Streptococcus mitis: walking the line between commensalism and pathogenesis

Abstract

Streptococcus mitis is a viridans streptococcus and a normal commensal of the human oropharynx. However, S. mitis can escape from this niche and cause a variety of infectious complications including infective endocarditis, bacteraemia and septicaemia. It uses a variety of strategies to effectively colonize the human oropharynx. These include expression of adhesins, immunoglobulin A proteases and toxins, and modulation of the host immune system. These various colonization factors allow S. mitis to compete for space and nutrients in the face of its more pathogenic oropharyngeal microbial neighbours. However, it is likely that in vulnerable immune-compromised patients S. mitis will use the same colonization and immune modulation factors as virulence factors promoting its opportunistic pathogenesis. The recent publication of a complete genome sequence for S. mitis strain B6 will allow researchers to thoroughly investigate which genes are involved in S. mitis host colonization and pathogenesis. Moreover, it will help to give insight into where S. mitis fits in the complicated oral microbiome. This review will discuss the current knowledge of S. mitis factors involved in host colonization, their potential role in virulence and what needs to be done to fully understand how a an oral commensal successfully transitions to a virulent pathogen.

Protective Role of the Capsule and Impact of Serotype 4 Switching on Streptococcus mitis

“…Most of the deaths caused by S. pneumoniae are a result of pneumonia, bacteremia, or meningitis, and in virtually all cases, these diseases are caused by encapsulated strains. In contrast, S. mitis is only occasionally associated with diseases (10)(11)(12)(13). Its potential as a probiotic microorganism has been previously reported (14), but concerns about its pathogenic potential have been raised (15).…”

“…Its potential as a probiotic microorganism has been previously reported (14), but concerns about its pathogenic potential have been raised (15). Despite the ubiquitous prevalence of S. mitis as a human colonizer, few studies have addressed the molecular mechanisms involved in S. mitis commensalism or pathogenicity (12).…”

0991 Relationship between the microbiota in different sections of the gastrointestinal tract, and the body weight of broiler chickens

“…For example, the S. anginosus group bacteria are associated with infections at multiple body sites, and abscess formation (Ruoff 1988;Belko et al 2002;Bert et al 1998). S. mutans group bacteria (Loesche 1986;Simon-Soro and Mira 2015) and S. mitis group bacteria (Mitchell 2011;Catto et al 1987) are known pathogens of the buccal cavity. In humans, S. acidominius is a known pathogen that causes invasive diseases (Wu et al 2014) such as pneumonia (Baker and Carlson 2008;Akaike et al 1988), meningitis (Finkelstein et al 2003) and brain abscess (Cone et al 2007).…”

Balanoposthitis caused by Streptococcus mitis/oralis

“…The recently published whole genome sequence of S. mitis B6 strain may facilitate better understanding of this organism. 2 Ours is a case of frank balanoposthitis caused by S. mitis/ oralis in an immunocompetent young adult. The clinical picture, extensive invasion of the neutrophils by the organism, and its isolation in pure culture confirms the pathogenic role of S. mitis/oralis.…”

“…2 According to their composition, beazoars have been classified into 3 major types: phytobezoars, trichobezoars and pharmacobezoars. Bezoars composed of hair or hair-like fibres are called trichobezoars.…”