Pseudomonas

Pseudomonas is a gram-negative bacteria. It is a genus belonging to the Pseudomonadaceae family. There are about 144 species in this genus. Most of the Pseudomonas species are saprotrophic, meaning they release enzymes that break down big substances into small ones. 

## History
Pseudomonas is one of the earliest found bacteria. It was first called 'Bacterium aeruginosm' by Schroter in 1872. However, in 1894, German botanist Walter Migula classified it as *Pseudomonas aeruginosa*. In Greek, pseudo means false and monas means “unit”. This bacteria is associated with many chronic infections and is considered dangerous due to its resistance to many antibiotics. There has been an increase in the number of species discovered year by year. In 2013, 10 species have been found and 6 more in the subsequent year. The classification was based on the physiological and biochemical properties.

## Phylogeny
The basic tool which is used to classify Pseudomonas is the 16S rRNA gene.  However, it is hard to differentiate closely related Pseudomonas species, thus genes such as atpD, gyrB, rpoB, recA, and rpoD are also used in the taxonomy of Pseudomonas.Using gyrB and rpoD in phylogenetic analysis, Pseudomonas came from two predominant clusters; intrageneric cluster I (IGC I) and intrageneric cluster II (IGC II). 

IGC I consists of two sub clusters, the ‘*Pseudomonas aeruginosa* complex’  comprises of *Pseudomonas aeruginosa, Pseudomonas alcaligenes, Pseudomonas citronellolis, Pseudomonas mendocina, Pseudomonas oleovorans* and *Pseudomonas pseudoalcaligenes,* and the ‘*Pseudomonas stutzeri* complex’, comprises of *Pseudomonas balearica* and *Pseudomonas stutzeri*. 

IGC II consists of three subclusters, the ‘*Pseudomonas syringae* complex’, the ‘*Pseudomonas fluorescens* complex’ and the ‘*Pseudomonas putida* complex’.  The ‘*Pseudomonas syringae* complex’ are phytopathogens and pathovars. The former encompasses *Pseudomonas amygdali, Pseudomonas caricapapayae, Pseudomonas cichorii, Pseudomonas ficuserectae* and *Pseudomonas viridiflava*  and the latter consists of *Pseudomonas savastanoi* and *Pseudomonas syringae*. The ‘*Pseudomonas fluorescens* complex’ is divided into two subpopulations, the ‘*Pseudomonas fluorescens* lineage’ and the ‘*Pseudomonas chlororaphis* lineage’. The ‘*Pseudomonas fluorescens* lineage’ contains *Pseudomonas fluorescens* biotypes A, B and C, *Pseudomonas azotoformans, Pseudomonas marginalis* pathovars, *Pseudomonas mucidolens*, *Pseudomonas synxantha* and *Pseudomonas tolaasii*, while the ‘*Pseudomonas chlororaphis* lineage’ includes *Pseudomonas chlororaphis, Pseudomonas agarici, Pseudomonas asplenii* and *Pseudomonas corrugata*. The ‘*Pseudomonas putida* complex’ comprises of *Pseudomonas putida* and *Pseudomonas fulva*.

## Clinical manifestations 
More than 25 species of Pseudomonas cause diseases in humans. Species such as *Pseudomonas aeruginosa, Pseudomonas fluorescens, Pseudomonas putida, Pseudomonas cepacia, Pseudomonas stutzeri, Pseudomonas maltophilia,* and *Pseudomonas putrefaciens* are said to cause opportunistic infections in humans.  Opportunistic infections more commonly affect people with weak immune systems compared to the ones with stronger immune system. Only two of the species are known to cause specific disease. These are *Pseudomonas mallei* and *Pseudomonas pseudomallei* which cause glanders and melioidosis respectively. However, the most common species involved in clinical problems is *Pseudomonas aeruginosa*. The common clinical problems caused by *Pseudomonas aeruginosa* is shown in the following bullet points.

 where the green part indicates endocarditis]]
 in a neonatal. This is the alimentary tract with the stomach at the top and the anus towards the end. It shows intestinal necrosis and the perforated site is shown with an arrow.]]
 associated with bronchiectasis. The big holes represent the dilated bronchi which was caused by increased production of thick mucus. This becomes the breeding ground for bacteria such as *Pseudomonas aeruginosa*.]]
* Bone and joint infections (BJI): It has been noted that *Pseudomonas aeruginosa* infections are the most difficult to treat compared to other BJIs.
** Osteomyelitis
** Constrictive Pericarditis
* Central Nervous System (CNS) infections
** Brain Abscess
** Community-acquired *Pseudomonas aeruginosa* meningitis: It commonly occurs after surgery.
* Ear infections
** Keratitis
** Ophthalmia neonatorum: It is rare and the complications are eyelid edema, erythema, and purulent discharge causing corneal perforation, endophthalmitis, blindness, and also death if not treated properly.
* Gastro-intestinal(GI) infections
** Epidemic diarrhoea: *Pseudomonas aeruginosa* causes enterocolitis in children. One of the common symptoms of enterocolitis is diarrhoea. 
** Necrotising enterocolitis
** Neutropenic Enterocolitis (Typhlitis): It commonly affects immunocompromised patients.
** Shanghai fever
* Genitourinary(GU) infections
** Epididymitis
** Urinary tract infections (UTIs): *Pseudomonas aeruginosa* is the common cause of nosocomial UTIs.
** Ventilator-associated pneumonia (VAP)
* Sepsis
* Skin and soft tissue infections
** Ecthyma gangrenosum (EG): It is rare but has very high mortality rate ranging from 38%-77%.
** Dermatitis: It is a form of mild cutaneous infection.
** Necrotizing fasciitis: It is rare with only 12 cases recorded so far.

## Biotechnology 
Pseudomonas strains have been useful in the biotechnology field. The table below shows the Pseudomonas strains and their respective uses.

## References