Viridans streptococci

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The division of living beings into systematics is a continuous subject of research. Different systematic classifications exist side by side and one after the other. The taxon treated here has become obsolete due to new research or is not part of the group systematics presented in the German-language Wikipedia.

Viridans streptococci are gram-positive , spherical bacteria from the genus Streptococcus ( streptococci ). It is not a single species , but rather a group with numerous different Streptococcus species, which are listed in further subgroups. The name is historically based and is used in medical microbiology . Sometimes the term Streptococcus viridans group or the term “ Streptococcus viridans ” can also be found, which is, however, misleading because a binomial refers to a species. The Viridans streptococci belong to the "greening streptococci" (Latin viridans : "greening") and occur in the oropharynx. That is why they are also known as " oral streptococci". They are the most common bacterial pathogen in slow-progressing inflammation of the heart wall ( endocarditis lenta ). Representatives of the Mutans subgroup (e.g. Streptococcus mutans ) cause tooth decay . However, most of the species within the Viridans streptococci are generally non- pathogenic .

features

Common features

Viridans streptococci is a name for a large group of generally non- pathogenic streptococci .

Viridans streptococci exist as cocci-shaped cells which, like many streptococci, are arranged in chains. Like all members of the genus , they do not form endospores . The Gram stain is positive. On blood agar , the colonies that have grown show a greening halo, which is typical for α-hemolysis . That is why they are referred to as α-hemolytic streptococci or as “greening streptococci”, viridans from Latin means “to make green” or “to produce a green color”. The eponymous haemolysis behavior only applies to the bacteria originally assigned to this group (see section Systematics and Taxonomy ).

Furthermore, a common feature is that at 10 ° C no more growth takes place, while at 45 ° C most representatives can still multiply. Compared to sodium chloride (common salt) they act moderately tolerant, however, takes place in a nutrient medium with 6.5% NaCl no growth.

Differentiating characteristics from other streptococci

The differentiation of the Viridans streptococci from Streptococcus pneumoniae , which also belongs to the α-hemolytic streptococci, is of medical importance . They can be differentiated with an Optochin test , since the Viridans streptococcus is Optochin-resistant. In addition, the cells of S. pneumoniae exist as diplococci, the pathogenic forms are typically encapsulated . The Viridans streptococci do not have a polysaccharide capsule. The antigens of Lancefield group C, Lancefield group A (typical for S. pyogenes and other A streptococci ), Lancefield group B (typical for S. agalactiae ) and Lancefield group D (typical for enterococci) are also absent ).

Occurrence

The organisms are often found in the oral cavity and in the ear, nose and throat area of humans. Some species have also been isolated from other parts of the body (including the skin ) and from faeces . Associated species have also been detected in the plaque of various animal species.

Systematics and taxonomy

The counting of the viridans streptococci species are members of the genus Streptococcus in the family of Streptococcaceae in the order of Lactobacillales (lactic acid bacteria) that the Department of Firmicutes belong.

At the beginning of the 20th century it was assumed that it was a specific species that was called " Streptococcus viridans " and could be distinguished from " Streptococcus hemolyticus ". The naming refers to the hemolysis behavior on blood agar. Streptococci that perform α-hemolysis were also known as “greening streptococci”. In contrast, there were the β-hemolytic streptococci (then “ Streptococcus hemolyticus ”), which were recognized as pathogens early on.

With the discovery and investigation of further streptococci it soon became apparent that there were too many differences in addition to the haemolytic behavior than this seemed acceptable to representatives of a species. Therefore, James Morgan Sherman made an attempt to further subdivide in 1937 and designated the first group as viridans streptococci , i.e. Viridans streptococci. This term has been found in specialist literature ever since. As a result, the 1980 Approved Lists of Bacterial Names, based on the newly organized Bacteriological Code , does not list any “ Streptococcus viridans ” species.

The group of Viridans streptococci grew with ever new species, and γ-hemolytic streptococci are also among them - these do not perform hemolysis. This led to the suggestion that this group should be better named "oral streptococci" according to their occurrence. Phylogenetic studies at the end of the 20th century show a division into four different subgroups within this group, each of which comprises several species and which are named after a typical species.

  • The anginosus group , also known as the anginosus streptococci or the streptococcus anginosus group, with S. anginosus as a typical representative. This is sometimes also called the Milleri group or " Streptococcus milleri ".
  • The Mitis group, also known as the Mitis streptococci or Streptococcus mitis group, with S. mitis as a typical representative. In the medical literature it is also referred to as the Sanguis group, after the " S. sanguis ", which is also part of the current nomenclature and is referred to as Streptococcus sanguinis .
  • The Mutans group, which is also referred to as the Mutans Streptococci or Streptococcus mutans group, with S. mutans as a typical representative.
  • The Salivarius group, also known as Salivarius-Streptococci or Streptococcus-salivarius-group, with S. salivarius as a typical representative.

The so-called Bovis group should not be regarded as belonging to the “oral streptococci” group. Although its representatives also show α-hemolysis (or γ-hemolysis), they also have the Lancefield group D antigens. The species after which the group was named ( S. bovis ) is called Streptococcus equinus according to current nomenclature .

Medical importance

Historically, a distinction has been made between the Viridans streptococci (α-hemolytic) and the pyogenes group (β-hemolytic) because the former were not as important as pathogens. However, diseases can also be caused by some species in this group, which is why they are referred to as facultative pathogenic or opportunistic pathogens .

Diseases

Streptococcus mutans , S. sobrinus and other representatives increase the formation of caries . Other types can also be implicated in oral infections. If they get into the bloodstream, they can cause endocarditis , especially in people with heart valve damage . For example, after tooth extraction, they can get into the bloodstream and stick to fibrin deposits on the damaged heart valve. Viridans streptococci are the most common cause of bacterial endocarditis at around 50–70%. This subacute bacterial endocarditis is also known as endocarditis lenta .

Representatives of the anginosus group can be involved in purulent inflammation ( abscesses ). Representatives of this group very rarely cause meningitis . Several species have been identified as relevant pathogens in immunocompromised patients.

diagnosis

The diagnosis of endocarditis is based on echocardiography ( TEE ). A microbiological diagnosis using blood culture should be carried out on three independently obtained samples.

therapy

Depending on the clinical picture, different antibiotics are used, viridans streptococci are sensitive to penicillin . Also ceftriaxone and cefotaxime or, alternatively, vancomycin are used. In the case of bacterial endocarditis, however, empirical treatment is always given first until a definitive pathogen detection, possibly with an antibiogram , is available.

prophylaxis

Prophylaxis against bacterial endocarditis is only considered useful in a few patients (see endocarditis ).

swell

literature

  • Jeremy M. Hardie, Robert A. Whiley: The Genus Streptococcus - Oral (Chapter 1.2.2) . In: Martin Dworkin, Stanley Falkow, Eugene Rosenberg, Karl-Heinz Schleifer, Erko Stackebrandt (eds.): The Prokaryotes. A Handbook on the Biology of Bacteria, Volume 4: Bacteria: Firmicutes, Cyanobacteria . 3. Edition. Springer-Verlag, New York 2006, ISBN 0-387-25494-3 , pp. 76-107 , doi : 10.1007 / 0-387-30744-3_2 (English).

Individual evidence

  1. ↑ a b c d Jean Euzéby, Aidan C. Parte: Genus Streptococcus. In: List of Prokaryotic names with Standing in Nomenclature ( LPSN ). Retrieved July 22, 2014 .
  2. ↑ a b c d JM Sherman: The Streptococci . In: Bacteriological reviews . tape 1 , no. 1 , December 1937, ISSN  0005-3678 , pp. 3-97 , PMID 16350049 , PMC 440821 (free full text).
  3. ↑ a b c d e f g Sören Gatermann, Klaus Miksits: Streptokokken . In: Helmut Hahn, Stefan HE Kaufmann, Thomas F. Schulz, Sebastian Suerbaum (eds.): Medical microbiology and infectious diseases . 6th edition. Springer Verlag, Heidelberg 2009, ISBN 978-3-540-46359-7 , p. 203-221 .
  4. ↑ a b c d e Jeremy M. Hardie, Robert A. Whiley: The Genus Streptococcus - Oral. In: The Prokaryotes. A Handbook on the Biology of Bacteria, Volume 4: Bacteria: Firmicutes, Cyanobacteria. Edited by M. Dworkin, S. Falkow, E. Rosenberg, K.-H. Schleifer, E. Stackebrandt. 3. Edition. Springer Verlag, New York 2006, ISBN 978-0-387-25494-4 , pp. 76-107
  5. ↑ Approved Lists of Bacterial Names . In: VBD Skerman, Vicki McGowan, PHA Sneath (Eds.): International Journal of Systematic Bacteriology . tape  30 , no. 1 , 1980, p. 225-420 , doi : 10.1099 / 00207713-30-1-225 (English, sgmjournals.org [PDF; 17.0 MB ; accessed on April 13, 2014]). PDF, 17.0 MB ( Memento of the original from January 22, 2013 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.  @1@ 2Template: Webachiv / IABot / ijs.sgmjournals.org
  6. ↑ a b Henrik Holtmann, Monika Bobkowski BASICS Medical Microbiology, Virology and Hygiene, Elsevier, Urban and Fischer, 2008
  7. ^ Marianne Abele-Horn: Antimicrobial Therapy. Decision support for the treatment and prophylaxis of infectious diseases. With the collaboration of Werner Heinz, Hartwig Klinker, Johann Schurz and August Stich, 2nd, revised and expanded edition. Peter Wiehl, Marburg 2009, ISBN 978-3-927219-14-4 , p. 367.
  8. ↑ B. Al-Nawas, M. Block, G. Ertl, D. Franzen, C. Gohlke-Bärwolf, M. Herrmann, D. Horstkotte, WV Kern, H.-H. Kramer, A. Moritz, CK Naber, G. Peters, B. Plicht, G. Wahl, K. Werdan: Annotated summary of the guidelines of the European Society of Cardiology on infectious endocarditis . In: The cardiologist . tape 4 , no. 4 , July 24, 2010, ISSN  1864-9718 , p. 285–294 , doi : 10.1007 / s12181-010-0282-2 (new edition 2009).
  9. ↑ NICE: prophylaxis against infective endocarditis. In: NICE. March 17, 2008, accessed on February 7, 2012 (English, Guidance / Clinical Guidelines).