First description of Enterococcus faecalis small colony variant in a patient with aortic valve endocarditis

Abstract number: O363

Wellinghausen N., Sigge A.

Objective: Small colony variants (SCV) constitute a slow-growing subpopulation of bacteria with distinctive phenotypic and pathogenic traits. To our knowledge, SCV are not yet described in enterococci. We discovered SCV of Enterococcus faecalis in blood cultures of a patient with aortic valve endocarditis and characterised the structural particularities of the phenotype.

Case report and results: A 74-year old female patient who underwent aortic valve replacement with a bovine bioprothesis three years ago presented to the emergency department with persistent fatigue. By trans­oesophageal echocardiography vegetations on the aortic valve were documented. In two out of two blood cultures E. faecalis susceptible to ampicillin and imipenem, and intermediate susceptible to rifampicin was grown. In addition to typical E. faecalis colonies, a SCV phenotype consisting of small pin-point colonies was detected in both blood cultures. Typing by pulsed-field gel electrophoresis revealed clonal identity of both phenotypes. Antimicrobial susceptibility as tested on blood-containing Mueller-Hinton agar was comparable. In order to characterise the SCV further we performed light, scanning electron microscopy (SEM), and transmission EM (TEM) of both phenotypes. In the Gram-stain, the SCV showed Gram-positive, inhomogenous cocci with irregular size while the isogenic normal phenotype appeared homogenously. By SEM, SCV varied in size between one-fourth and up to eight times the size of the normal phenotype. Irregular and multiple divisions were observed in SCV. In addition, debris covered SCV isolates and an intercellular substance was more abundant in SCV than in the normal phenotype. By TEM, multiple and irregular cross walls, large swollen-appearing cells as well as empty cells were observed in the SCV (Fig. 1). Growth curves of both phenotypes revealed marked slower growth of the SCV. The patient was treated with imipenem and rifampicin for six weeks and suffered from a relapse of the endocarditis three weeks later, requiring replacement of the prosthetic aortic valve. After another six weeks of antimicrobial therapy with ampicillin and gentamicin the patient recovered.

Conclusion:Enterococcus faecalis is able to form a SCV phenotype with impaired growth characteristics and distinctive ultrastructural alterations observed by light microscopy and EM. Further studies are underway to investigate alterations in cellular metabolism in enterococcal SCV.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Location: Barcelona, Spain
Presentation type:
Back to top