Growth temperature regulates the induction of beta-lactamase in Pseudomonas fluorescens through modulation of the outer membrane permeation of a beta-lactam-inducing antibiotic.

The psychrotrophic bacterium, Pseudomonas fluorescens strain MFO, is more sensitive to the beta-lactam mezlocillin at a low growth temperature (i.e. 8 degrees C) than at a higher growth temperature (28 degrees C). An early effect of this antibiotic at all temperatures is bacterial filamentation, but this occurs later at 8 degrees C than at 28 degrees C, which suggests a lower permeability of the cell envelopes to mezlocillin at low growth temperature. beta-Lactamase production is later induced by mezlocillin, but the level of this induction also depends on the growth temperature, the overall induction being much less efficient at 8 degrees C. It is hypothesized that the periplasmic concentration of the drug might be too low at 8 degrees C to allow efficient beta-lactamase induction; this hypothesis was confirmed by the demonstration that beta-lactamase production is drastically enhanced in cells cultivated at 8 degrees C permeabilized for 10 min by Na-EDTA. In addition, induction kinetic curves display a marked dependence upon growth temperature. A rapid saturation was evident when mezlocillin concentrations were increased at 8 degrees C; this was not seen at 28 degrees C at up to 1000 micrograms mezlocillin ml-1. The results are discussed in terms of two different routes of drug permeation, depending on the growth temperature.