Serratia
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Serratia infection Microchapters |
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Diagnosis |
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Serratia On the Web |
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American Roentgen Ray Society Images of Serratia |
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S. entomophila |
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Microbiological Characteristics
Serratia is a ubiquitous opportunistic pathogen that is frequently present in food, soil, plants, animals, and damp conditions.
- Serratia is a short, lactose-forming, Gram-negative, facultatively anaerobic, rod-shaped bacteria of the Enterobacteriaceae family.
- It contains enzymes that facilitate its survival under oxygenated conditions against reactive oxygen species: superoxide dismutase, catalase, and peroxidase.
- Serratia has a unique thin cell wall that contains lipopolysaccharides (LPS) that does not resemble the LPS-containing cell walls of other Gram-negative bacteria.
- Out of a total of 12 Serratia species (see Scientific Classification Table), 8 have been reported to be infectious in humans. To view list of infectiuous Serratia species, click here.
- Clinically, Serratia may infect multiple organ systems. It may be responsible for urinary tract infection, pneumonia , osteomyelitis, meningitis, endocarditis, intra-abdominal infections, and eye and tear duct infections (conjunctivitis, keratitis, endophthalmitis).
Serratia is notoriously known for its antimicrobial resistance due to the presence of R-factorand efflux pumps.
- R-factor are genes on plasmids that code for antibiotic resistancemay and may be transferred from one strain to another.
- Efflux pumps, such as the SdeXY, SdeY, and ABC-type efflux pumps, may eliminate toxins. These pumps may reduce susceptibility to antimicrobial agents, such as erythromycin, tetracycline, norfloxacin, benzalkonium chloride, ethidium bromide, acriflavine, and rhodamine.
Taxonomy
Serratia belongs to the following higher order taxa:
- Bacteria (Domain); Proteobacteria (Phylum); Gamma Proteobacteria (Class); Enterobacteriales (Order); Enterobacteriaceae (Family); Serratia (Genus).
Serratia marcescens
- S. marcescens is a thin, motile (flagellated), non-septated, Gram-negative, facultatively anaerobic rod-shaped bacteria that can grow in temperatures ranging from 5–40°C and in pH levels ranging from 5 to 9.
- S. marcescens is able to perform casein hydrolysis, which facilitates the production of extracellular metalloproteases thought to function in cell-to-extracellular matrix interactions.
- S. marcescens also exhibits tryptophan- and citrate-degradation. Pyruvic acid, an end-product of tryptophan degradation, and carbon, an end-product of citrate degradation, are then incorporated into metabolic processes.
- S. marcescens produces a reddish-orange (bloody) pigment called prodigiosin. Not all strains, however, are able to produce prodigiosin. It is thought that during an infection, the production of prodigiosin, a human antigen, is limited to avoid the triggering of human immune responses.
- Identification of the organism may be done via the following tests:
- Methyl red test, which determines if a microorganism performs mixed-acid fermentation. Typically, S. marcescens results in a negative test due to the production of 2, 3-butanediol and ethanol.
- Voges-Proskauer test, which determines the organism's ability to convert pyruvatet to acetonin. Typically, S. marcescens results in a positive test.
- Nitrate test, which determines the organism's ability to produce nitrate products. Typically, S. marcescens results in a positive test.
Identification
The following table demonstrates the microbiological characteristics of S. marcescens:
| Test | Result[1] |
|---|---|
| Gram stain | - |
| Oxidase | - |
| Indole production | - |
| Methyl Red | >70% - |
| Voges-Proskaeur | + |
| Citrate (Simmons) | + |
| Hydrogen sulfide production | - |
| Urea hydrolysis | >70% - |
| Phenylalanine deaminase | - |
| Lysine decarboxylase | + |
| Motility | + |
| Gelatin hydrolysis, 22°C | + |
| Acid from lactose | - |
| Acid from glucose | + |
| Acid from maltose | + |
| Acid from mannitol | + |
| Acid from sucrose | + |
| Nitrate reduction | + (to nitrite) |
| Deoxyribonuclease, 25°C | + |
| Lipase | + |
| Pigment | some biovars produce red |
| Catalase production (24h) | + |
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![Blood agar base plate cultivated colonial growth of Gram-negative, rod-shaped and facultatively anaerobic Serratia marcescens bacteria. From Public Health Image Library (PHIL). [2]](/images/3/36/Enterobacteria40.jpeg)
Blood agar base plate cultivated colonial growth of Gram-negative, rod-shaped and facultatively anaerobic Serratia marcescens bacteria. From Public Health Image Library (PHIL). [2]
![Blood agar base plate cultivated colonial growth of Gram-negative, rod-shaped and facultatively anaerobic Serratia marcescens bacteria. From Public Health Image Library (PHIL). [2]](/index.php/File:Enterobacteria40.jpeg)
References
- ↑ Bergey's Manuals of Determinative Bacteriology, by John G. Holt, 9th ed. Lippincott Williams & Wilkins, 15 January 1994. pp. 217
- ↑ "Public Health Image Library (PHIL)".