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Infection
with P. aeruginosa begins in childhood, even in the early months of
life, with nonmucoid strains being acquired first.
1.
What is a
“mucoid” strain of pseudomonas aeruginosa?
·
A mutant strain
of pseudomonas aerug. that produces an alginate coat that give them a
mucoid appearance
·
Thought to be in
response to neutrophils that attempt to kill the bacteria via peroxides
Mucoid conversion of Pseudomonas
aeruginosa by hydrogen peroxide: a mechanism for virulence activation in
the cystic fibrosis lung.
Mathee K; Ciofu O; Sternberg C; Lindum PW;
Campbell JI; Jensen P; Johnsen AH; Givskov M; Ohman DE; Molin S; Hoiby
N; Kharazmi A
Microbiology 1999
Jun;145 ( Pt 6):1349-57
To mimic the inflammatory environment of
the CF lung, P. aeruginosa PAO1, a typical non-mucoid strain, was grown
in a biofilm. This was treated with low levels of H2O2, as if released
by the PMNs, and the formation of mucoid variants was observed.
When a P. aeruginosa biofilm was
repeatedly exposed to activated PMNs in vitro, mucoid variants were also
observed, mimicking in vivo observations. Thus, PMNs and their oxygen
by-products may cause P. aeruginosa to undergo the typical adaptation to
the intractable mu- coid form in the CF lung.
2.
What is the
significance of the alginate (polysaccharide) coat?
·
Alginate that is
produced by mucoid Pseudomonas aeruginosa interferes with phagocytic
killing
·
Immune system
is unable to kill these mucoid organisms, promoting pseudomonas aerug.
colonization of the lungs
·
This mucoid
phenotype is seen infrequently in non-CF populations, but occurs in over
75 percent of P. aeruginosa isolated from patients with CF
3.
What is the
significance of pseudomonas aerug. colonization of the lungs?
·
Patients with CF
die from respiratory failure because of a gradual loss of lung function.
This results from the chronic inflammatory process perpetuated by P.
aeruginosa, which colonizes the lung for periods of up to 40 years.
The inflammation is triggered by the host response to the organism, not
by tissue invasion.
·
Epidemiologic
studies show that chronic infection with Pseudomonas aeruginosa is an
independent risk factor for accelerated loss of pulmonary function and
decreased survival.
4.
Are these mucoid strains
resistant to anti-biotics? Not
based on alginate coat
These organisms are extremely
difficult to eradicate once established, and can be isolated repeatedly
over the course of many years. This phenomenon is due to:
·
Poor penetration
of the antibiotics into purulent airway secretions
·
The alginate
that is produced by mucoid Pseudomonas aerug interferes with phagocytic
killing
·
Native or
acquired antibiotic resistance
·
CF-related
defects in mucosal defenses |