ORIGINAL ARTICLE DOI: 10.3904/kjim.2011.26.1.89 Epidemiology of Ciprofloxacin Resistance and Its Relationship to Extended-Spectrum β-Lactamase Production in Proteus mirabilis Bacteremia Kyung Mok Sohn1,2, Cheol-In Kang1, Eun-Jeong Joo1, Young Eun Ha1, Doo Ryeon Chung1, Kyong Ran Peck1, Nam Yong Lee3, and Jae-Hoon Song1 1Division of Infectious Diseases, Department of Internal Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul; 2Division of Infectious Diseases, Department of Internal Medicine, Chungnam National University Hospital, Daejeon; 3Department of Laboratory Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea 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. (Korean J Intern Med 2011;26:89-93) Keywords: Proteus mirabilis; Ciprofloxacin; Drug resistance; Bacterial; Risk factors; Cephalosporin resistance INTRODUCTION Proteus mirabilis can cause a variety of community- or hospital-acquired infections, including urinary tract, intra- abdominal, and bloodstream infections [1,2]. Antimicrobial resistance has been reported increasingly for this species, and increased resistance to extended-spectrum cephalosporins due to the production of extended-spec- trum β-lactamases (ESBLs) has become of great concern [1,3,4]. Consequently, carbapenem has emerged as the agent of choice for the treatment of serious infections caused by ESBL-producing pathogens. Fluoroquinolones may be an effective alternative antimicrobial therapy. However, similar to Escherichia coli and Klebsiella pneu- moniae, the incidence of ciprofloxacin resistance in P. mirabilis isolates is increasing [5,6]. Received: May 6, 2010 Revised : August 30, 2010 Accepted: September 28, 2010 Correspondence to Cheol-In Kang, M.D. Division of Infectious Diseases, Department of Internal Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, 50 Irwon-dong, Gangnam-gu, Seoul 135-710, Korea Tel: 82-2-3410-0324, Fax: 82-2-3410-0064, Email: collacin@hotmail.com