Streptococcus equinus

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Streptococcus equinus
Systematics
Department : Firmicutes
Class : Bacilli
Order : Lactic acid bacteria (Lactobacillales)
Family : Streptococcaceae
Genre : Streptococcus
Type : Streptococcus equinus
Scientific name
Streptococcus equinus
Andrewes & Horder 1906

Streptococcus equinus (formerly known as Streptococcus bovis ) is a type of bacteria from the genus Streptococcus ( German : Streptococcus). These are gram-positive bacteria, the cells are facultatively anaerobic , they can live with or without oxygen. In most cases, Streptococcus equinus does not cause any disease in humans, but in rare cases it has beendescribedas a pathogen , including when septicemia occurs (blood poisoning). It occurs in the intestines or in the feces of horses , cattle and humans.

The taxonomy of Streptococcus equinus and Streptococcus bovis has changed frequently since the 1980s. Originally they were known as two different types . In the course of time, other, similar bacteria were researched, some of which have been described as separate species, although they are very similar to the species mentioned. It was not until the beginning of the 21st century that, as a result of phylogenetic studies, these were classified as S. bovis / S. equinus group contained strains of bacteria changed. It was determined that S. equinus is the correct name and S. bovis is a synonym that emerged later .

features

Appearance

The cells of Streptococcus equinus are cocci-shaped and are arranged in pairs or in short chains. Streptococcus equinus , like all species of the genus , does not form endospores . The species cannot move on its own, so it is not motile . The Gram stain is positive.

After incubation for 18 hours at 37 ° C. , the cells grow into small, white colonies on solid nutrient media . When viewed from above, these are round with a clearly defined edge and appear shiny. Some bacterial strains show α-hemolysis on blood agar , which can be recognized by the green color of the blood. However, the haemolysis behavior is not uniform, other strains are γ-haemolytic, they do not perform haemolysis.

Growth and metabolism

The metabolism and energy exchange of Streptococcus equinus is chemo - heterotrophic . The species can reproduce in the presence and absence of oxygen , the metabolism is thus facultatively anaerobic . The growth occurs best when the oxygen content is reduced. An atmosphere enriched with carbon dioxide is often used for cultivation , with 5–10% CO 2 . The temperatures usually used for cultivation are in the range of 35-37 ° C, so the bacterium is one of the mesophilic organisms. The cultivation works optimally on tryptone soy agar (TSA) with the addition of yeast extract at a pH value in the neutral range and a temperature of 37 ° C. S. equinus is tolerant of bile salts and still grows in a nutrient medium that contains 40% bile salts. It is also moderately tolerant of sodium chloride (table salt), but no growth occurs in a nutrient medium with 6.5% NaCl.

S. equinus is one of the lactic acid bacteria and can use various carbohydrates for energy production in a fermentation . A characteristic of fermentation ( fermentation ) is that the substrates are broken down without oxygen. The typical fermentation product for lactic acid bacteria is lactic acid , which is why this metabolic pathway is called lactic acid fermentation . It is able to utilize the monosaccharides glucose and fructose as well as the disaccharides maltose and sucrose with acid formation, whereas this is not the case with the sugar alcohols sorbitol and mannitol .

Further biochemical characteristics or enzymes in the metabolism are detected in a " colorful series " in order to identify a bacterium. S. equinus shows negative behavior in the catalase and oxidase tests . It has the enzyme β-glucosidase. However, he does not have the enzyme urease to urea to exploit. In addition, the enzyme arginine dihydrolase ( EC  3.5.3.6 ) is not present, so that no ammonia is split off from the amino acid arginine . The Voges-Proskauer test is positive, so acetoin is formed. It is also capable of aesculin hydrolysis . It is resistant to bacitracin and is resistant to the Optochin test .

Until it was established that S. bovis and S. equinus are the same species (see section Systematics ), it was difficult to differentiate them on the basis of phenotypic characteristics. A few distinguishing features were the fermentative degradation of lactose under acid formation (positive or negative) or trehalose (negative or positive) and the ability to hydrolysis of starch (positive or negative).

Chemotaxonomy

To subdivide the streptococci, the hemolytic behavior and existing antigens are assessed. For the β-hemolytic streptococci, the serological examination using the Lancefield classification has proven itself. Here, antigens that are part of the bacterial cell wall are detected. This classification was partly extended to other Streptococcus species, provided that they have the appropriate antigens. Streptococcus equinus belongs to Lancefield group D, which also includes some Enterococcus species. Teichonic acids act as antigen here .

genetics

The genome of the Streptococcus equinus ATCC 9812 type strain was completely sequenced in 2011 . The investigation was carried out as part of the Human Microbiome Project to identify and characterize the human microbiome . The bacterial strain used was isolated from a human intestine . So far (as of 2014) 10 other bacterial strains have been genetically examined, including strains that were originally assigned to Streptococcus bovis . The genome size of the S. equinus ATCC 700338 strain (formerly known as S. bovis ATCC 700338) is 2051 kilobase pairs (kb), which corresponds to about 45% of the genome size of Escherichia coli . There are 2088 proteins annotated . The result of the sequencing shows a GC content (the proportion of the nucleobases guanine and cytosine ) in the bacterial DNA of 37.2  mol percent , the GC content for the type strain is also 37 mol percent. This is comparable with the other Streptococcus species, whose GC content in the DNA is between 34 and 46 mol percent.

For phylogenetic studies, the nucleotides of the 16S rRNA, a typical representative of ribosomal RNA for prokaryotes , were also determined . In 2001 this led to the first subdivision of Streptococcus bovis / S. equinus group into the species then designated as S. bovis , S. caprinus , S. equinus , S. gallolyticus , S. infantarius and S. macedonicus . The great similarity of the nucleotide sequences of the 16S rRNA (> 97%) has already been described, but this is also the case with other, closely related Streptococcus species. For a better differentiation, a certain gene in the DNA was selected as the target sequence and examined using the polymerase chain reaction (PCR). It is the sodA gene which codes for the manganese -dependent superoxide dismutase (Mn-SOD) encoding . The results show a very good agreement between S. bovis and S. equinus , which were jointly assigned to cluster C, the divergence is less than 1%. This is confirmed by the results of the DNA-DNA hybridization , which show an agreement of> 90%, while the agreement with strains of the other clusters is <53%.

Pathogenicity

Streptococcus equinus is assigned to risk group 2 by the Biological Agents Ordinance in conjunction with the TRBA ( Technical Rules for Biological Agents) 466 . There is also an indication that it is pathogenic for humans and vertebrates , but that normally there is no transmission between the two host groups .

Occurrence

Streptococcus bovis was considered a normal part of the intestinal flora of cattle and other ruminants . The species name also refers to this , bovis from Latin means "of the cattle" ( genitive ). Streptococcus equinus, on the other hand, has been characterized as a common component of the intestinal flora of horses , and several strains have been isolated from the faeces of horses. In this case, too, the species name refers to the habitat , equinus from Latin means “belonging to the horses”. In the course of time, isolates from humans that were identified as S. bovis were also obtained, although the identification in the 1970s must not be regarded as reliable from today's perspective. In addition, the medical literature at that time did not differentiate between the groups already known as biotypes , so that some of the strains identified as S. bovis biotype II are, according to the current state of knowledge, other Streptococcus species, especially around S. gallolyticus . Bacterial strains belonging to the species known as Streptococcus equinus according to the current nomenclature were therefore predominantly isolated from the intestines or the feces of cattle, horses and humans.

Systematics

In the past, in addition to the name Streptococcus equinus Andrewes & Horder 1906, the nomenclature as Streptococcus bovis Orla-Jensen 1919 was common for the bacterium . As early as the 1950s there were reports of difficulties in distinguishing between the two bacteria , which were then kept as separate species . The genetic and biochemical methods of investigation introduced over time confirmed the similarity. In 1984 studies on the type phyla of the two species revealed a close relationship, so it was proposed to combine them into one species. Subsequent genetic tests (see section Genetics ) from 2002 confirmed this. Similar bacterial strains had already been described previously, some of which were classified as separate species, but which also showed great similarity in phenotypic characteristics with S. bovis and S. equinus . Over a certain period of time, this ambiguous taxonomy was taken into account to the extent that the term S. bovis / S. equinus complex or group was used. Additional difficulties for taxonomy arose from the description of strains that were predominantly of clinical origin and were designated as S. bovis biotype II or S. bovis (var.). In 2002, the species then called S. alactolyticus , S. bovis , S. caprinus , S. equinus , S. gallolyticus , S. infantarius , S. macedonicus , S. pasteurianus and S. waius were included in the complex. Although they were also similar in terms of genotypic characteristics, phylogenetic studies showed that some of them are separate species, in other cases subspecies and finally in other cases members of the same species.

At a meeting of the commission responsible for the nomenclature and systematics of prokaryotes ( International Committee on Systematics of Prokaryotes ) it was decided in July 2002 that S. bovis is a younger synonym for Streptococcus equinus . It was published in May 2003. The previous name is used as a synonym. Another result of the meeting was the establishment of several species and subspecies, some of which, however, were classified differently after further phylogenetic studies. According to the current status (2014), the following species and subspecies are known that previously belonged to S. bovis / S. equinus complex:

  • Streptococcus alactolyticus Farrow et al. 1985 (older synonym from S. intestinalis Robinson et al. 1988)
  • Streptococcus equinus Andrewes & Horder 1906 (older synonym of S. bovis Orla-Jensen 1919)
  • Streptococcus gallolyticus Osawa et al. 1996 (older synonym from S. caprinus Brooker et al. 1996)
    • S. gallolyticus subsp. gallolyticus (Osawa et al. 1996) Schlegel et al. 2003 emend. Beck et al. 2008
    • S. gallolyticus subsp. macedonicus (Tsakalidou et al. 1998) Schlegel et al. 2003 (previously called S. macedonicus Tsakalidou et al. 1998, older synonym of S. waius Flint et al. 1999)
    • S. gallolyticus subsp. pasteurianus (Poyart et al. 2002) Schlegel et al. 2003 emend. Beck et al. 2008 (previously referred to as S. pasteurianus Poyart et al. 2002)
  • Streptococcus infantarius Schlegel et al. 2000
  • Streptococcus lutetiensis Poyart et al. 2002 (previously referred to as S. infantarius subsp. Coli Schlegel et al. 2003)

Medical importance

Human medicine

When assessing the pathogenicity for humans, the changed system is of great importance. As already described, it became apparent as early as the 1980s that the clinical isolates then designated as S. bovis belong to a different biotype, which was initially designated as S. bovis biotype II or S. bovis (var.). This distinction was often not included in the medical literature; the pathogen was simply referred to as S. bovis . According to the current state of knowledge, these isolates are other Streptococcus species, especially S. gallolyticus and its subspecies. The new system established since 2002 is seldom taken into account in the medical literature. On the other hand, there are also literature sources in which attention is drawn to the changed systematics and it is explained that pathogens that were previously identified as S. bovis now belong to different species, in particular S. gallolyticus .

The following example should clarify the effects: In a 1997 reported case of septic arthritis , S. bovis was identified as the pathogen and this was confirmed by a genetic comparison with other strains isolated from human blood. The strains designated as very similar are the bacterial strains ATCC 43143 and ATCC 43144 stored in the collection of microorganisms in the USA. According to the current system, these strains are not S. bovis but S. gallolyticus subsp. gallolyticus or S. gallolyticus subsp. pasteurianus . This can be understood with the current state of knowledge, but if you only know the medical article as the source, you get the impression that S. bovis or S. equinus are the pathogen described.

It can therefore be assumed that S. equinus does not cause diseases in humans in most cases. The uncertainty as to whether the clinical isolates associated with diseases can actually be traced back to this species was taken into account in the Biological Agents Ordinance with assignment to risk group 2. In the medical literature it is reported that Streptococcus equinus (usually referred to as S. bovis ) can in rare cases lead to the occurrence of septicemia (blood poisoning), meningitis (meningitis), wound infections or endocarditis . It is also discussed that infections of the intestine with S. equinus (usually referred to as S. bovis ) are a risk factor for the development of colon cancer . The exact pathophysiology of carcinogenesis due to infection with S. equinus is not yet known. In addition, it should be noted that the changed systematics is hardly taken into account in clinical practice and it can be assumed that S. gallolyticus is associated with colon cancer.

Antibiotic therapy for infections with Streptococcus bovis is carried out with penicillin , alternatively with ceftriaxone or cefotaxime .

Veterinary medicine

Of veterinary importance Streptococcus equinus (mostly as S. bovis ) as a pathogen in mastitis in cattle.

Individual evidence

  1. ↑ a b c d e f g h i j k l m n Claire Poyart, Gilles Quesne, Patrick Trieu-Cuot: Taxonomic dissection of the Streptococcus bovis group by analysis of manganese-dependent superoxide dismutase gene (sodA) sequences: reclassification of ' Streptococcus infantarius subsp. coli as Streptococcus lutetiensis sp. nov. and of Streptococcus bovis biotype 11.2 as Streptococcus pasteurianus sp. nov. In: International journal of systematic and evolutionary microbiology. Vol. 52, No. 4, July 2002, pp. 1247-1255, ISSN  1466-5026 . doi : 10.1099 / 00207713-52-4-1247 . PMID 12148636 .
  2. ↑ a b c d e Royce G. Knight, David M. Shlaes: Physiological Characteristics and Deoxyribonucleic Acid Relatedness of Human Isolates of Streptococcus bovis and Streptococcus bovis (var.). In: International Journal of Systematic Bacteriology. Volume 35, No. 3, July 1985, pp. 357-361, ISSN  0020-7713 . doi : 10.1099 / 00207713-35-3-357 .
  3. ↑ Catalog of microorganisms. In: Website of the Leibniz Institute DSMZ - German Collection of Microorganisms and Cell Cultures GmbH . Retrieved July 10, 2014 .
  4. ↑ a b Patrick Cleary, Qi Cheng: Medically Important Beta-Hemolytic Streptococci. 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. 109-110
  5. ^ A b c R. Fuller, LGM Newland: The serological grouping of three strains of Streptococcus equinus. In: Journal of General Microbiology. Volume 31, No. 3, June 1963, pp. 431-434, ISSN  0022-1287 . doi : 10.1099 / 00221287-31-3-431 . PMID 13960231 .
  6. ↑ Streptococcus equinus ATCC 9812 - Reference genome for the Human Microbiome Project. In: BioProject website of the National Center for Biotechnology Information (NCBI). Retrieved July 11, 2014 .
  7. ↑ a b Streptococcus equinus ATCC 9812. In: Website Genomes Online Database (GOLD) . Retrieved July 11, 2014 .
  8. ↑ a b c Streptococcus equinus. In: National Center for Biotechnology Information (NCBI) Genome website . Retrieved July 11, 2014 .
  9. ↑ Michael T. Madigan, John M. Martinko, Jack Parker: Brock Microbiology. German translation edited by Werner Goebel, 1st edition. Spektrum Akademischer Verlag GmbH, Heidelberg / Berlin 2000, ISBN 978-3-8274-0566-1 , pp. 559-563.
  10. ↑ TRBA (Technical Rules for Biological Agents) 466: Classification of prokaryotes (Bacteria and Archaea) into risk groups. In: Website of the Federal Institute for Occupational Safety and Health (BAuA). April 25, 2012, p. 211 , accessed April 30, 2014 .
  11. ↑ a b c d Jean Euzéby, Aidan C. Parte: Genus Streptococcus. In: List of Prokaryotic names with Standing in Nomenclature ( LPSN ). Retrieved July 10, 2014 .
  12. ↑ JAE Farrow, J. Kruze et al. a .: Taxonomic Studies on Streptococcus bovis and Streptococcus equinus: Description of Streptococcus alactolyticus sp. nov. and Streptococcus saccharolyticus sp. nov. In: Systematic and Applied Microbiology. Vol 5, No. 4, December 1984, pp. 467-482, ISSN  0723-2020 . doi : 10.1016 / S0723-2020 (84) 80004-1 .
  13. ↑ a b c d L. Schlegel, F. Grimont u. a .: Reappraisal of the taxonomy of the Streptococcus bovis / Streptococcus equinus complex and related species: description of Streptococcus gallolyticus subsp. gallolyticus subsp. nov., S. gallolyticus subsp. macedonicus subsp. nov. and S. gallolyticus subsp. pasteurianus subsp. nov. In: International journal of systematic and evolutionary microbiology. Volume 53, No. 3, May 2003, pp. 631-645, ISSN  1466-5026 . doi : 10.1099 / ijs.0.02361-0 . PMID 12807180 .
  14. ^ RA Whiley, M. Kilian: International Committee on Systematics of Prokaryotes Subcommittee on the taxonomy of staphylococci and streptococci: Minutes of the closed meeting, July 31, 2002, Paris, France. In: International journal of systematic and evolutionary microbiology. Volume 53, No. 3, May 2003, pp. 915-917, ISSN  1466-5026 . doi : 10.1099 / ijs.0.02589-0 .
  15. ↑ Taxonomy Browser Streptococcus equinus. In: National Center for Biotechnology Information (NCBI) website . Retrieved July 10, 2014 .
  16. ↑ a b J. S. Gold, S. Bayar, RR Salem: Association of Streptococcus bovis bacteremia with colonic neoplasia and extracolonic malignancy. In: Archives of surgery (Chicago, Ill.: 1960). Volume 139, No. 7, July 2004, pp. 760-765, ISSN  0004-0010 . doi : 10.1001 / archsurg.139.7.760 . PMID 15249410 .
  17. ↑ a b W. Alazmi, M. Bustamante u. a .: The association of Streptococcus bovis bacteremia and gastrointestinal diseases: a retrospective analysis. In: Digestive diseases and sciences. Volume 51, No. 4, April 2006, pp. 732-736, ISSN  0163-2116 . doi : 10.1007 / s10620-006-3199-7 . PMID 16614996 .
  18. ↑ B. O'Brien, B. Dyer, et al. a .: Streptococcus bovis bacteremia as the initial presentation of carcinoma of the gallbladder. In: The West Virginia medical journal. Volume 110, No. 2, March-April 2014, pp. 32-33, ISSN  0043-3284 . PMID 24902466 .
  19. ↑ a b A. Boleij, MM van Gelder u. a .: Clinical Importance of Streptococcus gallolyticus infection among colorectal cancer patients: systematic review and meta-analysis. In: Clinical Infectious Diseases . Volume 53, No. 9, November 2011, pp. 870-878, ISSN  1537-6591 . doi : 10.1093 / cid / cir609 . PMID 21960713 . (Review).
  20. ↑ RJ Grant, WY Shang, TR Whitehead: Isolated septic arthritis due to Streptococcus bovis. In: Clinical Infectious Diseases . Volume 24, No. 5, May 1997, p. 1021, ISSN  1058-4838 . PMID 9142824 .
  21. ↑ Microbiology Collections. In: American Type Culture Collection website . Retrieved July 12, 2014 .
  22. ↑ S. Galdy, G. Nastasi: Streptococcus bovis endocarditis and colon cancer: myth or reality? A case report and literature review. In: BMJ Case Reports. Volume 2012, December 2012, ISSN  1757-790X . doi : 10.1136 / bcr-2012-006961 . PMID 23220436 . (Review).
  23. ^ 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. 267.
  24. ^ EI Garvie, AJ Bramley: Streptococcus bovis - an approach to its classification and its importance as a cause of bovine mastitis. In: The Journal of applied bacteriology. Volume 46, No. 3, June 1979, pp. 557-566, ISSN  0021-8847 . PMID 479054 .