Pseudomonas aeruginosa
Mindy Merenghi

Pseudomonas aeruginosa is a Gram-negative, rod-shaped bacterium in the Gamma Proteobacteria class.  The metabolism is respiratory, and never fermentative.  It can grow in the absence of oxygen (facultative aerobe), with NO3 as the respiratory electron acceptor.  The bacterium is very low-maintenance when it comes nutrition.  It does not require organic growth factors, and can use over seventy-five organic compounds for growth.  In a lab setting, acetate and ammonium sulfate in a medium will satisfy it.  The optimum growth temperature is 37 degrees C, but it can grow in temperatures up to 42 degrees C.  Not only is it tolerant to temperature, but also to salts and dyes, weak antiseptics, and antibiotics.  It produces a characteristic fruity, sweet odor.  A unique capability of some strains of this bacterium is the production of soluble blue pigments, one being the fluorescent pigment pyoverdin.  The other pigment is pyocyanin, which is a blue pus produced by the bacteria in some infections of the body.  It is causes impairments and disruptions in the human body.  A derivative of pyocyanin, called pyochelin, is a siderophore is also produced in low iron environments.

The microbe is free-living, usually found in moist environments like soil, marshes, and water, like the other members of the Pseudomonas genus.  P. aeruginosa may also be found in a biofilm on surfaces or in a planktonic form as a unicellular organism.  It is motile by means of one single polar flagellum and it is actually one of the fastest swimming bacteria found in pond water samples.

However, this microbe is not as innocent as it first sounds.  P. aeruginosa’s versatile characteristics allow it to be found in a variety of places and conditions.  It is a common plant and animal pathogen and is the “poster bacteria” of an opportunistic human pathogen.  If a person is immunosuppresed or has a tissue that is compromised in any way, this bacterium can be invasive or toxigenic.  Some of the high-risk people include cancer patients, burn victims, diabetics, and people with cystic fibrosis or AIDS.  It can cause infections of the urinary tract, soft tissues, bone and joints, ears, eyes, central nervous system, and gastrointestinal tract.  As a human pathogen, it is found mostly in hospitals; in food, sinks, toilets, mops, instruments such as respiratory equipment, or even transferred from the hands of healthy visitors or hospital staff.  In fact, it causes about 10% of all hospital-acquired infections.  This is of major concern because of the bacterium’s high resistance to antibiotics.  Since it is Gram-negative, the outer membrane protects it from antibiotics it has developed resistance because it lives among antibiotic producing bacteria and fungi in the soil.  In addition, the biofilm protects it and it also has antibiotic resistant plasmids, which are passed along in genes to other bacteria.

Pseudomonas aeruginosa possesses multiple virulence determinants that allow for the organism to thrive in many parts of the body.  It uses pili with the aid of protease enzymes in attachment to epithelial cells, such as in the respiratory tract.  The bacterium has capsules or slime layers that protect it from antibodies, lymphocytes, and phagocytes.  In order to invade tissues, it produces extracellular enzymes such as elastase and alkaline protease.  There are also three soluble proteins involved in invasion, which are cytotoxin (mw 25 kDa) and two hemolysins.  It produces the extracellular toxins Exoenzyme S and Exotoxin A and also LPS, which is characteristic of Gram-negative bacteria.  All of these characteristics lead to a wide variety of diseases.

The bacterium, Pseudomonas aeruginosa, is unusual because it is considered an environmental microbe, but is a common (and sometimes even fatal) opportunistic pathogen in humans.  It is also noted for its resistance to most antibiotics and the diverse conditions in which it can survive.


*Disclaimer - This report was written by a student participaring in a microbiology course at the Missouri University of Science and Technology. The accuracy of the contents of this report is not guaranteed and it is recommended that you seek additional sources of information to verify the contents.


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