BACKGROUND: Antibiotic resistance typically confers a biological fitness cost on bacteria that can be manifested as a decreased growth rate in culture media and experimental animals. However, there are limited experimental data on the relative fitness of resistant and susceptible bacteria during growth in their natural environment. OBJECTIVE: We have developed a @entity1 competition model to investigate the relative fitness of antibiotic-resistant and -susceptible bacteria. MATERIALS AND METHODS: A non-epidemic @entity5938 was isolated from skin, and a @entity1215 -resistant (RifR) clone was selected. The RifR marker was used to distinguish the inoculated strains from the resident population of coagulase-negative staphylococci. The RifR strains were further selected for resistance to @entity2177 (CipR) and @entity12119 (FusR). A 1:1 mix of susceptible and resistant bacteria was applied on the forearms of 12 volunteers. Competition was monitored by sampling bacteria from skin and determining their relative numbers. RESULTS: Resistance to @entity2177 due to @entity30939 mutations did not decrease the growth rate in vitro, and the CipR/CipS ratio was close to 1 during day 1 and 3 in the in vivo competition experiments. In contrast, @entity12119 resistance due to fusA mutations resulted in a decrease in the growth rate in vitro and a considerable loss of fitness in the competition. The FusR/FusS ratio diminished from 1.3 to 0.023 in 3 days. CONCLUSIONS: These data show that @entity1 volunteers can be used as a simple and relevant model to study the biological cost of resistance.

Fitness of antibiotic resistant XXXX assessed by competition on the skin of @entity1 volunteers.

@entity1 :: ('9606', 'Species') :: ['human'] @entity30939 :: ('23113', 'Gene') :: ['parC'] @entity12119 :: ('MESH:D005672', 'Chemical') :: ['fusidic acid'] @entity5938 :: ('1282', 'Species') :: ['Staphylococcus epidermidis strain'] @entity2177 :: ('MESH:D002939', 'Chemical') :: ['ciprofloxacin'] @entity1215 :: ('MESH:D012293', 'Chemical') :: ['rifampicin']
@entity5938 :: (1282,Species) :: ['Staphylococcus epidermidis']
