Ecological temporal stability of Staphylococcus aureus nasal carriage

Area of Science:

• Microbiology
• Epidemiology
• Genetics

Background:

• Staphylococcus aureus is a common colonizer of humans.
• Understanding colonization dynamics is crucial for infection control.
• Longitudinal studies using precise genotyping are needed.

Purpose of the Study:

• To investigate the dynamics of Staphylococcus aureus colonization in healthy carriers.
• To determine the frequency of strain changes, colonization loss, and acquisition.
• To identify factors associated with colonization persistence or clearance.

Main Methods:

• Longitudinal study of 266 healthy carriers over approximately 1 year.
• Precise genotyping methods including amplified fragment length polymorphism (AFLP), spa typing, and double-locus sequence typing (DLST).
• Analysis of bacterial counts and spa locus mutation rates.

Main Results:

• Strain replacement was rare; only 7 out of 89 initially colonized carriers acquired a new strain.
• Approximately one-third of carriers eliminated S. aureus colonization, with similar numbers becoming newly colonized.
• Lower bacterial counts were associated with a higher probability of eliminating colonization.
• A high mutation rate was observed in the spa locus (6/53 strains).
• No overall change in S. aureus genotype composition was detected across the study population.

Conclusions:

• Staphylococcus aureus strain replacement is infrequent in healthy carriers.
• Colonization dynamics involve both clearance and acquisition, influenced by bacterial load.
• The spa locus exhibits a high mutation rate, potentially impacting strain typing accuracy.
• Overall S. aureus genotype composition remains stable in this carrier population over time.