Activity of fosfomycin and R-plasmid conferring fosfomycin resistance among some clinical bacteria isolates in Nigeria.

The in vitro activity of fosfomycin (an antibiotic that has clinically not been widely used in Nigeria) against 516 clinical bacteria isolates and the screening for the presence of R plasmid conferring resistance to fosfomycin among the test bacteria isolates were determined. In the presence of added glucose-6-phosphate (25 micrograms/ml) to the growth medium, all the isolates were inhibited at fosfomycin minimum inhibitory concentrations (MIC) of less than or equal to 32-64 micrograms/ml. Without the glucose-6-phosphate, fosfomycin had MIC75, MIC70, MIC48, and MIC20 at 64 micrograms/ml against Escherichia coli, Pseudomonas aeruginosa, Klebsiella spp., and Serratia spp., respectively, while the rest of the strains maintained about the same susceptibility as in the presence of glucose-6-phosphate. An R plasmid of about 59 megadaltons in size, conferring resistance to streptomycin, ampicillin, carbenicillin, and fosfomycin, was obtained from a Serratia liquifacens isolated in an area where fosfomycin had not been clinically used.