Colistin-resistant isolates of Klebsiella pneumoniae emerging in intensive care unit patients:: first report of a multiclonal cluster

Objectives: Infections due to multidrug-resistant (MDR) Gram-negative pathogens in the ICU have prompted the use of colistin, an antibiotic forgotten for decades. The aim of this retrospective observational study was to record and present the emergence of colistin-resistant Klebsiella pneumoniae (CRKB) in a Greek ICU. Methods: In a new university tertiary hospital, the first patients admitted in the ICU were already colonized or infected with MDR pathogens, and this led to frequent colistin use as part of empirical or microbiological ly documented therapy. Colistin resistance was defined as MIC >4 mg/L by the Etest method. All CRKB isolated in surveillance cultures or clinical specimens in the ICU during the period 2004-5 were recorded along with patients' characteristics. Results: Eighteen CRKB were isolated from 13 patients over a 16 month period, representing either colonizing or infective isolates. Patients' mean age was 70 years, with a mean APACHE 11 score at admission of 22. They all had a long hospitalization (median 69 days) and a long administration of colistin (median 27 days). Colistin-resistant isolates were implicated as pathogens in two bacteraemias, a ventilator-associated pneumonia and two soft tissue infections. Repetitive extragenic palindromic PCR identified six distinct clones, and horizontal transmission was also documented. Conclusions: Selective pressure due to extensive or inadequate colistin use may lead to the emergence of colistin resistance among K. pneumoniae isolates, jeopardizing treatment options in the ICU, potentially increasing morbidity and mortality of critically ill patients and necessitating prudent use of colistin.