Closing The Brief Case: A Variant on a Classic—Abiotrophia defectiva Endocarditis with Discitis

ANSWERS TO SELF-ASSESSMENT QUESTIONS

• 1.Abiotrophia defectiva grows best on which media?
  • a.TSA media with 5% sheep blood agar
  • b.MacConkey agar
  • c.Enriched chocolate agar
  • d.Columbia CNA media with 5% sheep blood agarAnswer: c. Abiotrophia defectiva grows best on enriched chocolate agar. Both Abiotrophia and Granulicatella species are fastidious organisms which require supplemental l-cysteine or pyridoxal hydrochloride for growth, both of which are absent from most routine media. Growth is not supported on sheep blood, MacConkey, or CNA agars.
• 2.Abiotrophia and Granulicatella species are most reliably susceptible to which antimicrobial?
  • a.Vancomycin
  • b.Meropenem
  • c.Gentamicin
  • d.CeftriaxoneAnswer: a. Vancomycin is the most reliably susceptible antimicrobial for these species. Susceptibilities to ceftriaxone and penicillin vary significantly between Abiotrophia and Granulicatella species. While broader-spectrum drugs such as carbapenems, gentamicin, and vancomycin are more reliably effective, de-escalation to penicillin and ceftriaxone requires susceptibility testing due to the unpredictable susceptibility profiles.
• 3.
  What is the prevalence of infective endocarditis caused by Abiotrophia and Granulicatella species?

  • a.
    <5%
  • b.
    10%
  • c.
    20%
  • d.
    >25%Answer: a. Abiotrophia and Granulicatella species are rare causes of infective endocarditis, contributing to <5% of total disease etiologies. Because they are fastidious organisms and can present as culture-negative endocarditis, their prevalence may be underestimated. The clinical presentation of endocarditis caused by Abiotrophia often includes fever, vegetations, cardiac murmur, and, occasionally, emboli.

TAKE-HOME POINTS

• Abiotrophia and Granulicatella species (formerly termed “nutritionally variant streptococci”) have unique growth requirements and will not thrive on routine blood agar, growing best on enriched chocolate agar.

• Abiotrophia and Granulicatella species can be distinguished from most other Streptococcus-like species by satellite growth along a staphylococcal streak. Relevant biochemical properties include lack of growth in 6.5% NaCl broth and pyrrolidonyl aminopeptidase (PYR) and leucine aminopeptidase (LAP) activity.

• The lack of detection by rapid molecular identification platforms in conjunction with Gram stain morphology consistent with Gram-positive cocci in pairs or chains should raise suspicions for Abiotrophia and Granulicatella species.

• Abiotrophia and Granulicatella species have variable susceptibility to penicillin and ceftriaxone, requiring antimicrobial susceptibility testing for optimal management.

See https://doi.org/10.1128/JCM.03093-20 in this issue for case presentation and discussion.