Pseudomonas Aeruginosa Pseudomonas aeruginosa Research Paper Julie Johnson Pseudomonas aeruginosa is a versatile gram negative bacterium that grows in soil, marshes, and coastal marine habitats, as well as on plant and animal tissues.
People with cystic fibrosis, burn victims, individuals with cancer, and persons infected with HIV are particularly at risk of disease resulting from Pseudomonas aeruginosa. Unlike many environmental bacteria, Pseudomonas aeruginosa has a remarkable capacity to cause disease in susceptible hosts. It has the ability to adapt to and thrive in many ecological niches, from water and soil to plant and animal tissues. The bacterium is capable of utilizing a wide range of organic compounds as food sources, thus giving it an exceptional ability to colonize ecological niches where nutrients are limited. Pseudomonas aeruginosa can produce a number of toxic proteins, which not only cause extensive tissue damage, but also interfere with the human immune systems defense mechanisms.
These proteins range from potent toxins that enter and kill host cells at or near the site of colonization to degradative enzymes that permanently disrupt the cell membranes and connective tissues in various organs. In people with cystic fibrosis the most serious complication is respiratory tract infection by the ubiquitous bacterium Pseudomonas aeruginosa. CF is one of the most common fatal genetic disorders in the United States, affecting about 30,000 individuals. A comparable number of people in Europe also have CF. It is most prevalent in the Caucasian population, occurring in one of every 3,300 live births.
The gene involved in cystic fibrosis was identified in 1989. Located on human chromosome 7, it codes for a protein called the cystic fibrosis transmembrane conductance regulator (CFTR). This protein, normally produced in a number of tissues throughout the body, regulates the movement of salt and water in and out of these cells. The abnormality in the CFTR gene alters the CFTR protein in people with cystic fibrosis. As a result, one hallmark of CF is the presence of a thick mucus secretion which clogs the bronchial tubes in the lungs and plugs the exit passages from pancreas and intestines, leading to loss of function of these organs.
Progressive lung disease is the predominant cause of illness and death in people with CF. Mucus blocks the airway passages and results in a predisposition toward chronic bacterial infections. Although the genetic defect underlying CF has been characterized, exactly how and why individuals become infected with Pseudomonas is unknown. The lungs of most children with CF become colonized by Pseudomonas aeruginosa before their 10th birthday.
Chronic infection with these bacteria reduces an individuals quality of life, causing acute symptoms of cough, sputum production, and inflammation, which causes repeated exacerbations or episodes of intense breathing problems. Eventually leading to scarring and destruction of lung tissue and, ultimately, death. While it is clear that antibiotic therapy directed against these organisms lengthens the life span of individuals with CF, increasing antibiotic resistance develops. Although antibiotics can decrease the frequency and duration of these attacks, the bacterium establishes a permanent residence and can never be completely eliminated from the lungs. Management of cystic fibrosis lung disease requires a multipronged approach.
Outpatient management of pulmonary exacerbation usually includes a combination of 2 IV antipseudomonal antibiotics (an aminoglycoside plus a beta-lactam), appropriate antimicrobial treatment, effective airway clearance, optimization of nutritional status, and anti-inflammatory therapies. Additionally, prevention of respiratory viral disease and avoidance of exposure to irritants, such as smoke, is recommended. Usual duration of therapy is 14 to 21 days, and clinical response is assessed by physical exam, pulmonary function tests, nutritional status, and exercise tolerance. Microbial eradication is not a therapeudic end point. Choice of antibiotics should be based on culture and sensitivity of the sputum. Emergence of antibiotic-resistant species, such as Pseudomonas aeruginosa, has required close monitoring of antibiotic susceptibility patterns and strict infection-control policies.
Administration of chronic intermittent inhaled antipseudomonal therapy (tobramycin solution for inhalation), over a 6 month period was shown to improve FEV by 11.9%, decrease the bacterial density, and reduce hospitalization in CF patients chronically infected with Pseudomonas aeruginosa. Following 92 weeks of therapy with inhaled tobramycin, the mean % change in FEV was 4.7% above baseline. There was no increase in the utilization of antipseudomonal therapy despite an increase in MIC at the end of 12 treatment cycles. Decreases in Pseudomonas aeruginosa tobramycin susceptibility were not predictive of a lack of clinical response, i.e. lung function, to inhaled tobramycin. A potential role for aggressive antipseudomonal therapy that is currently under study involves the use of inhaled tobramycin in young patients at the time of initial colonization.
Researchers are hopeful that early, aggressive intervention may be effective in eradication of Pseudomonas aeruginosa, and therefore, will have a dramatic impact on the natural history of cystic fibrosis. One of the major factors that makes Pseudomonas aeruginosa difficult to eradicate is the overproduction of a sugar-like substance, alginate. One of the regulators of alginate production, the AlgR protein, has recently been shown to be involved with the function of pili (tiny hair-like appendages on the outside of the bacteria). Pili are involved in the initial stages of Pseudomonas aeruginosa infection of CF lungs. The AlgR protein, thus, may regulate not only genes controlling alginate production, but other Pseudomonas aeruginosa genes involved in the infection process.
A current study is investigating this by isolating genes that are regulated by AlgR and characterizing those genes to determine whether they are used by Pseudomonas aeruginosa to evade the bodys immune response and cause disease. The effects of the isolated genes will be measured on the ability of the bacteria to bind to the cells lining the airway and to avoid ingestion and destruction of defending white blood cells. Results from these studies will give insight into the disease causing mechanisms in Pseudomonas aeruginosa and may lead to alternate methods of infection prevention in the CF patient. Complications associated with Pseudomonas aeruginosa lung infections in CF patients are the result of a multitude of pathogenic mechanisms in the respiratory tract created by the underlying chloride channel defect. Gene mapping studies of Pseudomonas aeruginosa will help researchers and clinicians better understand local gene expression and the evolution of Pseudomonas aeruginosa as it has adapted to the CF lung. Researchers are using new genetic tools to study bacterial virulence mechanisms during infection with Pseudomonas aeruginosa.
Two techniques employed to determine the extent of genomic variation among different Pseudomonas aeruginosa clinical isolates are macroevolutional and microevolutional analysis. In macroevolutional analysis DNA arrays were used to identify genes in clinical strains of Pseudomonas aeruginosa that were absent in strain PA01 (the Pseudomonas Genome Project strain sequence). Using labeled genomic DNA probes, strains were assessed for reaction with PA01 probes, which represented sequences unique for the clinical strains. The isolates were sequenced and assembled into contigs, or contiguous coding regions, to determine the genetic structure of the strains. Using 2 clinical strains, the first isolated from a catheterized patient with a urinary tract infection and the second isolated from an infant with CF, researchers obtained a collection of genes specific to these 2 strains. Analysis of DNA sequences in these clones revealed that the majority of the genes did not share any sequence similarity with any other genes in the Genome Project database.
In each case, the percent G+C content was lower than 64% for most of the strain-specific sequences, suggesting that those traits were acquired by horizontal gene transfer. In microevolutional analysis, low-passage DNA sequencing of genomes was used to identify sequences unique to clinical isolates and to compare the genomic variations among them as well as to the Pseudomonas aeruginosa PA01 strain. In addition to generating sequence data that define unique genes in the genomes of these 2 clinical isolates, this approach has been extremely useful in defining regions that are present in the genome of PA01 and absent from the genomes of these 2 clinical strains. These DNA segments define unstable genetic elements that may encode proteins that are potentially deleterious for survival in the host.
Lastly, DNA sequences of several loci that accumulate single nucleotide mutations also have been identified. The long-range goal of the genomic comparison project is to correlate the genomic makeup of Pseudomonas aeruginosa strains with specific infections and to monitor the evolution of virulent traits expressed by this pathogen. There is continuous research being done of the mapping of the genome of Pseudomonas aeruginosa, which may lead to potential new treatments for patients with cystic fibrosis. A team of researchers at the University of Washington Genome Center and PathoGenesis Corporation collaborated to complete this genome sequence genetic map. In fact researchers are already using knowledge about the genetic instructions of Pseudomonas to identify targets for novel drug strategies. They will take the gene sequencing data and attempt to define the molecular mechanisms of infection for Pseudomonas aeruginosa.
They want to see which genes are needed for survival in its human host and which are needed for drug resistance. Pseudomonas aeruginosa is the largest of the 25 bacteria that scientists have sequenced so far. The largest previously sequenced bacterium was Escherichia coli, which has 4.6 million base pairs and approximately 4,200 genes. Pseudomonas aeruginosa, by contrast, has more than 6 million base pairs and approximately 5,500 genes. Preliminary work suggests that the high number of genes in Pseudomonas aeruginosa allow it to adapt and survive in many different environments, whereas most bacteria live within a small niche. Indoor plumbing, in particular, is especially hospitable to Pseudomonas aeruginosa.
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