Characterization of genetic changes associated with daptomycin nonsusceptibility in Staphylococcus aureus.

Zhuo Ma,Meenakshi Malik,Janice Pata,Erica Lasek-Nesselquist,Warren E Rose,Riddhi Shah,Jackson Lu,George Sakoulas,Kathleen Mcdonough,George Oliva,Ryan Schneider,Manjunath P Pai,Ulrich Nübel

doi:10.1371/journal.pone.0198366

Abstract

The extensive use of daptomycin (DAP) for treatment of methicillin-resistant Staphylococcus aureus (MRSA) infections in the last decade has led to the emergence of DAP non-susceptible (DNS) Staphylococcus aureus strains. A better understanding of the molecular changes underlying DAP-non-susceptibility is required for early diagnosis and intervention with alternate combination therapies. The phenotypic changes associated with DNS strains have been well established. However, the genotypic changes—especially the kinetics of expression of the genes responsible for DAP-non-susceptibility are not well understood. In this study, we used three clinically derived isogenic pairs of DAP-susceptible (DAP-S) and DNS S. aureus strains to study gene expression profiles with the objective of identifying the potential genotypic changes associated with DAP-nonsusceptibility. We determined the expression profiles of genes involved in cell membrane (CM) charge, autolysis, cell wall (CW) synthesis, and penicillin binding proteins in DAP-S and DNS isogenic pairs. Our results demonstrate characteristic expression profiles for mprF, dltABCD, vraS, femB, and pbp2a genes, which are common to all the DNS S. aureus strains tested. Whole genome sequencing of DAP-S and DNS clinical isolates of S. aureus showed non-synonymous mutations in all DNS strains in genes involved in CM charge, CM composition, CW thickness and CW composition. To conclude, this study unravels some of the complex molecular changes involved in the development of DAP-nonsusceptibility by demonstrating distinct differences in gene expression profiles and mutations in the DNS S. aureus strains. This knowledge will aid in rapid identification of DNS S. aureus in clinical settings.

Highlights

The past decade has seen a steep rise in antibiotic resistance amongst Gram-positive bacterial pathogens including Staphylococcus aureus
We evaluated the expression profile of genes involved in cell membrane (CM) charge, autolysis, cell wall (CW) synthesis and penicillin binding proteins using three DAP-S/DAP non-susceptible (DNS) isogenic pairs A6300/ A6298, R6837/R6838 JH1/JH4-JH5 isolated from patients
Isogenic pairs of susceptible parent strains of DAP-S and DNS A6300/A6298 isolated from a patient suffering from bacteremia and prosthetic joint infection in a hospital in Massachusetts [30], R6837/R6838 isolated from a patient at Westchester Medical Center, New York [31], and JH1/JH4 isogenic pair recovered from a congenital heart disease patient following treatment failure with vancomycin rifampin and imipenem at Johns Hopkins in Baltimore, MD [34]

Summary

Introduction

The past decade has seen a steep rise in antibiotic resistance amongst Gram-positive bacterial pathogens including Staphylococcus aureus. Reports indicate that 95% of the clinical isolates of S. aureus in the USA are penicillin resistant and more than 50% are methicillin resistant (MRSA) [1]. Daptomycin (DAP) was approved for clinical use in the USA in 2003 for treatment of infections caused by methicillin-susceptible (MSSA), MRSA, and VISA strains. In 2006, DAP was approved for the treatment of bacteremia and right sided endocarditis caused by MSSA and MRSA [3]. In clinical settings; prolonged underdosing of DAP, ineffective penetration of DAP due to infective endocarditis or osteomyelitis, and previous exposure to antimicrobial peptides or glycopeptide antimicrobials have resulted in emergence of DAP non-susceptible (DNS) S. aureus strains [7,8,9,10]

Methods

Results

Conclusion