Pseudomonas, Stenotrophomonas, Burkholderia

Introduction
The taxonomy of the genera Pseudomonas, Stenotrophomonas, and Burkholderia is largely distinct and constantly changing, yet there are many common features that these genera exhibit – for example, they cause nosocomial infections. The individual genera are further classified into higher units, namely the families Pseudomonadaceae, Burkholderiaceae, Xanthomonadaceae, the orders Pseudomonadales, Burkholderiales, Xanthomonadales, and the classes Gammaproteobacteria, and Betaproteobacteria.

General characteristics
The genera Pseudomonas, Stenotrophomonas, and Burkholderia belong to the non-sporulating gram-negative bacteria. Acording to the structure of the bacterial wall, they appear pink in Gram stain. They are strictly aerobic microorganisms, requiring oxygen for their life. They get their energy by splitting glucose, i.e. aerobic oxidation. However, some bacteria, such as Pseudomonas aeruginosa, have the ability to form biofilms in the human body that allow them to persist in the macroorganism.

Morphology
The shape of these Gram-negative bacteria is usually in the form of slender, slightly curved rods. Older bacteria may form coccoid structures that further form pairs or short chains. In order to move actively, most bacteria are equipped with flagellums. An exception is the non-moving Burkholderia mallei.

Cultivation
Bacteria of the above-mentioned genera are relatively easy to cultivate, mainly due to their aerobic nature. They commonly grow on blood agar, on Endo agar, even on ordinary peptone agar. An important condition for the cultivation of these representatives is sufficient humidity. For successful cultivation, it is preferable to incubate the bacteria at 30 °C. The commonly used temperature of 35-37 °C could cause the colony to be covered by other accompanying microflora for which a higher temperature is optimal. The only distinctive features that can be observed in some cultured colonies are pigment colouration or a characteristic odour.

Enzymes
Another important feature of the described bacteria is the production of enzymes including proteases, lipases, and elastases. All are characterized by the production of catalase and most have been shown to have cytochrome oxidase activity. Certain types of enzymes are of high medical significance because they damage the macroorganism – such as pyochelin.

Pathogenesis and epidemiology
Infections caused by members of the genera Pseudomonas, Stenotrophomonas, and Burkholderia do not usually affect healthy individuals. The disease usually affects individuals with weakened immunity. In such cases, an infection can lead to death. The spread of infection occurs most often in health care settings where microorganisms colonize endotracheal catheters, flexilla, or indwelling catheters. Thus, members of each genus can be referred to as agents of nosocomial infections.

Therapy
Therapy of diseases caused by these gram-negative bacteria is quite difficult. The microbes show high resistance to antibiotics.

Specific genera

 * Pseudomonas
 * P. aeruginosa
 * P. alcaligenes
 * P. fluorescens
 * P. mendocina
 * P. putida
 * P. stutzeri


 * Stenotrophomonas
 * Stenotrophomonas maltophilia


 * Burkholderia
 * Burkholderia cepacia
 * Burkholderia mallei
 * Burkholderia pseudomallei