3.2.3 Vancomycin-resistant Enterococci

Enterococci are gastro-intestinal commensals of humans and other animals. They are moderately virulent, mainly in the context of healthcare i.e. they are largely a HCAI pathogen, although they can cause urinary tract infection in healthy individuals. They cause infections related to prosthetic materials such as intravascular devices, mechanical heart valves and joint implants, that can be extremely difficult to treat.

VRE strains of Enterococcus, most commonly Enterococcus faecium, cause outbreaks among cancer and critical care patients with infections that are hard to treat and require expensive antimicrobials.

E. faecium is intrinsically resistant to β-lactams, including amoxicillin which is active against other Enterococci such as E. faecalis, which means that the loss of vancomycin sensitivity is important. Other species exist that are intrinsically resistant to vancomycin e.g. E. gallinarum and E. casseliflavus, but these only cause sporadic infections in humans (CDC, 2010).

There are a number of resistant phenotypes and genes involved in VRE, the main ones of clinical concern being those with the vanA phenotype. This is mediated by the vanA operon, a two-component system which leads to high level resistance to both vancomycin and teicoplanin (the most commonly used glycopeptide antimicrobials). The vanA operon is transmitted via a plasmid so can move between strains and species. It is found chiefly in E. faecium and occasionally in E. faecalis. Other resistant phenotypes, for example vanB, are of less clinical or veterinary importance (Cetinkaya et al., 2000).

Figure 7 Dairy-source foods derived from cows and goats are a potential source of zoonoses.

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Both fluoroquinolone-resistant Campylobacter and Salmonella infections are major zoonoses and there are few antimicrobial treatment options. The infections can easily be acquired from food of animal origin if food hygiene is not strictly applied.

Figure 7 Dairy-source foods derived from cows and goats are a potential source of zoonoses.

Enterococci of animal origin are important from the One Health perspective as a source of resistance genes entering the human food chain.