Nalidixic acid—a good marker of fluoroquinolone resistance mechanisms in Escherichia coli
ABSTRACT The purpose of this study was to evaluate how ciprofloxacin, pefloxacin, and nalidixic acid disks perform in screening fluoroquinolone resistance mechanisms in 278 Escherichia coli isolates collected from a prospective clinical material. Antimicrobial susceptibility testing of ciprofloxacin...
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American Society for Microbiology
2025-07-01
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| Series: | Microbiology Spectrum |
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| Online Access: | https://journals.asm.org/doi/10.1128/spectrum.01974-24 |
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| author | Sofia Kalinen Heini Kallio Teemu Kallonen Juha Knaapila Tarja Lamminen Pentti Huovinen Peter Boström Antti J. Hakanen Marianne Gunell |
| author_facet | Sofia Kalinen Heini Kallio Teemu Kallonen Juha Knaapila Tarja Lamminen Pentti Huovinen Peter Boström Antti J. Hakanen Marianne Gunell |
| author_sort | Sofia Kalinen |
| collection | DOAJ |
| description | ABSTRACT The purpose of this study was to evaluate how ciprofloxacin, pefloxacin, and nalidixic acid disks perform in screening fluoroquinolone resistance mechanisms in 278 Escherichia coli isolates collected from a prospective clinical material. Antimicrobial susceptibility testing of ciprofloxacin, pefloxacin, and nalidixic acid was performed with the disk diffusion method. PCR-based and sequencing methods were used to detect chromosomal mutations in the gyrA and parC genes and the presence of plasmid-mediated qnr and aac(6′)-1b-cr genes. In addition, whole-genome sequencing was used to confirm these results. Our results show that fluoroquinolone resistance mechanisms were discovered, even in ciprofloxacin-susceptible isolates, and plasmid-mediated low-level fluoroquinolone resistance is easily missed if only ciprofloxacin disk is used. E. coli strains with chromosomal gyrA and/or parC mutations were well detected with pefloxacin disk. However, nalidixic acid was a superior tool to detect and differentiate between low- (plasmid-mediated) and high-level (chromosomal mutations) fluoroquinolone resistance in E. coli. Thus, more clinical studies are needed to evaluate the clinical relevance of fluoroquinolone resistance mechanisms in enteric bacteria and pathogens that show potential but are not yet phenotypically fluoroquinolone-resistant.IMPORTANCEWe show in our clinical setting that fluoroquinolone resistance mechanisms are discovered, even among phenotypically fluoroquinolone-susceptible Escherichia coli isolates. When plasmid-mediated quinolone-resistance determinants are present, they are a potential risk for treatment failures due to accumulation of resistance mechanisms during the antimicrobial treatment. Therefore, when it is clinically relevant, fluoroquinolone resistance mechanisms in E. coli should be monitored more closely, and we also recommend testing nalidixic acid susceptibility. |
| format | Article |
| id | doaj-art-4033edb4160c40ffa035cce48cc94a6a |
| institution | Kabale University |
| issn | 2165-0497 |
| language | English |
| publishDate | 2025-07-01 |
| publisher | American Society for Microbiology |
| record_format | Article |
| series | Microbiology Spectrum |
| spelling | doaj-art-4033edb4160c40ffa035cce48cc94a6a2025-08-20T03:32:55ZengAmerican Society for MicrobiologyMicrobiology Spectrum2165-04972025-07-0113710.1128/spectrum.01974-24Nalidixic acid—a good marker of fluoroquinolone resistance mechanisms in Escherichia coliSofia Kalinen0Heini Kallio1Teemu Kallonen2Juha Knaapila3Tarja Lamminen4Pentti Huovinen5Peter Boström6Antti J. Hakanen7Marianne Gunell8Institute of Biomedicine, University of Turku, Turku, FinlandInstitute of Biomedicine, University of Turku, Turku, FinlandDepartment of Clinical Microbiology, Turku Clinical Microbiome Bank, Turku University Hospital, Turku, FinlandDepartment of Urology, Turku University Hospital, Turku, FinlandDepartment of Urology, Turku University Hospital, Turku, FinlandInstitute of Biomedicine, University of Turku, Turku, FinlandDepartment of Urology, Turku University Hospital, Turku, FinlandInstitute of Biomedicine, University of Turku, Turku, FinlandInstitute of Biomedicine, University of Turku, Turku, FinlandABSTRACT The purpose of this study was to evaluate how ciprofloxacin, pefloxacin, and nalidixic acid disks perform in screening fluoroquinolone resistance mechanisms in 278 Escherichia coli isolates collected from a prospective clinical material. Antimicrobial susceptibility testing of ciprofloxacin, pefloxacin, and nalidixic acid was performed with the disk diffusion method. PCR-based and sequencing methods were used to detect chromosomal mutations in the gyrA and parC genes and the presence of plasmid-mediated qnr and aac(6′)-1b-cr genes. In addition, whole-genome sequencing was used to confirm these results. Our results show that fluoroquinolone resistance mechanisms were discovered, even in ciprofloxacin-susceptible isolates, and plasmid-mediated low-level fluoroquinolone resistance is easily missed if only ciprofloxacin disk is used. E. coli strains with chromosomal gyrA and/or parC mutations were well detected with pefloxacin disk. However, nalidixic acid was a superior tool to detect and differentiate between low- (plasmid-mediated) and high-level (chromosomal mutations) fluoroquinolone resistance in E. coli. Thus, more clinical studies are needed to evaluate the clinical relevance of fluoroquinolone resistance mechanisms in enteric bacteria and pathogens that show potential but are not yet phenotypically fluoroquinolone-resistant.IMPORTANCEWe show in our clinical setting that fluoroquinolone resistance mechanisms are discovered, even among phenotypically fluoroquinolone-susceptible Escherichia coli isolates. When plasmid-mediated quinolone-resistance determinants are present, they are a potential risk for treatment failures due to accumulation of resistance mechanisms during the antimicrobial treatment. Therefore, when it is clinically relevant, fluoroquinolone resistance mechanisms in E. coli should be monitored more closely, and we also recommend testing nalidixic acid susceptibility.https://journals.asm.org/doi/10.1128/spectrum.01974-24fluoroquinolonedrug resistance mechanismsEscherichia colinalidixic acidciprofloxacinpefloxacin |
| spellingShingle | Sofia Kalinen Heini Kallio Teemu Kallonen Juha Knaapila Tarja Lamminen Pentti Huovinen Peter Boström Antti J. Hakanen Marianne Gunell Nalidixic acid—a good marker of fluoroquinolone resistance mechanisms in Escherichia coli Microbiology Spectrum fluoroquinolone drug resistance mechanisms Escherichia coli nalidixic acid ciprofloxacin pefloxacin |
| title | Nalidixic acid—a good marker of fluoroquinolone resistance mechanisms in Escherichia coli |
| title_full | Nalidixic acid—a good marker of fluoroquinolone resistance mechanisms in Escherichia coli |
| title_fullStr | Nalidixic acid—a good marker of fluoroquinolone resistance mechanisms in Escherichia coli |
| title_full_unstemmed | Nalidixic acid—a good marker of fluoroquinolone resistance mechanisms in Escherichia coli |
| title_short | Nalidixic acid—a good marker of fluoroquinolone resistance mechanisms in Escherichia coli |
| title_sort | nalidixic acid a good marker of fluoroquinolone resistance mechanisms in escherichia coli |
| topic | fluoroquinolone drug resistance mechanisms Escherichia coli nalidixic acid ciprofloxacin pefloxacin |
| url | https://journals.asm.org/doi/10.1128/spectrum.01974-24 |
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