Application of pulsed field gel electrophoresis [PFGE] for typing of stenotrophomonus maltophilia isolated from nosocomial ventilator associated pneumonia in ICU patients

ABSTRACT

Stenotrophomonus maltophilia is a multidrug resistant nosocomial pathogen for which optimal typing methods are needed to estimate epidemiologic relatedness especially among Intensive Care Unit [ICU]. Ventilator associated pneumonia [VAP] is a common complication in mechanically ventilated patients and it is accompanied by increased mortality. Pulsed field gel electrophoresis [PFGE] was applied to 12 nosocomial strains isolated from patients had VAP and six environmental specimens in ICU in Bahrain Hospital over 15 months period in 2004-2005. Antibiogram as a phenotypic marker failed to discriminate between these isolates. Five antibiogram patterns were identified among 18 isolates with predominance of pattern [I] that resisted five chemotherapeutic agents in 5 isolates [27.8%]. All the strains were sensitive to trimethoprim-sulfamethoxazole but only 72.2%, 55.6%, 44.4%, 22.2% and 11.1% were sensitive to minocycline, levofloxacin, ticarcillin-clavulanic acid, ceftazidime and chloramphenicol respectively. All the strains were typable by the genotypic marker PFGE. It revealed 14 patterns among 18 clinical and innate environmental isolates with a small two clusters included 3 strains that were epidemiologically related. Ten genotypic patterns were detected among twelve clinical isolates meanwhile six patterns were detected among the six environmental isolates. There were similar isolated PFGE patterns between environmental and clinical isolates suggestive of the source of infection to those patients and evidence of patient to patient transmission. These different genotypic patterns indicated different sources and genetic diversity of this opportunistic pathogen. This study proved high typability, sensitivity and discriminatory power of PFGE method for typing of nosocomial Stenotrophomonus maltophilia. It is recommended to add another genotypic marker in further studies like random amplified polymorphic DNA analysis [RAPD] to increase and augment the sensitivity and discriminatory power for typing of this important pathogen and trace the different sources of nosocomial infection