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

Michael R Yeaman,Arnold S Bayer,Liana C Chan,Nagendra N Mishra

doi:10.3390/antibiotics10040404

Michael R Yeaman, Arnold S Bayer + Show 2 more

Open Access

https://doi.org/10.3390/antibiotics10040404

Copy DOI

Abstract

Streptococcus mitis-oralis (S. mitis-oralis) infections are increasingly prevalent in specific populations, including neutropenic cancer and endocarditis patients. S. mitis-oralis strains have a propensity to evolve rapid, high-level and durable resistance to daptomycin (DAP-R) in vitro and in vivo, although the mechanism(s) involved remain incompletely defined. We examined mechanisms of DAP-R versus cross-resistance to cationic host defense peptides (HDPs), using an isogenic S. mitis-oralis strain-pair: (i) DAP-susceptible (DAP-S) parental 351-WT (DAP MIC = 0.5 µg/mL), and its (ii) DAP-R variant 351-D10 (DAP MIC > 256 µg/mL). DAP binding was quantified by flow cytometry, in-parallel with temporal (1–4 h) killing by either DAP or comparative prototypic cationic HDPs (hNP-1; LL-37). Multicolor flow cytometry was used to determine kinetic cell responses associated with resistance or susceptibility to these molecules. While overall DAP binding was similar between strains, a significant subpopulation of 351-D10 cells hyper-accumulated DAP (>2–4-fold vs. 351-WT). Further, both DAP and hNP-1 induced cell membrane (CM) hyper-polarization in 351-WT, corresponding to significantly greater temporal DAP-killing (vs. 351-D10). No strain-specific differences in CM permeabilization, lipid turnover or regulated cell death were observed post-exposure to DAP, hNP-1 or LL-37. Thus, the adaptive energetics of the CM appear coupled to the outcomes of interactions of S. mitis-oralis with DAP and selected HDPs. In contrast, altered CM permeabilization, proposed as a major mechanism of action of both DAP and HDPs, did not differentiate DAP-S vs. DAP-R phenotypes in this S. mitis-oralis strain-pair.

Highlights

The Streptococcus mitis-oralis (S. mitis-oralis) subgroup of viridans group streptococci (VGS) includes S. mitis, S. oralis, S. gordonii and S. parasanguinis [1,2,3,4]. This subgroup, especially S. mitis, is an important and emerging cause of serious community- and hospitalacquired infections, including infective endocarditis and sepsis syndromes in neutropenic cancer patients (i.e., “toxic Strep shock syndrome”) [1,2,3,4,5,6,7,8]
Despite several distinct media conditions tested (PBS, MuellerHinton broth (MHB) or RPMI), the DAP resistance phenotypes (DAP-R) 351-D10 strain consistently exhibited a substantial subpopulation frequency of cells that exhibited high-level binding of BODIPY-DAP (>102 relative fluorescent units (RFUs))
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]

Summary

Introduction

The Streptococcus mitis-oralis (S. mitis-oralis) subgroup of viridans group streptococci (VGS) includes S. mitis, S. oralis, S. gordonii and S. parasanguinis [1,2,3,4]. A similar DAP-R phenomenon was seen following exposure to DAP alone in simulated cardiac endocarditis vegetations ex vivo [14] and in vivo within vegetations from experimental animals with endocarditis initially infected with a DAP-S parental strain [13]. Such extremely high-level DAP-R phenotypes have only rarely been observed among DAP-R S. aureus or enterococci [15,16,17,18]

Methods

Results

Conclusion