Dr Apurba Sastry, Ms Shuruthi Kirubakaran, Dr Sarumathi Dhandapani, Dr Ketan Priyadarshi,
Volume 19, Issue 5 (9-2025)
Abstract
ABSTRACT
Background: The emergence of multi-drug resistant organisms has limited the choice of therapeutic options to treat infections. The lack of development of new antimicrobials paved the way for considering the reassessment of older antibiotics like fosfomycin. In this context, we assessed the in-vitro effect of fosfomycin against carbapenem- resistant Enterobacterales and methicillin-resistant Staphylococcus aureus on bloodstream isolates by agar dilution, disk diffusion and screen agar.
Material & Methods: All the 141 consecutive blood isolates which were resistant to carbapenem and 62 MRSA blood culture isolates were collected over a period of 8 months. The methods such as fosfomycin agar dilution (0.25 µg/ml to 512 µg/ml) , Kirby-Bauer disk diffusion (150μg of fosfomycin + 50μg of glucose -6-phosphate) and fosfomycin screen agar (32 µg/ml, 48µg/ml & 64µg/ml) were performed. All the three methods are interpreted using EUCAST guidelines. The agreement between the new method and the reference method was calculated.
Results: Among the tested isolates, 100 % of MRSA followed by E. coli (86.4%), K.pneumoniae (65.2%) and E.cloacae (50%) were susceptible to fosfomycin. The MIC50 and MIC90 of fosfomycin was 0.5µg/ml and 2µg/ml for MRSA, 16µg/ml and 32µg/ml for K.pneumoniae, 4µg/ml and 16µg/ml for E.coli, 8µg/ml and 32µg/ml for E.cloacae respectively.
Conclusion: In this study, we observed that fosfomycin has a good in-vitro effect on most of the carbapenem resistant Enterobacterales and MRSA isolates tested.
Key words: Fosfomycin; susceptibility testing; antibiotic resistance; MRSA; carbapenem resistant Enterobacterales; MIC
Short running title: In vitro fosfomycin susceptibility
