Jadyn Anderson

With antibiotic resistance becoming increasingly prevalent in clinical settings, older antibiotics such as fosfomycin are being investigated to determine their effectiveness against bacterial infections. Fosfomycin is a first line drug for the treatment of uncomplicated UTIs and has shown activity against both gram-negative and gram-positive pathogens, as well as multidrug resistant infections. However, its use is limited in clinical settings, as Clinical and Laboratory Standards Institute (CLSI) recommends a reference method which is resource- and labor-intensive for the determination of minimal inhibitory concentration (MIC). We performed three common MIC methods, broth microdilution, agar dilution, and disk diffusion, to analyze the categorical and essential agreement between them. Thus far, we have seen perfect categorical agreement, but not essential agreement. We believe this may be due in part to the presence of inner colonies found during disk diffusion, which may be more evident and problematic in some MIC methods than others. We plan to further investigate these inner colonies, determining their MICs and performing genomic studies which will help determine if they are clinically relevant. Depending on the results of these studies, we will be able to make better recommendations on the use of agar dilution as a reference method for fosfomycin, as well as the use of fosfomycin in general.