Pseudomonas & Burkholderia
1-introduction
Pseudomonads
are Gram-negative, aerobic, rod-shaped bacteria with widespread
occurrence in nature, especially in damp biotopes.
The
relevant virulence factors are: exotoxin A, exoenzyme S, cytotoxin,
various metal proteases, and two types of phospholipase C. the
lipopolysaccharide of the outer membrane also plays an important role
in the pathogenesis. Pseudomonas infections occur only in patients
with weakened immune defense systems, The most important species in
this group from a medical point of view is P. aeruginosa.
P.
aeruginosa frequently contributes to nosocomial infections, notably
pneumonias in cystic fibrosis, colonization of burn wounds,
endocarditis in drug addicts, postoperative wound infection, urinary
tract infection,
sepsis.
Numerous other Pseudomonas species and the species of the genera Burkholderia are occasionally found in pathogenic roles in immunosuppressed patients. B. mallei causes malleus (glanders) and B. pseudomallei causes melioidois ,a disease of wild rodents caused by the bacterium. It can be transmitted to humans, possibly by rat fleas, causing pneumonia, multiple abscesses, and septicemia, It is often fatal.
2-Classification of Some of the Medically Important Pseudomonads
Order: Pseudomonadales
Family:
Pseudomonadaceae
Genus
: Pseudomonas
Genus and species
I
Fluorescent group Pseudomonas aeruginosa
Pseudomonas fluorescens
Pseudomonas putida
Nonfluorescent group Pseudomonas stutzeri
Pseudomonas mendocina
II
Burkholderia pseudomallei
Burkholderia mallei
Burkholderia cepacia
3-Morphology
and identification
3-1-Typical Organisms
P
aeruginosa is motile and rod-shaped with one to several polar
flagella. , measuring about 0.6 x 2?m. It is
gram-negative and occurs as single bacteria, in pairs, and
occasionally in short chains.
3-2-culture Characteristics
P
aeruginosa is an obligate aerobe that grows readily on many types of
culture media. Some strains hemolyze blood. P aeruginosa forms smooth
round colonies with a fluorescent greenish color due to the
fluorescent pigment pyoverdin . It often produces the nonfluorescent
bluish pigment pyocyanin, which diffuses into the agar. Other
Pseudomonas species do not produce pyocyanin.Some strains produce the
dark red pigment pyorubin or the black pigment pyomelanin. Some
strains can produce a viscous extracellular slime layer.
Gram stain of Pseudomonas aeruginosa, which are about 0.6 x 2?. Original magnification x 1000.
Pseudomonas
aeruginosa on a 10 cm Mueller-Hinton agar plate. Individual colonies
are 3–4 mm in diameter. The organism produces pyocyanin, which
is blue, and pyoverdin, which is green. Together these pigments
produce the blue green color that is seen in the agar around the
pseudomonas growth
Variation
in colony morphology of Pseudomonas aeruginosa. A: Green-gray
colonies 6–8 mm in diameter on a 10 cm blood agar plate; the
blood in the agar around the colonies shows hemolysis. B: Silver
toned dry colonies on a similar blood agar plate; no hemolysis is
present (the dark shadow in the lower part of the picture is from a
label on the back of the petri dish).
3-3-Growth Characteristics
P
aeruginosa grows well at 37–42°C; its growth at 42°C
helps differentiate it from other Pseudomonas species in the
fluorescent group. It is oxidase-positive. It does not ferment
carbohydrates, but many strains oxidize glucose. Identification is
usually based on colonial morphology, oxidase positivity, the
presence of characteristic pigments, and growth at 42°C.
3-4-Diagnostic Laboratory
Tests
3-4-1-Specimens
Specimens
from skin lesions, pus, urine, blood, spinal fluid, sputum, and other
material should be obtained as indicated by the type of
infection.
3-4-2-Smears
Gram-negative
rods are often seen in smears. There are no specific morphologic
characteristics that differentiate pseudomonads in specimens from
enteric or other gram-negative rods.
3-4-3-Culture
Specimens
are plated on blood agar and the differential media commonly used to
grow the enteric gram-negative rods. Pseudomonads grow readily on
most of these media, but they may grow more slowly than the enterics.
P aeruginosa does not ferment lactose and is easily differentiated
from the lactose-fermenting bacteria. Culture is the specific test
for diagnosis of P aeruginosa infection.
The
combination of characteristic oxidase positive colonies, pyocyanin
production and the ability to grow at 42°C is sufficient to
distinguish P. aeruginosa from other Pseudomonas species.
SELECCIÓN DOSIFICACIÓN Y TOLERANCIA A FUNGICIDAS DE PSEUDOMONAS FLUORESCENS
Tags: pseudomonas, rodshaped, 1introduction, burkholderia, gramnegative, aerobic, pseudomonads