Cardiobacterium spp (C hominis, C valvarum)

Bacteria:

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 and identification:

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.

API 20NE – may misidentify it as Pasteurella.
MALDI ToF
16s rRNA PCR

Clinical presentation:

• Endocarditis – Subacute endocarditis almost exclusively in adults with a preexisting valvular disease usually after a dental procedure, oral infection or upper GI endoscopy. the
  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.

Antibiotic susceptibility:

• 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.