Enterococci have two types of resistance to vancomycin: acquired and intrinsic (natural). Some types of enterococci bacteria acquire the resistance when other bacteria come in contact with enterococci and share genetic information—scientists believe enterococci acquired the gene that resists vancomycin from bacteria in the digestive tract. Acquired resistance has been noted with two clinically important forms of enterococci: E. faecium and E. faecalis.
Of the dozen or so types of enterococci bacteria, some, such as E. gallinarum and E. casseliflavus, have an inherent, low-level resistance to vancomycin. These are very uncommon strains, however, and are of limited clinical significance.
If you have an enterococcal infection, it is crucial that your healthcare providers quickly identify the strain, so that they can determine how best to treat you and prevent patient-to-patient transmission. They will want to know if the strain infecting you is resistant to vancomycin, and if so, is the resistance intrinsic or acquired? If the resistance is acquired, does the strain contain specific genes that can share resistance traits with other bacteria, thus making it able to spread disease?
Tests are available to make those diagnoses.
Some healthcare practitioners, as part of their normal infection control procedures, will test you for the presence of VRE to learn whether you might be infected or colonized with the bacterium. This helps facilities know whether specific procedures should be used to reduce the potential spread of VRE.