Effects of antibiotics at sub-minimal inhibitory concentrations on the morphology of Streptococcus mutans and Lactobacillus acidophilus

Abstract

Sub-minimal inhibitory concentrations (sub-MICs) of antibiotics may have significant impact on the morphology and biochemical characteristics of target bacteria. This study aimed to examine the morphological changes to sub-MICs of antibiotics observed in bacterial cells from Gram-positive oral species, Streptococcus mutans and Lactobacillus acidophilus. The MICs for both amoxicillin and doxycycline were determined by broth dilution method. Individual cells of S . mutans increased in length after incubation with sub-MIC of amoxicillin, whereas its chain length increased in response to a sub-MIC of doxycycline. The lengths of individual bacterial cells of L. acidophilus decreased after incubation with sub-MICs of either amoxicillin or doxycycline. These results of suggest that sub- MICs of amoxicillin and doxycycline induce morphological changes in both S. mutans and L. acidophilus. Further studies are required to determine the significance of these findings for host-pathogen interactions and development of dental diseases.