429-Pseudomonas

What combination of biochemical traits definitively identifies Pseudomonas as distinct from Enterobacteriaceae?

Oxidase positive

non-fermenter

obligate aerobe

Why is the oxidase test critical in differentiating Pseudomonas from enteric bacteria?

Pseudomonas has cytochrome c oxidase (oxidase +), while Enterobacteriaceae do not (oxidase −)

What does it mean that Pseudomonas is an “oxidizer but not a fermenter”?

It metabolizes glucose only in the presence of oxygen (aerobically), not anaerobically

How does the O-F glucose test confirm Pseudomonas metabolism?

Only the open tube (aerobic) turns yellow → confirms oxidative metabolism

What TSI result would you expect for Pseudomonas and why?

K/K (red/red) → no carbohydrate fermentation

What is the significance of Pseudomonas being an obligate aerobe in lab testing?

It will only metabolize substrates in oxygen-rich conditions

What does the oxidase test detect, and what is the result for Pseudomonas?

Detects cytochrome c oxidase → positive (purple)

What does the nitrate reduction test evaluate?

Ability to reduce nitrate → nitrite or nitrogen gas

If no color change occurs after nitrate reagents A & B, what is the next step?

Add zinc

Red → negative

No color → positive

What does the lysine decarboxylase test measure?

Ability to remove COOH from lysine → increases pH

How do you interpret a purple lysine decarboxylase test?

Positive → alkaline environment (decarboxylation occurred)

What does MacConkey agar reveal about Pseudomonas?

Growth without lactose fermentation → colorless colonies

What is the significance of oil overlay in O-F and decarboxylase tests?

Creates anaerobic conditions → distinguishes fermentation vs oxidation

What is the mechanism of Exotoxin A in Pseudomonas?

Ribosylates EF-2 → inhibits protein synthesis → cell death

What is the function of the Type III secretion system (T3SS)?

Injects toxins directly into host cells

What are the effects of T3SS effector proteins (ExoS, ExoT, ExoU, ExoY)?

Disrupt cytoskeleton

Break cell junctions

Induce apoptosis

Increase cAMP

What role does alginate play in Pseudomonas infections?

Biofilm formation + protection from phagocytosis + antibiotic resistance

How does pyocyanin contribute to virulence?

Produces reactive oxygen species → damages host cells + suppresses immune system

What is the role of pyoverdine?

Iron chelation → enhances bacterial growth

What do elastase and alkaline protease do?

Elastase → destroys connective tissue

Protease → degrades immune components (NETs, cytokines)

What is the function of phospholipase C?

Cleaves membrane phospholipids → tissue damage

What is quorum sensing (PQS + HSL) and why is it important?

Cell-to-cell signaling → regulates virulence and biofilm formation

What is the role of endotoxin (LPS) in Pseudomonas?

Causes inflammation, fever, shock via TLR-4 activation

What pigments are produced by Pseudomonas aeruginosa?

Pyocyanin → blue-green

Pyoverdine → fluorescent

Why are mucoid colonies significant in Pseudomonas?

Indicate alginate production → biofilm formation (especially in CF patients)

What smell is characteristic of Pseudomonas and what causes it?

Grape-like odor → aminoacetophenone

What does beta hemolysis indicate on blood agar?

Complete RBC lysis → virulence

What is the significance of fluorescence under UV light?

Indicates pyoverdine production

What unique visual trait may confuse students on agar plates?

Metallic sheen + pigment diffusion

What types of infections are most commonly caused by P. aeruginosa?

Burn/wound infections

Pneumonia (CF patients)

UTIs

Bacteremia

Ear infections (swimmers)

Why are cystic fibrosis patients especially vulnerable to Pseudomonas?

Biofilm formation (alginate) → chronic lung infection

What clinical specimens are used to detect Pseudomonas?

Sputum, wound swabs, urine, blood

Why is Pseudomonas considered a major nosocomial pathogen?

Survives in hospital environments + highly antibiotic resistant

What mechanisms contribute to antibiotic resistance in Pseudomonas?

Efflux pumps, biofilms, altered cell surfaces, dormancy

What distinguishes Pseudomonas aeruginosa from P. fluorescens?

Growth at 42°C (aeruginosa grows, fluorescens does not)

What infections are associated with P. fluorescens?

Opportunistic infections (UTI, respiratory, wound, bacteremia)

What organism is associated with cystic fibrosis besides P. aeruginosa?

Burkholderia cepacia

If a Gram-negative rod is oxidase + and does not ferment glucose, what is the most likely organism?

Pseudomonas

If an organism produces blue-green pigment and grows at 42°C, what is it?

Pseudomonas aeruginosa

If only the aerobic O-F tube is yellow, what type of metabolism is present?

Oxidative metabolism

What is the fastest way to rule out Enterobacteriaceae?

Oxidase positive result