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O043 - ANTIBIOTIC-TOLERANT PERSISTERS ARE RELEVANT IN STREPTOCOCCUS PNEUMONIAE (ID 445)
Abstract
Background
Persisters are a subpopulation of cells that are tolerant to lethal concentrations of antibiotics. This phenotypic variation is widespread among bacterial species and is involved in a variety of chronic and recurrent infections. Surprisingly, little to nothing is known about persistence in S. pneumoniae. The aim of this study was to make a first characterization of persistence in Streptococcus pneumoniae.
Methods
First, a valid long-living in vitro model was optimized using different strategies (comparison of growth media, addition of catalase or choline chloride) to prolong stationary phase survival by setting-up planktonic growth curves which would enable in vitro persistence assays. Second, time-kill curves were obtained by treating pneumococci with high concentrations of antibiotics (amoxicillin, cefuroxime, moxifloxacin and vancomycin) in different growth phases. Mathematical modeling of these killing dynamics was used to assess the presence of persisters since these would lead to biphasic patterns. To exclude resistance, persisters were re-grown and time-kill curves as well as antibiotic susceptibility was determined.
Results
The best condition to reach stable stationary phase survival up till 24 hours was by using Mueller-Hinton Broth supplemented with 5% lysed horse blood as liquid growth medium. Pneumococci treated with 100-fold MIC of the antibiotics resulted in time-kill curves showing a biphasic killing pattern, which is proof of presence of persisters. Resistance was excluded as similar time-kill curves were obtained from regrown persisters compared to the original strain and they remained susceptible to the antibiotics.
Conclusions
This research provides a first proof that antibiotic-tolerant persister cells are present in Streptococcus pneumoniae cultures.