Fatty-acid profiles and expression of the fabM gene in a fluoride-resistant strain of Streptococcus mutans

Abstract

Objective: The aim of this study was to compare the membrane fatty acid profile and expression of the fabM gene in a fluoride-resistant Streptococcus mutans strain with those of its wild-type counterpart. Additionally, we aimed to investigate whether mutations were present in the fabM gene of the fluoride-resistant strain.

Design: A fluoride-resistant strain of S. mutans was obtained by step-by-step induction in vitro. The fluoride-resistant strain and its wild-type counterpart were grown anaerobically in a brain heart infusion broth, harvested and resuspended in a salt solution for an acid survival assay and a pH-drop experiment. The membrane fatty acid profile was determined by gas chromatography-mass spectrometry. Expression of the fabM gene was quantified by real-time PCR. The fabM gene was also sequenced.

Results: The ability of the fluoride-resistant strain to resist acid stress was greater than that of the wild-type strain. A significant difference in the amount of long-chain monounsaturated fatty acids between the fluoride-resistant strain and the wild-type strain was detected in acidic condition (P<0.01). In addition, the level of fabM mRNA in the fluoride-resistant strain was significantly higher than that of the wild-type strain in the acidic condition as well (P<0.01). However, the sequence of the fabM gene from the fluoride-resistant strain was 100% homologous with that from the wild-type strain.

Conclusions: The membrane fatty acid profile and expression of the fabM gene in the fluoride-resistant strain were altered compared to the wild-type strain in acidic conditions, but no differences were found in the sequence of the fabM gene.