抄録
Antimicrobial actions of p-hydroxybenzoate alkyl esters (parabens) and two formalin derivatives, Quarternium 15 (Q15) and imidazolidinyl urea (IDU), which are commonly used in cosmetics and toiletries as preservatives or bactericides, were evaluated against Klebsiella pneumoniae using a technique of microbial calorimetry. With parabens, which are known to have bacteriostatic actions, increased concentrations caused changes in the growth thermograms of the microorganism characterized by a suppression in the slopes at the exponential growth phase. In contrast, with Q15 and IDU, which are known to have rather strong bactericidal effects the growth thermograms shifted toward a longer incubation time in proportion to the drug concentration while their shapes were unchanged. These two types of actions were compared in terms of two indexes: the changes in the growth rate constant and in the apparent growth retardation. In the case of bacteriostatic drugs such as parabens, antimicrobial actions resulted in the growth retardation due to the lowering of the growth rate constant. In contrast, bactericidal drugs such as formalin preservatives did not affect the growth rate constant and caused only an apparent retardation in growth. The observed difference in the change of growth thermogram patterns is discussed in terms of a difference in the two drug potency curves drawn on the basis of the two indexes.
