Patients With Cystic Fibrosis To Have Pseudomonas Aeruginosa Biology Essay

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Pseudomonas Aeruginosa is one of the most common infection in patients with cystic fibrosis. 1 in 2500 people has cystic fibrosis and infections can cause a rapid deterioration of patients' health if not treated early enough. The manifestation of the disease can start as early as newly born and may progress to over 50 years old [2] with the mean age of life expectancy of 35 years old [1]. Cystic fibrosis patient may present with various complications.

Cystic fibrosis is a recessive inherited disease that is caused by a deletion in the CFTR gene, resulting in a dysfunction chloride ion channel in patients' cells[3]. Too much salt and not enough water enters the cells resulting in a production of thick mucus, forming clogs in parts of the body that produces secretions[4]. This will lead to accumulation of fluid in organs that may result in infections by opportunistic bacteria. Most patients with Cystic Fibrosis will eventually develop respiratory infections by[5] Pseudomonas Aeruginosa as the thick mucus collecting in the lungs and airways provides an excellent environment for the bacteria to colonise, grow and multiply. [4, 5]

Patients can also suffer from other problems including infertility, malabsoption as the small intestine fail to secrete enzymes to aid digestion of food, and liver failure due to blockage of the bile duct. [4]

Background on Pseudomonas Aeruginosa(P. Aeruginosa)[3]

P. Aeruginosa is a rod, gram negative bacteria, belonging to the Pseudomonadaceae family. It is referred to as free living bacteria as it is easily found in soil, water and also plants. It is an opportunistic pathogen and is one of the most common causes for hospital acquired infections. The organism usually infect patients who are immunocompromised, but this is an exception in cystic fibrosis patients. Patients with cystic fibrosis has a high levels of antibodies, but they are unable to clear the organism from the body.

All strains of P. Aeruginosa are motile and have single flagellum.[5] They can withstand temperature up to 42 degrees celcius, allowing them to live in hot and moist environment like in the human body. It is known that P. Aeruginosa has three main colony categories, the first one being a small, rough colony which can be found in soils and water, the second one being a smooth colony type with 'fried egg' appearance which is large, smooth with flat edges, elevated appearance and the third one which is also a smooth colony type but with mucoid appearance instead. The third type is often associated with respiratory and urinary tract infections. The strains of P. Aeruginosa produces two types of soluble pigments - fluorescent pigment pyoverdin and blue pigment pyocyanin.

The links between Pseudomonas Aeruginosa infections and cystic fibrosis [5]

One of the most common problems with cystic fibrosis patients is respiratory infections with P. Aeruginosa as cystic fibrosis patients accumulate mucus or fluid in their lungs and airways, suitable for the growth of the organism. Once the infection is established in the lungs, it is no longer possible to eradicate it.

For this establishment to occur, the non-mucoid phenotype of P. Aeruginosa converts into a mucoid phenotype which causes an overproduction of exopolysaccharide alginate due to mutations in genes that is involved in alginate biosynthesis. The alginate provides some protection to the bacteria from phagocytosis by neutrophils and innate immune responses which are supposed to clear the organism from the airways. The mucoid phenotype is important in establishing this chronic infection, causes a rapid decline in lung function and poor prognosis.

It is also thought that AlgT gene that allow expression for alginate biosynthesis will suppress expression of flagella gene causing the organism to become immotile, protecting them from antibodies.

P. Aeruginosa may also adapt to patients' lung environment by forming micro-colonies and complex biofilm formation. By being in biofilms, the organism can be protected from the body's self defence system, causing neutrophils stimulated to undergo apoptosis or necrosis releasing free radicals and protease into the airways. Protection by biofilms also mean that the organism is protected against drug penetration, making the eradication process impossible.

P. Aeruginosa strains also has a different expression of lipopolysaccharide (LPS) from other bacteria, frequently a defective LPS in O-side chains, making compliment-mediated killing less effective towards the organism. All of these factors allow P. Aeruginosa to be resistant to elimination from cystic fibrosis patients.[3]

Due to the difficulties in eradicating P. Aeruginosa once the organism has colonised patients airways, it is important that the infection of this organism is to be caught as early as possible. In the early stage of infection, the organism is most likely to be in smaller quantities, motile and have not become mucoid or developed into a biofilm. Aggressive antibiotic treatments may be effective with monitoring of patient's progress. Intravenous antibiotics may be offered depending on patient's condition at the time.

Once the organism has invaded the lungs and the airways, patients are usually treated with various course of antibiotics, addressing patient's symptoms to prolong life. Pulmonary exacerbations is very common in patients as well as development of chronic infections which may progress to lung failure if it is very chronic. Some people may then require lung transplant to improve lung function.[4]

Due to a variety of antibiotics used for treatments at a large scale, resistance to antibiotic treatments is a common occurrence in many strains of P. Aeruginosa.[3] This may be related to the permeability barrier by the gram negative outer membrane of the organism causing them to become resistant to antibiotics.

It is also thought that P. Aeruginosa could maintain antibiotic resistance plasmid (R factors and RTFs factors) via horizontal gene transfer, transduction or conjugation.[3] Cross infections between cystic fibrosis patient is also thought to contribute in the organism to develop resistance to different types of antibiotics with few left that are thought to be still effective such as the fluoroquinolines, gentamicin and carbenicillin.[4], [3] Not all strains of P. Aeruginosa can be treated with these antibiotics as some has developed resistance.

Conclusion

It is hard to prevent cystic fibrosis in patients due to the nature of the disease being genetic. The primary concern for patients will be development of chronic infections especially by Pseudomonas Aeruginosa. Therefore, it is very important to prevent and identify the infection early to allow good prognosis to patients. It is hoped in the future, medical breakthroughs and effective drug therapies can be developed to eradicate the bacterial infection for the benefit of the patients, especially with cystic fibrosis.

[1-5]

1. Cystic Fibrosis Trust. Cystic Fibrosis 16th June 2010]; Available from: http://www.cftrust.org.uk/aboutcf/faqs#common.

2. Cystic Fibrosis Trust, UK CF Registry Annual Data Report 2008. 2009.

3. Kenneth Todar. Todar's Online Textbook of Bacteriology. 2008 [cited 2010 16th June 2010]; Available from: http://www.textbookofbacteriology.net/pseudomonas.htmlAvailable from: http://www.textbookofbacteriology.net/pseudomonas_2.htmlAvailable from: http://www.textbookofbacteriology.net/pseudomonas_3.htmlAvailable from: http://www.textbookofbacteriology.net/pseudomonas_4.html.

4. NHS UK. Cystic Fibrosis. 2010 16th June 2010]; Available from: http://www.nhs.uk/conditions/cystic-fibrosis/pages/introduction.aspxAvailable from: http://www.nhs.uk/Conditions/cystic-fibrosis/Pages/Symptoms.aspxAvailable from: http://www.nhs.uk/Conditions/cystic-fibrosis/Pages/Causes.aspxAvailable from: http://www.nhs.uk/Conditions/cystic-fibrosis/Pages/Diagnosis.aspxAvailable from: http://www.nhs.uk/Conditions/cystic-fibrosis/Pages/Treatment.aspx.

5. Hodson, M., D. Geddes, and A. Bush, Cystic Fibrosis. 3rd ed. 2007, London: Hodder Arnold. 503.

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