Pseudomonas Aeruginosa Infection and Biofilm Production in Immunocompromised Individuals
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Bold Section Introduction Pseudomonas aeruginosa was first discovered and described as a distinct species by Pasture in the nineteenth century. It was studied as a pathogen, however, first by Carle Gessard, who noted that it turned bandages blue and green when exposed to ultra-violent radiation. Though outstanding advances in both microscopy and genetics, much more is currently known about this incredible species, which is extremely metabolically diverse, ubiquitous, and a devastating opportunistic pathogen. To begin, P. aeruginosa is gram negative bacterium with one flagella (Lederber, 2000). The flagellum plays an extremely important role in the production and assembly of biofilm formation. It is also a facultative anaerobe, but its optimal metabolism is aerobic respiration. In the absence of oxygen, it can respire anaerobically using nitrate or an alternate electron acceptor(Costerton, 1999). However, it often cannot grow when it is simultaneously a pathogen and not exposed to oxygen, as is common in the depth of the biofilm. Many cells thus often remain in a un-dividing state when in a biofilm. This, however, works in P. aeruginosa’s favor, as many antibiotics cannot kill cells that are not actively growing or dividing (Stewart, 2001). Furthermore, it can catabolize a variety of organic molecules, even carcinogens such as benzoate. This incredible nutritional and metabolic versatility and diversity allows it to survive attack by both phage and human induced antimicrobial agents, as well as live in a diverse arrays of environments. It is found ubiquitously, in environments as diverse as hospitals, sewage, animals, plants, water, and the soil. It is also the most predominant organism in oligotrophic aquatic ecosystems. Furthermore, in the soil, P. aeruginosa is an important ecological bacteria, breaking down the polycyclic aromatic hydrocarbons, and catabolizing important molcuelcules such as rhamnolipids, quinolones, and hydrogen cyanide (Lederberg, 2000).This versatility allows it to be the most abundant organism on earth. Despite this abundance, it is a pathogen. However, it only acts opportunistically, rarely infecting healthy individuals. It is common in immunocompromised patients, such as people suffering from AIDS or cancer (Lederberg, 2000). Cystic Fibrosis (CF) patients have an abundance of salt in their respiratory tract due to faulty CFTR chloride channels; this prevents the production and action of chemicals and proteins used by the immune system to prevent infection. As a result, many CF patients are chronically infected by P. aeruginosa, causing severe pulmonary inflammation and damage. As a result, the median life expectant of CF patients is 30 years old (Steward, 2001). Because of its prevalence in hospitals and selective pathogenesis, it infects two thirds of the critically ill hospitalized patients. Unfortunately, it is an extremely invasive pathogen, with a mortality rate of 40-60%. The mortality rate is extremely high because of the biofilm nature of P. aeruginosa. When a pathogen in the human lungs, it often forms biofilms, communities of bacterial cells attached to an inert or living surface and enclosed in a extracellular polysaccharide matrixes. These biofilms release planktonic bacteria, which are dispersed to spread the infection to other tissues or host organism. Many antibiotics kill the planktonic bacteria. However, antibiotics fail to kill the bacterium in the biofilm; for this reason, after antibiotic therapy is complete, the biofilm continues to produce planktonic bacteria and the infection reoccurs. Biofilms are inherently resistant to antibiotics, weather in the form of bacteriophages, amoebae, or chemical biocides (Lederberg, 2000).
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[Sample reference] Takai, K., Sugai, A., Itoh, T., and Horikoshi, K. "Palaeococcus ferrophilus gen. nov., sp. nov., a barophilic, hyperthermophilic archaeon from a deep-sea hydrothermal vent chimney". International Journal of Systematic and Evolutionary Microbiology. 2000. Volume 50. p. 489-500. Edited by student of Joan Slonczewski for BIOL 238 Microbiology, 2009, Kenyon College.