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Pseudomonas aeruginosa is a common Gram-negative , rod-shaped bacterium that can cause disease in plants and animals, including humans. A species of considerable medical importance, P. The organism is considered opportunistic insofar as serious infection often occurs during existing diseases or conditions — most notably cystic fibrosis and traumatic burns.
It is also found generally in the immunocompromised but can infect the immunocompetent as in hot tub folliculitis. When more advanced antibiotic drug regimens are needed adverse effects may result. It is citrate , catalase , and oxidase positive.
It is found in soil, water, skin flora , and most man-made environments throughout the world. It thrives not only in normal atmospheres, but also in low-oxygen atmospheres, thus has colonized many natural and artificial environments.
It uses a wide range of organic material for food; in animals, its versatility enables the organism to infect damaged tissues or those with reduced immunity. The symptoms of such infections are generalized inflammation and sepsis. If such colonizations occur in critical body organs, such as the lungs , the urinary tract , and kidneys , the results can be fatal. It is also able to decompose hydrocarbons and has been used to break down tarballs and oil from oil spills.
The word Pseudomonas means "false unit", from the Greek pseudo Greek: The stem word mon was used early in the history of microbiology to refer to germs , e. The species name aeruginosa is a Latin word meaning verdigris "copper rust" , referring to the blue-green color of laboratory cultures of the species.
This blue-green pigment is a combination of two metabolites of P. Another assertion is that the word may be derived from the Greek prefix ae- meaning "old or aged", and the suffix ruginosa means wrinkled or bumpy. The names pyocyanin and pyoverdine are from the Greek, with pyo- , meaning "pus", [5] cyanin , meaning "blue", and verdine , meaning "green". Pyoverdine in the absence of pyocyanin is a fluorescent-yellow color. The genome of P.
This part of the genome is the P. This organism can achieve anaerobic growth with nitrate or nitrite as a terminal electron acceptor. When oxygen, nitrate, and nitrite are absent, it is able to ferment arginine and pyruvate by substrate-level phosphorylation. These biofilms are found in the lungs of people with cystic fibrosis and primary ciliary dyskinesia, and can prove fatal. However, iron is not easily accessible because it is not commonly found in the environment. Iron is usually found in a largely insoluble ferric form.
To overcome this and regulate proper intake of iron, P. The bacterium that produced the siderophores does not necessarily receive the direct benefit of iron intake. Rather, all members of the cellular population are equally likely to access the iron-siderophore complexes. Members of the cellular population that can efficiently produce these siderophores are commonly referred to as cooperators; members that produce little to no siderophores are often referred to as cheaters.
Research has shown when cooperators and cheaters are grown together, cooperators have a decrease in fitness, while cheaters have an increase in fitness. These observations suggest that having a mix of cooperators and cheaters can reduce the virulent nature of P. An opportunistic , nosocomial pathogen of immunocompromised individuals, P. It is the most common cause of infections of burn injuries and of the outer ear otitis externa , and is the most frequent colonizer of medical devices e.
Pseudomonas can be spread by equipment that gets contaminated and is not properly cleaned or on the hands of healthcare workers. However, salicylic acid can inhibit pyocyanin production. Cystic fibrosis patients are also predisposed to P. Since these bacteria like moist environments, such as hot tubs and swimming pools, they can cause skin rash or swimmer's ear.
The organism is also associated with the skin lesion ecthyma gangrenosum. Without elongation factor 2, eukaryotic cells cannot synthesize proteins and necrotise. The release of intracellular contents induces an immunologic response in immunocompetent patients. Increasingly, it is becoming recognized that the iron-acquiring siderophore , pyoverdine , also functions as a toxin by removing iron from mitochondria , inflicting damage on this organelle.
Phenazines are redox-active pigments produced by P. These pigments are involved in quorum sensing , virulence , and iron acquisition. Two operons are involved in phenazine biosynthesis: Three key genes, phzH , phzM , and phzS convert phenazinecarboxylic acid to the phenazines mentioned above.
Though phenazine biosynthesis is well studied, questions remain as to the final structure of the brown phenazine pyomelanin. When pyocyanin biosynthesis is inhibited, a decrease in P.
With low phosphate levels, P. In higher plants, P. Regulation of gene expression can occur through cell-cell communication or quorum sensing QS via the production of small molecules called autoinducers.
The extracellular accumulation of these molecules signals to bacteria to alter gene expression and coordinate behavior. Another form of gene regulation that allows the bacteria to rapidly adapt to surrounding changes is through environmental signaling. Recent studies have discovered anaerobiosis can significantly impact the major regulatory circuit of QS. This important link between QS and anaerobiosis has a significant impact on production of virulence factors of this organism.
They often cannot be treated effectively with traditional antibiotic therapy. Biofilms seem to protect these bacteria from adverse environmental factors. Researchers consider it important to learn more about the molecular mechanisms that cause the switch from planktonic growth to a biofilm phenotype and about the role of QS in treatment-resistant bacteria such as P.
This should contribute to better clinical management of chronically infected patients, and should lead to the development of new drugs. Many genes and factors affect biofilm formation in P. One of the main gene operons responsible for the initiation and maintaining the biofilm is the PSL operon. It is also responsible for the sequestering of the extracellular polymeric substance matrix. This matrix is composed of nucleic acids, amino acids, carbohydrates, and various ions.
This matrix is one of the main resistance mechanisms in the biofilms of P. Cyclic di-GMP is a major contributor to biofilm adherent properties. This signalling molecule in high quantities makes superadherent biofilms. When suppressed, the biofilms are less adherent and easier to treat. Recent studies have shown that the dispersed cells from P. Recently, scientists have been examining the possible genetic basis for P.
One locus identified as being an important genetic determinant of the resistance in this species is ndvB , which encodes periplasmic glucans that may interact with antibiotics and cause them to become sequestered into the periplasm.
These results suggest a genetic basis exists behind bacterial antibiotic resistance, rather than the biofilm simply acting as a diffusion barrier to the antibiotic.
Depending on the nature of infection, an appropriate specimen is collected and sent to a bacteriology laboratory for identification. In mixed cultures, it can be isolated as clear colonies on MacConkey agar as it does not ferment lactose which will test positive for oxidase.
A TSI slant is often used to distinguish nonfermenting Pseudomonas species from enteric pathogens in faecal specimens. The isolation of P. Often, no treatment is needed. In certain conditions, P. These can be used to identify the organism. Definitive clinical identification of P. It should usually be possible to guide treatment according to laboratory sensitivities, rather than choosing an antibiotic empirically. If antibiotics are started empirically, then every effort should be made to obtain cultures before administering first dose of antibiotic , and the choice of antibiotic used should be reviewed when the culture results are available.
Due to widespread resistance to many common first-line antibiotics, carbapenems , polymyxins , and more recently tigecycline were considered to be the drugs of choice; however, resistance to these drugs has also been reported. Despite this, they are still being used in areas where resistance has not yet been reported. Combination therapy after rigorous antimicrobial susceptibility testing has been found to be the best course of action in the treatment of multidrug-resistant P.
Some next-generation antibiotics that are reported as being active against P. However, these require more clinical trials for standardization. Therefore, research for the discovery of new antibiotics and drugs against P. Antibiotics that may have activity against P. As fluoroquinolone is one of the few antibiotics widely effective against P. On the rare occasions where infection is superficial and limited for example, ear infections or nail infections , topical gentamicin or colistin may be used.
For pseudomonal wound infections, acetic acid with concentrations from 0. Usually a sterile gauze soaked with acetic acid is placed on the wound after irrigation with normal saline. Dressing would be done once per day. One of the most worrisome characteristics of P. Development of multidrug resistance by P. Hypermutation favours the selection of mutation-driven antibiotic resistance in P.
Some recent studies have shown phenotypic resistance associated to biofilm formation or to the emergence of small-colony variants may be important in the response of P.
Mechanisms underlying antibiotic resistance have been found to include production of antibiotic-degrading or antibiotic-inactivating enzymes, outer membrane proteins to evict the antibiotics and mutations to change antibiotic targets. An important factor found to be associated with antibiotic resistance is the decrease in the virulence capabilities of the resistant strain.