Pseudomonas aeruginosa susceptible only to colistin in intensive care unit patients.

Background: Gram-negative bacilli, including multi-drug-resistant (MDR) Pseudomonas aeruginosa, are responsible for severe intensive care unit (ICU)-acquired infections, mainly pneumonia and bacteremia. The aim of this study was to determine the incidence of MDR strains of Pseudomonas in patients undergoing cardiac surgery, to elucidate the effectiveness of treating these patients with colistin, and to assess the safety of the drug.

Methods: A prospective study was conducted among 1,452 patients who underwent surgery for a variety of cardiac lesions over a one-year period, and who spent a portion of the recovery period in the surgical ICU. Their case histories were analyzed to identify infectious complications. Diagnosis of infection was based on clinical data, and the pathogen was tested with respect to its susceptibility to colistin (polymyxin E). The clinical response to the antibiotic was evaluated.

Results: Over the 12-month period, among 115 infected patients, 15 were affected by strains of P. aeruginosa. In 10 patients, this pathogen proved resistant to all potentially active antibiotics except colistin. All of the affected patients were being ventilated mechanically, and eight of them presented with ventilator-associated pneumonia (VAP), whereas one patient suffered a deep incisional surgical site infection and bacteremia and the remaining patient had a superficial infection of a lower-extremity vein graft donor site. The MDR pathogen was introduced to the hospital by three patients transferred from three institutions. All patients were treated with intravenous colistin. In cases of VAP, aerosolized colistin was added. Deterioration of renal function occurred in three patients (30%), all of whom had a history of renal insufficiency. Cure or clinical improvement was observed in seven patients (70%), whereas four patients, including one who improved initially, developed sepsis and died with multiple organ dysfunction syndrome (mortality rate 40%).

Conclusions: The increasing prevalence of MDR P. aeruginosa in ICU patients has rekindled interest in polymyxins, which had been abandoned because of toxic side effects. Colistin retained significant in vitro activity against this virulent organism, had an acceptable safety profile, and should be considered as a treatment option in critically ill patients with infection caused by MDR gram-negative bacilli. Aerosolized colistin may merit further consideration as a therapeutic intervention for patients with refractory pulmonary infections.