Do we know everything about Streptococcus mitis: From alpha to omega?

Abstract

Background: A 45 year old male was admitted with jaundice, abdominal pain and respiratory distress. He had history of chronic alcoholism. Materials and Methods: Blood tests revealed a raised leucocyte count of 19000/microlitre, high levels of bilirubin, amylase and lipase. Radiological investigations including chest x-ray, USG, CECT, and MRI gave findings of cholelithiasis, pancreatic pseudocyst, left sided pleural effusion and left lower lobe collapse. MRCP diagnosed choledocholithiasis. Pseudocyst fluid was aspirated and sent for culture and sensitivity. Results: Culture yielded pure growth of capsulated gram positive diplococci resembling Streptococcus pneumoniae. However, it was bile-insoluble and hence pure colonies were sent for confirmation by Vitek-2. Vitek-2 confirmed it to Streptococcus mitis sensitive to erythromycin, levofloxacin, linezolid and vancomycin. The patient responded to the antibiotics after surgery and was discharged. Conclusion: Streptococcus mitis is considered to be an oral commensal, sometimes causing infective endocarditis. However, as it contains almost all the virulence factors carried by it's close relative S. pneumoniae, and also can masquerade itself to the latter morphologically and biochemically to a great extent, it seems to walk a thin line between being a harmless commensal and a virulent pathogen. This incidence of infecting a pancreatic pseudocyst should make a microbiologist alert of considering a probability of it's increasing pathogenicity range.