Earlier generation quinolones can be useful in identifyingHaemophilus influenzaestrains with low susceptibility to quinolone isolated from paediatric patients. Issue 8 (August 2019)

• Record Type: Journal Article
• Authors: Tanaka, Emi; Wajima, Takeaki; Noguchi, Norihisa
• Is Part Of: Journal of medical microbiology. Volume 68:Issue 8(2019)
• Publication Date: 2019-08
• Subjects: nalidixic acid -- pipemidic acid -- Haemophilus influenzae -- quinolone low susceptibility; Medical microbiology -- Periodicals; 616.9041
• DOI: 10.1099/jmm.0.001027
• Languages: English
• ISSNs: 0022-2615

Abstract

Abstract : Purpose. : Haemophilus influenzae strains with low susceptibility to quinolones have recently emerged in the paediatric field in Japan. These strains are judged as 'susceptible' in routine susceptibility tests, although they may survive after quinolone treatment. Therefore, we aimed to construct a simple and cost‐effective identification method for low‐susceptibility strains using disc diffusion assays. Methodology. : A total of 33 H . influenzae clinical isolates and a control strain were used. For the disc diffusion assay, levofloxacin, norfloxacin, nalidixic acid and pipemidic acid were employed. Correlations between the inhibition zone diameter and amino acid substitutions were evaluated. Results. : All of the tested strains formed clear inhibition zones on both levofloxacin and norfloxacin discs. By contrast, none of the low‐susceptibility strains showed inhibition zones against nalidixic acid, while the low‐susceptibility strains with amino acid substitutions in both GyrA and ParC did not show inhibition zones against pipemidic acid discs, indicating that low‐susceptibility strains can be detected with high sensitivity and specificity by the presence or absence of inhibition zones for earlier quinolones. Conclusion. : A disc diffusion test combining results from nalidixic acid and pipemidic acid can detect low‐susceptibility strains harbouring amino acid substitutions without the need for genetic analysis. This test can help reduce inappropriate and unnecessary fluoroquinolone use.