Oral mitis group streptococci: A silent majority in our oral cavity

Abstract

Members of the oral mitis group streptococci including Streptococcus oralis, Streptococcus sanguinis, and Streptococcus gordonii are the most abundant inhabitants of human oral cavity and dental plaque, and have been implicated in infectious complications such as bacteremia and infective endocarditis. Oral mitis group streptococci are genetically close to Streptococcus pneumoniae; however, they do not produce cytolysin (pneumolysin), which is a key virulence factor of S. pneumoniae. Similar to S. pneumoniae, oral mitis group streptococci possess several cell surface proteins that bind to the cell surface components of host mammalian cells. S. sanguinis expresses long filamentous pili that bind to the matrix proteins of host cells. The cell wall–anchored nuclease of S. sanguinis contributes to the evasion of the neutrophil extracellular trap by digesting its web‐like extracellular DNA. Oral mitis group streptococci produce glucosyltransferases, which synthesize glucan (glucose polymer) from sucrose of dietary origin. Neuraminidase (NA) is a virulent factor in oral mitis group streptococci. Influenza type A virus (IAV) relies on viral NA activity to release progeny viruses from infected cells and spread the infection, and NA‐producing oral streptococci elevate the risk of IAV infection. Moreover, oral mitis group streptococci produce hydrogen peroxide (H2O2) as a by‐product of sugar metabolism. Although the concentrations of streptococcal H2O2 are low (1–2 mM), they play important roles in bacterial competition in the oral cavity and evasion of phagocytosis by host macrophages and neutrophils. In this review, we intended to describe the diverse pathogenicity of oral mitis group streptococci.

Update of the list of qualified presumption of safety (QPS) recommended microbiological agents intentionally added to food or feed as notified to EFSA 17: suitability of taxonomic units notified to EFSA until September 2022

“…S. oralis may cause various diseases such as meningitis, endocarditis and bloodstream infections in which streptococcal surface proteins and other virulence factors might be involved (Basaranoglu et al., 2019; Cruz Cardoso et al., 2021; Nakamura et al., 2021; Okahashi et al., 2022b).…”

Hypothiocyanite and host–microbe interactions

“…Dual oxidase enzymes (DUOX) also produce H 2 O 2 , including that which LPO uses to generate SCN − in mucosal airways (Sarr et al, 2018). Additionally, H 2 O 2 is produced by some bacteria, including commensal oral streptococci and the pathobiont Streptococcus pneumoniae (Mraheil et al, 2021; Okahashi et al, 2022).…”

Severity of acute lung injury in aspiration pneumonia model mice transplanted with human oral microflora

“…A significant correlation between oral microflora and the development of respiratory diseases such as aspiration pneumonia has been shown in patients with communityacquired pneumonia. 9,10 Regarding the mechanism of aspiration pneumonia severity, an imbalance in the microflora and subsequent alterations in systemic immune homeostasis are assumed to be the factors that aggravate the condition. 4 In healthy individuals, aspiration pneumonia is uncommon, even if aspiration of saliva or oral contents into the lungs occurs.…”

“…However, oral bacteria such as Streptococcus oralis are no longer regarded as accidental contamination in the affected area of aspiration pneumonia during sample collection but are considered actual factors in the development of pneumonia. A significant correlation between oral microflora and the development of respiratory diseases such as aspiration pneumonia has been shown in patients with community‐acquired pneumonia 9,10 …”