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The dlt genes play a role in antimicrobial tolerance of Streptococcus mutans biofilms
- Nilsson, Martin, Rybtke, Morten, Givskov, Michael, Høiby, Niels, Twetman, Svante, Tolker-Nielsen, Tim
- International journal of antimicrobial agents 2016 v.48 no.3 pp. 298-304
- Streptococcus mutans, biofilm, confocal laser scanning microscopy, drugs, genes, gentamicin, glass, minimum inhibitory concentration, mutants, plankton, screening, teichoic acids, transposons
- Microbial biofilms are tolerant to antibiotic treatment and therefore cause problematic infections. Knowledge about the molecular mechanisms underlying biofilm-associated antimicrobial tolerance will aid the development of antibiofilm drugs. Screening of a Streptococcus mutans transposon mutant library for genes that are important for biofilm-associated antimicrobial tolerance provided evidence that the dlt genes play a role in the tolerance of S. mutans biofilms towards gentamicin. The minimum bactericidal concentration for biofilm cells (MBC-B) for a dltA transposon mutant was eight-fold lower than that of the wild-type. The minimum bactericidal concentration for planktonic cells (MBC-P) was only slightly reduced, indicating that the mechanism involved in the observed antimicrobial tolerance has a predominant role specifically in biofilms. Experiments with a knockout dltA mutant and complemented strain confirmed that the dlt genes in S. mutans play a role in biofilm-associated tolerance to gentamicin. Confocal laser scanning microscopy analyses of biofilms grown on glass slides showed that the dltA mutant produced roughly the same amount of biofilm as the wild-type, indicating that the reduced antimicrobial tolerance of the dltA mutant is not due to a defect in biofilm formation. The products of the dlt genes have been shown to mediate alanylation of teichoic acids, and in accordance the dltA mutant showed a more negatively charged surface than the wild-type, which likely is an important factor in the reduced tolerance of the dltA mutant biofilms towards the positively charged gentamicin.