Pseudomonas aeruginosa bacteraemia: independent risk factors for mortality and impact of resistance on outcome

The rates of multidrug-resistant, extensively drug-resistant and pandrug-resistant isolates amongst non-fermenting Gram-negative bacilli, particularly Pseudomonas aeruginosa, have risen worldwide. The clinical consequence of resistance and the impact of adverse treatment on the outcome of patients with P. aeruginosa bacteraemia remain unclear. To better understand the predictors of mortality, the clinical consequence of resistance and the impact of inappropriate therapy on patient outcomes, we analysed the first episode of P. aeruginosa bacteraemia in patients from a Brazilian tertiary-care hospital during the period from May 2009 to August 2011. Antimicrobial susceptibility testing was conducted; phenotypic detection of metallo-β-lactamase (MBL) and PCR of MBL genes were performed on carbapenem-resistant strains. Amongst the 120 P. aeruginosa isolates, 45.8 % were resistant to carbapenem and 36 strains were tested for MBL detection. A total of 30 % were phenotypically positive and, of these, 77.8 % expressed an MBL gene, bla(SPM-1) (57 %) and bla(VIM-type) (43 %). The resistance rates to ceftazidime, cefepime, piperacillin/tazobactam, carbapenem, fluoroquinolone and aminoglycoside were 55, 42.5, 35, 45.8, 44 and 44 %, respectively. Previous antibiotic use, length of a hospital stay ≥30 days prior to P. aeruginosa, haemodialysis, tracheostomy, pulmonary source of bacteraemia and Intensive Care Unit admission were common independent risk factors for antimicrobial resistance. Cefepime resistance, multidrug resistance and extensive drug resistance were independently associated with inappropriate therapy, which was an important predictor of mortality, being synergistic with the severity of the underlying disease.