High prevalence of imipenem-resistant and metallo-beta-lactamase-producing Pseudomonas aeruginosa in the Burns Hospital in Tunisia: detection of a novel class 1 integron.

Pseudomonas aeruginosa is one of the most important causes of nosocomial infections, and its eradication is very difficult due to its multidrug resistance. The objective of the present study was to characterize the metallo-beta-lactamases (MBLs), integrons, OprD modifications and virulence factors of P. aeruginosa strains isolated from burn patients and to analyze their genetic relatedness by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Sixty-seven P. aeruginosa isolates were recovered from different clinical samples of burn patients hospitalized in the Intensive Care Burn Unit of the Centre de Traumatologie et des Grands Brulés (Ben Arous, Tunisia), and MBLs and alterations in porin OprD were analyzed among imipenem-resistant isolates. Class 1 and 2 integrons were studied by PCR and sequencing of corresponding variable regions. The presence of eight genes involved in the virulence of P. aeruginosa was investigated by PCR. Fourteen of the 36 imipenem-resistant P. aeruginosa (IRPA) isolates (38.8%) were MBLs producers and harbored the blaVIM-2 gene, in all cases included into class 1 integrons. A new class 1 integron was identified (intI1-blaOXA-10-aadB-blaVIM-2-aadB-blaOXA-10). Five sequence types were detected among IRPA isolates: ST1, ST112, ST238, ST308 and ST395. P. aeruginosa is a major nosocomial pathogen in patients suffering burns, and the spreading of multidrugs resistant and MBL-producing isolates should be controlled in burn units. Moreover, the implantation of infection control guidelines is crucial to decrease the morbidity and mortality of nosocomial infections due to multidrug resistant P. aeruginosa.