Streptococcus bovis group and biliary tract infections: an analysis of 51 cases

Streptococcus bovis is a well-known cause of endocarditis, but its role in other infections has not been well described. We analysed prospectively all patients with biliary tract infections caused by S. bovis group during the period 1988-2011. We selected those cases associated with cholangitis and cholecystitis, defined according to Tokyo guidelines. Identification of the strains was performed using the API 20 Strep and the GP card of the Vitek 2 system, and was confirmed by molecular methods. Our series included 51 cases (30 cholangitis and 21 cholecystitis). The associated microorganisms were: Streptococcus infantarius (biotype II/1) 29 cases (57%), Streptococcus gallolyticus subsp. pasteurianus (biotype II/2) 20 cases (39%) and Streptococcus gallolyticus subsp. gallolyticus (biotype I) two cases (4%). The only difference found between S. infantarius and S. gallolyticus subsp. pasteurianus was a greater association of the first with malignant strictures of the bile ducts: 48% (14/29) versus 5% (1/20), p <0.001. Thirty-seven of the cases also had bacteraemia, causing 20% (37/185) of all S. bovis bacteraemia, with differences between S. gallolyticus subsp. gallolyticus (2/112; 2%) and the other two microorganisms: S. infantarius and S. gallolyticus subsp. pasteurianus (35/73; 48%; p <0.001). The vast majority of biliary tract infections due to S. bovis group are caused by S. infantarius and S. gallolyticus subsp. pasteurianus (S. bovis biotype II), and nearly half of the bacteraemia due to these two species has a biliary source (43% of the S. infantarius and 56% of S. gallolyticus subsp. pasteurianus).