Listeria innocua: Difference between revisions
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==Application to Biotechnology== | ==Application to Biotechnology== | ||
Recently, researchers discovered that four isolates of Listeria spp. produced inhibitory activities against the pathogen L. monocytogenes. One of the isolates, Listeria innocua 743, was “selected for further study” (2). It was revealed that the plasmid of L. innocua produced two compounds: a bacteriosin and a protein “involved in immunity toward other bacteriosins” (2). A bacteriosin is a type of antibiotic. It is a small peptide molecule with 30-60 amino acid residues. Bacteriosins are commonly produced by lactic acid bacteria and other bacterial species, but this is the first known case of Listeria spp. producing bacteriosin. This discovery has beneficial implications for controlling Listeria monocytogenes, which presents a danger as a food-borne pathogen. Bacteriosin can be used to inhibit the growth of L. monocytogenes in processed foods, thereby making the ingestion of such foods much safer for humans. Furthermore, the bacteriosin produced by Listeria innocua 743 revealed a very broad spectrum inhibition of L. monocytogenes, which means that the antibiotic can inhibit a wide variety of L. monocytogenes strains (2). | |||
==Current Research== | ==Current Research== | ||
Revision as of 05:42, 4 June 2007
A Microbial Biorealm page on the genus Listeria innocua
Classification
Higher order taxa:
Bacteria; Firmicutes; Bacilli; Bacillales; Listeriaceae; Listeria
Species:
Listeria innocua
Description and significance
Listeria innocua is one of the six species belonging to the genus Listeria. It is widely found in the environment (such as soil) and food sources. It can survive in extreme pH and temperature, and high salt concentration (5). In terms of appearance, it is a rod-shaped Gram-positive bacterium. It is a non-spore forming bacterium. It may live individually or organize into chains with other Listeria innocua bacteria. It is a mesophile, operating at an optimal temperature range of 30-37 degrees Celsius. Listeria innocua very much resembles its other family members, the pathogenic Listeria monocytogenes (5). Listeria innocua was isolated from meat by a technique called surface adhesion immunofluorescence (3). Samples of meat were inoculated with L. innocua and incubated at 30 degrees Celsius for 14-18 hours in a broth. The cells were then isolated from the meat by surface adhesion onto a polycarbonate membrane attached to a microscope glass slide. Then immunofluorescent microscopy was employed to visualize the bacteria (3). Listeria innocua is important because it is very similar to the food-borne pathogen L. monocytogenes but non-pathogenic in character. Thus its genome was sequenced in order to compare it to the genome of L. monocytogenes to learn what makes the former pathogenic.
Genome structure
Listeria innocua has a circular chromosome made up of 3,011,209 base pairs, with a 37% G+C content (6). Only 2,973 protein-coding genes were discovered in L. innocua, while no function could be predicted for 37% of the genes (6). The genome encodes a great variety of regulatory, surface and transport proteins (5). This explains why Listeria species can adapt to and inhabit such a wide range of environments. Listeria innocua was found to be deficient in a 10-kb virulence locus, a cluster of genes that engenders pathogenicity to Listeria monocytogenes (5). This explains why L. innocua typically does not infect humans or animals. It also has a circular plasmid of 81,905 base pairs whose function is unknown (6).
Cell structure and metabolism
Listeria innocua are Gram-positive bacteria, meaning they have a thick cell wall for protection. The cell wall is studded with hydrophilic molecules such as teichoic acids to repel hydrophobic molecules such as drugs. These organisms also produce flagella and pili for motility. Listeria innocua have very complex metabolism. They are capable of metabolizing methane, sulfur and nitrogen, among many other organic and inorganic compounds (4). These organisms also carry out numerous biosynthetic pathways, including peptidoglycan synthesis. Listeria innocua, like other members of their genus, are facultative anaerobes, which means that they can metabolism glucose (and other simple sugars) in under both aerobic and anaerobic conditions. Under the aerobic metabolism of glucose, L. innocua forms lactic acid and acetic acid. However, under anaerobic conditions, the metabolism of glucose yields only lactic acid (4).
Ecology
Listeria species are unusual in that they can survive and multiply at both low and high temperatures. They can also endure a wide pH range of 4.4 to 9.8 (4). These facts help explain why they are ubiquitous in all types of environment. Listeria spp. are found in water, soil, vegetation, wild and domesticated animals, and humans. Cultivated land has less contamination of Listeria than uncultivated; sandy soil contains more Listeria than clay-like soil; untreated sewage water is a good breeding ground for Listeria. Since Listeria is also found in water sources, such as the sea, it is not surprising that fish, squids, crustaceans and other seafood have been found to contain the bacteria (8). This could be harmful for humans if the contamination is from L. monocytogenes because they are the pathogenic species that cause disease (5). Furthermore, human intervention, like effluents from food-processing plants, also increases the spread of Listeria into the environment (8).
Pathology
Listeria innocua, as its name suggests, is harmless to other organisms. It lacks the 10-kb virulence locus that is needed for pathogenicity. Out of the six species of Listeria, only L. monocytogenes causes a disease called listeriosis (8). The bacterium is pathogenic for both human and animal hosts. Listeriosis has a high fatality rate and ranks among the most frequent causes of death due to food poisoning. The ability of L. monocytogenes to resist food-processing conditions and refrigeration temperatures makes it a threat to public health via contamination of meat, poultry, seafood and dairy products (8).
Infection occurs in several detailed steps. First, the bacterium enters the host cell. Second, it escapes from the host’s phagosomal vacuole. Third, it multiplies in the cytosol. Finally, it spreads to other cells using actin-based motility. Each step in the infection process requires specific enzymes expressed by virulence factors located on the bacterium’s chromosome (8). For example, internaline genes encode internaline proteins which are responsible for the invasion of host epithelial cells; the gene hlyA encodes listeriolysin O and the gene plcA encodes PI-PLC, both of which are involved in the lysis of the phagosome (8).
Some symptoms associated with listeriosis include fever, muscle aches, diarrhea, vomiting and nausea. If the infection has spread to the brain or spinal column, additional symptoms include confusion, stiff neck, headache and loss of balance. Pregnant women, neonates, elderly people and people with depressed immune systems are most susceptible to listeriosis, which manifests as septicaemia, meningitis, or meningoencephalitis. Moreover, in pregnant women, the disease can cause spontaneous abortion (8).
Application to Biotechnology
Recently, researchers discovered that four isolates of Listeria spp. produced inhibitory activities against the pathogen L. monocytogenes. One of the isolates, Listeria innocua 743, was “selected for further study” (2). It was revealed that the plasmid of L. innocua produced two compounds: a bacteriosin and a protein “involved in immunity toward other bacteriosins” (2). A bacteriosin is a type of antibiotic. It is a small peptide molecule with 30-60 amino acid residues. Bacteriosins are commonly produced by lactic acid bacteria and other bacterial species, but this is the first known case of Listeria spp. producing bacteriosin. This discovery has beneficial implications for controlling Listeria monocytogenes, which presents a danger as a food-borne pathogen. Bacteriosin can be used to inhibit the growth of L. monocytogenes in processed foods, thereby making the ingestion of such foods much safer for humans. Furthermore, the bacteriosin produced by Listeria innocua 743 revealed a very broad spectrum inhibition of L. monocytogenes, which means that the antibiotic can inhibit a wide variety of L. monocytogenes strains (2).
Current Research
Enter summaries of the most recent research here--at least three required
References
Edited by student of Rachel Larsen and Kit Pogliano
