Invasion of human coronary artery endothelial cells by Streptococcus mutans OMZ175

Abstract

Introduction: Dissemination of oral bacteria into the bloodstream has been associated with eating, oral hygiene, and dental procedures; including tooth extraction, endodontic treatment, and periodontal surgery. Recently, studies identified Streptococcus mutans, the primary etiological agent of dental caries, as the most prevalent bacterial species found in clinical samples from patients who underwent heart valve and atheromatous plaque surgery.

Methods: By using antibiotic protection assays, we tested the capacity of 14 strains of S. mutans to invade primary human coronary artery endothelial cells (HCAEC).

Results: Serotype e strain B14 and serotype f strain OMZ175 of S. mutans were able to efficiently invade HCAEC. Among the tested strains, serotype f S. mutans OMZ175 was the most invasive, whereas strains of serotype c S. mutans, the most prevalent serotype in dental plaque, were not invasive. Based on its high invasion rate, we further investigated the invasive properties of serotype f OMZ175. Using transmission electron microscopy and antibiotic protection assays we demonstrate that S. mutans OMZ175 is capable of attaching to the HCAEC surface, entering the cells and surviving in HCAEC for at least 29 h.

Discussion: Our findings highlight a potential role for S. mutans in the pathogenesis of certain cardiovascular diseases.

Fig. 1

Invasive properties of Streptococcus mutans strains. The number of S. mutans colony-forming units (CFUs) recovered from the intracellular compartment of human coronary artery endothelial cells after 5 h of infection is shown. The data represent the log of the average ± SD of at least three independent experiments.

Fig. 2

Persistence of Streptococcus mutans in human coronary artery endothelial cells (HCAEC). The data represent the percentage of the initial inoculum of S. mutans that was able to reach the intracellular compartment of HCAEC and remained viable at different times. Values shown are log of means ± SD from at least three independent experiments.

Fig. 3

Electron micrographs of human coronary artery endothelial cells (HCAEC) invasion by Streptococcus mutans OMZ175 after 30 min (A), 5 h (B), and 29 h (C) of infection. The HCAEC monolayers co-cultured with S. mutans OMZ175 were fixed and prepared for transmission electron microscopy before being examined on a JEOL 100CX electron microscope. Upon entry, the bacteria were found in vacuoles (black arrows). At 5 and 29 h of infection, S. mutans was found to be either in vacuoles (black arrows) or free in the cytoplasm (white arrows).