The Clinical View on Streptococcus anginosus Group – Opportunistic Pathogens Coming Out of Hiding

Abstract

Three distinct streptococcal species: Streptococcus anginosus, Streptococcus intermedius, and Streptococcus constellatus, belonging to the Streptococcus anginosus group (SAG), also known as Streptococcus milleri group, have been attracting clinicians and microbiologists, not only as oral commensals but also as opportunistic pathogens. For years they have been simply classified as so called viridans streptococci, and distinct species were not associated with particular clinical manifestations. Therefore, description of SAG members are clearly underrepresented in the literature, compared to other medically relevant streptococci. However, the increasing number of reports of life-threatening infections caused by SAG indicates their emerging pathogenicity. The improved clinical data generated with the application of modern molecular diagnostic techniques allow for precise identification of individual species belonging to SAG. This review summarizes clinical reports on SAG infections and systematizes data on the occurrence of individual species at the site of infection. We also discuss the issue of proper microbiological diagnostics, which is crucial for further clinical treatment.

A Rare Case of Primary Purulent Pericarditis Caused by Streptococcus constellatus

“…These Gram-positive pathogens can normally colonize the upper respiratory, digestive, and genitourinary tracts. However, in favorable conditions, SAG can cause invasive or non-invasive pyogenic infections and involve multiple organs [ 8 ]. Since purulent pericarditis is mostly caused by hematogenous seeding of bacteria, it is important to find a primary infection source.…”

Virulence factors of Streptococcus anginosus – a molecular perspective

“…S. anginosus was also recovered from patients in co-infections with other species, e.g., Mycobacterium tuberculosis , and Eikenella corrodens ( Rabuñal et al, 2009 ; Patel et al, 2020 ). All these data strongly suggest that S. anginosus should be viewed as an emerging opportunistic pathogen of substantial clinical importance ( Reißmann et al, 2010 ; Pilarczyk-Zurek et al, 2022 ).…”

“…Formerly, these three species were regarded by European and Japanese microbiologists as a single species “ Streptococcus milleri .” However, they were distinguished by microbiologists from North America. [reviewed in ( Coykendall, 1989 ) and recently in ( Pilarczyk-Zurek et al, 2022 )]. Previously, SAG was classed in a diverse group of streptococci called the viridans group which was poorly characterized( Coykendall, 1989 ).…”

“…It should be noted here that detection of Lancefield antigen and biochemical tests used in laboratory practice for SAG identification, and even mass spectrometry (MALDI-TOF-MS), do not allow a reliable identification at species level and the results should be viewed with caution ( Whiley et al, 1990 ; Wenzler et al, 2015 ). The precise SAG species identification can be achieved with the use of the molecular biology-based methods; the SAG identification issues have been recently reviewed in ( Pilarczyk-Zurek et al, 2022 ).…”

“…In the past all SAG species were considered to be human commensals, part of the healthy human microbiota, commonly residing on mucosal membranes of the oral cavity, preferentially found in dental plaques, but also on mucosal membranes of the gastrointestinal, upper respiratory, and urogenital tracts ( Hamada and Slade, 1980 ; Whiley et al, 1992 ). However, more and more data link SAG members with health problems in humans, especially in immunocompromised, cancer, or cystic fibrosis patients [reviewed in ( Pilarczyk-Zurek et al, 2022 )]. According to observations, the clinical syndromes differed depending on the SAG species involved: S. constellatus was associated with odontogenic, soft tissue, pleuropulmonary, and intra-abdominal abscesses, S. intermedius with pleuropulmonary infections, abscesses of brain, and deep soft tissues, whereas S. anginosus was rarely responsible for abscesses and more frequently than two other SAGs was isolated from blood, infected soft tissues, and urine ( Whiley et al, 1992 ; Clarridge et al, 2001 ; Junckerstorff et al, 2014 ; Issa et al, 2020 ; Jiang et al, 2020 ).…”