Journal Article

The Prevalence of Fluoroquinolone Resistance Mechanisms in Colonizing <i>Escherichia coli</i> Isolates Recovered from Hospitalized Patients

Ebbing Lautenbach, Joshua P. Metlay, Xiangqun Mao, Xiaoyan Han, Neil O. Fishman, Warren B. Bilker, Pam Tolomeo, Mary Wheeler and Irving Nachamkin

in Clinical Infectious Diseases

Published on behalf of Infectious Diseases Society of America

Volume 51, issue 3, pages 280-285
Published in print August 2010 | ISSN: 1058-4838
Published online August 2010 | e-ISSN: 1537-6591 | DOI: http://dx.doi.org/10.1086/653931
The Prevalence of Fluoroquinolone Resistance Mechanisms in Colonizing Escherichia coli Isolates Recovered from Hospitalized Patients

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Background. Fluoroquinolones are the most commonly prescribed antimicrobials. The epidemiology of fecal colonization with Escherichia coli demonstrating reduced susceptibility to fluoroquinolones remains unclear.

Methods. During a 3-year period (15 September 2004 through 19 October 2007), all patients hospitalized for >3 days were approached for fecal sampling. All E. coli isolates with reduced susceptibility to fluoroquinolones (minimum inhibitory concentration [MIC] of levofloxacin, ⩾0.125 µg/mL) were identified. We characterized gyrA and parC mutations and organic solvent tolerance. Isolates were compared using pulsed-field gel electrophoresis.

Results. Of 353 patients colonized with E. coli demonstrating reduced fluoroquinolone susceptibility, 300 (85.0%) had ⩾1 gyrA mutation, 161 (45.6%) had ⩾1 parC mutation, and 171 (48.6%) demonstrated organic solvent tolerance. The mean numbers of total mutations (ie, gyrA and parC) for E. coli isolates with a levofloxacin MIC of ⩾8 µg/mL versus <8.0 µg/mL were 2.70 and 0.82 (P < .001). Of the 136 E. coli isolates with a levofloxacin MIC of <8 µg/mL, 90 (66.2%) demonstrated a nalidixic acid MIC of ⩾16 µg/mL. Significant differences were found over time in the proportion of E. coli isolates demonstrating gyrA mutation, parC mutation, and organic solvent tolerance. There was little evidence of clonal spread of isolates.

Conclusions. Gastrointestinal tract colonization with E. coli demonstrating reduced susceptibility to levofloxacin is common. Although 40% of study isolates exhibited a levofloxacin MIC of <8 µg/mL (and would thus be missed by current Clinical and Laboratory Standards Institute breakpoints), nalidixic acid resistance may be a useful marker for detection of such isolates. Significant temporal changes occurred in the proportion of isolates exhibiting various resistance mechanisms.

Journal Article.  4285 words.  Illustrated.

Subjects: Infectious Diseases ; Immunology ; Public Health and Epidemiology ; Microbiology

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