Persistence of a Staphylococcus aureus small-colony variant under antibiotic pressure in vivo

Area of Science:

• Microbiology
• Infectious Diseases
• Bacterial Pathogenesis

Background:

• Staphylococcus aureus small-colony variants (SCVs) are linked to persistent infections.
• Bovine mastitis caused by S. aureus is challenging to treat with standard antibiotics.

Purpose of the Study:

• To evaluate the colonization and persistence of S. aureus Newbould and its hemB mutant (SCV phenotype) in mouse mammary glands under antibiotic pressure.
• To understand the role of the SCV phenotype in S. aureus persistence during antimicrobial therapy.

Main Methods:

• Comparison of S. aureus Newbould and an isogenic hemB mutant (SCV) in a mouse mammary gland colonization model.
• Assessment of bacterial persistence following administration of cephapirin at 1 or 2 mg kg(-1).
• In vitro susceptibility testing of both strains to cephapirin.

Main Results:

• The hemB mutant exhibited significantly reduced tissue colonization compared to the parental strain.
• In vitro, the hemB mutant showed similar susceptibility to cephapirin as S. aureus Newbould.
• Despite reduced colonization, the hemB mutant was over 100 times more persistent in mammary glands than the parental strain under antibiotic treatment.

Conclusions:

• The SCV phenotype in S. aureus, while impairing initial colonization, enhances bacterial persistence in mammary glands during antibiotic treatment.
• The SCV phenotype may be a key factor in the in vivo persistence of S. aureus under antimicrobial pressure.
• These findings offer insights into the mechanisms behind chronic and difficult-to-eradicate S. aureus infections.