3.2.2 Vancomycin-resistant S.aureus

Vancomycin is important against S. aureus as it can be used for MRSA strains or when β-lactams cannot be used. VISA refers to organisms with intermediate resistance while hVISA refers to subpopulations of organisms with intermediate resistance in a single culture. VRSA organisms are fully resistant to vancomycin. VISA, hVISA and VRSA therefore refer to S.aureus strains with varying degrees of resistance to vancomycin and using a number of resistance mechanisms. They have been found in increasing numbers in recent years in isolates from both humans and livestock and are a potential future threat (Al-Amery et al., 2019; Cong et al., 2020; Shariati et al., 2020).

Of greatest concern is the presence of the VanA genes, originally found in vancomycin-resistant Enterococci (VRE) (see Section 3.2.3), but other mechanisms can also lead to antimicrobial treatment failure and so are still important.