Butyricimonas virosa bacteraemia identified by MALDI-TOF.

Abstract

We read with interest the recent report by Ulger Toprak et al. [1] reporting the first case of Butyricimonas virosa bacteraemia published earlier this year. Here we describe the case of a 72-year-old man with colon cancer who presented with septic shock after aortic aneurysm surgery, with Butyricimonas virosa recovered from blood cultures. This anaerobic bacteria and related species had been previously described in rat and human faecal material [2], [3] but never before in an infectious context in humans. The authors point out that this Gram-negative anaerobic bacterium produced catalase, was inhibited on Bacteroides bile aesculin agar and was resistant to kanamycin (1 mg), vancomycin (5 μg) and colistin sulfate (10 μg). This phenotypic features were suggestive of a Prevotella spp. However, 16S rRNA sequencing demonstrated a 99% nucleotide identity with B. virosa [1]. Recently we also identified a case of B. virosa bacteraemia in a 81-year-old male veteran who developed a fever 18 days after a Whipple procedure for adenocarcinoma of the duodenum. Two sets of blood samples were drawn for culture. Gram-negative rods were isolated from the anaerobic blood culture bottle of one set during the fifth day of incubation, after masked subculture of a blood culture bottle triggering positive with a negative Gram stain. Consistent with the report of Ulger Toprak et al. [1], our isolate grew anaerobically on Brucella blood agar (Becton Dickinson, Franklin Lakes, NJ, USA), and on Gram stain appeared as a small Gram-negative rod. Our isolate was catalase positive and was resistant to kanamycin (1 mg), vancomycin (5 μg) and colistin sulfate (10 μg). Utilizing RapID Ana testing (bioMerieux, Marcy l’Etoile, France), the isolate was found to be positive for β-galactosidase, N-acetyl-β-glucosaminidase, indole, leucyl glycine and pyroglutamic acid arylamidase, as was the previously reported isolate; however, a conclusive identification could not be made. The isolate was then evaluated by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF) (MicroFlex LT; Bruker Daltonics, Leipzig, Germany) with and without a formic acid extraction. Vitek MS identified three separate colonies of the bacterium as Butyricimonas virosa (score = 2.531, MALDI Biotyper 3.1). Our patient recovered without antimicrobial treatment. Molecular identification technologies such as 16S rRNA sequencing and MALDI-TOF provide microbiologists with a much richer understanding of clinical anaerobic bacteriology. Without MALDI-TOF, we would not have correctly identified this organism. Proper identification of significant isolates may help to better define the relationships between particular pathogens and clinical syndromes.