The Influence of pH on the Antibacterial Action of Subtilin A

Abstract

SUMMARY: The influence of pH value on the antibacterial action of subtilin A has been demonstrated by survivor counts, inhibition of respiration, and pH gradient plates. Staphylococcus aureus is more sensitive to subtilin as the pH value increases ; Eschmichia coli is more sensitive as the pH value decreases. The results are analogous to those obtained by other investigators working with cationic detergents, and are consistent with the hypothesis that the basic surface-active antibiotics kill bacteria by the same general mechanism as do the quaternary ammonium germicides. A survey of the growth inhibition of other organisms on pH gradient plates indicates that Bacillus cereus behaves like S. aureus, while B. wgaterium, Corpebactem'um poinsettiae, and Streptococcus faecalis behave like E . coli.A pH/rnobility curve for subtilin A, obtained by paper electrophoretic studies, indicates no striking changes in the charge of the molecule over the pH range 4~9 , although the presence of at least one free a-amino group is indicated by inflexion points in the range of pH 6-7. The isoelectric point of subtilin A a t ionic strength 0.1 is approximately 6-7.The use of sectored, square-shaped Petri dishes for pH-gradient plate studies with germicides is described.

A note on pH gradient plates for fungal growth studies

“…The effects of antimicrobial agents can also be shown with pH gradient plates (Sacks & Pence 1958;Heifitz et a/. 1974).…”

“…shows the pH gradient determined for uninoculated plates after incubation for various intervals at 25°C. The plates are quite stable for up to 5 d, with maximal change at the pH extremes(Sacks 1956). Gradient plates are reproducible; pH determination on five different plates, 48 h after preparation on two separate days, showed an average standard deviation of 0.12 pH units at each grid centre.…”

“…1983) and preparation of numerous plates or flasks. A pH gradient agar plate (Sacks 1956) can be prepared simply by the addition of mono-or dibasic phosphate to two complementary agar wedges, providing a gradient with a pH range from about 5.6 to 7.8. Because of the limited pH range, pH gradient plates have only rarely been used in fungal studies (Darken 1962).…”

Origin of Antibacterial Activity of ZnO Nanoparticles: The Roles of Protonic and Electronic Conductions

“…However, the variation of antibacterial activity is observed by the change of dopant, indicating that the antibacterial activity is not mainly dominated by metal ion release. Sacks et al reported that the antibacterial activity can be improved by the increase of pH in the solution . Subsequently, it was also reported that the concentration of hydroxyl defect can be controlled by solid particles such as ZnO, MgO, and so on .…”