Development of a Pefloxacin Disk Diffusion Method for Detection of Fluoroquinolone-Resistant Salmonella enterica.

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).

Skov R ，Matuschek E ，Sjölund-Karlsson M ，Åhman J ，Petersen A ，Stegger M ，Torpdahl M ，Kahlmeter G ... -  《-》

Validation of Pefloxacin for detection of fluoroquinolone (FQ) resistance among Salmonella Typhi with special reference to GyrB mutations.

Inayath SB ，Broor S ，Gupta R ，Agarwal P ，Majumder S ，Anveshi AK ，Gaind R ... -  《-》

Prevalence of plasmid-mediated quinolone resistance and mutations in the gyrase and topoisomerase IV genes in Salmonella isolated from 12 tertiary-care hospitals in Korea.

Jeong HS ，Kim JA ，Shin JH ，Chang CL ，Jeong J ，Cho JH ，Kim MN ，Kim S ，Kim YR ，Lee CH ，Lee K ，Lee MA ，Lee WG ，Shin JH ，Lee JN ... -  《-》

Evaluation of Surrogate Disk Tests for Detection of Ciprofloxacin and Levofloxacin Resistance in Clinical Isolates of Salmonella enterica.

Detection of fluoroquinolone resistance in Salmonella enterica has become increasingly difficult due to evolving resistance mechanisms to this antimicrobial class in this organism. We evaluated two quinolone disks and five fluoroquinolone disks for their ability to act as a surrogate agent for the detection of fluoroquinolone resistance in a collection of 136 S. enterica isolates, including 111 with intermediate or resistant ciprofloxacin MICs mediated by a variety of resistance mechanisms. Ciprofloxacin, ofloxacin, and pefloxacin disks detected all isolates resistant to ciprofloxacin (0% very major error) and yielded false resistance (major error) in 8, 4, and 12% of susceptible isolates, respectively. Ciprofloxacin and pefloxacin provided clearer differentiation of susceptible and resistant isolates.

Deak E ，Skov R ，Hindler JA ，Humphries RM ... -  《-》

Quinolone Resistance Mechanisms Among Salmonella enterica in Malaysia.

Thong KL ，Ngoi ST ，Chai LC ，Teh CS ... -  《-》