The present study is planned to verify the microbiological and the clinical efficacy of a 28-day treatment period with prulifloxacin 600 mg in comparison with 28-day treatment period with levofloxacin 500 mg, both administered once daily, in patients with CBP. Safety and tolerability of a 28-day treatment period with prulifloxacin 600 mg will be also evaluated in comparison to levofloxacin 500 mg.