Effects of weak acids, UV and proton motive force inhibitors on pyrazinamide activity against Mycobacterium tuberculosis in vitro.
BACKGROUND
Pyrazinamide is a paradoxical frontline tuberculosis drug characterized by high sterilizing in vivo activity but poor in vitro activity. Pyrazinamide is thought to act by the entrapment of pyrazinoic acid in the bacterial cell, leading to acidification and membrane damage. Consequently, the effects of weak acids and molecules affecting membranes added to pyrazinamide were studied.


OBJECTIVE
To examine the effects of weak acids, UV, oxidative stress and additional energy inhibitors on pyrazinamide activity in vitro against Mycobacterium tuberculosis as well as the effect of pyrazinamide on Escherichia coli ampicillin persisters.


METHODS
Drug exposure experiments followed by cfu counts were performed to determine the effects of the above various factors on pyrazinamide activity in vitro against M. tuberculosis.


RESULTS
Some weak acids such as benzoic acid, sorbic acid and propyl hydroxybenzoic acid could enhance the activity of pyrazinamide in vitro against old tubercle bacilli but not young bacilli whereas other weak acids such as salicylic acid and lactic acid did not appear to enhance pyrazinamide activity. While energy inhibitors carbonylcyanide m-chlorophenylhydrazone and dinitrophenol enhanced pyrazinamide activity for old tubercle bacilli but not young bacilli, valinomycin and KCN increased pyrazinamide activity for both young and old bacilli. Oxidative stresses due to H2O2 and menadione did not have a significant effect on pyrazinamide activity. UV, which presumably damages the membrane, enhanced the activity of pyrazinamide. Pyrazinamide, which otherwise has no activity against actively growing E. coli bacteria, could kill non-growing starved E. coli and also ampicillin-tolerant persisters.


CONCLUSIONS
Some weak acids, UV and various energy inhibitors were found to enhance the activity of pyrazinamide in vitro against M. tuberculosis. Pyrazinamide shows preferential activity against both M. tuberculosis and E. coli persisters over the growing forms.
Wade
Mary Margaret
MM
Department of Molecular Microbiology and Immunology, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, MD 21205, USA.
Zhang
Ying
Y
D000667:Ampicillin / Q000494:pharmacology; D000995:Antitubercular Agents / Q000494:pharmacology*; D002264:Carboxylic Acids / Q000494:pharmacology*; D004249:DNA Damage / Q000502:physiology; D004357:Drug Synergism; D004926:Escherichia coli / Q000187:drug effects; D008826:Microbial Sensitivity Tests; D009169:Mycobacterium tuberculosis / Q000187:drug effects* / Q000378:metabolism / Q000528:radiation effects*; D018384:Oxidative Stress / Q000502:physiology; D018892:Proton-Motive Force / Q000187:drug effects*; D011718:Pyrazinamide / Q000494:pharmacology*; D014466:Ultraviolet Rays
D000995:Antitubercular Agents; D002264:Carboxylic Acids; D011718:Pyrazinamide; D000667:Ampicillin