Which lab tests are performed in the diagnosis of group D streptococcus (GDS) infections?

Updated: Mar 02, 2021
  • Author: Shirin A Mazumder, MD, FIDSA; Chief Editor: Michael Stuart Bronze, MD  more...
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Basic laboratory studies to evaluate for Streptococcus group D infections should include CBC count, electrolyte evaluation, creatinine level, and LFTs.

Blood cultures

Blood cultures are the most important tests.

Blood culture results are usually positive during the first 24-48 hours. In cases of endocarditis and sustained bacteremia, blood culture results are positive.

Gram stain from the blood culture bottles demonstrates gram-positive cocci in pairs or chains. S bovis cannot be differentiated from other streptococci using Gram staining.

Differentiating S bovis from Streptococcus salivarius is sometimes very difficult because S salivarius yields a positive reaction on the bile-esculin test. This happens with approximately 20% of the isolates.

Sensitivity testing is recommended, although most S bovis strains are exquisitely sensitive to penicillin. In a study by Mouton et al on 19 strains of S bovis, the minimal inhibitory concentrations (MICs) 50 and 90 were, respectively, 0.06 mg/L (susceptible) and 1 mg/L (intermediate susceptibility). The highest MIC was 2 mg/L (resistant). [13]

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