TABLE 1.

Densities of viable bacteria at three different times

AntibioticaMIC (μg/ml)Range of densities of viable bacteriab (CFU/ml) at:
0 h4 h24 h
None (control)3.1 × 105-1.1 × 1062.8 × 108-6.7 × 1082.3 × 109-3.6 × 109
CIP0.0084.2 × 105-1.0 × 1062.9 × 103-9.4 × 1031.0 × 101-1.3 × 104
AMP1.54.2 × 105-1.0 × 1062.4 × 103-1.1 × 1040-5.0 × 101c
RIF83.1 × 105-1.1 × 1061.1 × 103-4.1 × 1041.0 × 103-8.0 × 103
STR23.1 × 105-1.1 × 1060-3.7 × 103d0-8.4 × 108e
TET23.1 × 105-1.1 × 1061.9 × 104-3.8 × 1040-7.0 × 103c
  • a Abbreviations: CIP, ciprofloxacin; AMP, ampicillin; RIF, rifampin; STR, streptomycin; TET, tetracycline.

  • b Estimated range of densities of viable bacteria initially (0 h) and at 4 and 24 h in 10-ml cultures of E. coli CAB1 with different antibiotics (n = 10 per drug) and in antibiotic-free controls (n = 3). Antibiotic concentrations were as follows: 0.0625 μg/ml for ciprofloxacin and 24 μg/ml for ampicillin, rifampin, streptomycin, and tetracycline.

  • c Nine cultures had viable cells (>101), and for one culture, no colonies were obtained by plating 0.1 ml on LB agar.

  • d Nine cultures had more than 103 viable cells, and for one culture, no colonies were obtained by plating 0.1 ml on LB agar.

  • e Two cultures had high densities of viable cells (>108), and for eight cultures, no colonies were obtained by plating 0.1 ml on LB agar.