Clonal spread of imipenem-resistant Pseudomonas aeruginosa in the intensive care unit of a Turkish hospital

Pseudomonas aeruginosa may cause life-threatening infections, especially in nosocomial settings. Although carbapenems are considered as one of the mos t effective alternatives in antipseudomonal therapy, resistance to the carb apenem group of antibacterials is a growing problem. In the first 6 months of 1997, P. aeruginosa isolates that were resistant to almost all antipseud omonal agents including imipenem were recovered from various specimens from intensive care unit (ICU) patients. Isolates with the same antibiogram pro file caused a small outbreak in May 1997. A retrospective case-control stud y revealed that the major risk factors for infection/colonization with mult iresistant P. aeruginosa were prolonged stay in the ICU (p <0.001), previou s and lengthy imipenem. usage (p <0.001 and p <0.0001, respectively), and m echanical ventilation (p <0.001). Analytical isoelectric focusing of the so nicates prepared from the isolates showed that each isolate produced 1-5 be ta-lactamases, enzymes with isoelectric points (pIs) of 5.1, 6.4, 8.5-8.7 b eing the most prevalent. DNA macrorestriction patterns of imipenem-resistan t isolates were distinct from those of the imipenem-sensitive isolates reco vered from ICU patients during the same interval and from the environmental isolates (controls). Thus, our results indicate that colonized patients ap pear to be the major source for cross-contamination of other patients and i f imipenem is selected for empirical therapy, emergence of resistant strain s should be anticipated and appropriate precautions taken.