Cardiobacterium spp
(C hominis, C valvarum)

Published 18.7.21

Microaerophilic, pleomorphic gram-negative bacillus often with swelling of one or both ends and retained crystal violet dye at the poles.

It is a part of the normal flora of the nose and throat.

Culture

• A slow-growing organism, blood culture may take longer than usual to flag positive. The fluid culture may not have turbidity associated with growth (consider a blind subculture).

• Grows on blood, chocolate and Mueller-Hinton agar in the presence of 5% CO2 and humidity. They grow poorly on MacConkey agar.

C hominis is slow-growing (may take days to grow), producing small alpha-haemolytic colonies with a serpentine growth pattern from the edge to the adjacent colonies.

• Oxidase +ve, catalase -ve, Indole +ve.

• C valvarum is more fastidious and produces smaller non-haemolytic colonies.

• Phenylphosphonate reaction – C valvarum is negative, C hominis is positive.

Identification

• API 20NE – may misidentify it as Pasteurella.

• MALDI ToF

• 16s rRNA PCR

• Endocarditis – Subacute endocarditis almost exclusively in adults with a preexisting valvular disease usually after a dental procedure, oral infection or upper GI endoscopy.
  In children, it is associated with underlying congenital heart disease.
  Mortality 10%.
  Insidious onset endocarditis (2-5 months), splenomegaly, anaemia, haematuria, immune glomerulonephritis, often without fever. The vegetation is often large and needs surgery.
  Large vessel emboli are a common association.
  Complications – septic arthritis, discitis, mycotic aneurysm and neurological involvement.

• Soft tissue infection

• Peritoneal catheter-related infection.

It is susceptible to -

• Penicillin, ampicillin,

• Cephalosporins,

• Fluoroquinolones – ciprofloxacin and levofloxacin,

• Chloramphenicol

• Tetracycline – tetracycline, doxycycline

Variable susceptibility:

• Aminoglycosides,

• Erythromycin, and

• Clindamycin

Treatment is usually a beta-lactam (amoxicillin/ceftriaxone) with/without aminoglycoside or ciprofloxacin.