Pseudomonas aeruginosa

This bacterium causes urinary tract infections, respiratory system infections, dermatitis, soft tissue infections, bacteremia and a variety of systemic infections, particularly in cancer and AIDS patients who are immunosuppressed.

This photograph depicts the colonial growth pattern displayed by Pseudomonas aeruginosa bacteria, also known as Bacillus pyocyaneus, having been cultured on a Xylose Lysine Sodium Deoxycholate (XLD) agar plate.

The current classification of the genus Pseudomonas is divided into 5 groups based on ribosomal RNA (rRNA)/DNA homology. Of the more than 20 pseudomonal species that have been found from human clinical specimens, the following 4 representative organisms:

• Ps. aeruginosa (homology group I)
• Ps. cepacia (group II)
• Ps. pseudomallei (group II)
• Ps. mallei (group II)

From eMedicine:

Pseudomonas aeruginosa Overview
* Pseudomonas Infection
* Ecthyma Gangrenosum
*External Ear, Malignant External Otitis

Pseudomonas aeruginosa, an increasingly prevalent opportunistic human pathogen, is the most common gram-negative bacterium found in nosocomial (hospital-acquired) infections.

P. aeruginosa is responsible for 16% of nosocomial pneumonia cases, 12% of hospital-acquired urinary tract infections, 8% of surgical wound infections, and 10% of bloodstream infections. Immunocompromised patients, such as neutropenic cancer and bone marrow transplant patients, are particularly susceptible to opportunistic infections. In this group of patients, P. aeruginosa is responsible for pneumonia and septicemia with attributable deaths reaching 30%. P. aeruginosa is also one of the most common and lethal pathogens responsible for ventilator-associated pneumonia in intubated patients, with directly attributable death rates reaching 38%. In burn patients, P. aeruginosa bacteremia has declined as a result of better wound treatment and dietary changes (removal of raw vegetables, which can be contaminated with P. aeruginosa, from the diet). However, P. aeruginosa bacteremia is associated with 50% of deaths.

Cystic fibrosis (CF) patients are characteristically susceptible to chronic infection by P. aeruginosa, which is responsible for high rates of illness and death in this population. The capacity of P. aeruginosa to produce such diverse, often overwhelming infections is due to an arsenal of virulence factors. Many extracellular virulence factors secreted by           P. aeruginosa have been shown to be controlled by a complex regulatory circuit involving cell-to-cell signaling systems that allow the bacteria to produce these factors in a coordinated, cell-density–dependent manner.

Proteases are assumed to play a major role during acute P. aeruginosa infection.

P. aeruginosa produces several proteases including LasB elastase, LasA elastase, and alkaline protease. The role of alkaline protease in tissue invasion and systemic infections is unclear; however, its role in corneal infections may be substantial. The ability of P. aeruginosa to destroy the protein elastin is a major virulence determinant during acute infection. Elastin is a major part of human lung tissue and is responsible for lung expansion and contraction. Moreover, elastin is an important component of blood vessels, which rely on it for their resilience. The concerted activity of two enzymes, LasB elastase and LasA elastase, is responsible for elastolytic activity. Elastolytic activity is believed to destroy elastin-containing human lung tissue and cause the pulmonary hemorrhages of invasive P. aeruginosa infections. LasB elastase is a zinc metalloprotease that acts on a number of proteins including elastin. LasB elastase10 times that of P. aeruginosa alkaline protease and an activity toward casein approximately four times that of trypsin. The LasA elastase is a serine protease that acts synergistically with LasB elastase to degrade elastin. LasA elastase nicks elastin, rendering it sensitive to degradation by other proteases such as LasB elastase, alkaline protease, and neutrophil elastase. Both LasB elastase and LasA elastase have been found in the sputum of CF patients during pulmonary exacerbation. However, the role of LasB elastase in tissue destruction during the chronic phase of CF is less clear. It has been postulated that during this phase, antibodies present in high titers neutralize LasB elastase, and elastin damaged by minute amounts of LasA is degraded mostly by neutrophil elastase. LasB elastase degrades not only elastin but also fibrin and collagen. It can inactivate substances such as human immunoglobulins G and A, airway lysozyme, complement components, and substances involved in protecting the respiratory tract against proteases such as a-1-proteinase inhibitor and bronchial mucus proteinase inhibitor. Therefore, LasB elastase not only destroys tissue components but also interferes with host defense mechanisms. Studies in animal models show that mutants defective in LasB elastase production are less virulent than their parent strains, which supports the role of LasB elastase as a virulence factor. is highly efficient, with a proteolytic activity approximately.

Complete genome sequence of Pseudomonas aeruginosa PA01

Pseudomonas aeruginosa PA01 Genome Page

Pseudomonas Genome Data Base

PFGE

Pseudomonas aeruginosa PFGE protocol (HPA.UK)

PFGE method

Organism-------Pseudomonas aeruginosa

Recommended lysis enzyme--proteinase K

Restriction enzyme----------------SpeI,XbaI

Approximate no. of-----------20–25,40–50
restriction Fragments

Fragments size-------------10–700,10–300
range (kb)

Identification of glucose non-fermenting Gram-negative rods

Pseudomonas
Pseudomonas species is a ubiquitous, aerobic gram-negative bacillus.

Reservoirs in nature include soil, vegetation, and water.

Reservoirs in a hospital include sinks, toilets, mops, respiratory therapy, and dialysis equipment.

It exhibits intrinsic resistance to many antibiotics and disinfectants.
Pseudomonas adheres to host cells by pili and nonpili adhesins. It produces a polysaccharide capsule that allows the organism to adhere to epithelial cells, inhibits phagocytosis,and confers protection against antibiotic activity.

Patients with cystic fibrosis are more likely to be infected with a strain whose colony appears mucoid because of the presence of the capsule.
Pseudomonas produces multiple toxins and enzymes, which contribute to its virulence.Its lipopolysaccharide endotoxin and exotoxin A appear to cause most of the systemic manifestations of Pseudomonas disease. Exotoxin A blocks protein synthesis in host cells, causing direct cytotoxicity. It mediates systemic toxic effects as well. It is similar in function to diphtheria toxin but is structurally and immunologically distinct. Endotoxin contributes to the development of many of the symptoms and signs of sepsis, including fever, leukocytosis, and hypotension.

Antibiotic resistance is another important aspect of its virulence. It is intrinsically resistant to numerous antibiotics and has acquired resistance to others through various means. The polysaccharide capsule prevents the penetration of many antibiotics into Pseudomonas. Penetration of antibiotic into the Pseudomonas cell is usually through pores in the outer membrane. Mutation of these porin proteins appears to be a primary mechanism of its antibiotic resistance. Multidrug efflux pumps and b-lactamase production also contribute to the antibiotic resistance that so frequently complicates the treatment of Pseudomonas infections.

Some P. aeruginosa strains produce a diffusable pigment: pyocyanin, which gives the colonies a blue color; fluorescein, which gives them a yellow color; or pyorubin, which gives them a red-brown color. Pyocyanin also
seems to aid in the virulence of the organism by stimulating an inflammatory response and by producing toxic oxygen radicals.

Clinically significant infections with P. aeruginosa should not be treated with single-drug therapy, because the bacteria can develop resistance when single drugs are employed. The newer quinolones, including ciprofloxacin, are active against Pseudomonas. Quinolones inhibit bacterial DNA synthesis by blocking DNA gyrase. The fluorinated forms of ciprofloxacin and norfloxacin have low toxicity and greater antibacterial activity than the earlier forms. Plasmids code for enzymes that determine the active transport of various antimicrobials across the cell membrane.