Dear Colleagues,

The major challenge that clinicians face when treating infections is antibiotic resistance. Over the past three decades, severe infections in healthcare environments caused by multiresistant Gram-positive bacteria have been making headlines worldwide. The success of these pathogens lies mainly in their changing epidemiology and genetic flexibility, frequently leading to alterations in their genetic repertoire, namely the gain or loss of antimicrobial resistance (AMR) and virulence genes carried in mobile genetic elements, or the emergence of compensatory mutations mediating fitness and adaptation.

What is so special about these multidrug-resistant bacteria? Where do staphylococci and enterococci rank in the top-ten hospital-associated pathogens? Which are the factors promoting the continuous evolution and maintenance of well-adapted and high-risk clones?

S. aureus, particularly methicillin-resistant S. aureus (MRSA), occurs in clonal waves of multidrug-resistant clones. The reason for the rise and fall of specific strain types remains poorly understood. Coagulase-negative staphylococci are important reservoirs of antibiotic resistance and virulence for S. aureus and have been involved in the evolution and emergence of new antibiotic resistance determinants.

Enterococci are intrinsically resistant, may harbor different degrees of resistance to several antimicrobial classes, and have acquired resistance multiple times over their evolutionary history. The occurrence of the so called “van-alphabet” through the acquisition of plasmid-encoded vancomycin resistance, has become the paradigm of the post-antibiotic era. The transfer of plasmids and large genomic regions is the basis of their genomic plasticity and adaptability to the ever-changing hospital environment.

This Special Issue will focus on the phenotypic and molecular strategies adopted by staphylococci and enterococci that allow for fast adaptation, the development of multidrug resistance, and refractoriness to effective therapy.

Knowledge in this field will help in understanding the emergence of pathogenic clones and the genetic variation underlying clinically relevant changes, as well as in pinpointing novel targets for antibiotics, vaccines or immunotherapy.

Dr. Floriana Campanile
Dr. Maria Miragaia
Guest Editors

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• hospital-acquired pathogens
• multidrug-resistant Gram-positive isolates
• genotypic characteristics of staphylococci and enterococci
• mechanisms of antibiotic resistance
• evolving antibacterial strategies