Lactococcus lactis endocarditis and liver abscess in an immunocompetent patient: a case report and review of the literature

Abstract

Background: Over the last two decades, several cases of infections caused by Lactococcus lactis have been reported. This Gram-positive coccus is considered non-pathogenic for humans. However, in some rare cases, it can cause serious infections such as endocarditis, peritonitis, and intra-abdominal infections.

Case presentation: A 56-year-old Moroccan patient was admitted to the hospital because of diffuse abdominal pain and fever. The patient had no past medical history. Five days before his admission, he developed abdominal pain in the right lower quadrant along with chills and feverish sensations. Investigations showed a liver abscess, which was drained, and the microbiological study of the pus revealed Lactococcus lactis subsp. cremoris. Three days after admission, control computed tomography objectified splenic infarctions. Cardiac explorations were performed and showed a floating vegetation on the ventricle side of the aortic valve. We retained the diagnosis of infectious endocarditis according to the modified Duke criteria. The patient was declared afebrile on day 5 and the evolution was clinically and biologically favorable. Lactococcus lactis subsp. cremoris, formerly known as Streptococcus cremoris, is a rare cause of human infections. The first case of Lactococcus lactis cremoris endocarditis was reported in 1955. This organism includes three subspecies: lactis, cremoris, and hordniae. A MEDLINE and Scopus search showed only 13 cases of infectious endocarditis due to Lactococcus lactis, with subsp. cremoris identified in four of the cases.

Conclusions: To our knowledge, this is the first case report of the co-occurrence of Lactococcus lactis endocarditis and liver abscess. Despite its reported low virulence and good response to antibiotic treatment, Lactococcus lactis endocarditis must be considered a serious disease. It is imperative for a clinician to suspect this microorganism of causing endocarditis when they notice signs of infectious endocarditis in a patient with a history of consumption of unpasteurized dairy products or contact with farm animals. The finding of a liver abscess should lead to an investigation of endocarditis, even in previously healthy patients without obvious clinical signs of endocarditis.

Keywords: Endocarditis; Lactococcus lactis; Lactococcus lactis subsp. cremoris; Liver abscess; Splenic infarction.

Fig. 1

Abdominal computed tomography revealed a multiloculated hypodensity in segment VII, suggesting a liver abscess (white arrowhead)

Fig. 2

Thoracic computed tomography revealed a mild predominantly right bilateral pleural effusion (white arrowheads)

Fig. 3

Control abdominal computed tomography revealed areas of splenic infarction (white arrowheads)

Fig. 4

Transesophageal echocardiography showed a floating and vibratile vegetation measuring 8 × 5 mm on the ventricular side of the aortic valve

Fig. 5

Control computed tomography on follow-up after 2 months showed almost complete regression of the liver abscess and splenic infarctions