BACTERICIDAL EFFECTS OF CHLOROQUINE ON ESCHERICHIA COLI : The effects of chloroquine on the viability of growing and non-growing Escherichia co1i in a MOPS (3-(N-Morpholino)-propanesulphonic acid) buffered medium, and its effect on thymidine utilisation

BACTERICIDAL EFFECTS OF CHLOROQUINE ON ESCHERICHIA COLI : The effects of chloroquine on the viability of growing and non-growing Escherichia co1i in a MOPS (3-(N-Morpholino)-propanesulphonic acid) buffered medium, and its effect on thymidine utilisation

Abstract:

The bactericidal effects of chloroquine on growing and nongrowing cells of Escherichia coli NCTC 1093 were investigated under controlled experimental conditions in a MOPS buffered minimal salts medium. Changes in cell mass and viable cell numbers were determined by measurements of absorbance at 600nm, and by viable cell counts respectively. At pH 7.4, the approximate minimum bactericidal concentration of chloroquine for the organism was 1.0 x 10-3M. This concentration caused about 3 log cycles of kill within 2 hours, with an initial short lag before kill commenced. Variation in the drug concentration up to a ten-fold increase had no significant effect en the rate of kill, although the time of maintenance of that rate was increased. In nongrowing (glucose-starved) cells treated with the same drug concentrations, however, there was virtually no loss in viability for at least 3 hours, except with the highest drug concentration used. Removal of glucose from cultures treated with chloroquine did not appear to affect bactericidal activity. The effect of pH on the action of chloroquine was also examined. A four-fold increase in activity was observed with increase in pH from 6.7 to 7.7, and calculations indicated that both the monoprotonated and diprotonated forms of chloroquine were biologically active, but that the diprotonated form was only l/25th as effective as the monoprotonated Cellular uptake studies of chloroquine by a direct method, using C-labelled chloroquine suggested a biphasic uptake process, a rapid initial passive uptake followed by a slower active one. The latter apparently did not occur in the absence of glucose. The effect of the drug on the utilisation of thymidine by E. coli cells was investigated. Chloroquine rapidly and strongly inhibited both the uptake and incorporation of 14C-thymidine into the cells, and caused a breakdown of preformed DNA. This work establishes the bactericidal action of chloroquine against growing cells of E. coli, and indicates that its antibacterial activity has some similarity to the phenomenon of thymineless death

BACTERICIDAL EFFECTS OF CHLOROQUINE ON ESCHERICHIA COLI : The effects of chloroquine on the viability of growing and non-growing Escherichia co1i in a MOPS (3-(N-Morpholino)-propanesulphonic acid) buffered medium, and its effect on thymidine utilisation