title: The dlt genes play a role in antimicrobial tolerance of Streptococcus mutans biofilms.
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.
authors: Costerton Biofilm Centre, Department of Immunology and Microbiology, Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3B, Copenhagen DK-2200, Denmark.
authors: Martin
authors: M
authors: Nilsson
authors: Costerton Biofilm Centre, Department of Immunology and Microbiology, Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3B, Copenhagen DK-2200, Denmark.
authors: Morten
authors: M
authors: Rybtke
authors: 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.
authors: Michael
authors: M
authors: Givskov
authors: 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.
authors: Niels
authors: N
authors: Høiby
authors: Department of Odontology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
authors: Svante
authors: S
authors: Twetman
authors: 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.
authors: Tim
authors: T
authors: Tolker-Nielsen
mesh_terms: D000890:Anti-Infective Agents / Q000494:pharmacology*; D018441:Biofilms / Q000187:drug effects*; D019729:Carbon-Oxygen Ligases / Q000235:genetics / Q000378:metabolism*; D004251:DNA Transposable Elements; D004361:Drug Tolerance; D017353:Gene Deletion; D005816:Genetic Complementation Test; D005820:Genetic Testing; D016254:Mutagenesis, Insertional; D013295:Streptococcus mutans / Q000187:drug effects* / Q000235:genetics / Q000502:physiology*; D013682:Teichoic Acids / Q000378:metabolism
chemical_list: D000890:Anti-Infective Agents; D004251:DNA Transposable Elements; D013682:Teichoic Acids; D019729:Carbon-Oxygen Ligases
keywords: Antimicrobial tolerance; Biofilm; Gentamicin; Streptococcus mutans