Stepwise decrease in daptomycin susceptibility in clinical Staphylococcus aureus isolates associated with an initial...

Area of Science:

• Microbiology
• Genetics
• Infectious Diseases

Background:

• Daptomycin is a crucial antibiotic for treating methicillin-resistant Staphylococcus aureus (MRSA) infections.
• The development of daptomycin nonsusceptibility during therapy is linked to genetic alterations, but their specific roles are not fully understood.

Purpose of the Study:

• To investigate the genetic underpinnings of daptomycin nonsusceptibility and associated phenotypic changes in MRSA.
• To elucidate the contributions of serial genetic mutations selected during daptomycin therapy.

Main Methods:

• Analysis of four isogenic MRSA strains isolated from a patient before and during daptomycin treatment.
• Genomic sequencing to identify mutations and phenotypic characterization of each strain.

Main Results:

• An early mutation in rpoB conferred broad-spectrum antibiotic resistance and pleiotropic effects, including altered cell wall thickness and reduced virulence.
• A subsequent mutation in clpX partially restored growth without affecting antibiotic susceptibility.
• The final isolate, exhibiting daptomycin nonsusceptibility, carried an mprF mutation and showed restored cell wall thickness with increased vraSR transcription.

Conclusions:

• Sequential genetic mutations selected in vivo drive the emergence of daptomycin nonsusceptibility in MRSA.
• These mutations impact bacterial fitness, virulence, and cell wall homeostasis.
• Understanding these evolutionary pathways is critical for managing daptomycin-resistant infections.