Isolated apical intracavitary left ventricular abscess in a normal heart: a rare complication of Streptococcus milleri endocarditis

Streptococcus sinensis may react with Lancefield group F antiserum

Lancefield group F streptococci have been found almost exclusively as members of the ‘Streptococcus milleri’ group, although they have been reported very occasionally in some other streptococcal species. Among 302 patients with bacteraemia caused by viridans streptococci over a 6-year period, three cases were caused byStreptococcus sinensis(type strain HKU4T, HKU5 and HKU6). All three patients had infective endocarditis complicating their underlying chronic rheumatic heart diseases. Gene sequencing showed no base differences between the 16S rRNA gene sequences of HKU5 and HKU6 and that of HKU4T. All three strains were Gram-positive, non-spore-forming cocci arranged in chains. All grew on sheep blood agar as α-haemolytic, grey colonies of 0.5–1 mm in diameter after 24 h incubation at 37 °C in ambient air. Lancefield grouping revealed that HKU5 and HKU6 were Lancefield group F, but HKU4Twas non-groupable with Lancefield groups A, B, C, D, F or G antisera. HKU4Twas identified by the Vitek system (GPI), API system (20 STREP) and ATB system (ID32 STREP) as 99 %Streptococcus intermedius, 51.3 %S. intermediusand 99.9 %Streptococcus anginosus, respectively. Using the same tests, HKU5 was identified as 87 %Streptococcus sanguinis/Streptococcus gordonii, 59 %Streptococcus salivariusand 99.6 %S. anginosus, respectively, and HKU6 as 87 %S. sanguinis/S.gordonii, 77 %Streptococcus pneumoniaeand 98.3 %S. anginosus, respectively. The present data revealed that a proportion of Lancefield group F streptococci could beS. sinensis. Lancefield group F streptococci should not be automatically reported as ‘S. milleri'.

"Streptococcus milleri" endocarditis caused by Streptococcus anginosus

Unlike other viridans streptococci, members of the "Streptococcus milleri group" are often associated with abscess formation, but are only rare causes of infective endocarditis. Although it has been shown that almost all S. intermedius isolates and most S. constellatus isolates, but only 19% of S. anginosus isolates, were associated with abscess formation, no report has addressed the relative importance of the 3 species of the "S. milleri group" in infective endocarditis. During a 5-year period (April 1997 through March 2002), 6 cases of "S. milleri" endocarditis (out of 377 cases of infective endocarditis), that fulfil the Duke's criteria for the diagnosis of infective endocarditis, were encountered. All 6 "S. milleri" isolates were identified as S. anginosus by 16S ribosomal RNA (rRNA) gene sequencing. Three patients had underlying chronic rheumatic heart disease and 1 was an IV drug abuser. Five had monomicrobial bacteremia, and 1 had polymicrobial (S. anginosus, S. mitis, Granulicatella adiacens, and Slackia exigua) bacteremia. Two patients died. None of the 6 isolates were identified by the Vitek system (GPI) or the API system (20 STREP) at >95% confidence. All 6 isolates were sensitive to penicillin G (MIC 0.008-0.064 microg/mL), cefalothin, erythromycin, clindamycin, and vancomycin. Accurate identification to the species level, by 16S rRNA gene sequencing, in cases of bacteremia caused by members of the "S. milleri group", would have direct implication on the underlying disease process, hence guiding diagnosis and treatment. Infective endocarditis should be actively looked for in cases of monomicrobial S. anginosus bacteremia, especially if the organism is recovered in multiple blood cultures.