TABLE 3.

Bactericidal activities of various antibiotics, DNase I, or each antibiotic together with DNase I against bacteria in 24-h-old biofilms

Treatment (n = 3)Bacterial count (log10 CFU/well)a
A. baumanniiH. influenzaeK. pneumoniaeE. coliP. aeruginosaS. aureusS. pyogenes
Control8.32 ± 0.308.46 ± 0.658.67 ± 1.308.92 ± 0.558.71 ± 0.659.83 ± 0.518.32 ± 1.58
DNase I8.34 ± 0.208.41 ± 0.258.60 ± 1.118.37 ± 0.478.58 ± 0.90*9.80 ± 0.45*8.24 ± 1.10
Ampicillin8.29 ± 0.158.44 ± 0.308.33 ± 1.008.55 ± 0.77*8.62 ± 1.009.51 ± 0.40*8.16 ± 0.77
Ampicillin + DNase I7.30 ± 0.11**7.34 ± 0.41**7.37 ± 0.50**7.27 ± 0.28**7.48 ± 1.34**8.60 ± 1.09**7.18 ± 0.81
Cefotaxime8.32 ± 0.268.45 ± 0.438.54 ± 0.978.66 ± 0.818.68 ± 0.409.67 ± 0.36*8.20 ± 0.25
Cefotaxime + DNase I7.26 ± 0.10**7.38 ± 0.20**7.53 ± 0.77**7.51 ± 0.97**7.38 ± 0.72**8.20 ± 0.55**6.70 ± 1.00**
Levofloxacin8.26 ± 0.158.25 ± 0.658.62 ± 0.878.46 ± 0.76*8.69 ± 1.157.39 ± 0.35*6.39 ± 0.40
Levofloxacin + DNase I6.76 ± 1.52**6.78 ± 0.77**7.28 ± 0.62**6.75 ± 1.36**6.60 ± 0.52**6.35 ± 0.64**5.31 ± 0.65**
Rifampin8.15 ± 0.418.14 ± 0.55*8.50 ± 0.758.58 ± 0.73*8.56 ± 0.657.50 ± 0.41*6.44 ± 0.55
Rifampin + DNase I6.68 ± 1.05**6.79 ± 1.687.18 ± 0.68**7.19 ± 0.61**6.38 ± 1.25**6.60 ± 1.07**5.65 ± 1.93**
AzithromycinND***8.14 ± 0.89NDNDND9.75 ± 1.068.24 ± 0.68
Azithromycin + DNase IND7.19 ± 0.36NDNDND9.19 ± 0.87**8.10 ± 0.43**
  • a Viable cells (log10 CFU/well) were measured after 24 h of growth in the presence of antibiotic at 50 times the MIC or DNase I (5 μg/ml), or both, as described in Materials and Methods. The results are the means ± standard errors of the means from three independent experiments, with viable counts done in triplicate. *, significantly different from the corresponding value for the control (P < 0.05); all other values are not significantly different; **, significantly different from the corresponding value for the antibiotic-treated biofilms (P < 0.05); all other values are not significantly different; ND, not done.