[Biological cost associated with fosfomycin resistance in Escherichia coli isolates from urinary tract infections].
Resistance to fosfomycin develops rapidly in experimental conditions, although despite its frequent use in UTI, resistance in E. coli, the main uropathogen, is very low (1-3%), and has remained so for many years. The objective of this study was to ascertain whether E. coli fosfomycin-resistant strains have less fitness than those that are fosfomycin-sensitive in competing, and would therefore tend to disappear in their competition with fosfomycin-sensitive strains in the absence of antibiotics. Fosfomycin-resistant strains (n=11) with different phenotypes of resistance to other antibiotics were used. All but one were lactose (+). Fosfomycin-susceptible strains (n=15) that had the same phenotypes of resistance to other antibiotics as the resistant strains and which had the opposite pattern of lactose fermentation were also used. Thirty-three (33) competition experiments by pairs of strains were conducted in nutrient broth. Equal amounts of the strains were challenged (approx. 50% and approx. 50%) for 4 days, with a daily change to a new medium. Five differential counts were performed on days 0, 1, 2, 3 and 4. In 20 experiments (60.6%) there was a relative increase in the fosfomycin-sensitive strain. In 6 experiments (18.2%) there was a relative increase in the fosfomycin-resistant strain. In 7 experiments (21.2%), on the fourth day none of the strains reached 60%. When the data of the 26 (20+6) experiments in which there were changes were analyzed by the chi2 test there was a statistically significant difference (p=0.044). Resistance to fosfomycin could entail a biological cost (less fitness) for the majority of the E. coli strains assayed.
Alós
J I
JI
Servicio de Microbiología, Hospital de Móstoles, Móstoles, Madrid. España. nachoalos@microb.net
García-Peña
P
P
Tamayo
J
J
D015169:Colony Count, Microbial; D024881:Drug Resistance, Bacterial / Q000502:physiology*; D024901:Drug Resistance, Multiple, Bacterial / Q000502:physiology; D004926:Escherichia coli / Q000187:drug effects* / Q000302:isolation & purification / Q000378:metabolism; D004927:Escherichia coli Infections / Q000382:microbiology*; D005285:Fermentation; D005578:Fosfomycin / Q000494:pharmacology*; D006801:Humans; D007785:Lactose / Q000378:metabolism*; D010641:Phenotype; D012641:Selection, Genetic; D014552:Urinary Tract Infections / Q000382:microbiology*
D005578:Fosfomycin; D007785:Lactose