agar-entrapped organisms.