Serratia

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Serratia
Serratia marcescens colonies on the surface of an agar gel in a petri dish

Serratia marcescens colonies on the surface of an agar gel in a petri dish

Systematics
Domain : Bacteria (bacteria)
Department : Proteobacteria
Class : Gammaproteobacteria
Order : Enterobacterales
Family : Enterobacteriaceae
Genre : Serratia
Scientific name
Serratia
Bizio 1823

When bacteria of the genus Serratia is a group of Gram-negative , facultative anaerobic rod-shaped bacteria of the family Enterobacteriaceae (Enterobacteriaceae). In German they are called serratia . A well-known species from the genus is Serratia marcescens , which is characterized by red pigmentation. Like other enterobacteria, Serratia species occur in the intestine , but they are also ubiquitous in other habitats. They occur in water, in the soil, in animals and on plants. They can be pathogenic for some insects , on the other hand cases of symbioses are also known. Many Serratia species are non-pathogenic in humans or have only rarely been identified as pathogens (e.g. from bacteremia and pneumonia). However, there have been isolated reports of nosocomial infections in children's wards and intensive care units. The systematics within the genus Serratia has changed several times since the beginning of the 20th century. In the past, bacteria with a red or pink coloring of the colonies were often classified as Serratia species . Currently (as of 2014) 15 different species are known.

features

Appearance

The cells of Serratia species are rod-shaped and actively mobile ( motile ) through flagella . The Gram stain is negative. Colonies grown on solid culture media are often characterized by red pigmentation . The prodigiosin produced by the bacteria is responsible for this . The colonies on a nutrient medium, but also on bread, polenta or hosts, are reminiscent of drops of blood (compare blood miracles ). The phenomenon was first described in Serratia marcescens , but other Serratia species (e.g. S. plymuthica and S. rubidaea ) also grow as red to pink-colored colonies. There are also non-pigmented bacterial strains .

Growth and metabolism

Serratia species use various organic compounds as a source of energy and to build up cellular structures, this is possible in oxidative or fermentative energy metabolism . They are thus facultatively anaerobic and chemoorgano-heterotrophic . You can utilize various carbohydrates with the formation of gas and acid. Regarding the products that are formed during fermentation , they belong to the Enterobacteriaceae that carry out 2,3-butanediol fermentation . The substrates they use can be used to identify Serratia species or to distinguish them from other representatives of the Enterobacteriaceae (see section Evidence ). As is typical for Enterobacteriaceae, the catalase test is positive and the oxidase test is negative. The particular smell that S. odorifera , S. ficaria and some strains of S. rubidaea give off is caused by alkyl methoxypyrazines ( derivatives of pyrazine ) produced by the bacteria . The main component is 3-isopropyl-2-methoxy-5-methylpyrazine . A similar compound, 2-isopropyl-3-methoxypyrazine , is found in potatoes , where it creates the “earthy” note in the smell and taste. The smell of these Serratia species is also described as potato-like.

Simple nutrient media are suitable for cultivation ; no special growth factors are necessary. Serratia species are mesophilic , growth takes place in a temperature range of 20–37 ° C, colonies are already visible after one day of incubation . For biochemical detection reactions, incubation at 30 ° C is recommended; pigment formation also occurs more at 30 ° C than at 37 ° C. Some Serratia species are psychrotolerant and still grow at 5 ° C (e.g. S. ficaria , S. fonticola and S. odorifera ). Other species such as S. entomophila and S. marcescens still grow at 40 ° C. A sodium chloride content of up to 40 g / L in the nutrient medium is tolerated. Growth occurs up to a pH of 9.

Chemotaxonomy

The GC content , ie the proportion of the nucleobases guanine and cytosine in the bacterial DNA , is 52–60  mol percent . Components of the bacterial cell act as antigens , the somatic O-antigens and the H-antigens are of diagnostic importance (compare the Kauffmann-White scheme used for salmonella ). The fatty acids found in the membrane lipids are mainly molecules with an even number of carbon atoms and no double bond ( saturated fatty acids ), such as myristic acid (tetradecanoic acid, C14: 0), palmitic acid (hexadecanoic acid, C16: 0) and stearic acid (octadecanoic acid, C18: 0) , also a fatty acid with a hydroxy group (3-hydroxy-tetradecanoic acid ) occurs.

Pathogenicity

Many Serratia species are non-pathogenic or have only rarely been identified as pathogens . Nosocomial infections in children's wards and intensive care units did occur, however, affecting premature babies or adult patients with impaired immune defenses . This is v. a. about S. marcescens , whose importance as a nosocomial pathogen is growing.

S. entomophila , S. ficaria , S. fonticola , S. odorifera , S. plymuthica , S. quinivorans and S. ureilytica are non-pathogenic and are classified in risk group  1 by the Biological Agents Ordinance in conjunction with the TRBA ( Technical Rules for Biological Agents) 466 assigned.

proof

S. odorifera in semi-solid SIM agar (H 2 S formation negative, indole test weakly positive, motility positive)

For cultivation of Serratia no particular are growth factors needed so simple culture media on peptone basis as tryptic soy agar are suitable. Minimal media are also defined that contain exactly the chemical compounds that are necessary for growth. In addition, Serratia species, with the exception of S. fonticola , are resistant to thallium salts . For the isolation of Serratia species from environmental samples, the so-called CT medium is therefore recommended, a minimal medium that contains caprylic acid as an energy and carbon source and thallium (I) sulfate . Biochemical features, such as the enzymes present and the resulting metabolic properties, can be used in a colored row to identify Serratia species or to distinguish them from other representatives of the Enterobacteriaceae.

The carbohydrates that they can utilize include, for example, the monosaccharides fructose , galactose , glucose , mannose and ribose , the disaccharides maltose and trehalose, and the sugar alcohols glycerol (glycerol) and mannitol . In the literature, Serratia is mostly described as lactose- negative, with the individual species there is no uniform picture with regard to lactose utilization. In the case of several types, the indication is "variable", i. That is, there are both strains that can break down lactose and strains that cannot. With S. marcescens the different behavior is used to differentiate the biotypes. In general, only S. rubidae and S. fonticola are positive for lactose detection due to acid formation. Interestingly, the ONPG test is positive for all Serratia species. This biochemical evidence shows that they have the enzyme β-galactosidase , with which lactose is hydrolyzed into the two components glucose and galactose . Tests in which the lactose breakdown is detected via the formation of acid may show a negative result because too little acid is produced.

The enzyme urease is not present, only S. ureilytica is an exception and can break down urea . Serratia species have lipases , proteolytic enzymes that are used to hydrolyze gelatine , for example , and the enzyme deoxyribonuclease (DNase). However, some strains of S. fonticola show negative results when tested accordingly. There is no formation of hydrogen sulfide (H 2 S). Nitrate is reduced to nitrite . The Voges-Proskauer reaction is positive, acetoin is formed. In contrast, the indole test is negative, only S. odorifera is able to produce indole.

In order to identify the individual Serratia species, tests are suitable that are based on the breakdown of various organic compounds and indicate the metabolic products formed in the process. This are miniaturized test systems better suited than the oxidation-fermentation test . The compounds useful for this are, for example, adonitol , L - arabinose , D - and L - arabitol , dulcitol , D - melibiose , L - rhamnose and D - sorbitol .

A serological differentiation of different strains of S. marcescens is common. In this case, be antibodies against the somatic O antigens and justified by the flagellar H antigens used. Several serotypes (e.g. O5: H2, O5: H3 and others) are combined into one biotype (e.g. S. marcescens biotype A1a). A bio-group consists of several biotypes (e.g. S. marcescens bio-group A1). This typing is used, for example, for nosocomial infections in order to find out the path of infection . In S. ficaria , S. plymuthica , S. proteamaculans and S. rubidaea there are also classifications of the serotypes based on this.

Systematics

External system

The genus Serratia belongs to the family of Enterobacteriaceae (Enterobacteria) in the order of Enterobacteriales, which belongs to the class of Gammaproteobacteria . The Enterobacteriaceae form a large group of gram-negative bacteria to which u. a. the genera Citrobacter , Enterobacter , Escherichia , Klebsiella , Proteus , Raoultella , Salmonella , Shigella and Yersinia belong, some representatives of which are important as pathogens. In the past it has been discussed whether Serratia should be included in the Klebsielleae tribe due to phenotypic similarities with Klebsiella and other genera . However, further research since the 1970s shows that Serratia is quite different from these. The tribal rank is no longer common since the revision (1990) of the International Code of Nomenclature of Bacteria (Bacteriological Code).

Internal system

In 1823, Bartolomeo Bizio described red-pigmented microorganisms that he had discovered on polenta and called them Serratia marcescens . This is considered to be the first description of the species and genus. Bizio chose the generic name in honor of Serafino Serrati, an Italian physicist . At the beginning of the 20th century, more than 70 differently named Serratia species were known. At the time, it was not possible to distinguish whether they were species or synonyms of a species; their common feature was the red or pink color of the colonies. A total of 23 species were named in the first edition of Bergey's Manual of Systematic Bacteriology from 1923. The number of known species of Serratia has since decreased, in the 1960s and 1970s it was assumed that S. marcescens was the only species in the genus.

With the help of modern investigation methods , such as DNA-DNA hybridization , it was possible to show that different bacterial strains differ significantly from one another, so that the establishment of different species appears justified. A numerical taxonomy was also used during this transition period , e.g. B. the designation as Serratia III, the classification as a biotype or biogroup was common practice. In the 1980 Approved Lists of Bacterial Names based on the newly organized Bacteriological Code, eight species were finally recognized: S. fonticola , S. liquefaciens , S. marcescens , S. marinorubra , S odorifera , S. plymuthica , S. proteamaculans and S. rubidaea .

Currently (as of 2014) the genus includes the following species and subspecies , S. marcescens is the type species.

  • Serratia marcescens subsp. marcescens ( Bizio 1823) Ajithkumar et al. 2003
  • Serratia marcescens subsp. sakuensis Ajithkumar et al. 2003

The question of whether S. marinorubra and S. rubidaea (both are listed on the Approved Lists of Bacterial Names ) are two different species occupied the microbiologists for a long period of time. An incorrect type strain for S. marinorubra that is identical to that of S. rubidaea was erroneously given on the list . According to the rules of the Bacteriological Code, both are homotypic synonyms , with the name S. marinorubra having priority (it is older). Also S. liquefaciens and S. proteamaculans were the subject of taxonomic debates. However, research by Grimont & Grimont has shown that they are two different species. They also discovered a subspecies of S. proteamaculans in 1983 , which was raised to species status as S. quinivorans in 2002 . With Serratia profundus is an unrecognized type, whose name was not validly published.

Occurrence and ecology

Serratia species are almost ubiquitous . They occur in water, in the soil , in animals and on plants. They also colonize the human intestine less frequently than other Enterobacteriaceae . Regarding the habitats there are definitely differences between the species.

water

Freshwater is an important habitat of S. fonticola , S. grimesii , S. liquefaciens , S. marcescens , S. plymuthica and S. rubidaea (or referred to as S. marinorubra ). S. ureilytica was discovered in the Indian river Torsa . Serratia strains that produce prodigiosin are toxic to protozoa , which is an advantage for bacteria in colonizing water and soil. Further research has shown that the pigmented strains are more likely to be found in well or spring water , while non-pigmented strains are more typical of polluted river water.

Insects and other invertebrata

Serratia species are often found in various insects . There are examples of this in the orders of locusts (Orthoptera), termites (Isoptera), beetles (Coleoptera), butterflies (Lepidoptera), hymenoptera (Hymenoptera) and two-winged (Diptera). Mainly S. liquefaciens , S. marcescens and S. plymuthica were detected . Serratia species can be pathogenic for some insects ; the enzyme chitinase they produce is considered a virulence factor . However, Serratia species are also found in healthy insects, for example in the intestines. Also symbioses of bacteria and insects are known. During the development of Tetanops myopaeformis , a species of fly , the larvae ( maggots ) are found on sugar beets . S. liquefaciens and S. marcescens are present at all stages of development of the insect . It is assumed that they participate in the metamorphosis by breaking down chitin in the puparium (doll's shell).

S. symbiotica is an endosymbiont of the black bean louse ( Aphis fabae ). The bacterium is not seen as an obligatory symbiont, but as a not absolutely necessary (facultative or secondary) symbiont that benefits from the community. S. symbiotica can also be cultivated in vitro , which is not always possible with endosymbionts due to the special adaptation of their metabolism. It occurs in several representatives of the tube aphids (Aphididae) and can be found in the cytoplasm of certain cells. It plays a role in protecting against parasites.

In New Zealand, Costelytra zealandica is important as a pasture pest . The larvae of Costelytra zealandica ( grass grubs , "grass maggots") multiply in grass or clover and feed on it. After four to six years, their population decreases dramatically, which is attributed to a disease known as amber disease . Research has shown that S. entomophila and S. proteamaculans are responsible for colonizing the larval intestines. Suspensions of entomophila p are applied to the grazing areas to combat the pests.

S. glossinae was found in the midgut of the tsetse fly Glossina palpalis gambiensis . Glossina species are vectors for protozoa of the genus Trypanosoma , whichcause sleeping sickness . The microbial flora of Glossina species is researched in order to prevent the transmission of protozoa with the help of bacteria or to damage the tsetse fly. S. nematodiphila lives in symbiosis with the nematode -Art Heterorhabditidoides chongmingensis , which in turn is pathogenic to insects.

Vertebrata

Even with the vertebrates (Vertebrata) are Serratia TYPES represented, sometimes associated with infectious diseases was prepared often they are non-pathogenic part of the microbial flora. The isolation of smaller mammals and the surrounding territory - plants and soil - was particularly successful in S. liquefaciens and S. proteamaculans . Chronic infections in cold blooded animals are sometimes associated with Serratia . Serratia species have also been detected in healthy eared turtles ( Pseudemys scripta elegans ), other turtles and geckos . In a systematic investigation of faecal samples from European wild birds, S. fonticola was found several times. Serratia strains were found in the intestines of approximately 40% of the trapped rodents and shrews without any signs of infection on autopsy of the animals.

plants

S. proteamaculans was 1919 the tropical plant king-Protea ( Protea Cynaroides ) from the kind of sugar bushes ( Protea discovered) and a leaf disease ( English leaf spot disease ) to be associated. Similar lesions on the leaves of Protea , tobacco plants (genus Nicotiana ) and bean plants can also be produced by S. marcescens and S. rubidaea and are interpreted as a hypersensitivity reaction . S. ficaria was discovered in the common fig ( Ficus carica ). Together with certain biotypes of S. marcescens it is part of the microbial flora of the fig wasp Blastophaga psenes (fig gall wasp ). Due to the complex processes involved in pollination (in addition to the fig gall wasp, two fig varieties are also required in order to obtain edible fruit), the two Serratia species can be found in the insect, the galls formed and the fruit.

S. rubidaea is typically found in coconuts , in the pulp and in coconut milk made from it. S. quinivorans has been isolated from sugar beets and their rhizosphere . Several Serratia species (in addition to S. proteamaculans especially S. liquefaciens ) have also been detected on many other plants, where they contribute as reducing agents ( destructors ) to the breakdown of organic material. They can also be found on plant-based foods, such as lettuce , cauliflower and Brussels sprouts . A possible transmission of pathogenic Serratia species in the hospital via the raw food served is being discussed.

Medical importance

Human medicine

The species S. marcescens and S. liquefaciens are of human medical importance, S. marcescens especially in connection with nosocomial infections ("hospital infections "). It is considered to be an opportunistic pathogen that can cause infections in patients with a weakened immune system . These are sepsis , wound infections, endocarditis , urinary tract infections and infections of the respiratory tract . Imipenem , meropenem , ertapenem , ciprofloxacin or levofloxacin are used for antibiotic therapy , alternatively gentamicin and amikacin .

Veterinary medicine

Poultry and thus also poultry meat or eggs used as food can be contaminated with Serratia species , for example S. marcescens has been detected in the digestive tract of hens without the animals appearing to be impaired. Serratia also plays a subordinate role as a pathogen causing mastitis in cows . Various studies have shown that it was diagnosed as the cause of the disease in 0.2–1.5% of cases. Serratia species, especially S. grimesii and S. liquefaciens , have occasionally been detected in milk , especially raw milk , or in milk products .

Web links

Commons : Serratia  - collection of images, videos and audio files

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literature

  • Francine Grimont, Patrick AD Grimont: The Genus Serratia (Chapter 3.3.11) . In: Martin Dworkin, Stanley Falkow, Eugene Rosenberg, Karl-Heinz Schleifer, Erko Stackebrandt (eds.): The Prokaryotes. A Handbook on the Biology of Bacteria, Volume 6: Proteobacteria: Gamma Subclass . 3. Edition. Springer-Verlag, New York 2006, ISBN 978-0-387-25496-8 , pp. 219-244 , doi : 10.1007 / 0-387-30746-x_11 .

Individual evidence

  1. ^ 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.
  2. a b c d e f g Hans G. Schlegel, Christiane Zaborosch: General microbiology . 7th edition. Thieme Verlag, Stuttgart / New York 1992, ISBN 3-13-444607-3 , p. 307-313 .
  3. a b c d e f g h Michael T. Madigan, John M. Martinko, Jack Parker: Brock Mikrobiologie. German translation edited by Werner Goebel, 1st edition. Spektrum Akademischer Verlag GmbH, Heidelberg / Berlin 2000, ISBN 3-8274-0566-1 , pp. 531-536.
  4. a b c d e f g h i j F. Grimont, PAD Grimont: The Genus Serratia. In: The Prokaryotes. A Handbook on the Biology of Bacteria, Volume 6. 2006, pp. 219-220.
  5. a b c d F. Grimont, PAD Grimont: The Genus Serratia. In: The Prokaryotes. A Handbook on the Biology of Bacteria, Volume 6. 2006, pp. 228-229.
  6. a b c d e f g h F. Grimont, PAD Grimont: The Genus Serratia. In: The Prokaryotes. A Handbook on the Biology of Bacteria, Volume 6. 2006, pp. 230-233.
  7. a b c F. Grimont, PAD Grimont: The Genus Serratia. In: The Prokaryotes. A Handbook on the Biology of Bacteria, Volume 6. 2006, pp. 233-236.
  8. jp / nhh / dpa: After the death of a premature baby in Berlin: a baby infected with Serratia germs out of danger. In: Focus . October 22, 2012. Retrieved October 25, 2012 .
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  17. a b P. AD Grimont, TA Jackson et al. a .: Serratia entomophila sp. nov. Associated with Amber Disease in the New Zealand Grass Grub Costelytra zealandica. In: International Journal of Systematic Bacteriology. Volume 38, No. 1, January 1988, pp. 1-6, ISSN  0020-7713 . doi : 10.1099 / 00207713-38-1-1 .
  18. a b P. AD Grimont, F. Grimont, MP Starr: Serratia ficaria sp. nov., a bacterial species associated with Smyrna figs and the fig waspBlastophaga psenes. In: Current Microbiology. Vol. 2, No. 5, September 1979, pp. 277-282, ISSN  0343-8651 . doi : 10.1007 / BF02602859 .
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  22. ^ A b P. AD Grimont, F. Grimont, MP Starr: Comment on the Request to the Judicial Commission to Conserve the Specific Epithet liquefaciens over the Specific Epithet proteamaculans in the Name of the Organism Currently Known as Serratia liquefaciens. In: International Journal of Systematic Bacteriology. Volume 31, No. 2, April 1981, pp. 211-212, ISSN  0020-7713 . doi : 10.1099 / 00207713-31-2-211 .
  23. a b C. X. Zhang, SY Yang and a .: Serratia nematodiphila sp. nov., associated symbiotically with the entomopathogenic nematode Heterorhabditidoides chongmingensis (Rhabditida: Rhabditidae). In: International Journal of Systematic and Evolutionary Microbiology. Volume 59, No. 7, July 2009, pp. 1603-1608, ISSN  1466-5026 . doi : 10.1099 / ijs.0.003871-0 . PMID 19578149 .
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