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

Two cases of Aerococcus urinae endocarditis are reported. The organism is n ot included in any database of commercial identification systems at this ti me. Formation of tetrades and positive reactions for leucine arylamidase an d beta-glucuronidase pointed strongly to A. urinae. The cellular fatty acid pattern was similar to that of Aerococcus viridans, with predominantly C-1 6:0, C-18:1 omega 9c and C-18:0; the presence of C-18:1 omega 7t differenti ated our isolates from A. viridans and can support the diagnosis of A, urin ae. Furthermore, susceptibility to penicillin but resistance to cotrimoxazo le represents a pattern opposite to that of A, viridans. Minimal inhibition concentrations of gentamicin and netilmicin were less than or equal to 64 mg/l but those of tobramycin were greater than or equal to 256 mg/l. Penici llin combined with either gentamicin or netilmicin showed distinct synergy in killing kinetics. These combinations seem to be the appropriate regimen to treat A. urinae endocarditis.