Epidemiology of Ciprofloxacin Resistance and Its Relationship to Extended-Spectrum β-Lactamase Production in Proteus mirabilis Bacteremia

BACKGROUND/AIMS We evaluated the clinical features of ciprofloxacin-resistant Proteus mirabilis bacteremia and risk factors for ciprofloxacin resistance. METHODS From October 2000 to July 2009, 37 patients with clinically significant P. mirabilis bacteremia were identified and data from patients with ciprofloxacin-resistant and ciprofloxacin-susceptible P. mirabilis bacteremia were compared. RESULTS The most common underlying diseases were neurologic disease (37.8%) and solid tumors (29.7%). The most common site of infection was the urinary tract (35.1%). Ten of the 37 patients (27.0%) were infected with ciprofloxacin-resistant isolates, and univariate analysis revealed a significant relationship between ciprofloxacin-resistant P. mirabilis bacteremia and neurologic disease, recent operation, L-tube insertion, percutaneous tube use, and extended-spectrum β-lactamase (ESBL) production (all p < 0.05). ESBL was detected in six of 10 (60%) ciprofloxacin-resistant isolates, while only three of 27 (11%) ciprofloxacin-susceptible isolates produced ESBL (p = 0.005). In a logistic regression analysis, ESBL production remained a significant factor associated with ciprofloxacin resistance, after adjusting for other variables. CONCLUSIONS These data indicate a close association between ciprofloxacin resistance and ESBL-production in P. mirabilis bacteremia. This association is particularly troublesome because the therapeutic options for serious infections caused by ESBL-producing P. mirabilis are severely restricted.