Methicillin-susceptible and -resistant Staphylococcus aureus with high-level antiseptic and low-level mupirocin...

Area of Science:

• Microbiology
• Infectious Diseases
• Antimicrobial Resistance

Background:

• Staphylococcus aureus is a common cause of hospital-acquired infections.
• Mupirocin and antiseptics are vital for controlling S. aureus colonization and infections.
• Emergence of resistance threatens treatment efficacy.

Purpose of the Study:

• To determine the prevalence and spread of mupirocin and antiseptic resistance in S. aureus.
• To investigate the genetic basis of resistance (mupA, qacA/B, smr genes).
• To understand the relationship between resistance, bacterial strains (ST239, MRSA, MSSA), and clinical outcomes.

Main Methods:

• Isolation of S. aureus from nares and infection sites of hospitalized patients.
• Antimicrobial susceptibility testing (disk diffusion, MICs) for mupirocin and antiseptics.
• PCR detection of mupA, qacA/B, and smr resistance genes.

Main Results:

• 10 (3.8%) S. aureus isolates harbored the mupA gene, conferring mupirocin resistance.
• The mupA gene was more common in ST239 isolates (70%).
• qacA/B and smr genes were frequently found in MRSA (70.5% and 6.3%, respectively) but rarely in MSSA (1.8%).
• Isolates with antiseptic resistance genes showed significantly higher MICs for benzethonium chloride, benzalkonium chloride, and chlorhexidine digluconate.
• ST239 strains with identical resistance patterns were isolated from both nares and infection sites, suggesting endogenous spread.

Conclusions:

• Widespread mupirocin and antiseptic resistance exists in S. aureus within a Malaysian tertiary hospital.
• ST239 MRSA strains are significant carriers of both mupirocin (mupA) and antiseptic resistance genes (qacA/B, smr).
• Co-occurrence of resistance genes leads to elevated MICs, necessitating enhanced infection control strategies and monitoring of emerging resistant strains like ST1.