Phosphonate Antibiotic

Discovery

Fosfomycin was first discovered in Spain from cultures of the Streptomyces species and was originally named "Phosphonomycin" (Hendlin et al., 1969). The antibiotic was found to inhibit cell wall synthesis in both gram-positive and gram-negative bacteria. About 14 years later in vitro testing demonstrated that the action of this antibiotic requires the presence of glucose-6-phosphate (Andrews, 1983). The antibiotic needs to be carried into the cells by the L-a-glycerophosphate transport system and/or the hexose-phosphate transport system, which is induced by the presence of glucose-6-phosphate.

Fosfomycin is used orally in its calcium salt form, intravenously as the more water-soluble disodium salt, and more as Fosfomycin-tromethamine, a more recent formulation and recommended in the treatment of uncomplicated urinary tract infections (Popovic et al., 2010).

Overview of Chemistry

Its simple structure consists of the active, bactericidal epoxy group and a directly bonded carbon atom to the centrally positioned phosphorous or a C-P bond (Figure 1). It inhibits a step, early in the murein/peptidoglycan synthesis in proliferating bacteria. The antibiotic forms a covalent adduct when the epoxide group reacts to the enzyme. Learn more about the mechanism of action of fosfomycin.

Figure 1. Chemical structure of a phosphonic acid antibiotic - Fosfomycin

Types

Fosfomycin is the only member of the group of epoxide antibiotics that is currently approved by the US FDA for clinical use. Other members e.g., fosmidomycin and alafosfalin (Raz, 2012) are not used clinically.

Resistance

The primary methods for fosfomycin to enter into gram-negative bacteria is via the L-alpha-glycerophosphate transport system (glpT) or the hexose phosphate transport system (uhpT), induced in the presence of glucose-6-phosphate (Kahan et al., 1974). Mutations in these transport proteins can lead to fosfomycin resistance. In addition, any changes in the PEP:sugar phosphotransferase system (PTS) and adenylate cyclase activity, both of which result in decreased cAMP levels and impact induction of the glpT transport also lead to fosfomycin resistance (Popovic et al., 2010). All these changes occur due to mutations in the bacterial chromosome.

The first instance of plasmid-mediated fosfomycin resistance was reported in Serratia marcescens due to the fosA gene in a transposable genetic element (Mendoza et al., 1980). The FosA is a glutathione S-transferase that catalyzes the covalent linkage of glutathione to fosfomycin, inactivating the antibiotic. Other similar enzymes have also been identified in Enterobacteriaceae, Pseudomonas spp., Acinetobacter spp., Staphylococcus spp., and Bacillus spp. (Popovic et al., 2010).

Learn more about fosfomycin resistance.

References

Andrews, J. M., Baquero, F., Beltran, J. M., Canton, E., Crokaert, F., Gobernado, M., Gomez-Ius, R., Loza, E., Navarro, M., Olay, T., Rodriguez, A., Vicente, M. V., Wise, R., Yourassowsky, E. (1983) International collaborative study on standardization of bacterial sensitivity to fosfomycin. J Antimicrob Chemother. 12(4):357-61. https://doi.org/10.1093/jac/12.4.357

Hendlin, D., Stapley, E. O., Jackson, M., Wallick, H., Miller, A. K., Wolf, F. J., Miller, T. W., Chaiet, L., Kahan, F. M., Foltz, E. L., Woodruff, H. B., Mata, J. M., Hernandez, S., Mochales, S. (1969) Phosphonomycin, a new antibiotic produced by strains of streptomyces. Science. 166(3901):122-3. https://doi.org/10.1126/science.166.3901.122

Kahan, F. M., Kahan, J. S., Cassidy, P. J., Kropp, H. (1974) The mechanism of action of fosfomycin (phosphonomycin). Ann N Y Acad Sci. 235(0):364-86. https://doi.org/10.1111/j.1749-6632.1974.tb43277.x

Mendoza, C., Garcia, J. M., Llaneza, J., Mendez, F. J., Hardisson, C., Ortiz, J. M. (1980) Plasmid-determined resistance to fosfomycin in Serratia marcescens. Antimicrob Agents Chemother. 18(2):215-9. https://doi.org/10.1128/aac.18.2.215

Popovic, M., Steinort, D., Pillai, S., Joukhadar, C. (2010) Fosfomycin: an old, new friend? Eur J Clin Microbiol Infect Dis. 29(2):127-42. https://doi.org/10.1007/s10096-009-0833-2

Raz, R. (2012) Fosfomycin: an old--new antibiotic. Clin Microbiol Infect. 18(1):4-7. https://doi.org/10.1111/j.1469-0691.2011.03636.x