Cell Wall-mediated Changes in Sensitivity of Bacillus megaterium to Chlorhexidine and 2-Phenoxyethanol, Associated with Growth Rate and Nutrient Limitation

The resistance of chemostat-grown cultures of Bacillus megaterium (asporogenous) to the bactericidal action of chlorhexidine and 2-phenoxyethanol varied with growth rate and nutrient-limitation. Phosphate-limited cultures (P-lim) showed little change in sensitivity to either drug with changes in growth rate. Magnesium-limited (Mg-lim) and carbon-limited (C-lim) cultures, however, increased in sensitivity to both agents as growth rate was increased from 0.13–0.45 h. Minimum lytic concentrations of the agents were not significantly different for protoplasts prepared from these suspensions except of Mg-lim when sensitivity to chlorhexidine increased with growth rate. Lysozyme sensitivity of the cells varied with growth rate and nutrient limitation. Results support the idea that in addition to other effects of growth rate and nutrient-limitation environmentally-induced changes in envelope structure and/or composition radically influenced penetration of these agents to their targets.