We report a case of a 66-year-old male patient who presented with a lung abscess caused by Pseudomonas aeruginosa and concomitant bacteremia. The patient had been receiving chemoradiotherapy for lung cancer for four weeks before a fever suddenly developed. A blood culture returned positive for P. aeruginosa and computed tomography newly demonstrated a mass in the right lung, prompting the initiation of piperacillin/tazobactam (PIPC/TAZ) therapy. The pathogen acquired resistance to PIPC/TAZ after 12 days, requiring a switch to meropenem (MEPM). However, the organism was found to have become resistant to MEPM five days after the change in therapy. Treatment with ceftolozane/tazobactam (CTLZ/TAZ), a novel agent, was therefore begun, leading to a gradual improvement in the clinical course. CTLZ/TAZ therapy was continued for five weeks. Thereafter the patient was discharged and completed the 12-week therapy by taking levofloxacin orally for the following four weeks.
P. aeruginosa can rapidly acquire resistance to many kinds of antimicrobial agent. However, the present case demonstrated that P. aeruginosa may be less able to acquire resistance to CTLZ/TAZ even during long-term continuous therapy. CTLZ/TAZ can thus help improve the clinical course of an infection.