title: Development of a Pefloxacin Disk Diffusion Method for Detection of Fluoroquinolone-Resistant Salmonella enterica.
abstract: Fluoroquinolones (FQs) are among the drugs of choice for treatment of Salmonella infections. However, fluoroquinolone resistance is increasing in Salmonella due to chromosomal mutations in the quinolone resistance-determining regions (QRDRs) of the topoisomerase genes gyrA, gyrB, parC, and parE and/or plasmid-mediated quinolone resistance (PMQR) mechanisms including qnr variants, aac(6')-Ib-cr, qepA, and oqxAB. Some of these mutations cause only subtle increases in the MIC, i.e., MICs ranging from 0.12 to 0.25 mg/liter for ciprofloxacin (just above the wild-type MIC of ≤0.06 mg/liter). These isolates are difficult to detect with standard ciprofloxacin disk diffusion, and plasmid-mediated resistance, such as qnr, is often not detected by the nalidixic acid screen test. We evaluated 16 quinolone/fluoroquinolone disks for their ability to detect low-level-resistant Salmonella enterica isolates that are not serotype Typhi. A total of 153 Salmonella isolates characterized for the presence (n = 104) or absence (n = 49) of gyrA and/or parC topoisomerase mutations, qnrA, qnrB, qnrD, qnrS, aac(6')-Ib-cr, or qepA genes were investigated. All isolates were MIC tested by broth microdilution against ciprofloxacin, levofloxacin, and ofloxacin and by disk diffusion using EUCAST or CLSI methodology. MIC determination correctly categorized all isolates as either wild-type isolates (MIC of ≤0.06 mg/liter and absence of resistance genes) or non-wild-type isolates (MIC of >0.06 mg/liter and presence of a resistance gene). Disk diffusion using these antibiotics and nalidixic acid failed to detect some low-level-resistant isolates, whereas the 5-μg pefloxacin disk correctly identified all resistant isolates. However, pefloxacin will not detect isolates having aac(6')-Ib-cr as the only resistance determinant. The pefloxacin disk assay was approved and implemented by EUCAST (in 2014) and CLSI (in 2015).
authors: Statens Serum Institut (SSI), Copenhagen, Denmark rsk@ssi.dk.
authors: Robert
authors: R
authors: Skov
authors: EUCAST Development Laboratory (EDL), Växjö, Sweden.
authors: Erika
authors: E
authors: Matuschek
authors: Division of Foodborne, Waterborne, and Environmental Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA.
authors: Maria
authors: M
authors: Sjölund-Karlsson
authors: EUCAST Development Laboratory (EDL), Växjö, Sweden.
authors: Jenny
authors: J
authors: Åhman
authors: Statens Serum Institut (SSI), Copenhagen, Denmark.
authors: Andreas
authors: A
authors: Petersen
authors: Statens Serum Institut (SSI), Copenhagen, Denmark.
authors: Marc
authors: M
authors: Stegger
authors: Statens Serum Institut (SSI), Copenhagen, Denmark.
authors: Mia
authors: M
authors: Torpdahl
authors: EUCAST Development Laboratory (EDL), Växjö, Sweden.
authors: Gunnar
authors: G
authors: Kahlmeter
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology* / Q000627:therapeutic use; D016470:Bacteremia / Q000188:drug therapy / Q000382:microbiology; D001483:Base Sequence; D002939:Ciprofloxacin / Q000627:therapeutic use; D027081:DNA Gyrase / Q000235:genetics; D027101:DNA Topoisomerase IV / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics; D052978:Disk Diffusion Antimicrobial Tests / Q000379:methods*; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics*; D006801:Humans; D064704:Levofloxacin / Q000494:pharmacology; D009268:Nalidixic Acid / Q000494:pharmacology; D015242:Ofloxacin / Q000494:pharmacology; D015366:Pefloxacin / Q000494:pharmacology*; D012480:Salmonella Infections / Q000188:drug therapy* / Q000382:microbiology; D019779:Salmonella enterica / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D017422:Sequence Analysis, DNA
chemical_list: D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; D015366:Pefloxacin; D009268:Nalidixic Acid; D002939:Ciprofloxacin; D064704:Levofloxacin; D015242:Ofloxacin; D027101:DNA Topoisomerase IV; D027081:DNA Gyrase