RAPID PROCEDURE FOR ACID ADAPTATION OF ORAL LACTIC-ACID BACTERIA AND FURTHER CHARACTERIZATION OF THE RESPONSE

Acid-adaptive responses could be induced readily in oral lactic-acid b acteria by growing them in batch cultures with excess sugar or more co nveniently and rapidly by transferring cells to acidified growth media for the time required for biomass doubling. The response of Streptoco ccus mutans GS-5 was induced in a progressive rather than all-or-nothi ng way, and the extent of acid tolerance was inversely related to the pH of the inducing medium over a range from 8.5 to 5. The weak acids f luoride, acetate, or lactate did not measurably enhance acid adaptatio n, and so the response did not appear to depend primarily on changes i n Delta pH or the proton motive force across the cell membrane. Transc ription and translation to form new proteins did appear to be necessar y, as indicated by inhibition of adaptation by rifampin or chloramphen icol and by lack of adaptation by cells suspended in phosphate buffer at pH 5. Streptococcus salivarius and Lactobacillus casei were acid ad apted by the rapid method, and the method appeared to be generally use ful for oral lactic-acid bacteria. The rapid induction of the response in multiple oral lactic-acid bacteria suggests that it is of general importance for maintaining a diversity of organisms in the oral microb iota, which is regularly subjected to acid stresses.