Fosfomycin—Overcoming Problematic In Vitro Susceptibility Testing and Tricky Result Interpretation: Comparison of Three Fosfomycin Susceptibility Testing Methods
<b>Background:</b> Fosfomycin (FOS) is an older antimicrobial agent newly rediscovered as a possible treatment for infections with limited therapeutic options (e.g., Gram-negative bacteria with difficult-to-treat resistance, DTR), especially in intravenous form. However, for correct usag...
Saved in:
| Main Authors: | , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
MDPI AG
2024-11-01
|
| Series: | Antibiotics |
| Subjects: | |
| Online Access: | https://www.mdpi.com/2079-6382/13/11/1049 |
| Tags: |
Add Tag
No Tags, Be the first to tag this record!
|
| Summary: | <b>Background:</b> Fosfomycin (FOS) is an older antimicrobial agent newly rediscovered as a possible treatment for infections with limited therapeutic options (e.g., Gram-negative bacteria with difficult-to-treat resistance, DTR), especially in intravenous form. However, for correct usage of FOS, it is necessary to have a reliable susceptibility testing method suitable for routine practice and robust interpretation criteria. <b>Results:</b> The results were interpreted according to 2023 interpretation criteria provided by the European Committee on Antimicrobial Susceptibility Testing (EUCAST). DTR Gram-negatives were more likely to be resistant to FOS (45% in Enterobacterales and 20% in <i>P. aeruginosa</i>) than non-DTR (10% and 6.7%, resp.). All isolates of <i>S. aureus</i> were susceptible to FOS. In Gram-negatives, all agreement values were unacceptable. Etest<sup>®</sup> performed better in the DTR cohort (categorical agreement, CA, 80%) than in the non-DTR cohort (CA 45.7%). There were no very major errors (VREs) observed in <i>P. aeruginosa</i>. <i>S. aureus</i> had surprisingly low essential agreement (EA) rates (53% for MRSA and 47% for MSSA) for Etest<sup>®</sup>, but categorical agreement was 100%. <b>Methods:</b> A total of 130 bacterial isolates were tested and compared using the disc diffusion method (DD) and gradient strip method (Etest<sup>®</sup>) with the reference method (agar dilution, AD). The spectrum of isolates tested was as follows: 40 Enterobacterales (20 DTR vs. 20 non-DTR), 30 <i>Pseudomonas aeruginosa</i> (15 DTR vs. 15 non-DTR), and 60 <i>Staphylococcus aureus</i> (30 methicillin-susceptible, MSSA, vs. 30 methicillin-resistant, MRSA). <b>Conclusions:</b> Neither one of the tested methods was identified as a suitable alternative to AD. It would be beneficial to define more interpretation criteria, at least in some instances. |
|---|---|
| ISSN: | 2079-6382 |