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International Journal of Microbiology
Volume 2012, Article ID 454065, 5 pages
Research Article

LiF Reduces MICs of Antibiotics against Clinical Isolates of Gram-Positive and Gram-Negative Bacteria

1Faculté de Médecine Vétérinaire, Université de Montréal, Saint-Hyacinthe, QC, Canada
2Département de Microbiologie-Immunologie, Université de Montréal, CRCHUM Hôpital Hôtel-Dieu de Montréal, 3840 rue St-Urbain, Montréal, QC, Canada H2W 1T8

Received 22 July 2011; Accepted 16 December 2011

Academic Editor: David C. Straus

Copyright © 2012 H. C. Syed and M. Ravaoarinoro. 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.


Antibiotic resistance is an ever-growing problem yet the development of new antibiotics has slowed to a trickle, giving rise to the use of combination therapy to eradicate infections. The purpose of this study was to evaluate the combined inhibitory effect of lithium fluoride (LiF) and commonly used antimicrobials on the growth of the following bacteria: Enterococcus faecalis, Staphyloccoccus aureus, Escherichia coli, Pseudomonas aeruginosa, Acinetobacter baumannii, Klebsiella pneumoniae, Serratia marcescens, and Streptococcus pneumoniae. The in vitro activities of ceftazidime, sulfamethoxazole-trimethoprim, streptomycin, erythromycin, amoxicillin, and ciprofloxacin, doxycycline, alone or combined with LiF were performed by microdilution method. MICs were determined visually following 18–20 h of incubation at 37°C. We observed reduced MICs of antibiotics associated with LiF ranging from two-fold to sixteen-fold. The strongest decreases of MICs observed were for streptomycin and erythromycin associated with LiF against Acinetobacter baumannii and Streptococcus pneumoniae. An eight-fold reduction was recorded for streptomycin against S. pneumoniae whereas an eight-fold and a sixteen-fold reduction were obtained for erythromycin against A. baumannii and S. pneumoniae. This suggests that LiF exhibits a synergistic effect with a wide range of antibiotics and is indicative of its potential as an adjuvant in antibiotic therapy.