Cefiderocol Antimicrobial Susceptibility Testing by Disk Diffusion: Influence of Agar Media and Inhibition Zone Morphology in <i>K. pneumoniae</i> Metallo-β-lactamase
Accurate antimicrobial susceptibility testing (AST) of cefiderocol remains a diagnostic challenge, especially in infections caused by metallo-β-lactamase (MBL)-producing <i>Klebsiella pneumoniae</i>. While disk diffusion offers a cost-effective alternative to broth microdilution, it is h...
Saved in:
| Main Authors: | , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
MDPI AG
2025-05-01
|
| Series: | Antibiotics |
| Subjects: | |
| Online Access: | https://www.mdpi.com/2079-6382/14/5/527 |
| Tags: |
Add Tag
No Tags, Be the first to tag this record!
|
| _version_ | 1849327661336231936 |
|---|---|
| author | Maciej Saar Anna Wawrzyk Dorota Pastuszak-Lewandoska Filip Bielec |
| author_facet | Maciej Saar Anna Wawrzyk Dorota Pastuszak-Lewandoska Filip Bielec |
| author_sort | Maciej Saar |
| collection | DOAJ |
| description | Accurate antimicrobial susceptibility testing (AST) of cefiderocol remains a diagnostic challenge, especially in infections caused by metallo-β-lactamase (MBL)-producing <i>Klebsiella pneumoniae</i>. While disk diffusion offers a cost-effective alternative to broth microdilution, it is highly sensitive to factors such as media composition and the presence of atypical colony morphology. The objective of this study was to evaluate how different agar media and interpretations of isolated colonies affect the performance and reliability of cefiderocol AST by disk diffusion. A total of 50 clinical <i>K. pneumoniae</i> MBL isolates were tested using disk diffusion on Columbia with blood, MacConkey, and chromogenic agars from three manufacturers. Inhibition zones were compared with MICs from broth microdilution. Statistical analyses included paired <i>t</i>-tests and Spearman correlation to assess media effects and zone morphology impact. Variability in inhibition zone diameters was observed between media, notably with chromogenic agar. The most consistent results were obtained using Graso Biotech and Thermo Fisher Columbia with blood agar. Isolated colonies were observed in over half the samples and, depending on how they were interpreted, led to major changes in classification accuracy. Up to 64% of results fell into the EUCAST area of technical uncertainty (ATU), and categorical agreement varied across media and interpretive criteria. Disk diffusion for cefiderocol may be used in resource-limited settings but only if rigorously standardized using validated media, consistent zone reading, and ATU-aware interpretive strategies. In borderline cases or when morphological anomalies are present, broth microdilution should be considered the sole reliable method. Clinical microbiologists are advised to exercise caution with ambiguous results and seek expert or confirmatory testing when needed. |
| format | Article |
| id | doaj-art-c8e6e419da144f48968d47089e12408b |
| institution | Kabale University |
| issn | 2079-6382 |
| language | English |
| publishDate | 2025-05-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Antibiotics |
| spelling | doaj-art-c8e6e419da144f48968d47089e12408b2025-08-20T03:47:48ZengMDPI AGAntibiotics2079-63822025-05-0114552710.3390/antibiotics14050527Cefiderocol Antimicrobial Susceptibility Testing by Disk Diffusion: Influence of Agar Media and Inhibition Zone Morphology in <i>K. pneumoniae</i> Metallo-β-lactamaseMaciej Saar0Anna Wawrzyk1Dorota Pastuszak-Lewandoska2Filip Bielec3Department of Microbiology and Laboratory Medical Immunology, Medical University of Lodz, 90-151 Lodz, PolandDepartment of Basic Biomedical Science, Faculty of Pharmaceutical Sciences in Sosnowiec, Medical University of Silesia, 41-205 Sosnowiec, PolandDepartment of Microbiology and Laboratory Medical Immunology, Medical University of Lodz, 90-151 Lodz, PolandDepartment of Microbiology and Laboratory Medical Immunology, Medical University of Lodz, 90-151 Lodz, PolandAccurate antimicrobial susceptibility testing (AST) of cefiderocol remains a diagnostic challenge, especially in infections caused by metallo-β-lactamase (MBL)-producing <i>Klebsiella pneumoniae</i>. While disk diffusion offers a cost-effective alternative to broth microdilution, it is highly sensitive to factors such as media composition and the presence of atypical colony morphology. The objective of this study was to evaluate how different agar media and interpretations of isolated colonies affect the performance and reliability of cefiderocol AST by disk diffusion. A total of 50 clinical <i>K. pneumoniae</i> MBL isolates were tested using disk diffusion on Columbia with blood, MacConkey, and chromogenic agars from three manufacturers. Inhibition zones were compared with MICs from broth microdilution. Statistical analyses included paired <i>t</i>-tests and Spearman correlation to assess media effects and zone morphology impact. Variability in inhibition zone diameters was observed between media, notably with chromogenic agar. The most consistent results were obtained using Graso Biotech and Thermo Fisher Columbia with blood agar. Isolated colonies were observed in over half the samples and, depending on how they were interpreted, led to major changes in classification accuracy. Up to 64% of results fell into the EUCAST area of technical uncertainty (ATU), and categorical agreement varied across media and interpretive criteria. Disk diffusion for cefiderocol may be used in resource-limited settings but only if rigorously standardized using validated media, consistent zone reading, and ATU-aware interpretive strategies. In borderline cases or when morphological anomalies are present, broth microdilution should be considered the sole reliable method. Clinical microbiologists are advised to exercise caution with ambiguous results and seek expert or confirmatory testing when needed.https://www.mdpi.com/2079-6382/14/5/527antimicrobial susceptibility testingarea of technical uncertaintycefiderocolcolony interpretationdisk diffusioninhibition zone morphology |
| spellingShingle | Maciej Saar Anna Wawrzyk Dorota Pastuszak-Lewandoska Filip Bielec Cefiderocol Antimicrobial Susceptibility Testing by Disk Diffusion: Influence of Agar Media and Inhibition Zone Morphology in <i>K. pneumoniae</i> Metallo-β-lactamase Antibiotics antimicrobial susceptibility testing area of technical uncertainty cefiderocol colony interpretation disk diffusion inhibition zone morphology |
| title | Cefiderocol Antimicrobial Susceptibility Testing by Disk Diffusion: Influence of Agar Media and Inhibition Zone Morphology in <i>K. pneumoniae</i> Metallo-β-lactamase |
| title_full | Cefiderocol Antimicrobial Susceptibility Testing by Disk Diffusion: Influence of Agar Media and Inhibition Zone Morphology in <i>K. pneumoniae</i> Metallo-β-lactamase |
| title_fullStr | Cefiderocol Antimicrobial Susceptibility Testing by Disk Diffusion: Influence of Agar Media and Inhibition Zone Morphology in <i>K. pneumoniae</i> Metallo-β-lactamase |
| title_full_unstemmed | Cefiderocol Antimicrobial Susceptibility Testing by Disk Diffusion: Influence of Agar Media and Inhibition Zone Morphology in <i>K. pneumoniae</i> Metallo-β-lactamase |
| title_short | Cefiderocol Antimicrobial Susceptibility Testing by Disk Diffusion: Influence of Agar Media and Inhibition Zone Morphology in <i>K. pneumoniae</i> Metallo-β-lactamase |
| title_sort | cefiderocol antimicrobial susceptibility testing by disk diffusion influence of agar media and inhibition zone morphology in i k pneumoniae i metallo β lactamase |
| topic | antimicrobial susceptibility testing area of technical uncertainty cefiderocol colony interpretation disk diffusion inhibition zone morphology |
| url | https://www.mdpi.com/2079-6382/14/5/527 |
| work_keys_str_mv | AT maciejsaar cefiderocolantimicrobialsusceptibilitytestingbydiskdiffusioninfluenceofagarmediaandinhibitionzonemorphologyinikpneumoniaeimetalloblactamase AT annawawrzyk cefiderocolantimicrobialsusceptibilitytestingbydiskdiffusioninfluenceofagarmediaandinhibitionzonemorphologyinikpneumoniaeimetalloblactamase AT dorotapastuszaklewandoska cefiderocolantimicrobialsusceptibilitytestingbydiskdiffusioninfluenceofagarmediaandinhibitionzonemorphologyinikpneumoniaeimetalloblactamase AT filipbielec cefiderocolantimicrobialsusceptibilitytestingbydiskdiffusioninfluenceofagarmediaandinhibitionzonemorphologyinikpneumoniaeimetalloblactamase |