Survival of Staphylococcus aureus ST398 in the human nose after artificial inoculation

Area of Science:

• Microbiology
• Infectious Diseases
• Bacterial Pathogenesis

Background:

• Methicillin-resistant Staphylococcus aureus (MRSA) ST398, originating from animals, is often considered a poor colonizer of the human nasal environment.
• Understanding the colonization dynamics of animal-associated S. aureus strains in humans is crucial for public health and infection control.

Purpose of the Study:

• To investigate the colonization capacity of a bovine S. aureus ST398 strain compared to a human S. aureus strain in the human nasal cavity.
• To assess the survival and competitive ability of S. aureus ST398 in a human host environment.

Main Methods:

• 16 healthy volunteers were inoculated with a mixture of human MSSA strain 1036 (ST931) and bovine MSSA strain 5062 (ST398).
• Participants underwent nasal cultures for 21 days post-inoculation to monitor bacterial survival and loads.
• Analysis included comparing elimination rates, bacterial loads, and the presence of mobile genetic elements.

Main Results:

• The bovine ST398 strain (5062) demonstrated robust survival, with significantly higher bacterial loads on days 7 and 21 compared to the human strain (1036).
• While the human strain was eliminated faster (median 14 days), the difference was not statistically significant (p=0.065).
• In several volunteers, the ST398 strain outnumbered the human strain, indicating strong competitive ability.

Conclusions:

• Staphylococcus aureus ST398, even of bovine origin, can effectively compete with and colonize the human nasal niche.
• The study challenges the perception of S. aureus ST398 as a transient colonizer, highlighting its potential for sustained presence in humans.
• No acquisition or loss of mobile genetic elements was observed in either strain during the 21-day follow-up period.