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Infectious Diseases in Obstetrics and Gynecology
Volume 9, Issue 1, Pages 41-45

Effect of Metronidazole on the Growth of Vaginal Lactobacilli in vitro

1Department of Obstetrics and Gynecology, Rush-Presbyterian-St. Luke’sMedical Center, 1653 W. Congress Pkwy, 720 Pav., Chicago, IL 60612, USA
2Department of Obstetrics and Gynecology, State University of Campinas (Unicamp), Sao Paulo, Brazil

Received 27 October 2000; Accepted 15 November 2000

Copyright © 2001 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Objective: To determine whether metronidazole has an adverse effect on the growth of Lactobacillus.

Methods: Hydrogen peroxide- and bacteriocin-producing strains of Lactobacillus were used as test strains. Concentrations of metronidazole used ranged from 128 to 7000 μg/ml. Susceptibility to metronidazole was conducted by the broth microdilution method recommended by the National Committee for Clinical Laboratory Standards.

Results: Growth of Lactobacillus was partially inhibited at concentrations between 1000 and 4000 μg/ml (p = 0.014). Concentrations ≥ 5000 μg/ml completely inhibited growth of Lactobacillus. Concentrations between 128 and 256 μg/ml stimulated growth of Lactobacillus (p = 0.025 and 0.005, respectively). Concentrations of metronidazole between 64 and 128 μg/ml or ≥ 512 μg/ml did not have an inhibitory or a stimulatory effect on the growth of Lactobacillus compared to the control.

Conclusions: High concentration of metronidazole, i.e. between 1000 and 4000 μg/ml, partially inhibited the growth of Lactobacillus. Concentrations ≥ 5000 μg/ml completely suppressed the growth of Lactobacillus. Concentrations between ≥ 128 and ≤ 256 μg/ml stimulated the growth of Lactobacillus. Further investigation to determine the ideal concentration of metronidazole is needed in order to use the antimicrobial agent effectively in the treatment of bacterial vaginosis.