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Mechanisms of Action: Physiological Effects

AI-2/LuxS Is Involved in Increased Biofilm Formation by Streptococcus intermedius in the Presence of Antibiotics

Nibras A. Ahmed, Fernanda C. Petersen, Anne A. Scheie
Nibras A. Ahmed
Department of Oral Biology, Faculty of Dentistry, University of Oslo, Oslo, Norway
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  • For correspondence: nibrasayad@yahoo.com
Fernanda C. Petersen
Department of Oral Biology, Faculty of Dentistry, University of Oslo, Oslo, Norway
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Anne A. Scheie
Department of Oral Biology, Faculty of Dentistry, University of Oslo, Oslo, Norway
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DOI: 10.1128/AAC.00546-09
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  • FIG. 1.
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    FIG. 1.

    Biofilm formation by S. intermedius WT (continuous line), luxS mutant SI006 (dotted line), and luxS mutant SI006 supplemented with 0.8 nM DPD (interrupted line) following 12 h of incubation in the presence of sub-MICs of ampicillin (A), ciprofloxacin (B), and tetracycline (C). The data points represent mean values (n = 9) with the standard errors of the means. *, significant increase (P ≤ 0.05) in biofilm formation by S. intermedius WT (continuous line) but not luxS mutant SI006 (dotted line); OD530, optical density at 530 nm.

  • FIG. 2.
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    FIG. 2.

    Scanning electron microscopy images of biofilms of the S. intermedius WT (A), luxS mutant SI006 (B), and luxS mutant SI006 supplemented with 0.8 nM DPD (C) following 12 h of incubation in the absence of antibiotics (control) (panels 1) and in the presence of 0.04 μg/ml ampicillin (panels 2), 0.15 μg/ml ciprofloxacin (panels 3), or 0.08 μg/ml tetracycline (panels 4).

  • FIG. 3.
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    FIG. 3.

    Luminescence (ATP level) as a measure of metabolic activity in planktonic cell cultures determined by the BacTiter-Glo viability assay following 12 h of incubation of the S. intermedius WT (continuous line), luxS mutant SI006 (dotted line), and luxS mutant SI006 supplemented with 0.8 nM AI-2 (interrupted line) in the presence of sub-MICs of ampicillin (A), ciprofloxacin (B), and tetracycline (C). The data points represent mean values (n = 12) with the standard errors of the means. *, significantly higher (P≤ 0.05) ATP levels in the S. intermedius WT (continuous line) than in the luxS mutant SI006 (dotted line).

Tables

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  • TABLE 1.

    Biofilm CFU of S. intermedius WT, luxS mutant SI006, and DPD-supplemented luxS mutant SI006 cultured in medium with or without antibiotics at sub-MICs

    Drug and concn (μg/ml)CFU (105/ml)a
    WTSI006SI006 + DPD
    0.00 (control)402.9 (26.88)310.8 (17.10)413.7 (24.47)
    Ampicillin
        0.02486.2 (64.04)324.1 (25.43)459.5 (29.33)
        0.04621.6 (64.77)268.6 (28.65)686.0 (65.32)
        0.06894.7 (182.65)162.1 (36.63)819.2 (43.61)
    Ciprofloxacin
        0.10768.1 (42.63)324.1 (24.96)814.7 (47.58)
        0.15663.8 (36.30)333.0 (25.04)768.1 (44.00)
        0.20577.2 (32.39)131.0 (19.28)519.5 (36.40)
    Tetracycline
        0.05779.2 (61.02)333.0 (16.49)828.1 (25.83)
        0.07637.1 (66.99)253.1 (17.20)708.2 (53.33)
        0.10610.5 (76.86)108.8 (37.27)486.2 (48.24)
    • ↵ a Data are for six isolates of each strain and condition. Values in parentheses are standard errors of the means.

  • TABLE 2.

    CFU in planktonic cultures of S. intermedius WT, luxS mutant SI006, and DPD-supplemented luxS mutant SI006 cultured with or without antibiotics at sub-MICs

    Drug and concn (μg/ml)CFU (108/ml)a
    WTSI006SI006 + DPD
    Ampicillin
        0.00 (control)771.7 (35.14)798.3 (37.09)793.3 (42.40)
        0.0661.2 (4.01)41.8 (3.43)48.7 (55.06)
        0.0843.3 (3.45)16.4 (1.7)39.1 (6.31)
        0.1045.3 (6.72)10.3 (4.22)39.6 (6.31)
        0.1220.7 (1.79)8.5 (1.39)18.4 (2.48)
    Ciprofloxacin
        0.00 (control)756.9 (62.98)708.1 (47.64)768.6 (46.24)
        0.205.87 (0.52)2.60 (0.51)5.30 (0.21)
        0.255.14 (0.77)1.16 (0.26)4.72 (0.67)
        0.303.12 (0.38)0.74 (0.17)3.1 (0.37)
        0.352.6 (0.34)0.4 (0.13)2.3 (0.18)
    Tetracycline
        0.00 (control)791.7 (44.10)757.5 (80.14)790.8 (90.09)
        0.0861.9 (6.58)11.2 (2.88)38.4 (4.87)
        0.1044.5 (8.52)5.7 (1.16)25.2 (2.72)
        0.1232.0 (5.92)3.0 (0.94)16.3 (1.86)
        0.1524.2 (5.23)2.0 (0.73)10.1 (1.75)
    • ↵ a Data are for six isolates of each strain and condition. Values in parentheses are standard errors of the means.

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AI-2/LuxS Is Involved in Increased Biofilm Formation by Streptococcus intermedius in the Presence of Antibiotics
Nibras A. Ahmed, Fernanda C. Petersen, Anne A. Scheie
Antimicrobial Agents and Chemotherapy Sep 2009, 53 (10) 4258-4263; DOI: 10.1128/AAC.00546-09

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AI-2/LuxS Is Involved in Increased Biofilm Formation by Streptococcus intermedius in the Presence of Antibiotics
Nibras A. Ahmed, Fernanda C. Petersen, Anne A. Scheie
Antimicrobial Agents and Chemotherapy Sep 2009, 53 (10) 4258-4263; DOI: 10.1128/AAC.00546-09
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KEYWORDS

Anti-Bacterial Agents
Bacterial Proteins
biofilms
Carbon-Sulfur Lyases
Homoserine
Streptococcus intermedius

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