These -lactamase producing strains are susceptible to ampicil- lin-sulbactam and to vancomycin. Intrinsic penicillin resistance is uncommon in E faecalis but is common in E faecium. It is reasonable to treat patients with E faecalis IE caused by strains that are intrinsically resistant to penicillin with a combination of vancomycin plus gentamicin. Recommendations for treatment of IE caused by these strains are shown in Table 14. Recommendations 1. Vancomycin should be administered only if a patient is unable to tolerate penicillin or ampicillin (Class I; Level of Evidence B). 2. It is reasonable that patients with NVE receive 6 weeks of vancomycin-gentamicin therapy and that patients with PVE receive at least 6 weeks of ther- apy (Class IIa; Level of Evidence B). 3. Patients with E faecalis IE caused by strains that are intrinsically resistant to penicillin should be treated with a combination of vancomycin plus gentamicin (Class I; Level of Evidence B). Enterococcal Endocarditis Resistant to Penicillin, Aminoglycosides, and Vancomycin The rapid emergence of vancomycin-resistant enterococci has become a global issue of major clinical importance. Most of these strains are E faecium, and as many as 95% of strains express multidrug resistance to vancomycin, aminoglyco- sides, and penicillins. Only about 3% of E faecalis strains are multidrug resistant, and many vancomycin-resistant E faecalis are penicillin susceptible. Fortunately, E faecium IE is uncom- mon. Most of the reports of multidrug-resistant E faecium IE are single case reports, reports of a small number of collected cases, or cases reported in new drug trials.200 Enterococci are considered to be resistant to vancomycin if MICs are >4 g/mL. Linezolid and daptomycin are the only 2 antimicrobial agents currently available in the United States that may be useful for the treatment of multidrug-resistant E faecium IE. 