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 most effective alternatives in antipseudomonal therapy, resistance to the carbapenem group of antibacterials is a growing problem. In the first 6 months of 1997, P. aeruginosa isolates that were resistant to almost all antipseudomonal agents including imipenem were recovered from various specimens from intensive care unit (ICU) patients. Isolates with the same antibiogram profile caused a small outbreak in May 1997. A retrospective case-control study revealed that the major risk factors for infection/colonization with multiresistant P. aeruginosa were prolonged stay in the ICU (p <0.001), previous and lengthy imipenem. usage (p <0.001 and p <0.0001, respectively), and mechanical ventilation (p <0.001). Analytical isoelectric focusing of the sonicates prepared from the isolates showed that each isolate produced 1-5 beta-lactamases, enzymes with isoelectric points (pIs) of 5.1, 6.4, 8.5-8.7 being the most prevalent. DNA macrorestriction patterns of imipenem-resistant isolates were distinct from those of the imipenem-sensitive isolates recovered from ICU patients during the same interval and from the environmental isolates (controls). Thus, our results indicate that colonized patients appear to be the major source for cross-contamination of other patients and if imipenem is selected for empirical therapy, emergence of resistant strains should be anticipated and appropriate precautions taken.