Molecular genotyping of isolates of Actinobacillus actinomycetemcomitans by pulsed-field gel electrophoresis after separate digestion with Sse8387I and XhoI

Recurrent infective endocarditis due to Aggregatibacter actinomycetemcomitans: reinfection or relapse?

Aggregatibacter actinomycetemcomitans is commonly part of the normal microflora of the human upper respiratory tract. It has been implicated in periodontal disease and various infections, particularly endocarditis. We report here what we believe to be the first case of recurrent infective endocarditis due to A. actinomycetemcomitans in a 44-year-old woman occurring 5 years after the initial episode. Genomic analysis proved that the strains were closely related. Despite efficient antibiotic treatment, surgery was necessary for recovery.

Resistance of fluorescent-labelled Actinobacillus actinomycetemcomitans strains to phagocytosis and killing by human neutrophils

Neutrophils are initially the predominant cells involved in the host defence of bacterial infections, including periodontal disease. Aggressive periodontitis is associated with Actinobacillus actinomycetemcomitans, a Gram-negative capnophilic microorganism. Infections caused by A. actinomycetemcomitans are not resolved by the host immune response despite the accumulation of neutrophils at the site of inflammation. To better understand the role of natural host defence mechanisms in A. actinomycetemcomitans infections, the interaction of phenotypically diverse strains of this pathogen with human neutrophils was assessed directly using techniques such as genetic labelling with the gene for green fluorescent protein, fluorescence-activated cell sorting and fluorescence imaging. The study included clinical isolates of A. actinomycetemcomitans represented by self-aggregating, biofilm-associated and isogenic planktonic variants. Data obtained showed that complement-mediated phagocytosis of A. actinomycetemcomitans was generally inefficient regardless of strain-specific serotype or leukotoxin production. Furthermore, the majority of ingested bacteria remained viable after exposure to neutrophils for 1 h. Interestingly, uptake of antibody-opsonized bacteria resulted in the rapid cell death of neutrophils. This was in contrast to ingestion of complement-opsonized bacteria, which did not affect neutrophil viability. The methods used in this study provided reliable and reproducible results with respect to adherence, phagocytosis and killing of A. actinomycetemcomitans when encountering human neutrophils.