Burden of Rifampicin- and Methicillin-Resistant Staphylococcus aureus in Italy

Area of Science:

• Microbiology
• Infectious Diseases
• Antimicrobial Resistance

Background:

• Methicillin-resistant Staphylococcus aureus (MRSA) infections are a significant healthcare concern.
• Rifampicin is a key antibiotic for MRSA treatment, but rifampicin resistance (RIF-R) is increasing globally.
• Italy shows a higher prevalence of RIF-R in multidrug-resistant MRSA (16.4%) compared to Europe (5.7%).

Purpose of the Study:

• To investigate the relationship between bacterial clones, rpoB gene mutations, and antimicrobial susceptibility profiles in RIF-R MRSA isolates from hospitalized patients in Italy.
• To understand the genetic and phenotypic characteristics of RIF-R MRSA strains.
• To assess the clinical implications of RIF-R MRSA in a healthcare setting.

Main Methods:

• Antimicrobial susceptibility testing using broth microdilution.
• Bacterial isolate characterization via MLST, SCCmec, and spa-typing.
• Analysis of the rpoB gene through PCR and sequence analysis.

Main Results:

• RIF-R MRSA isolates exhibited high rates of heterogeneous vancomycin-intermediate S. aureus (hVISA) (60%) and daptomycin nonsusceptibility (22%).
• Dominant MRSA clones included ST228-SCCmec I (44%), ST8-SCCmec IV (18%), ST239-SCCmec III (16%), ST5-SCCmec II (14%), and ST22-SCCmec IVh (4%).
• Thirteen distinct RpoB amino acid substitutions were identified, with H481N being common for low-level resistance, while other single or multiple mutations conferred high-level resistance.

Conclusions:

• The study identified ST228 as a prevalent clone in Italy, strongly associated with reduced susceptibility to glycopeptides (hVISA).
• The increasing prevalence of RIF-R MRSA strains with complex resistance mechanisms poses a serious threat to patient treatment.
• These findings highlight the difficulty in treating infections caused by these multidrug-resistant strains, even with novel antibiotics.