Metabolic changes associated with adaptive resistance to daptomycin in Streptococcus mitis-oralis

Abstract

Background Viridans group streptococci of the Streptococcus mitis-oralis subgroup are important endovascular pathogens. They can rapidly develop high-level and durable non-susceptibility to daptomycin both in vitro and in vivo upon exposure to daptomycin. Two consistent genetic adaptations associated with this phenotype (i.e., mutations in cdsA and pgsA) lead to the depletion of the phospholipids, phosphatidylglycerol and cardiolipin, from the bacterial membrane. Such alterations in phospholipid biosynthesis will modify carbon flow and change the bacterial metabolic status. To determine the metabolic differences between daptomycin-susceptible and non-susceptible bacteria, the physiology and metabolomes of S. mitis-oralis strains 351 (daptomycin-susceptible) and 351-D10 (daptomycin non-susceptible) were analyzed. S. mitis-oralis strain 351-D10 was made daptomycin non-susceptible through serial passage in the presence of daptomycin. Results Daptomycin non-susceptible S. mitis-oralis had significant alterations in glucose catabolism and a re-balancing of the redox status through amino acid biosynthesis relative to daptomycin susceptible S. mitis-oralis. These changes were accompanied by a reduced capacity to generate biomass, creating a fitness cost in exchange for daptomycin non-susceptibility. Conclusions S. mitis-oralis metabolism is altered in daptomycin non-susceptible bacteria relative to the daptomycin susceptible parent strain. As demonstrated in Staphylococcus aureus, inhibiting the metabolic changes that facilitate the transition from a daptomycin susceptible state to a non-susceptible one, inhibits daptomycin non-susceptibility. By preventing these metabolic adaptations in S. mitis-oralis, it should be possible to deter the formation of daptomycin non-susceptibility.

Mechanistic Fingerprinting Reveals Kinetic Signatures of Resistance to Daptomycin and Host Defense Peptides in Streptococcus mitis-oralis

“…A number of phenotypic, metabolic and genotypic analyses have studied potential mechanisms involved in phenotypic DAP-R in S. mitis-oralis , most of which have utilized the same DAP-S/DAP-R strain pair described above [ 19 , 20 , 21 , 22 , 23 , 29 , 31 , 32 , 33 ]. These studies identified potential mechanistic themes relevant to the current findings.…”

“…Recent metabolomic analyses of the current DAP-S/DAP-R S. mitis-oralis strain-pair also divulged interesting distinctions [ 22 ]. S .…”

“…mitis-oralis strains lack a classical tricarboxylic acid (TCA) cycle, grow preferentially in microaerophilic conditions and adapt their metabolic profile in transitioning from the DAP-S-to-DAP-R phenotype in a manner distinct from DAP-R S. aureus [ 38 ]. In this respect, the DAP-R 351-D10 strain exhibits delayed glucose catabolism (through glycolysis and lactate dehydrogenase) compared to DAP-S 351-WT [ 22 ]. As lactate dehydrogenase plays an important role in maintaining the redox balance, it is highly likely that a dysregulation in redox status contributes to the slower growth of the DAP-R S. mitis-oralis strain [ 22 ].…”

“…Susceptibilities of the study strains to DAP (previously reported) were determined using a microbroth dilution assay per recommendations of the Clinical Laboratory Standards Institute (CLSI) in calcium-supplemented (Ca 2+ ) Mueller-Hinton broth [ 19 , 20 , 21 , 22 , 23 ]. The DAP-S parental strain 351-WT has a DAP MIC of 0.5 µg/mL, while its isogenic DAP-R variant 351-D10 has an MIC > 256 µg/mL.…”

“…Recently, we reported that DAP-R in S. mitis-oralis involves unique mechanisms not previously documented in S. aureus and enterococci. These include: (i) major perturbations in cell membrane (CM) phospholipid repertoires, featuring the essential repression of two lipid species critical to DAP CM binding and oligomerization (phosphotidylglycerol and cardiolipin) [ 19 ], (ii) loss-of-function mutations in genes involved in biosynthesis of these phospholipids [ 19 , 20 , 21 ], (iii) corresponding shifts in metabolomic profiles of DAP-R strains, particularly involving glycolytic pathway intermediates [ 22 ] and (iv) altered DAP–CM interaction dynamics, characterized by enhanced ability to hyper-accumulate DAP in specific cells within a given streptococcal chain [ 19 , 21 ].…”