Background
Pseudomonas aeruginosa, P. aeruginosa, is considered a dangerous pathogen of human nosocomial infections, so infection often occurs in clinical settings. The pathogenicity of the bacterium is expressed in the infection of sites with purulent inflammatory processes and abscesses, which is particularly relevant to burn victims. Therefore, it is highly recommended to study the pathogenicity factors of this microorganism and to study its morphological and metabolic properties. The present work summarizes the results of such a study and provides descriptive material for P. aeruginosa.
Brief History
The Pseudomonas bacterial family is believed to have been first discovered and qualitatively described in wartime. More specifically, Pseudomonas aeruginosa was first discovered by C. E. Sedillot in 1850, although he did not isolate P. aeruginosa as such a bacterial culture (D’Abramo & Neumeyer, 2020). It was not until 1882 that French chemist Charles Gessard was able to isolate P. aeruginosa from the biomaterial of wound dressings of wounded soldiers (Chen, 2018). This isolate was a purulent-pathogenic mixture from which P. aeruginosa was obtained in its pure form. The classification aspects of microbiology have changed over time, as has the position of this taxon. The name of the species, literally meaning its color, was suggested by observation when the pathogen was found to have two characteristic pigments, giving it a blue and a green color simultaneously. Since then, no severe outbreaks, much fewer pandemics, of P. aeruginosa have been detected, but the pathogen has firmly taken its place as an opportunistic threat.
Morphology
It is known that P. aeruginosa belongs to the typical representatives of Gram-negative bacteria of bacilliform shape. Notably, the bacillus shape can be straight or curved, but this does not affect the toxic properties of P. aeruginosa. According to Batra (2018), this pathogen is highly motile, and its linear dimensions do not exceed 3 mm in length and 0.5 mm in width. At the same time, it is a species of non-colonial bacteria, which means that both free-living microorganisms and those existing in pairs and groups can be found in the isolate. Each bacterium has 1-2 polar flagella that allow free movement. Also notable is the fact that typically P. aeruginosa has no lipid or protein capsid or envelope, but some of the strains can produce a mucus-like starchy substance that has a protective effect (Lymn, 2018). This allows P. aeruginosa to survive even in challenging conditions and not to dry out in the sun.
Optimal Environmental Conditions
The prevalence of P. aeruginosa in nature is wide: this pathogen lives peacefully in water, soil, inside animals and plants, and on surfaces in clinical settings. Including water, P. aeruginosa can persist for extended periods — approximately one year — at 35-37°C (Wu et al., 2015). This ability accounts for the presence of P. aeruginosa in many non-sterile medical solutions, whether physiological solution or contact lens storage solution. At the same time, it should be understood that P. aeruginosa is an obligate aerobe, which means that the growth and biological activity of the pathogen are only possible when oxygen is abundant (Batra, 2018). However, this claim was refuted when it was found that the bacterium is capable of surviving in anaerobic conditions (Vatan et al., 2018). The widespread distribution of the pathogen is determined by its high adaptability to different environmental conditions and food raw materials. For example, the bacterium is resistant to high concentrations of salts and dyes and is also able to resist the action of weak antiseptics and antibiotics.
In humans, P. aeruginosa can become part of their normal microflora, especially in the axilla, groin, upper respiratory tract, and gastrointestinal tract. Adhesion to the epithelium is due to the presence of microvilli on the bacterial surface, and in the absence of fibronectin — due to weakened immunity — attachment is greatly facilitated (Alves et al., 2018). Thus, locally hospital infection is initiated at the site of open wounds, including those from burns. When penetrating deep tissues, P. aeruginosa can spread through the tissues or infect the urogenital organs directly when catheters are inserted. Consequently, it is acceptable to point out that violation of the sanitary conditions of the clinical room and the lack of sterility of the instruments used are contributing factors to the infection of the patient with P. aeruginosa.
Metabolism
As stated, P. aeruginosa is regarded as a typical obligate aerobic bacterium capable of energy production through denitrification mechanisms. At the same time, the bacterium is able to survive and exhibit toxicological activity under anaerobic conditions, producing energy through phosphorylation at the substrate level (Vatan et al., 2018). During this process, ATP formation occurs by direct transfer of the phosphate group to ADP from the substrate. Consequently, P. aeruginosa uses the Entner-Dudorov metabolic pathway for carbohydrate oxidation (BC, n.d.). It is also important to emphasize that P. aeruginosa is characterized by low saccharolytic activity with comparably high proteolytic activity. Among the metabolic products, pyocins, pyocyanin, and fluorescein, which give the microorganisms their characteristic blue-green color, stand out. When P. aeruginosa enters the body, the production of exotoxin A, which destroys the matrix of protein synthesis, and exoenzyme S, which causes pathogenetic processes in the respiratory organs, is observed.
References
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Batra, S. (2018). Morphology and culture characteristics of Pseudomonas aeruginosa (P.aerugunosa). Paramedics World. Web.
BC. (n.d.). Catabolism of carbohydrates. BC Campus.
Chen, S. (2018). Pseudomonas infection. MedScape. Web.
D’Abramo, F., & Neumeyer, S. (2020). A historical and political epistemology of microbes. Centaurus, 62(2), 321-330.
Lymn, E. (2018).How clean is the hand you’re shaking?Action. Web.
Vatan, A., Saltoglu, N., Yemisen, M., Balkan, I. I., Surme, S., Demiray, T.,… & Study Group, Cerrahpasa Diabetic Foot. (2018). Association between biofilm and multi/extensive drug resistance in diabetic foot infection. International Journal of Clinical Practice, 72(3), 1-8.
Wu, W., Jin, Y., Bai, F., & Jin, S. (2015). Pseudomonas aeruginosa. In Y. Tang, M. Sussman, & J. Schwartzman (Eds.), Molecular medical microbiology (pp. 753-767). Academic Press.