The effects of βbT‐lactams on the isoelectric focusing of βbT‐lactamases

Abstract

A range of concentrations of ceftazidime (4–64 mg I‐1) was shown to cause no induction of the TEM‐1 and TEM‐5 β‐lactamases produced by Escherichia coli Nb. Increasing the concentration of ceftazidime in cultures of E. coli Nb caused a concomitant increase in the intensity of a satellite band of pI 5.2. The same increase in this satellite band was observed when ceftazidime was added to cell‐free β‐lactamase peparations from E. coli Nb and the separate addition of 11 different β‐lactams to TEM‐1 showed that each compound produced its own unique pattern of satellite bands. In addition, the mixing of ceftazidime with TEM‐1 and 13 other TEM‐derived β‐lactamases caused a similar satellite band to be observed but ceftazidime did not have the same effect on PSE or SHV β‐lactamases. Consequently, the addition of ceftazidime to a β‐lactamase preparation prior to isoelectric focusing (IEF) may help to verify if a particular β‐lactamase is TEM‐derived. Purification of the satellite bands by electrodialysis and their subsequent re‐focusing demonstrated that the ceftazidime‐induced satellite bands can revert to a protein which has a pI similar to the parent band, illustrating the possible reversibility and dynamic nature of β‐lactamase satellite bands on IEF. These results enable a better interpretation to be made of β‐lactamase satellite bands observed on IEF.