Endocarditis due toAerococcus urinae: Diagnostic tests, fatty acid composition and killing kinetics

Two cases ofAerococcus urinae endocarditis are reported. The organism is not included in any database of commercial identification systems at this time. Formation of tetrades and positive reactions for leucine arylamidase and beta-glucuronidase pointed strongly toA. urinae. The cellular fatty acid pattern was similar to that ofAerococcus viridans, with predominantly C16∶0, C18∶1ω9c and C18∶0; the presence of C18∶1ω7t differentiated our isolates fromA. viridans and can support the diagnosis ofA. urinae. Furthermore, susceptibility to penicillin but resistance to cotrimoxazole represents a pattern opposite to that ofA. viridans. Minimal inhibition concentrations of gentamicin and netilmicin were≤64 mg/l but those of tobramycin were≥256 mg/l. Penicillin combined with either gentamicin or netilmicin showed distinct synergy in killing kinetics. These combinations seem to be the appropriate regimen to treatA. urinae endocarditis.