title: The glycerol-3-phosphate permease GlpT is the only fosfomycin transporter in Pseudomonas aeruginosa.
abstract: Fosfomycin is transported into Escherichia coli via both glycerol-3-phosphate (GlpT) and a hexose phosphate transporter (UhpT). Consequently, the inactivation of either glpT or uhpT confers increased fosfomycin resistance in this species. The inactivation of other genes, including ptsI and cyaA, also confers significant fosfomycin resistance. It has been assumed that identical mechanisms are responsible for fosfomycin transport into Pseudomonas aeruginosa cells. The study of an ordered library of insertion mutants in P. aeruginosa PA14 demonstrated that only insertions in glpT confer significant resistance. To explore the uniqueness of this resistance target in P. aeruginosa, the linkage between fosfomycin resistance and the use of glycerol-3-phosphate was tested. Fosfomycin-resistant (Fos-R) mutants were obtained in LB and minimal medium containing glycerol as the sole carbon source at a frequency of 10(-6). However, no Fos-R mutants grew on plates containing fosfomycin and glycerol-3-phosphate instead of glycerol (mutant frequency, < or = 5 x 10(-11)). In addition, 10 out of 10 independent spontaneous Fos-R mutants, obtained on LB-fosfomycin, harbored mutations in glpT, and in all cases the sensitivity to fosfomycin was recovered upon complementation with the wild-type glpT gene. The analysis of these mutants provides additional insights into the structure-function relationship of glycerol-3-phosphate the transporter in P. aeruginosa. Studies with glucose-6-phosphate and different mutant derivatives strongly suggest that P. aeruginosa lacks a specific transport system for this sugar. Thus, glpT seems to be the only fosfomycin resistance mutational target in P. aeruginosa. The high frequency of Fos-R mutations and their apparent lack of fitness cost suggest that Fos-R variants will be obtained easily in vivo upon the fosfomycin treatment of P. aeruginosa infections.
authors.affiliation: Centro Nacional de Biotecnología, Consejo Superior de Investigaciones Científicas, Madrid, Spain.
authors.forename: Alfredo
authors.initials: A
authors.lastname: Castañeda-García
authors.forename: Alexandro
authors.initials: A
authors.lastname: Rodríguez-Rojas
authors.forename: Javier R
authors.initials: JR
authors.lastname: Guelfo
authors.forename: Jesús
authors.initials: J
authors.lastname: Blázquez
mesh_terms: D000900:Anti-Bacterial Agents / Q000378:metabolism* / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology*; D018441:Biofilms / Q000187:drug effects / Q000254:growth & development; D001692:Biological Transport / Q000235:genetics / Q000502:physiology*; D024881:Drug Resistance, Bacterial / Q000235:genetics / Q000502:physiology; D005578:Fosfomycin / Q000378:metabolism* / Q000494:pharmacology; D005816:Genetic Complementation Test; D026901:Membrane Transport Proteins / Q000235:genetics / Q000502:physiology*; D008826:Microbial Sensitivity Tests; D009154:Mutation; D011550:Pseudomonas aeruginosa / Q000187:drug effects / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D026901:Membrane Transport Proteins; D005578:Fosfomycin