FREE ESSAY ON PSEUDOMONAS AERUGINOSA

PSEUDOMONAS AERUGINOSA

Pseudomonas aeruginosa
Research Paper
Julie Johnson
Pseudomonas aeruginosa is a versatile gram negative bacterium that grows in soil,
marshes, and coastal marine habitats, as well as on plant and animal tissues. People with
cystic fibrosis, burn victims, individuals with cancer, and persons infected with HIV are
particularly at risk of disease resulting from Pseudomonas aeruginosa. 
Unlike many environmental bacteria, Pseudomonas aeruginosa has a remarkable capacity to
cause disease in susceptible hosts. It has the ability to adapt to and thrive in many
ecological niches, from water and soil to plant and animal tissues. The bacterium is
capable of utilizing a wide range of organic compounds as food sources, thus giving it an
exceptional ability to colonize ecological niches where nutrients are limited.
Pseudomonas aeruginosa can produce a number of toxic proteins, which not only cause
extensive tissue damage, but also interfere with the human immune systems defense
mechanisms. These proteins range from potent toxins that enter and kill host cells at or
near the site of colonization to degradative enzymes that permanently disrupt the cell
membranes and connective tissues in various organs.
In people with cystic fibrosis the most serious complication is respiratory tract
infection by the ubiquitous bacterium Pseudomonas aeruginosa. CF is one of the most
common fatal genetic disorders in the United States, affecting about 30,000 individuals.
A comparable number of people in Europe also have CF. It is most prevalent in the
Caucasian population, occurring in one of every 3,300 live births. The gene involved in
cystic fibrosis was identified in 1989. Located on human chromosome 7, it codes for a
protein called the cystic fibrosis transmembrane conductance regulator (CFTR). This
protein, normally produced in a number of tissues throughout the body, regulates the
movement of salt and water in and out of these cells. The abnormality in the CFTR gene
alters the CFTR protein in people with cystic fibrosis. As a result, one hallmark of CF
is the presence of a thick mucus secretion which clogs the bronchial tubes in the lungs
and plugs the exit passages from pancreas and intestines, leading to loss of function of
these organs. 
Progressive lung disease is the predominant cause of illness and death in people with CF.
Mucus blocks the airway passages and results in a predisposition toward chronic bacterial
infections. Although the genetic defect underlying CF has been characterized, exactly how
and why individuals become infected with Pseudomonas is unknown. The lungs of most
children with CF become colonized by Pseudomonas aeruginosa before their 10th birthday.
Chronic infection with these bacteria reduces an individuals quality of life, causing
acute symptoms of cough, sputum production, and inflammation, which causes repeated
exacerbations or episodes of intense breathing problems. Eventually leading to scarring
and destruction of lung tissue and, ultimately, death. While it is clear that antibiotic
therapy directed against these organisms lengthens the life span of individuals with CF,
increasing antibiotic resistance develops. Although antibiotics can decrease the
frequency and duration of these attacks, the bacterium establishes a permanent residence
and can never be completely eliminated from the lungs.
Management of cystic fibrosis lung disease requires a multipronged approach. Outpatient
management of pulmonary exacerbation usually includes a combination of 2 IV
antipseudomonal antibiotics (an aminoglycoside plus a beta-lactam), appropriate
antimicrobial treatment, effective airway clearance, optimization of nutritional status,
and anti-inflammatory therapies. Additionally, prevention of respiratory viral disease
and avoidance of exposure to irritants, such as smoke, is recommended. Usual duration of
therapy is 14 to 21 days, and clinical response is assessed by physical exam, pulmonary
function tests, nutritional status, and exercise tolerance. Microbial eradication is not
a therapeudic end point. Choice of antibiotics should be based on culture and sensitivity
of the sputum. Emergence of antibiotic-resistant species, such as Pseudomonas aeruginosa,
has required close monitoring of antibiotic susceptibility patterns and strict
infection-control policies.
Administration of chronic intermittent inhaled antipseudomonal therapy (tobramycin
solution for inhalation), over a 6 month period was shown to improve FEV by 11.9%,
decrease the bacterial density, and reduce hospitalization in CF patients chronically
infected with Pseudomonas aeruginosa. Following 92 weeks of therapy with inhaled
tobramycin, the mean % change in FEV was 4.7% above baseline. There was no increase in
the utilization of antipseudomonal therapy despite an increase in MIC at the end of 12
treatment cycles. Decreases in Pseudomonas aeruginosa tobramycin susceptibility were not
predictive of a lack of clinical response, i.e. lung function, to inhaled tobramycin.
A potential role for aggressive antipseudomonal therapy that is currently under study
involves the use of inhaled tobramycin in young patients at the time of initial
colonization. Researchers are hopeful that early, aggressive intervention may be
effective in eradication of Pseudomonas aeruginosa, and therefore, will have a dramatic
impact on the natural history of cystic fibrosis.
One of the major factors that makes Pseudomonas aeruginosa difficult to eradicate is the
overproduction of a sugar-like substance, alginate. One of the regulators of alginate
production, the AlgR protein, has recently been shown to be involved with the function of
pili (tiny hair-like appendages on the outside of the bacteria). Pili are involved in the
initial stages of Pseudomonas aeruginosa infection of CF lungs. The AlgR protein, thus,
may regulate not only genes controlling alginate production, but other Pseudomonas
aeruginosa genes involved in the infection process. A current study is investigating this
by isolating genes that are regulated by AlgR and characterizing those genes to determine
whether they are used by Pseudomonas aeruginosa to evade the bodys immune response and
cause disease. The effects of the isolated genes will be measured on the ability of the
bacteria to bind to the cells lining the airway and to avoid ingestion and destruction of
defending white blood cells. Results from these studies will give insight into the
disease causing mechanisms in Pseudomonas aeruginosa and may lead to alternate methods of
infection prevention in the CF patient.
Complications associated with Pseudomonas aeruginosa lung infections in CF patients are
the result of a multitude of pathogenic mechanisms in the respiratory tract created by
the underlying chloride channel defect. Gene mapping studies of Pseudomonas aeruginosa
will help researchers and clinicians better understand local gene expression and the
evolution of Pseudomonas aeruginosa as it has adapted to the CF lung. Researchers are
using new genetic tools to study bacterial virulence mechanisms during infection with
Pseudomonas aeruginosa. Two techniques employed to determine the extent of genomic
variation among different Pseudomonas aeruginosa clinical isolates are macroevolutional
and microevolutional analysis.
In macroevolutional analysis DNA arrays were used to identify genes in clinical strains
of Pseudomonas aeruginosa that were absent in strain PA01 (the Pseudomonas Genome Project
strain sequence). Using labeled genomic DNA probes, strains were assessed for reaction
with PA01 probes, which represented sequences unique for the clinical strains. The
isolates were sequenced and assembled into contigs, or contiguous coding regions, to
determine the genetic structure of the strains. Using 2 clinical strains, the first
isolated from a catheterized patient with a urinary tract infection and the second
isolated from an infant with CF, researchers obtained a collection of genes specific to
these 2 strains. Analysis of DNA sequences in these clones revealed that the majority of
the genes did not share any sequence similarity with any other genes in the Genome
Project database. In each case, the percent G+C content was lower than 64% for most of
the strain-specific sequences, suggesting that those traits were acquired by horizontal
gene transfer.
In microevolutional analysis, low-passage DNA sequencing of genomes was used to identify
sequences unique to clinical isolates and to compare the genomic variations among them as
well as to the Pseudomonas aeruginosa PA01 strain. In addition to generating sequence
data that define unique genes in the genomes of these 2 clinical isolates, this approach
has been extremely useful in defining regions that are present in the genome of PA01 and
absent from the genomes of these 2 clinical strains. These DNA segments define unstable
genetic elements that may encode proteins that are potentially deleterious for survival
in the host. Lastly, DNA sequences of several loci that accumulate single nucleotide
mutations also have been identified.
The long-range goal of the genomic comparison project is to correlate the genomic makeup
of Pseudomonas aeruginosa strains with specific infections and to monitor the evolution
of virulent traits expressed by this pathogen.
There is continuous research being done of the mapping of the genome of Pseudomonas
aeruginosa, which may lead to potential new treatments for patients with cystic fibrosis.
A team of researchers at the University of Washington Genome Center and PathoGenesis
Corporation collaborated to complete this genome sequence genetic map. In fact
researchers are already using knowledge about the genetic instructions of Pseudomonas to
identify targets for novel drug strategies. They will take the gene sequencing data and
attempt to define the molecular mechanisms of infection for Pseudomonas aeruginosa. They
want to see which genes are needed for survival in its human host and which are needed
for drug resistance.
Pseudomonas aeruginosa is the largest of the 25 bacteria that scientists have sequenced
so far. The largest previously sequenced bacterium was Escherichia coli, which has 4.6
million base pairs and approximately 4,200 genes. Pseudomonas aeruginosa, by contrast,
has more than 6 million base pairs and approximately 5,500 genes. Preliminary work
suggests that the high number of genes in Pseudomonas aeruginosa allow it to adapt and
survive in many different environments, whereas most bacteria live within a small niche.
Indoor plumbing, in particular, is especially hospitable to Pseudomonas aeruginosa.
Typical disinfectants are not effective at eradicationg it so Pseudomonas aeruginosa can
be found on nearly every shower curtain and drain pipe around the world.
Functions of Pseudomonas aeruginosa that were previously unknown have been identified,
suggesting new avenues for drugs to treat serious lung infections caused by this
bacterium. Researchers now have a better understanding of why Pseudomonas aeruginosa is
naturally resistant to most antibiotics. As a result, they have new ideas on how to
identify antibiotics that might circumvent some of the bacterium's intrinsic drug
resistance mechanisms. The bacterium was sequenced based on one particular organism, or
isolate, that is the standard in laboratories. Variations are now being examined that
occur when the organism is taken from patients with cystic fibrosis. Scientists are
looking for not only how Pseudomonas aeruginosa differs from patient to patient, but what
happens to the organism inside the body. "We want to figure out what is different about
those clinical isolates, and how these isolates change over time during chronic
ingection" Olson, 142. With this information in hand, new windows of opportunity may
arise, suggesting that certain biochemical pathways or proteins within Pseudomona
aeruginosa are good targets for drug development. Pseudomonas aeruginosa is difficult to
overcome with antibiotics even in patients with new infections. Over time, treatment
becomes progressively more difficult; this is not unique to Pseudomonas aeruginosa.
Attempts to produce a vaccine for Pseudomonas aeruginosa have not resulted in a high
level of protection against subsequent infections. Previous studies have focused on
creating immunity against a single surface element of the bacterium. There is a study
going on now that is testing the feasibility of using an oral dose of an intact but
weakened or attenuated strain of Pseudomonas aeruginosa for vaccine development. This
approach has been used in vaccine production in other diseases and has resulted in an
immune response in the lung. Strains of Pseudomonas aeruginosa are being produced which
must be supplied with certain amino acids for growth, and thus should be able to survive
only under laboratory conditions. Plans are to feed these strains to mice to determine
whether the bacteria can cause disease, how long the bacteria survive, and whether an
immune response is generated in the lung. The long-term goal is to produce a safe vaccine
for use in the individuals with cystic fibrosis.
Pseudomonas aeruginosa infection is also common among persons infected with HIV. Most of
the patients who developed invasive Pseudomonas aeruginosa infections were severely
immunocompromised, with a mean CD4+ cell count of 31/uL and a history of lung injury.
These infections often occur at multiple sited, particularly the lungs and sinuses. Since
the advent of the routine use of HAART (highly active antiretroviral therapy), there has
been a striking decline in the incidence of invasive Pseudomonas aeruginosa disease.
Scientists suggest that HAART may in fact restore humoral immunity.
HIV positive adults often are plagued with severe pyrogenic infections that tend to
recur. In fact, recurrent bacterial pneumonia is considered an AIDS defining illness.
Haemophilus influenzae, Staphylococcus aureus, Streptococcus pneumoniae, and Moraxella
catarrhalis are the most frequently isolated pathogens. Pseudomonas aeruginosa infection
is yet another complication of late stage HIV disease. Mortality from Pseudomonas
aeruginosa infection in HIV positive patients is estimated at 22% to 36%. The literature
reveals that neutropenia, indwelling catheters, and hospitalization may be associated
with Pseudomonas aeruginosa infection, but traditional risk factors are not always
present.
Clinical records were reviewed of all patients with HIV infection seen at the outpatient
clinic of the Hospital of Saint Raphael between January 1992 and January 1998 to identify
patients who had invasive pseudomonal disease. Pseudomonas aeruginosa pneumonia was
defined as the presence of a febrile (temperature greater than 38.3*C) respiratory
illness, isolation of Pseudomonas aeruginosa as the sole pathogen from expectorated
sputum, and evidence of infiltrate on chest radiograph. Bronchitis was defined as a
productive cough. Otitis media was defined as the presence of a bulging or inflamed
tympanic membrane with purulent auditory canal drainage that grew Pseudomonas aeruginosa.
Sinusitis was defined as a febrile illness, headache, sinus tenderness, and purulent
nasal discharge that grew Pseudomonas aeruginosa. Bacteremia was defined as the isolation
of Pseudomonas aeruginosa from one or more blood cultures from a patient with clinical
signs of infection.
The hospital microbiology laboratory processed all specimens. Blood samples were
incubated in a Bac-T alert system. Expectorated sputum samples were inoculated onto blood
MacConkey and chocolate agar, and nasal aspirates were inoculated onto chocolate plates.
Antimicrobial susceptibilities were obtained using the Microscan walkaway system.
Medical records of patients who met the criteria for Pseudomonas aeruginosa pneumonia,
sinusitis, and otitis media were reviewed. Paying close attention to the following
variables: age, gender, race, self-reported risk of HIV acquisition, CD4+ cell count,
previous opportunistic infections, antiviral therapy, use of Pneumocystic carinii
pneumonia prophylaxis, prior pulmonary infection, signs and symptoms of disease on
presentation, therapeutic interventions, and clinical outcome, including death. Specific
antiviral regimens varied, most subjects were on a regimen that included one or two
reverse transcriptase inhibitors. Of the two patients who developed invasive Pseudomonas
aeruginosa infections following the routine use of HAART, one was receiving a three-drug
regimen, including a protease inhibitor, and the other did not comply with his antiviral
therapy.
Pseudomonas aeruginosa is an important cause of recurrent, community-acquired
sinopulmonary disease among HIV infected patients, even in the absence of traditional
risk factors. Several studies delineating the potential risks of pseudomonal infection in
the HIV population have found corticosteroid use, recent antibiotic exposure, PCP
prophylaxis with TMP-SMX, prior hospitalization, and neutropenia to be predictive of
Pseudomonas aeruginosa infection. The profound immunosuppression inherent in advanced HIV
disease may in fact be the most important risk factor for Pseudomonas aeruginosa
infection. Patients with pseudomonal disease were severely immunocompromised and suffered
from frequent opportunistic infections. Cell-mediated immunity is thought to play a vital
role in defending against Pseudomonas aeruginosa infection. Therefore, it is not
surprising that the loss of functionally active T cells that occurs with progressive HIV
infection was an important predisposing factor for pseudomonal disease.
Many patients with pseudomonal disease, including the two in whom infections developed
hollowing the initiation of HAART, had suffered previous pulmonary infections. This
suggests that chronic lung damage resulting from recurrent bacterial pneumonias and other
opportunistic infections may predispose a patient to subsequent pseudomonal disease.
Recurrent bacterial lung infections, combined with defective humoral immunity, may
contribute to the development of bronchiectasis in HIV infected patients. The destructive
nature of Pseudomonas aeruginosa in particular may make patients vulnerable to
bronchiectasis and lead to persistent bacterial colonization and relapsing pneumonia.
Pseudomonas aeruginosa produces an elastase that destroys the Pis that are normally
present in the bronchial tree and cleaves IgG, necessary for opsonization. In addition,
Pseudomonas aeruginosa releases endotoxin and results in a polyclonal increase in
immunoglobulins that are deposited as immune complexes, causing further lung damage.
Precisely how HAART affects this cascade of damage remains to be elucidated.
Defective humoral immunity is another possible contributing factor in the development of
Pseudomonas aeruginosa infections in patients with HIV. Although hypergammaglobulinemia
occurs commonly in patients with HIV disease, it selectively involves IgG subclasses 1
and 3, with relative deficiencies of IgG2 and IgG4. Adequate opsonization of encapsulated
organisms requires antibody to polysaccharide antigen, which consists primarily of IgG2.
In addition, it has been shown that most HIV infected patients with Pseudomonas
aeruginosa bacteria were unable to mount a specific IgG response to lipopolysaccharide
immunotypes despite the presence of hypergammaglobulinemia. Defective chemotaxis,
abnormal neutrophil degranulation, and impaired antibody response to new antigens have
all been seen in patients with AIDS.
Pseudomonas aeruginosa pneumonia and sinusitis frequently occurs together in AIDS
patients. In general, HIV infected patients are at increased risk for sinus infections,
especially when theCD4+ cell count falls below 200/uL. In addition to the immunologic
deficits associated with HIV infection, local factors may predispose the patient to sinus
disease. Persistent bacterial colonization along with the loss of mucosal integrity from
smoking or cocaine use may predispose a patient to recurrent bouts of sinusitis. In
addition, prior sinusitis and impaired sinus drainage, possibly from lymphoid
hyperplasia, may be risk factors for recurrent disease.
How HAART will affect the incidence of pseudomonal infections is still not clear. A
correlation between viral load and risk of opportunistic infections has been established,
and there has been a decline in AIDS related morbidity and mortality in patients treated
with aggressive anti-viral regimens. Most of the observed changes in immune competence
relate to cellular immunity rather then humoral immunity.
Thus, based on experiments, there is an anticipation of a decline in the incidence of
sinopulmonary disease caused by Pseudomonas aeruginosa. Prospective studies are necessary
to determine whether the patients with newly diagnosed HIV infection who have pulmonary
damage will develop pseudomonal disease and to better define the changing epidemiology,
optimal treatment strategies, and the role of adjunctive immunotherapies.
Now that scientists have completed the genome sequence genetic map of Pseudomonas
aeruginosa, it may lead to potential new treatments for patients with cystic fibrosis,
patients with HIV, and others who develop this type of infection. This map of the genome
provides scientists with a powerful tool that opens up new doors to develop innovative
therapies that will make a difference in many lives. 
Bibliography
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