Person-to-person transmission of E. coli resistant to fluoroquinolone drugs is rare among hospital patients
Bacteria (Escherichia coli) with resistance to levofloxacin and other fluoroquinolone antimicrobial drugs isolated from the gastrointestinal tract of hospital patients appear to be the result of independent mutation and selection, rather than patient-to-patient transmission, a new study found. Fluoroquinolones are the most commonly used antibiotics and E. coli resistance to these drugs is increasing.
The researchers isolated drug-resistant colonies of the bacterium from hospitalized patients and sequenced two genes (gyrA and parC) that can confer levofloxacin resistance. They identified 353 patients as colonized by E. coli with reduced susceptibility to fluoroquinolones. Among the drug-resistant isolates, 62 percent demonstrated a levofloxacin minimum inhibitory concentration (MIC) of 8 µg/mL or higher (the threshold for fluoroquinolone resistance). In addition, 87 percent of the isolates demonstrated a nalidixic acid MIC of at least 16 µg/mL, indicating lack of susceptibility to this drug as well. The mean number of gyrA mutations per isolate was 1.45 (range, 0-4). In contrast, the mean number of parC mutations was 0.51 (range, 0-2), but no isolate exhibited a parC mutation without having at least one gyrA mutation. Of two molecular typing clusters of 48 isolates and 17 isolates, only 5 patients had isolates from these clusters that met epidemiologic criteria for person-to-person transmission.
The findings were based on analysis of rectal swabs for E. coli among patients hospitalized for at least 3 days at two hospitals in the University of Pennsylvania Health System. The study was funded in part by the Agency for Healthcare Research and Quality (HS10399) to the University of Pennsylvania School of Medicine Center for Education and Research on Therapeutics (CERT). For more information on the CERTs program, visit http://www.certs.hhs.gov.
More details are in "The prevalence of fluoroquinolone resistance mechanisms in colonizing Escherichia coli isolates recovered from hospitalized patients," by Ebbing Lautenbach, M.D., M.P.H., M.S.C.E., Joshua P. Metlay, M.D., Ph.D., Xiangqun Mao, M.D., and others in the August 1, 2010, Clinical Infectious Diseases 51, pp.280-285.
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