Pseudomonas aeruginosa
About Pseudomonas aeruginosa
• gram-negative aerobe bacteria
• Commonly found in the environment
– At any moist location
• Common cause of nosocomial infections
P. aeruginosa is an opportunistic pathogen
• Extremely broad host spectrum
• Hardly any infections in the normal human host
• Severe immunodeficiencies and medical devices
predispose the patients to P. aeruginosa infections
• Broad spectrum of clinical symptoms
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Urinary tract infections
Pulmonary infections
Soft tissue infections
Sepsis
Bone and joint infections
Endocarditis
P. aeruginosa infections
• P. aeruginosa infections are of particular
concern for Cystic fibrosis patients
• Burn patients
• Hospitalised patients
– Case mortality rate for patients infected with P.
aeruginosa approaches 50%
Nosocomial infections
• Fourth most common isolated nosocomial
pathogen accounting for approx.
• 10 % of all hospital acquired infections.
• Patient-to-patient spread and direct patient contact
with environmental reservoirs
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disinfectants,
respiratory equipment,
food,
sinks, taps
Diagnosis of P. aeruginosa
• Isolation and lab identification of the pathogen
• P. aeruginosa grows well on most laboratory
media
• Identified on the basis of its:
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Gram morphology,
inability to ferment lactose,
a positive oxidase reaction,
its characteristic odor,
its ability to grow at 42° C.
Fluorescence is helpful in early identification of P.
aeruginosa colonies and may also help identify its
presence in wounds.
Treatment of P. aeruginosa infections
• P. aeruginosa is frequently resistant to
many commonly used antibiotics.
• To archive synergy a combination of e.g.
gentamicin and carbenicillin is frequently
used.
• No vaccines so far
Pathomechanisms
• Adhesion
– Pili, flagella and fimbriae
• Invasion
– Extracellular enzymes and toxins (proteases, elastase,
phospholipases, rhamnolipids, Exotoxin A)
• Dissemination
– Leukocidin inhibits neutrophils und leukocytes
– LPS (Endotoxin)
• Protection
– Capsule (Alginate)
Interbacterial Communication
Quorum Sensing in P. aeruginosa
McKnight et al, 2000
„....It is time to close the book on infectious
disease….“
William Stewart, Surgeon in a
message to the United State
Congress in 1969
Bacterial Biofilms
Biofilms in the environment
Catheter associated biofilms
Chronic biofilm infections
Despite even intensified antibiotic therapy,
no eradication of chronic P. aeruginosa
infections of the cystic fibrosis lung
Cystic fibrosis
• Most common life-threatening inherited genetic disorder
in the Caucasian population
• Mutation in the cystic fibrosis transmembrane conductance
regulator (CFTR) gene
• one in every 25 carry the mutated recessive gene and more
than 1 in 4000 live births suffer from CF.
• Life expectancy:
– Until the 1930s: the life expectancy of a baby with CF was only a few months,
– in the 1980s, most deaths from CF occurred in children and teenagers. Today with
improved treatments, nearly 40 percent of the CF population is aged 18 and older,
– for a person with CF the median age of survival is nearly 37 years.
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Cystic Fibrosis affects a number of organs in the body,
cycles of infection and inflammation lead to a progressive
deterioration of lung function.
Chronic infection of the
Cystic Fibrosis lung
CF and Transplantation Centre
•
360 patients regularyly attend the CF outpatient clinic at
the Medical School Hannover, Germany
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Informations of more than 500 CF patients in the local CF
register
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2000 – 2005: 100 lung transplantation / year at the MHH
Indications for lung transplantation
Lung Transplantation in Germany
Post lung transplant mortality
Chronic infectious diseases
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Slow progressing infections
Functional loss of the affected organ
Highly resistant to host defences and antimicrobial therapy
Recovery is rare
Role in the development of cancer, peptic ulcer and
possibly atherosclerosis
Why is traditional antimicrobial therapy
ineffective against biofilm bacteria?
Biofilms, City of microbes
Adaptation and survival is facilitated by diversity
Emergence of morphological distinct nichespecific phenotypes
From: Rainey R, Travisano M. Nature, 1998; 39: 69-72
Phenotypic Diversity via the selection of nichespecialists
„Small colony variants“ (SCV)
SCVs of P. aeruginosa in CF
• Slow growing subpopulations (3% of the P. aeruginosa
positive sputum specimens)
• SCVs exhibit an increased resistance towards a broad
spectrum of antimicrobial agents
• The recovery of SCV correlates with parameters revealing
poor lung function and an inhalative antimicrobial therapy
• Fast growing revertants can be isolated from the SCV
population
Auto-aggregation in liquid cultures
CupA encoded fimbria expression in P. aeruginosa
M. Rohde, GBF Braunschweig
Molecular Mechanisms controlling the
conversion to a SCV biofilm phenotype
Biofilms, City of microbes
Cooperative traits and coordinated behavior of
bacteria
Quorum Sensing in P. aeruginosa
McKnight et al, 2000
Pseudomonas Quinolone Signal (PQS)
Hydroxy Alkyl Quinolones
PQS
HHQ
PQS directly interacts with bacterial DNA in a
computed model
PQS enhances iron dependent DNA fragmentation
Control
DNA
DNA
DNA
+ PQS
DNA
+ HHQ
DNA
+ Fe(II)
DNA
+ PQS
+ Fe(II)
DNA
+ HHQ
+ Fe(II)
PQS enhances the fragmentation of DNA in vivo
PQS production is linked to the release of DNA
PAO1 wild-type
PQS non-producing mutant
Regulated DNA release in response to
environmental stresses
DNA breakdown products enhance PQS
production
Autoinductive PQS production cycle
PQS
PQS
Rhl
Quorum Sensing
pqsA-E transcription
Lectin
Cell death
DNA
Pyocyanin
Virulence factors
Biofilm formation
Phenotypic Diversity is PQS dependent
P. aeruginosa WT
P. aeruginosa PQS negative Mutante
Establishment of a chronic state of infection
Biofilm
Formation
Bacterial
Diversity
Chronic
Infections
Interbacterial
Communication
Molecular mechanisms underlying genetic
diversity
• Horizontal gene transfer
• Hypermutation
• Adaptive mutations
Tiling Arrays
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Microarray hybridisation-based method technique to find
mutations in bacterial genomes was used to study
metronidazole resistance in Helicobacter pylori
TJ Albert et al. Mutation discovery in bacterial genomes: metronidazole
resistance in Helicobacter pylori. Nature Methods 2, 951 - 953 (2005).
Thank You for your attention!
Systems Biology
• Prediction of the
impact of cellular
metabolism on the P.
aeruginosa quorum
sensing mediated
virulence phenotype
 Use a theoretical model to complete
the knowledge on the system, to plan
new experiments and to predict the
behavior of the system under changing
genetic or environmental conditions