TABLE 1.

Killing of K. pneumoniae by ampicillin (5,000 μg/ml) and ciprofloxacin (1.8 μg/ml) after 4 h of exposurea

StrainInoculumMediumLog reduction in no. of viable cells
ControlAmpicillinCiprofloxacin
Kp1Exponential-phase cultureComplete−0.77 ± 0.484.43 ± 0.664.14 ± 0.57
Stationary-phase cultureGlucose and nitrogen omitted−0.25 ± 0.30−0.21 ± 0.401.80 ± 0.28
Exponential-phase cultureGlucose and nitrogen omitted−0.424.542.17
Stationary-phase cultureComplete−0.923.012.69
Exponential-phase cultureSpent medium−0.814.692.92
Exponential-phase cultureSpent medium, glucose and nitrogen added−0.895.054.66
Resuspended biofilmComplete−2.502.27 ± 0.673.94
Resuspended biofilmGlucose and nitrogen omitted0.790.65 ± 0.621.26 ± 0.51
Resuspended antibiotic-treated biofilmComplete−0.604.053.30
Kp102Exponential-phase cultureComplete−1.484.62NDb
Kp1Intact biofilmComplete−0.11 ± 0.13−0.06 ± 0.081.02 ± 0.06
Kp102Intact biofilmComplete−0.19 ± 0.130.12 ± 0.140.90 ± 0.17
  • a The data are log reductions in viable-cell numbers. When three or more replicates were performed, the standard error of the mean is reported. All of the experiments were performed in batch suspension culture tests except for the intact biofilm data reported in the last two rows.

  • b ND, not determined.