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Volume 48, Number 3, June 2015

Risk factors of community-onset urinary tract infections caused by plasmid-mediated AmpC β-lactamase-producing Enterobacteriaceae 

Chi-Hung Lee, Yi-Tzu Lee, Che-Hsuan Kung, Wen-Wei Ku, Shu-Chen Kuo, Te-Li Chen, Chang-Phone Fung

Received: April 30, 2013    Revised: August 1, 2013    Accepted: August 20, 2013   


Corresponding author:

Shu-Chen Kuo
Division of Infectious Diseases, Taipei Veterans General Hospital, Taipei, Taiwan
Institute of Clinical Medicine, National Yang-Ming University, School of Medicine, Taipei, Taiwan
National Institute of Infectious Diseases and Vaccinology, National Health Research Institutes, Miaoli County, Taiwan
Corresponding author. Division of Infectious Diseases, Taipei Veterans General Hospital, Number 201, Section 2, Shih-Pai Road, Taipei 112, Taiwan. 


Background and purpose: 

The AmpC β-lactamase (AmpC)-producing Enterobacteriaceae emerged worldwide. This study was conducted to determine the risk factors of community-onset urinary tract infections (UTIs) caused by plasmid-mediated AmpC-producing Enterobacteriaceae. 



Patients who were diagnosed as community-onset UTIs caused by Enterobacteriaceae in a tertiary-care teaching hospital from December 2010 to January 2012 were included. Extended-spectrum β-lactamase (ESBL)-producing isolates were excluded. We identified plasmid-mediated AmpC-producing Enterobacteriaceae both phenotypically (by disk potentiation test and double-disk synergy test) and genotypically (by Multiplex polymerase chain reaction (PCR) assay). The demographic data, clinical characteristics, and risk factors of acquisition were described. 



Among the 323 non-ESBL-producing Enterobacteriaceae identified in community-onset UTIs, 50 isolates were phenotypically positive for AmpC. Escherichia coli was the most common AmpC-producing organism (60%), followed by Klebsiella pneumonia (8%), and Enterobacter cloacae and Proteus mirabilis (6% for each species). The independent risk factors for acquisition of AmpC-producing Enterobacteriaceae included prior history of cerebral vascular accident [odds ratio (OR) = 2.014; 95% confidence interval (CI) = 1.007–4.031; p = 0.0048], and prior use of fluoroquinolones (OR = 4.049; 95% CI = 1.759–9.319; p = 0.001) and cephamycin (OR = 9.683; 95% CI = 2.007–45.135; p = 0.004). AmpC-producing isolates were multidrug resistant. Carbapenems, cefepime, and piperacillin/tazobactam had the best in vitro efficacy. The most commonly identified plasmid-mediated AmpC gene was blaCIT, followed by blaDHA/blaEBC, and blaMOx. 



For community-onset UTIs, AmpC-producing Enterobacteriaceae should be suspected in those with prior history of cerebral vascular accident and prior use of antimicrobials. To treat these multiple-resistant isolates, carbapenems, cefepime, and piperacillin/tazobactam may be considered. 


Key words:

AmpC β-lactamase, Community-onset, Plasmid-mediated, Risk factors, Urinary tract infections