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Int J Antimicrob Agents. 2016 Sep;48(3):298-304. doi: 10.1016/j.ijantimicag.2016.06.019. Epub 2016 Jul 28.

The dlt genes play a role in antimicrobial tolerance of Streptococcus mutans biofilms.

Author information

1
Costerton Biofilm Centre, Department of Immunology and Microbiology, Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3B, Copenhagen DK-2200, Denmark.
2
Costerton Biofilm Centre, Department of Immunology and Microbiology, Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3B, Copenhagen DK-2200, Denmark; Singapore Centre on Environmental Life Sciences Engineering, Nanyang Technological University, Singapore.
3
Costerton Biofilm Centre, Department of Immunology and Microbiology, Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3B, Copenhagen DK-2200, Denmark; Department of Clinical Microbiology, University Hospital, Rigshospitalet, Copenhagen, Denmark.
4
Department of Odontology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
5
Costerton Biofilm Centre, Department of Immunology and Microbiology, Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3B, Copenhagen DK-2200, Denmark. Electronic address: ttn@sund.ku.dk.

Abstract

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.

KEYWORDS:

Antimicrobial tolerance; Biofilm; Gentamicin; Streptococcus mutans

[Indexed for MEDLINE]

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