Lecture 21 - Pseudomonas

What does Pseudomonas bacteria look like under the microscope?

Gram-neg rods (flagellated)

• Motile

Main distinctive features of pseudomonas

• Found in huge range of environments

• Does not usually cause disease in humans

• Frequently encountered as contaminants in clinical labs

When does Pseudomonas usually cause disease in humans?

Causes disease in immunocompromised individuals

• Opportunistic pathogen

Key identification features for P. aeruginosa

• Oxidase-pos

• Non-lactose fermenting

• Non-spore forming

• Beta-hemolytic

• Aerobic

If we were to grow P. aeruginosa on blood agar, what kind of patterns should we expect to see?

beta-hemolysis (lysis of RBCs)

T/F: P. aeruginosa can go dormant, is highly heat-resistant, and can withstand extreme heat, radiation, dehydration, and chemical damage

FALSE, it does not form endospores

T/F: If we were to place P. aeruginosa, in a non-aerobic environment, it would grow very well

FALSE, it is an aerobic bacteria

What are some “giveaways” of P. aeruginosa on agar?

• Smell: Grape or corn chips

• Texture: Metallic sheen

• Color: Pyocyanin and pyoverdin give GREEN color

  • Pyorubin/melanin can also give BROWNish color too

What is a common activity that can cause P. aeruginosa disease in healthy individuals?

Contact with contaminated water through activities like swimming in pools or using hot tubs

• Hot tub folliculitis

• Swimmers ear

What are the treatments for P. aeruginosa diseases like hot tub folliculitis or swimmers ear?

Antibiotics

What are some diseases caused by P. aeruginosa (opportunistic)?

• UTIs

• Pneumonia

• Wound infections (burn patients, diabetes)

• Chronic pulmonary infection (cystic fibrosis)

How does mutations in the CFTR lead to cystic fibrosis?

The CFTR protein usually modulates flow of water and chloride out of cells into secretions

Mutations lead to:

• Inefficient pumping causing THICK secretions

• Thick mucus builds up in airway leading to chronic infection/inflammation

Treatments for cystic fibrosis

• Antibiotic therapy

• Pulmonary hygiene

• Lung transplant

• CFTR modulator therapy

Why is P. aeruginosa so antibiotic resistant?

P. aeruginosa can rapidly evolve within the lung environment, leading to phenotypically distinct isolates even from a single clone.

What are the main factors that allow P. aeruginosa to be so persistent (years or decades) and antibiotic resistant?

• Biofilm formation

• Mucoid phenotype

• Genetic adaptability

P. aeruginosa biofilms are held together by a matrix made mainly of __________ (polysaccharides), proteins, and bacterial DNA/debris

alginate

Which of the following is NOT an advantage of biofilm formation?

A) Improves bacterial persistence
B) Protects bacteria from the immune system by inhibiting complement activation and reducing antibody opsonization
C) Enhances adherence to surfaces
D) Releases proteases for tissue destruction/invasion

D) Releases proteases for tissue destruction/invasion

Why do biofilms allow P. aeruginosa to be so antibiotic resistant?

• Cells in the biofilm undergo gene expression changes

• Have metabolically inactive cores that reduce antibiotic effectiveness

• Contain dormant cells that can survive treatment and reseed the biofilm, allowing the community to persist like a “superorganism”.

What is the mucoid phenotype in P. aeruginosa?

Overproduction of alginate, forming a capsule around bacteria.

Which one leads to worse clinical outcomes: Biofilms or mucoid?

Mucoid phenotype

How does mucoid phenotype increase virulence?

• Forms protected microcolonies

• Binds some antibiotics

• Shields bacteria from immune responses

T/F: Genetic differences among bacterial strains are greater than genetic differences among humans

TRUE

Role of single nucleotide polymorphisms (SNPs)

• Can change the coding sequence of genes, alter protein function

• SNPs are a large contributor to human (and bacterial) genetic variation

The concept of pan-genome is that some genes are ALWAYS found in an organism and some genes are VARIABLY found in an organism.

What is the difference if it is always present or variably present?

Always:

• Core genome

• Genes that are essential to that species

• Define what the organism really is, genetically

Variably:

• “Accessory genome”

• Genes that may offer some advantages in some

situations (antibiotic resistance, metabolic genes, etc.)

• Define what an organism can do.

T/F: The pan genome usually always consists of the core genome but the accessory genome can vary

FALSE, it comprises both the core and the entire accessory genome

The pan-genome is far (larger/smaller) than the genomic content of any single strain.

Larger

Antibiotic resistance genes, metabolic genes, and virulence islands make up a big fraction of the _____________ genome

accessory