A 53-year-old man comes to the emergency department due to 2 weeks of intermittent low-grade fevers and fatigue. Temperature is 38.5 C (101.3 F), blood pressure is 120/80 mm Hg, pulse is 92/min, and respirations are 16/min. On cardiovascular examination, an early diastolic murmur is present and best heard at the left sternal edge. Subungual splinter hemorrhages are seen. Laboratory study results show leukocytosis and an elevated erythrocyte sedimentation rate. Blood cultures are drawn and grow gram-positive cocci that synthesize dextrans from sucrose. The organism contributing to this patient's current condition is also associated with which of the following?
Viridans streptococci, notably Streptococcus mutans and S sanguinis, are normally present in the human mouth and are major contributors to tooth decay and the initiation of dental caries. These organisms also cause bacterial endocarditis, deep wound infections, abdominal abscesses, and septicemia. Viridans streptococci can adhere to tooth enamel and to fibrin-platelet aggregates on damaged heart valves due to their ability to produce insoluble extracellular polysaccharides (dextrans) using sucrose as a substrate. This colonization of host surfaces contributes to their ability to cause infection.
(Choice A) Anterior uveitis (inflammation of the iris) can be caused by infectious processes (eg, herpes viruses, syphilis, Lyme disease) and inflammatory conditions (eg, HLA-B27-related diseases, sarcoidosis). It is not associated with viridans streptococcal infections.
(Choice B) S bovis is associated with colon cancer, and patients with S bovis endocarditis should undergo colonoscopic evaluation to exclude neoplasia.
(Choice D) Erythema nodosum (erythematous to violaceous subcutaneous nodules usually appearing on the legs) is a nonspecific finding. It is associated with multiple bacterial infections, most commonly S pyogenes pharyngitis, but also Staphylococcus aureus, fungi (eg, coccidioidomycosis, histoplasmosis, blastomycosis), chlamydia, and others. It is also associated with Crohn disease, sarcoidosis, and other inflammatory conditions.
(Choices E and F) Poststreptococcal glomerulonephritis is a type III (immune complex-mediated) hypersensitivity reaction in which immune complexes deposit on the glomerular membrane and fix complement, leading to inflammation, renal dysfunction, hematuria, and nephritic range proteinuria. Migratory polyarthritis is a characteristic of rheumatic fever, an immune-mediated disease. These conditions typically follow infections with group A Streptococcus (S pyogenes), which does not produce dextrans.
Educational objective:
Viridans streptococci produce dextrans that aid them in colonizing host surfaces, such as dental enamel and heart valves. These organisms cause subacute bacterial endocarditis, classically in patients with preexisting cardiac valvular defects after dental manipulation.