Physiological effects of metronidazole on Clostridium pasteurianum

The physiological effects of metronidazole on the growth, viability, fermentation end-product production and cellular morphology of Clostridium pasteurianum cells growing logarithmically were studied. Metronidazole (a 5-nitroimidazole) was found to be the most potent of the nitroimidazole compounds tested against C. pasteurianum. It inhibited the growth rate of C. pasteurianum cultures by varying degrees over a range of drug concentrations (2.5-10 mg/L). Metronidazole had an immediate bactericidal effect at a concentration of 10 mg/L, killing 99.9% of cells within 5 min of drug addition. The same concentration caused an immediate cessation of fermentation end-product (acetate and butyrate) production in these cultures. These observations may be relevant to a proposed cell lysing mechanism which may form an additional mode of action of this important antibiotic.