A Microbial Biorealm page on the genus Eikenella corrodens
Higher order taxa
Bacteria; Proteobacteria; Betaproteobacteria; Neisseriales; Neisseriaceae; Eikenella
Description and significance
Eikenella corrodens is a periodontopathogen that inhibits the human oral cavity, intestinal tract, and genital tract. It was first isolated by Henriksen in 1948 and was first classified as Bacteriode corrodens by Eiken in 1958. In 1972, Jackson and Goodman renamed it Eikenella corrodens to avoid mixing it up with Bacteroides ureolyticus. Eikenella corrodens exists in colonies that typically release a musty or bleachy smell . It grows at a temperature from 35oC to 37oC. Its strain type is ATCC 23834, DSM 8340 . The plasmid DNA of Eikenella corrodens, pMU1, is used in various research such as on pilus-formation and colony morphology . Under a microscope, one can see three different regions of Eikenella corrodens: a clear and moist center, a visible ring that appears as droplet, and an outer growth ring. A unique feature of this bacterium is that it is capable of corroding agar plate culture; hence, the species name is corroden . Eikenella corrodens exists in dental plaque of both healthy people and periodontitis patients and can cause infections. Other clinical sources include head and neck infections and respiratory tract infections. Furthermore, it is responsible for about one quarter of all human hand bites infections and clenched-fist injuries .
Eikenella corrodens has a genome with a length of 8696 nt and has a 55% coding. It has a circular DNA chromosome. Plasmids have been identified in this bacterium and were labeled pMU1. Plasmid pMU1 has been widely used in various research such as colony morphology and pilus formation. Eikenella corrodens chromosome sequence was completed on June 6, 2005 at the Hiroyuki Azakami, Yamaguchi University, Department of Biological Chemistry, Japan . Although the sequence has been completed, the amount of base pairs and/or the number of chromosomes is still unknown.
Cell structure and metabolism
Eikenella corrodens is a Gram negative, facultative and anaerobic, non-motile, non-sporeforming pathogenic bacillus that exists in the form of a straight rod. E. corrodens has DNA chromosomes and plasmids but no RNA . Its plasmid, especially pMU1, is a useful source in Eikenella corrodens studies . This bacterium can survive under both aerobic and anaerobic conditions. However, under aerobic conditions, it requires the presence of Hemin (a heme oxygenaase) for growth. Growth on plates may be stimulated in a 3-10% CO2 environment, even though CO2 is not required . An important characteristic of Eikenella corrodens is that it is oxidase positive, which means that it can reduces nitrate to nitrite. This characteristic is important because E. corrodens generates energy mainly via oxidative deamination of proline in the oral cavity. A chemostat-growth experiment, with chemically defined media of different quantity of proline, verifies that this amino acid is the main source of ATP generation in Eikenella corroden. The biomass production per mole of proline is higher than any other amino acids. This bacterium generates proline by producing the enzyme proline iminopeptidase, which discharges the side-chain proline from the N-terminus of polypeptides .
The interaction of Eikenella corrodens and other subginival organisms may be fatal to patients with Down syndrome. Down syndrome children often develop severe periodontal disease at an early stage in their lives. Studies show that certain periodontopathogens, such as Eikenella corrodens, began to colonize in the oral cavity of children with Down syndrome. Eventually, with the parallel maturation of subgingival components such as P. gingivalis, these children will be more susceptible to gingival inflammation . Antibiotic such as tetracycline is often used to treat Eikenella corrodens infections. However, a recent study done by a group of doctors at the National Taiwan University confirms that this antibiotic cannot eliminate the bacterium completely. Periodontopathogens may re-infect the periodontal pockets in the oral cavity as soon as three months after the termination of the treatment. Thus, tetracycline has no real affect on Eikenella corrodens .
Since Eikenella corrodens inhabits the human oral cavity, intestinal tract, and genital tracts, any breakage in barriers (mucosal membranes, skin, etc) will be the prefect target for hematogenous spread and vital Eikenella infections. Prior illness that drained antibodies from the body immune system is also a perfect condition for Eikenella corrodens to invade; thus this bacterium is an opportunistic human pathogen . After the bacterium invaded the membrane, it will cause inflammation and pain. Symptoms of a Eikenella corrodens infection may be an onset of swelling, chills, high fever that lasts for days, local tenderness, and edema. Eikenella corrodens infection may lead to serious diseases such as periodontitis, osteomyelitis, meningitis, empyema, and endocarditis. Infections causes by this bacterium can be treated with antibiotics such as penicillin, ampicillin, and tetracycline .
Application to Biotechnology
Periodontobacteria communicate via Quorum sensing, a communication process that uses secreted chemical signaling molecules called autoinducers (AIs). Bacteria can come together to form colonies via this process. This colonizing ability allows them to control their population size, thus allowing them to adjust the expression of various physiological functions based on the changes in the population density. Eikenella corrodens was found to secrete type 2 signaling molecules, which requires the LuxS gene for synthesis. From an experiment, LuxS mutant’s capacity to colonized and form biofilm on polysterene surface is 1.3-fold greater than the wild type. Thus, Eikenella corrodens’s LuxS-dependent signal plays a key role in the biofilm formation of the oral cavity . In addition, Eikenella corrodens also produces the enzyme proline iminopeptidase, which free the side-chain proline from the N-terminus of polypeptides. This is significant in the process of ATP generation .
In a biology lab at the University of Missouri-Kansas, researchers isolated and examined Eikenella corrodens VA1. They found that this group of human pathogens exhibit two irreversible phases: piliated S-phase and non-piliated L-phase. When put into a solid agar medium, the piliated Eikenella corrodens formed small, corroding colonies whereas the non-piliated ones formed large, noncorroding colonies. Through the sequence analysis of the cloned genomic fragment of the S-phase Eikenella corrodens VA1, researchers discovered four potential ORFs (open Reading Frames) arranged in a single file. These four ORFs were labeled pilA1, pilA2, pilB, and hagA. PilA1 and pilA2 was found to be similar to the recombinase protein that codes for type IV pilin gene. PilB appeared to have similar sequence identity with the bacteria Dichelobacter nodosus FimB; and hagA revealed a protein that resembles hemagglutinin. These four ORFs are located in a region called pilA locus, which exists in both S-phase and L-phase. Transcription from this pilA locus region is almost exactly the same in both S and L-phases. Researchers also utilized the electron microscopy and immunochemical analysis to further seek out the differences between the two phases. As a result, they discovered that S-phase variants have three functions: synthesize, export, and assemble pilin into pili; while L-phase variants only synthesize pilin. They concluded that the differences in the functions of the S-and L-phases might be responsible for the phase variation in Eikenella corrodens .
In a similar research done by a group of scientists from the Department of Biological Chemistry at the Yamaguchi University, Japan, Eikenella corrodens 1073 plasmid DNA was isolated and studied to see if it is related to the pilus formation and colony morphology. A fragment was isolated from the plasmid DNA of Eikenella corrodens 1073 and labeled pMU1. Through the applications of Agarose gel electrophoresis and Southern analysis, these researchers were able to determine the nucleotides sequence of the pMU1 fragment and identified seven ORFs (open reading frames). Four of these ORFs are said to be similar to the ORFs in pJTPS1, which is found in a mutant of Ralstonia solanacearum (a phytopathogenic bacterium). The pMU1 ORFs were also found alike to the recombinase protein specific for type IV pilin gene. When the pMU1 fragment was introduced into Eikenella corrodens 23834 strain, pilus structure and corroding colonies formed on the cell surface. On the other hand, there was no trait of pilus structure on the Eikenella corrodens 1073 strain. This strain is called the transdormant strain. When researchers applied acridine orange to cure the pMU1, it remained inactive and non-corroding. With the current experimental results, it can be concluded that pMU1 somehow irreversibly impacts the pilus formation and therefore has an affect on the colony morphology .
At the Department of Oral Biology, State University of New York, Buffalo School of Dental Medicine, researchers aimed to evaluate the genetic diversity of Eikenella corrodens, a facultative bacillus that inhabits the oral cavity using restriction endonuclease analysis (REA). They also hope to be able to explore the applicability of REA in studying the transmission of this periodontopathogenic bacterium. The participants of this study were divided into two groups: Group 1 consists of 47 epidemiologically independent former patients of dental plaques vs 40 periodontitis patients with more than one oral infection. Group 2 consists of 40 isolates recovered from two periodontitis patients and two periodontally healthy subjects. Strain-specific restriction pattern, a pattern form from only isolates with common traits, occurred in Group 1 Eikenella corrodens. For Group 2 E. corrodens, three out of four participants have more than one clonal type E. corrodens. These researchers concluded that through the use of the restriction endonuclease analysis, the Gram negative oral bacteria is said to be genetically heterogeneous. Thus REA proved to be a useful technique in the epidemiologic search for E. corrodens infections .
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Edited by Eileen Pham, student of Rachel Larsen at University of California, San Diego.
Edited by KLB