Group D Streptococcus (GDS) Infections (Streptococcus bovis/Streptococcus gallolyticus) Workup

Updated: Mar 02, 2021
  • Author: Shirin A Mazumder, MD, FIDSA; Chief Editor: Michael Stuart Bronze, MD  more...
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Workup

Laboratory Studies

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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Imaging Studies

Echocardiography

Transthoracic or transesophageal (more sensitive) echocardiography frequently permits visualization of vegetations. Echocardiography should be performed in all patients with S bovis bacteremia. Vegetations associated with Group D streptococcal infections tend to be larger and can cause signficant valvular destruction [14] .

An absence of vegetation does not rule out infective endocarditis. For more information on echocardiography findings, see Infective Endocarditis.

Colonoscopy

This test is used to detect malignant lesions of the colon.

Colonoscopy should be performed in all patients with S. bovis bacteremia or endocarditis as there is an association with colonic neoplasia. There appears to be a increased association with malignancy with S. bovis biotype I than with S. bovis biotype II [15] .

Regular-interval follow-up colonoscopy should be performed in patients in whom no lesion is found on initial investigation.

Esophagogastroduodenoscopy

Esophagogastroduodenoscopy (EGD) is used to detect malignant lesions of the esophagus, stomach, and duodenum.

EGD should be performed in patients with S bovis bacteremia or endocarditis who have no evidence of colonic malignancy.

Liver ultrasonography and CT scanning

Both of these studies should be performed in cases of associated hepatobiliary disease.

Usually, liver ultrasonography is performed first, followed by CT scanning.

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Other Tests

Consider referral of the organism for formal MIC testing if the response to antibiotic therapy is unfavorable.

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