Enterococci are intrinsically resistant to cephalosporins, fluoroquinolones, clindamycin, fusidic acid, macrolides, trimethoprim and penicillin.
Enterococcus faecalis
- Usually susceptible to ampicillin, doxycycline and chloramphenicol.
- Nitrofurantoin may be useful for bacterial cystitis.
- Typically susceptible to fosfomycin.
- Typically effective reserved drugs include carbapenems, linezolid and vancomycin
- Synergistic combination of amoxicillin/ampicillin plus an aminoglycoside may be useful for serious infection as cell wall damaging effects of the beta-lactam enhance aminoglycoside penetration and activity
- In humans, ampicillin + ceftriaxone has been used in some patients with endocarditis, when aminoglycosides are contraindicated. This might be viable in animals as well. (This does not apply to E. faecium)
- For cystitis, it may be reasonable to use amoxicillin (22+ mg/kg PO q8h) even if the isolate is reported as resistant, because of the high drug levels in urine. The potential risks of treatment failure vs the risks associated with higher tier drugs must be considered, but trying amoxicillin may be reasonable.
Enterococcus faecium
- Often highly drug resistant
- May be susceptible to ampicillin but resistance is very common.
- Vancomycin and linezolid are reserved drugs to which enterococci are usually susceptible.
- Resistant to carbapenems and doxycycline.
- Nitrofurantoin may be useful for bacterial cystitis.
- Typically susceptible to fosfomycin.
- Synergistic combination of amoxicillin/ampicillin plus an aminoglycoside may be useful for serious infection as cell wall damaging effects of the beta-lactam enhance aminoglycoside penetration and activity.
- For cystitis, it may be reasonable to use amoxicillin (22+ mg/kg PO q8h) even if the isolate is reported as resistant, because of the high drug levels in urine. The potential risks of treatment failure vs the risks associated with higher tier drugs must be considered, but trying amoxicillin may be reasonable.
Other enterococci
- Generally susceptible to ampicillin.