Interaction of insulin with Burkholderia pseudomallei may be caused by a preservative

Abstract

Aim: To re-examine the previously reported in vitro interaction of insulin with Burkholderia pseudomallei, in the light of a suggestion that the interaction may have resulted from the presence of the preservative m-cresol in commercial preparations.

Methods: Broth culture studies of B pseudomallei were performed with and without the addition of m-cresol and various preparations of insulin.

Results: Growth of B pseudomallei was inhibited by m-cresol at the concentrations found in pharmaceutical insulin preparations, and by the insulin preparation Humulin R, but not by pure insulin.

Conclusions: The results of previous experiments may have been confounded by the presence of the preservative m-cresol.

Figure 1 Cumulative percentage of Burkholderia pseudomallei isolates (n = 100) susceptible to increasing concentrations of m-cresol.

Figure 2 Effects of different concentrations of m-cresol on growth of Burkholderia pseudomallei.

Figure 3 Optical densities during growth of Burkholderia pseudomallei in the presence of insulin or m-cresol. (Error bars represent 95% confidence intervals.)