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. 2019 Sep;38(9):1765-1771.
doi: 10.1007/s10096-019-03608-w. Epub 2019 Jun 18.

Phenotypic screening for quinolone resistance in Escherichia coli

Linus Dellgren  1   2 , Carina Claesson  2   3 , Marie Högdahl  2   3 , Jon Forsberg  2   4 , Håkan Hanberger  1   2 , Lennart E Nilsson  2 , Anita Hällgren  5   6
Affiliations

Phenotypic screening for quinolone resistance in Escherichia coli

Linus Dellgren et al. Eur J Clin Microbiol Infect Dis. 2019 Sep.

Abstract

Recent studies show that rectal colonization with low-level ciprofloxacin-resistant Escherichia coli (ciprofloxacin minimal inhibitory concentration (MIC) above the epidemiological cutoff point, but below the clinical breakpoint for resistance), i.e., in the range > 0.06-0.5 mg/L is an independent risk factor for febrile urinary tract infection after transrectal ultrasound-guided biopsy (TRUS-B) of the prostate, adding to the other risk posed by established ciprofloxacin resistance in E. coli (MIC > 0.5 mg/L) as currently defined. We aimed to identify the quinolone that by disk diffusion best discriminates phenotypic wild-type isolates (ciprofloxacin MIC ≤ 0.06 mg/L) of E. coli from isolates with acquired resistance, and to determine the resistance genotype of each isolate. The susceptibility of 108 E. coli isolates was evaluated by ciprofloxacin, levofloxacin, moxifloxacin, nalidixic acid, and pefloxacin disk diffusion and correlated to ciprofloxacin MIC (broth microdilution) using EUCAST methodology. Genotypic resistance was identified by PCR and DNA sequencing. The specificity was 100% for all quinolone disks. Sensitivity varied substantially, as follows: ciprofloxacin 59%, levofloxacin 46%, moxifloxacin 59%, nalidixic acid 97%, and pefloxacin 97%. We suggest that in situations where low-level quinolone resistance might be of importance, such as when screening for quinolone resistance in fecal samples pre-TRUS-B, a pefloxacin (S ≥ 24 mm) or nalidixic acid (S ≥ 19 mm) disk, or a combination of the two, should be used. In a setting where plasmid-mediated resistance is prevalent, pefloxacin might perform better than nalidixic acid.

Keywords: E. coli; PMQR; Susceptibility testing; Transrectal ultrasound (TRUS)-guided biopsy.

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Conflict of interest statement

The authors declare that they have no conflicts of interest.

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