Anaerobic, non-sporulating, Gram-positive bacilli bacteraemia characterized by 16S rRNA gene sequencing

Abstract

Owing to the difficulties in identifying anaerobic, non-sporulating, Gram-positive bacilli in clinical microbiology laboratories, the epidemiology and clinical spectrum of disease of many of these bacteria have been poorly understood. The application of 16S rRNA gene sequencing in characterizing bacteraemia due to anaerobic, non-sporulating Gram-positive bacilli during a 4-year period is described. The first case of Olsenella uli bacteraemia, in a patient with acute cholangitis, is also reported. Among 165 blood culture isolates of anaerobic, Gram-positive bacilli, 75 were identified as Propionibacterium acnes by phenotypic tests and 21 as members of other anaerobic, non-sporulating Gram-positive bacilli by 16S rRNA gene sequencing. Of these 96 isolates, 16 (17 %) were associated with cases of clinically significant bacteraemia, among which 10 (63 %) were caused by Eggerthella, four (25 %) by Lactobacillus and one (6 %) by each of Eubacterium tenue and O. uli. Five of the 10 Eggerthella isolates were Eggerthella lenta, whereas the other five belonged to two novel Eggerthella species, with Eggerthella hongkongensis being almost as prevalent as Eggerthella lenta. Underlying disease in the gastrointestinal tract, isolation of Eggerthella and Lactobacillus, and monomicrobial bacteraemia were associated with clinically significant bacteraemia, whereas isolation of P. acnes and polymicrobial bacteraemia were associated with pseudobacteraemia. Most patients with clinically significant bacteraemia had underlying diseases, with diseases in the gastrointestinal tract being most common. The overall mortality rate was 31 %. Immunocompromised patients with clinically significant bacteraemia due to anaerobic, non-sporulating, Gram-positive bacilli other than P. acnes should be treated with appropriate antibiotics. The unexpected frequency of isolation of Eggerthella from blood cultures and its association with clinically significant disease suggest that this genus is probably of high pathogenicity. Further studies to look for specific virulence factors are warranted.