It is a Genus that has more than 200 species that are mostly saprophytes found in the water and soil. Those species that are associated with human infections include:-
Pseudomonas aeruginosa (Pseudomonas pyocyanea), Pseudomonas Mallei, Pseudomonas Pseudomallei. Other species which are always isolated from human’s specimens and also thought to cause some infections.
The pathogenic of Pseudomonas aeruginosa has long been recognized especially as an infection acquired from hospitals. It always presents notoriety as an opportunistic pathogen because of its ability to adapt and it ability to resist many antibiotics and disinfectants.
It can be isolated from a wide variety of environmental. These include water, sewage and earth and sometime in hardy saprophytes. The ability of it to persisit and increase in number in wet places and on wet equipments in health facilities like washing rooms, kitchens is particularly important.
It is also isolated from plants, animals and insects. This shows its ability to thrive parasitically in many situations. It can also be found in stool and skin of healthy people.
Pseudomonas aeruginosa is a gram-negative bacillus, non-sporing and it is non-capsulated. It is motiles by virtue of a single polar flagellum. It is a strict aerobe but can grow anerobically in the presence of nitrate. It grows readily on a wide variety of laboratory media.
Most strains produce pigments; classically the colony and surrounding medium in greenish-blue due to production of pyocyanin and the yellow-green fluorescent pigment fluorescin. Some 10-15% of strains do not produce pigment although they may do so when grown on special media. Individual colonies can occur as 5 distinct types ranging from dwarf colonies to a large mucoid type, the common one colony is large, low-convex with an irregular surface and an edge that is translucent in comparison with the pigmented centre.
It gets its energy from carbohydrates by an oxidative rather than fermentative metabolism. When diagnosing Enterobacteriaceae either in sugar fermentation or urease production tests, Pseudomonas aeruginosa always appears not to be active and glucose is utilized. Other gram negatives are oxidase positive but none react as Pseudomonas aeruginosa that take 30 seconds to give a positive reaction.
Subtyping Pseudomonas aeruginosa require serology, bacteriophage-sensitivity and pyocin typing. The most reliable methods are sero-typing and pyocin typing. Basing on heat stable (O) antigens, 17 sero-types are recognized.
Production of pyocin by strain under test will determine the result of Pyocin typing. This demonstrated by the various patterns of inhibition given when tested against 13 indicator strain. In this way 105 pyocin types of Pseudomonas aeruginosa have been found.
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Pseudomonas aeruginosa can infect any external body parts or body organs. In any given community infection that is caused by Pseudomonas aeruginosa as mostly mild and also superficial. For example Otitis externa which is often chronic, but not disabling.
In hospitals, Pseudomonas infections are very common, very severe and vary. Pseudomonas infection is always localized for examples urinary tract infections, burns that are infected, infections of the eyes, infected ulcers and bedsores that are infected.
It can be generalized and isolated from blood specimen or post mortem from body organs in patients who are being treated with immunosuppressive drugs and older patients.
Children who are suffering from Cystic fibrosis are more susceptible to this infection. These organisms always produce exotoxins and variety of cytotoxic extracellular substances like lecithinase and pyocyanin.
The isolation of Pseudomonas aeruginosa is a simple procedure. The following the specimens used:-
Pyocin typing of isolated organism is undertaken for epidemiological purposes. Tests for antibodies in the patient’s serum have no place in diagnostic procedures at present.