Pseudomonas aeruginosa

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Pseudomonas aeruginosa
Pseudomonas aeruginosa and Staphylococcus aureus colonies.jpg
P. aeruginosa colony (right) on trypticase soy agar
Scientific classification
Kingdom: Bacteria
Phylum: Proteobacteria
Class: Gammaproteobacteria
Order: Pseudomonadales
Family: Pseudomonadaceae
Genus: Pseudomonas
Species: P. aeruginosa
Binomial name
Pseudomonas aeruginosa
(Schröter 1872)
Migula 1900
Type strain
ATCC 10145

CCUG 551
CFBP 2466
CIP 100720
DSM 50071
JCM 5962
LMG 1242
NBRC 12689
NCCB 76039
NCIMB 8295
NCTC 10332
NRRL B-771
VKM B-588

Synonyms

Bacterium aeruginosum Schroeter 1872
Bacterium aeruginosum Cohn 1872
Micrococcus pyocyaneus Zopf 1884
Bacillus aeruginosus (Schroeter 1872) Trevisan 1885
Bacillus pyocyaneus (Zopf 1884) Flügge 1886
Pseudomonas pyocyanea (Zopf 1884) Migula 1895
Bacterium pyocyaneum (Zopf 1884) Lehmann and Neumann 1896
Pseudomonas polycolor Clara 1930
Pseudomonas vendrelli nomen nudum 1938

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. aeruginosa is a prototypical "multidrug resistant (MDR) pathogen" recognised for its ubiquity, its intrinsically advanced antibiotic resistance mechanisms, and its association with serious illnesses – especially nosocomial infections such as ventilator-associated pneumonia and various sepsis syndromes.

The organism is considered opportunistic insofar as serious infection is often superimposed upon acute or chronic morbidity – most notably cystic fibrosis and traumatic burns – or found in immunocompromised individuals, but the organism does produce a range of clinically important infections in the immunocompetent and/or in situations where no pre-existing vulnerability is required e.g. hot tub folliculitis. In all infections produced by P. aeruginosa, treatment is dually complicated by the organism's resistance profile, which may lead to treatment failure and/or expose patients to untoward adverse effects from advanced antibiotic drug regimens. This dilemma is a central clinical problem in the field of antimicrobial resistance.

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 hypoxic 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.[1] Because it thrives on moist surfaces, this bacterium is also found on and in medical equipment, including catheters, causing cross-infections in hospitals and clinics. It is implicated in hot-tub rash. It is also able to decompose hydrocarbons and has been used to break down tarballs and oil from oil spills.[2] P. aeruginosa is not extremely virulent in comparison with other major pathogenic bacterial species – for example Staphylococcus aureus and Streptococcus pyogenes – though P. aeruginosa is capable of extensive colonization, and can aggregate into enduring biofilms.[3] P. aeruginosa does not fare especially well under suboptimal atmospheric conditions.

P. aeruginosa is among the Gram-negative bacilli commonly isolated from the exoskeletons and/or droppings of the cosmopolitan peridomestic cockroaches – including Periplaneta americana and Blatella germanica – which are often pervasive in households, as well as hospital settings. The importance of P. americana (and other vermin) as a potential reservoir or vector of P. aeruginosa continues to be studied.

Nomenclature[edit]

Pseudomonas aeruginosa culture.JPG

The word Pseudomonas means "false unit", from the Greek pseudo (Greek: ψευδο, false) and (Latin: monas, from Greek: μονος, a single unit). The stem word mon was used early in the history of microbiology to refer to germs, e.g., kingdom Monera.

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. aeruginosa, pyocyanin (blue) and pyoverdine (green), which impart the blue-green characteristic color of cultures. 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.[4]

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.

Gram-stained P. aeruginosa bacteria (pink-red rods)

Biology[edit]

Host Range and Symptoms of P. aeruginosa[edit]

P. aeruginosa is a pathogen that could be described as an archetype for opportunistic behavior. Its host range is extremely broad, and its ability to infect mammals like humans, invertebrates like nematodes, and a variety of plant species is a way in which it is unique from other plant pathogens. It is opportunistic because it attacks hosts with compromised defense systems, this could be due to previous disease or other environmental or biological factors. Certain strains of P. aeruginosa are able to infect the roots of plant species like Arabidopsis and sweet basil to cause the disease root rot. Symptoms of this disease include decaying root tissue with necrotic black patches on root tips. Often times the roots are brown or discolored and can be slimy, secondary symptoms include wilting and yellowing of plant leaves. There are other strains are able to cause soft rot in lettuce, symptoms of this include watery or soft feeling to plant tissues. Water lesions symptomatic of soft rot are caused by the release of pectate and other degrading enymes that bind plant cells and cause structures to fall apart.[citation needed]

Genome[edit]

The genome of P. aeruginosa is relatively large (5.5–6.8 Mb) and encodes between 5,500 and 6,000 open reading frames, depending on the strain;[6] 5,021 genes are present across the first five genomes analyzed, with at least 70% sequence identity. This set of genes is the P. aeruginosa core genome.[7]

strain: VRFPA04 C3719 PAO1 PA14 PACS2
genome size (bp) 6,818,030 6,222,097 6,264,404 6,537,648 6,492,423
ORFs 5,939 5,578 5,571 5,905 5,676

Metabolism[edit]

P. aeruginosa is a facultative anaerobe, as it is well adapted to proliferate in conditions of partial or total oxygen depletion. 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.[8] Adaptation to microaerobic or anaerobic environments is essential for certain lifestyles of P. aeruginosa, for example, during lung infection in cystic fibrosis patients, where thick layers of lung mucus and alginate surrounding mucoid bacterial cells can limit the diffusion of oxygen. P. aeruginosa growth within the human body can be asymptomatic until the bacteria form a biofilm, which overwhelms the immune system. These biofilms are found in the lungs of cystic fibrosis patients, and a leading cause of death among them.[9][10][11][12][13]

Pathogenesis[edit]

Phagocytosis of P. aeruginosa by neutrophil in patient with bloodstream infection (Gram stain)

An opportunistic, nosocomial pathogen of immunocompromised individuals, P. aeruginosa typically infects the airway, urinary tract, burns, and wounds, and also causes other blood infections.[14]

Infections Details and common associations High-risk groups
Pneumonia Diffuse bronchopneumonia Cystic fibrosis patients
Septic shock Associated with a purple-black skin lesion ecthyma gangrenosum Neutropenic patients
Urinary tract infection Urinary tract catheterization
Gastrointestinal infection Necrotising enterocolitis Premature infants and neutropenic cancer patients
Skin and soft tissue infections Hemorrhage and necrosis Burns victims and patients with wound infections

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.g., catheters). Pseudomonas can be spread by equipment that gets contaminated and is not properly cleaned or on the hands of healthcare workers.[15] Pseudomonas can, in rare circumstances, cause community-acquired pneumonias,[16] as well as ventilator-associated pneumonias, being one of the most common agents isolated in several studies.[17] Pyocyanin is a virulence factor of the bacteria and has been known to cause death in C. elegans by oxidative stress. However, salicylic acid can inhibit pyocyanin production.[18] One in ten hospital-acquired infections is from Pseudomonas. Cystic fibrosis patients are also predisposed to P. aeruginosa infection of the lungs. P. aeruginosa may also be a common cause of "hot-tub rash" (dermatitis), caused by lack of proper, periodic attention to water quality. Since these bacteria like moist environments, such as hot tubs and swimming pools, they can cause skin rash or swimmer's ear.[15] Pseudomonas is also a common cause of postoperative infection in radial keratotomy surgery patients. The organism is also associated with the skin lesion ecthyma gangrenosum. P. aeruginosa is frequently associated with osteomyelitis involving puncture wounds of the foot, believed to result from direct inoculation with P. aeruginosa via the foam padding found in tennis shoes, with diabetic patients at a higher risk.

Toxins[edit]

P. aeruginosa uses the virulence factor exotoxin A to inactivate eukaryotic elongation factor 2 via ADP-ribosylation in the host cell, much as the diphtheria toxin does. Without elongation factor 2, eukaryotic cells cannot synthesize proteins and necrotise. The release of intracellular contents induces an immunologic response in immunocompetent patients. In addition P. aeruginosa uses an exoenzyme, ExoU, which degrades the plasma membrane of eukaryotic cells, leading to lysis. 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.[19][20]

Phenazines[edit]

Phenazines are redox-active pigments produced by P. aeruginosa. These pigments are involved in quorum sensing, virulence, and iron acquisition.[21] P. aeruginosa produces several pigments all produced via a biosynthetic pathway. Pyocyanin, 1-Hydroxyphenazine, Phenazine-1-Carboxamide, 5-methylphenazine-1-carboxylic acid betaine, and Aeruginosin A. Two operons are involved in phenazine biosynthesis: phzA1B1C1D1E1F1G1 and phzA2B2C2D2E2F2G2.[22][23] These operons convert a chorismic acid to the phenazines mentioned above. Three key genes, phzH, phzM, and phzS convert phenazine-1-carboxylic 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. aeruginosa pathogenicity is observed in vitro.[23] This suggests that pyocyanin is most responsible for the initial colonization of P. aeruginosa in vivo.

Triggers[edit]

With low phosphate levels, P. aeruginosa has been found to activate from benign symbiont to express lethal toxins inside the intestinal tract and severely damage or kill the host, which can be mitigated by providing excess phosphate instead of antibiotics.[24]

Plants and invertebrates[edit]

In higher plants, P. aeruginosa induces soft rot, for example in Arabidopsis thaliana (Thale cress)[25] and Lactuca sativa (lettuce).[26][27] It is also pathogenic to invertebrate animals, including the nematode Caenorhabditis elegans,[28][29] the fruit fly Drosophila[30] and the moth Galleria mellonella.[31] The associations of virulence factors are the same for plant and animal infections.[26][32]

Quorum sensing[edit]

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. P. aeruginosa employs three interconnected QS systems — lasRl, rhlRl, and PQS — that each produce unique signaling molecules.[33] Detection of these molecules indicates P. aeruginosa is growing as biofilm within the lungs of cystic fibrosis patients.[34] QS is known to control expression of a number of virulence factors, including the pigment pyocyanin. 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.[35] Garlic experimentally blocks quorum sensing in P. aeruginosa.[36]

Biofilms and treatment resistance[edit]

Biofilms of P. aeruginosa can cause chronic opportunistic infections, which are a serious problem for medical care in industrialized societies, especially for immunocompromised patients and the elderly. They often cannot be treated effectively with traditional antibiotic therapy. Biofilms seem to protect these bacteria from adverse environmental factors. P. aeruginosa can cause nosocomial infections and is considered a model organism for the study of antibiotic-resistant bacteria. 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. aeruginosa. This should contribute to better clinical management of chronically infected patients, and should lead to the development of new drugs.[35]

Many genes and factors affect biofilm formation in P. aeruginosa. One of the main gene operons responsible for the initiation and maintaining the biofilm is the PSL operon.[37] This 15-gene operon is responsible for the cell-cell and cell-surface interactions required for cell communication. 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. aeruginosa.

Cdi-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. Polysaccharide synthesis locus (PSL) and cdi-GMP form a negative feedback loop. PSL stimulates cdi-GMP production, while high cd-GMP turns on the operon and increases activity of the operon.

Recent studies have shown that the dispersed cells from P. aeruginosa biofilms have lower c-di-GMP levels and different physiologies from those of planktonic and biofilm cells.[38][39] Such dispersed cells are found to be highly virulent against macrophages and C. elegans, but highly sensitive towards iron stress, as compared with planktonic cells.[38]

Recently, scientists have been examining the possible genetic basis for P. aeruginosa resistance to antibiotics such as tobramycin. 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.[40]

Diagnosis[edit]

Production of pyocyanin, water-soluble green pigment of P. aeruginosa (left tube)

Depending on the nature of infection, an appropriate specimen is collected and sent to a bacteriology laboratory for identification. As with most bacteriological specimens, a Gram stain is performed, which may show gram-negative rods and/or white blood cells. P. aeruginosa produces colonies with a characteristic "grape-like" or "fresh-tortilla" odor on bacteriological media. 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. Confirmatory tests include production of the blue-green pigment pyocyanin on cetrimide agar and growth at 42 °C. A TSI slant is often used to distinguish nonfermenting Pseudomonas species from enteric pathogens in faecal specimens.

When P. aeruginosa is isolated from a normally sterile site (blood, bone, deep collections), it is generally considered dangerous, and almost always requires treatment.[citation needed] However, P. aeruginosa is frequently isolated from nonsterile sites (mouth swabs, sputum, etc.), and, under these circumstances, it may represent colonization and not infection. The isolation of P. aeruginosa from nonsterile specimens should, therefore, be interpreted cautiously, and the advice of a microbiologist or infectious diseases physician/pharmacist should be sought prior to starting treatment. Often, no treatment is needed.

Treatment[edit]

Many P. aeruginosa isolates are resistant to a large range of antibiotics and may demonstrate additional resistance after unsuccessful treatment. 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.

The antibiogram of P. aeruginosa on Mueller-Hinton agar

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. Use of β-lactamase inhibitors such as sulbactam has been advised in combination with antibiotics to enhance antimicrobial action even in the presence of a certain level of resistance. Combination therapy after rigorous antimicrobial susceptibility testing has been found to be the best course of action in the treatment of multidrug-resistant P. aeruginosa. Some next-generation antibiotics that are reported as being active against P. aeruginosa include doripenem, ceftobiprole, and ceftaroline. However, these require more clinical trials for standardization. Therefore, research for the discovery of new antibiotics and drugs against P. aeruginosa is very much needed. Antibiotics that may have activity against P. aeruginosa include:

As fluoroquinolone is one of the few antibiotics widely effective against P. aeruginosa, in some hospitals, its use is severely restricted to avoid the development of resistant strains. On the rare occasions where infection is superficial and limited (for example, ear infections or nail infections), topical gentamicin or colistin may be used.

Antibiotic resistance[edit]

One of the most worrisome characteristics of P. aeruginosa is its low antibiotic susceptibility, which is attributable to a concerted action of multidrug efflux pumps with chromosomally encoded antibiotic resistance genes (e.g., mexAB, mexXY, etc.) and the low permeability of the bacterial cellular envelopes.[42] In addition to this intrinsic resistance, P. aeruginosa easily develops acquired resistance either by mutation in chromosomally encoded genes or by the horizontal gene transfer of antibiotic resistance determinants. Development of multidrug resistance by P. aeruginosa isolates requires several different genetic events, including acquisition of different mutations and/or horizontal transfer of antibiotic resistance genes. Hypermutation favours the selection of mutation-driven antibiotic resistance in P. aeruginosa strains producing chronic infections, whereas the clustering of several different antibiotic resistance genes in integrons favors the concerted acquisition of antibiotic resistance determinants. 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. aeruginosa populations to antibiotics treatment.[35]

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. Presence of antibiotic-degrading enzymes such as extended-spectrum β-lactamases like PER-1, PER-2, VEB-1, AmpC cephalosporinases, carbapenemases like serine oxacillinases, metallo-b-lactamases, OXA-type carbapenemases, aminoglycoside-modifying enzymes, among others have been reported. P. aeruginosa can also modify the targets of antibiotic action, for example methylation of 16S rRNA to prevent aminoglycoside binding and modification of DNA, or topoisomerase to protect it from the action of quinolones. P. aeruginosa has also been reported to possess multidrug efflux pumps like AdeABC and AdeDE efflux systems that confer resistance against number of antibiotic classes. An important factor found to be associated with antibiotic resistance is the decrease in the virulence capabilities of the resistant strain. Such findings have been reported in the case of rifampicin-resistant and colistin-resistant strains, in which decrease in infective ability, quorum sensing and motility have been documented.

Mutations in DNA gyrase are commonly associated with antibiotic resistance in P. aeruginosa has. These mutations, when combined with others, confer high resistance without hindering survival. Additionally, genes involved in cyclic-di-GMP signaling may contribute to resistance. When grown in vitro conditions designed to mimic a cystic fibrosis patient's lungs, these genes mutate repeatedly.[43]

Prevention[edit]

Probiotic prophylaxis may prevent colonization and delay onset of Pseudomonas infection in an ICU setting.[44] Immunoprophylaxis against Pseudomonas is being investigated.[45] The risk of contracting 'P. aeruginosa can be reduced by avoiding pools, hot tubs, and other bodies of standing water; regularly disinfecting and/or replacing equipment that regularly encounters moisture (such as contact lens equipment and solutions); and washing one's hands often (which is protective against many other pathogens as well). However, even the best hygiene practices cannot totally protect an individual against P. aeruginosa, given how common 'P. aeruginosa is in the environment.[46]

Experimental therapies[edit]

Phage therapy against P. aeruginosa has been investigated as a possible effective treatment, which can be combined with antibiotics, has no contraindications and minimal adverse effects. Phages are produced as sterile liquid, suitable for intake, applications etc.[47] Phage therapy against ear infections caused by P. aeruginosa was reported in the journal Clinical Otolaryngology in August 2009.[48]

Research[edit]

Experimental evolution[edit]

In 2013, Joao Xavier published on an experiment in which P. aeruginosa, when subjected to repeated rounds of conditions in which it needed to swarm to acquire food, developed the ability to "hyperswarm" at speeds 25% faster than baseline organisms, by developing multiple flagella, whereas the baseline organism has a single flagellum.[49] This result was notable in the field of experimental evolution in that it was highly repeatable.[50]

Identification[edit]

Test Results
Gram Stain -
Oxidase +
Indole Production -
Methyl Red -
Voges-Proskaeur -
Citrate +
Hydrogen Sulfide Production -
Urea Hydrolysis +
Phenylalanine Deaminase -
Lysine Decarboxylase -
Motility +
Gelatin Hydrolysis +
Acid from lactose -
acid from glucose -
acid from maltose -
acid from mannitol +
acid from sucrose -
nitrate reduction +
DNAse -
Lipase +
Pigment + (bluish green pigmentation)
Catalase +

[51]P. aeruginosa is a Gram-negative, aerobic (and at times facultatively anaerobic), bacillus with unipolar motility.[52] It has been identified as an opportunistic pathogen of both humans and plants.[53] P. aeruginosa is the type species of the genus Pseudomonas.[54]

In certain conditions, P. aeruginosa can secrete a variety of pigments, including pyocyanin (blue-green), pyoverdine (yellow-green and fluorescent), and pyorubin (red-brown). These can be used to identify the organism.[55]

Pseudomonas aeruginosa fluorescence under UV illumination

P. aeruginosa is often preliminarily identified by its pearlescent appearance and grape-like or tortilla-like odor in vitro. Definitive clinical identification of P. aeruginosa often includes identifying the production of both pyocyanin and fluorescein, as well as its ability to grow at 42 °C. P. aeruginosa is capable of growth in diesel and jet fuels, where it is known as a hydrocarbon-using microorganism, causing microbial corrosion.[56] It creates dark, gellish mats sometimes improperly called "algae" because of their appearance.[citation needed]

Pseudomonas aeruginosa as a Plant Pathogen[edit]

Host Range and Symptoms of P. aeruginosa[edit]

P. aeruginosa is a pathogen that could be described as an archetype for opportunistic behavior. Its host range is extremely broad, and its ability to infect mammals like humans, invertebrates like nematodes, and a variety of plant species is a way in which it is unique from other plant pathogens. It is opportunistic because it attacks hosts with compromised defense systems, this could be due to previous disease or other environmental or biological factors.

Certain strains of P. aeruginosa are able to infect the roots of plant species like Arabidopsis and sweet basil to cause the disease root rot. Symptoms of this disease include decaying root tissue with necrotic black patches on root tips. Often times the roots are brown or discolored and can be slimy, secondary symptoms include wilting and yellowing of plant leaves. There are other strains are able to cause soft rot in lettuce, symptoms of this include watery or soft feeling to plant tissues. Water lesions symptomatic of soft rot are caused by the release of pectate and other degrading enymes that bind plant cells and cause structures to fall apart.

Pathogenicity of P. aeruginosa[edit]

P. aeruginosa is a gram negative bacterium, its host range is extremely broad in that it is able to cause disease in mammals, non-mammalian animals like nematodes, and plants as well. P. aeruginosa is known to cause root rot in plant species, characterized by a softening and degrading of root tissues as well as black necrotic regions on root tips. How the pathogen is actually able to enter and infect the host has been studied extensively.

To analyze the mechanisms the bacteria uses to infect hosts, we can examine its interactions with a plant species, namely Sweet basil ( Ocimum basilicum). The pathogen is able to enter host plants via wounds or natural openings, sweet basil has evolved a way to detect infection of the pathogen, and upon entry the plant roots secrete excessive amounts of rosmarinic acid, a compound that has been shown to have antibacterial properties able to combat cells of P. aeruginosa. To counter this plant defense response, the pathogen has developed the ability to form a biofilm layer. These biofilms are an organized structure of attached cell colonies encased by an extracellular polymeric matrix, and are able to protect the bacterium from the effects of rosmarinic acid. The biofilms layers act as a means of resistance to the harsh environmental conditions created by the host plant. The pathogen can then go on to continue other processes, like the output of degradation enzymes that allow the bacteria to collect nutreince from plant cells. This sort of arms race between pathogen and host, where new genes arise that are able to confer some sort of resistance or tool to the organism’s advantage is known as the gene for gene concept, these sort of interactions are common across many different sorts of pathogen and host relationships.

Importance of P. aeruginosa[edit]

Certain strains of P. aeruginosa are able to cause soft rot in host plants, and therefore are a member of the bacterial soft rot pathogens, perhaps the most notable of these bacterial soft rot pathogens being Erwinia caratova. Soft rots commonly affect crops such as potato, carrot, tomato, and cucurbis, as well as cruciferous crops such as cabbage. More recently, there have been new reports of P. aeruginosa causing soft rot in onions. On a global scale, soft rots cause more crop losses than any other bacterial disease. In some cases, yield losses can be up to 100% due to substandard storage facility conditions. The problem of yield losses can be exacerbated when we take a look at how it affects different markets. A lack of available produce can lead to increases of produce prices, which can then go on to have other economic effects. All of these host crops carry enormous economic importance, onions, for example, where it has been estimated that 6.7 million acres are grown globally are known to be a household staple world wide. This crop is especially important for the developing economies of countries like, Egypt, Iran, and India, India being the world leader in onion production. This of course is just an example of the importance of one crop affected by P. aeruginosa, when we consider its ability to infect a range of hosts the need to control the pathogen becomes more clear. Understanding of these sorts of diseases is crucial in fighting them, and especially in the case of P. aeruginosa, where the pathogen has developed defenses that confer resistance to antibiotics, it is important to fully understand these bacterial mechanisms so we can develop new ways in treating them. With a growing global population, yield losses become more and more problematic

See also[edit]

References[edit]

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Additional Sources:

"Host Range and Symptoms of P. aeruginosa" Sources

Modeling P. aeruginosa Pathogenisis in Plant Hosts

"Importance of P. aeruginosa" Sources

“Effects of Phytobiocides in Controlling Soft Rot of Tomato”; Journal of Natural Sciences Research.

Wisconsin Horticulture. "Bacterial Soft Rot"

"Economics of Onion Cultivation and its Marketing Pattern in Satara District of Maharashtra". Barakade. September 2011

"First Report of Soft Rot on Onion Bulbs in Storage caused by Pseudomonas aeruginosa in Egypt." Hemida And-Alla, Ratering, Schnell, Bashandy. December 2011

Pathogenicity of Pseudomonas aeruginosa Sources:

"Pseudomonas aeruginosa - Plant root Interactions. Pathogenicity, Biofilm Formation, and Root Exudation". American Society of Plant Biologists. Walker, Bais, Deziel, Schweitzer, Rahme, Fall, Vivanco. Jan 2004

External links[edit]