Pseudomonas (Ditki Notes)

• Pseudomonas are Gram-negative, straight or slightly curved rods and do not catabolize glucose.
• These are aerobic organisms that, in the cystic fibrosis patient lungs, may form biofilms which will facilitate anaerobic respiration.
• Ubiquitous in the environment, often in soil and water.
• Flagellar and pili twitching motility is present.
• Oxidase-positive; aids in laboratory identification.
• Fruity, grape-like aroma.
• Survive on trace nutrients, even found in distilled water.

Pseudomonas Aeruginosa

• Causes opportunistic infections and is well-adapted for survival in patients with cystic fibrosis.
• Produces two pigments: Pyocyanin (bluish) and Pyoverdine (yellowish-green).

Virulence Factors

• Some factors are regulated by quorum sensing and work together in disease pathogenesis.
• Adhesins and pili help adherence to host cells.
• Biofilm production facilitates immune system evasion; important in infection of cystic fibrosis patients.
• Endotoxin, comprises lipopolysaccharide, produces symptoms of sepsis and shock.
• Polysaccharide capsule with alginate is anti-phagocytic, prevents clearance by antibodies, and upregulated in patients with cystic fibrosis.
• Exotoxins and enzymes are injected into host cells by Type III or into the tissues by Type II secretion systems.
• Exotoxin A inhibits protein synthesis and contributes to tissue necrosis.
• Pyoverdine regulates secretion of Exotoxin A and acts as a siderophore to "steal" iron.
• Pyocyanin increases intracellular levels of cytotoxic superoxide and hydrogen peroxide and promotes apoptosis of neutrophils; interferes with respiratory cilia and damages mucosal cells.
• Alkaline protease inhibits complement and contributes to tissue destruction.
• Exoenzymes S and T disrupt host cell actin cytoskeletons and promote cell death.
• Exoenzyme U is cytotoxic specifically to alveolar epithelial cells and macrophages.
• Exoenzyme Y causes edema.
• Elastases degrade complement and elastin.
• The host produces anti-elastase antibodies that form immune complexes, which their deposition in tissues contributes to damage and malfunction.

Opportunistic Infections

• Associated with hospital settings, especially in wet or moist areas.
• Innate immune deficiencies or trauma, especially burn wounds, promote Pseudomonas infections.
• Pulmonary infections range from mild tracheobronchitis to severe pneumonia with necrosis, particularly in patients with cystic fibrosis.
• Patients who rely on mechanical ventilation are also at a higher risk of infection.
• Skin and soft tissue infections, particularly from burn wounds, are common.
• Can cause folliculitis and nail infections from contaminated water in hot tubs, spas, and salons.
• Urinary tract infections occur particularly in patients with in-dwelling catheters.
• Osteochondritis can develop after puncture wound infection, which is common in foot wounds caused by stepping on contaminated nails or sharp objects or can also occur when infection spreads from other sites.
• Otitis externa ranges from mild (Swimmer's ear) to more severe cases, which are associated with diabetics and elderly people.
• Corneal infections, which can produce ulcers, can occur after trauma; especially corneal scratches caused by contact lenses.
• Bacteremia with a high mortality rate, often because of multi-drug resistant strains and the fact that infected patients tend to be immunocompromised.
• Ecthyma gangrenosum is characterized by necrotic and hemorrhagic skin lesions.

Antibiotic Resistance

• Intrinsic properties of their cell walls.
• Acquired resistance via horizontal gene transfer.
• Adaptive resistance; for example, environmental triggers in the lungs of cystic fibrosis patients induces upregulation of resistant mechanisms.

Additional Bacteria

• Burkholderia cepacia Complex comprises multiple species that are associated with pulmonary infections, urinary tract infections, and bacteremia and generally susceptible to treatment with Trimethoprim-sulfamethoxazole (TMP-SMX).
• Burkholderia pseudomallei causes melioidosis, aka, Whitmore's disease; cutaneous and pulmonary infections can be treated with TMP-SMX.
• Stenotrophomonas maltophilia causes pneumonia and bacteremia, and can also be treated with TMP-SMX.
• Acinetobacter species are associated with infections of the respiratory tract, urinary tract, and wounds; unfortunately, these species are resistant to many antibiotics.
• Moraxella catarrhalis is associated with Bronchial infections, sinusitis, and otitis; it is penicillin-resistant, but susceptible to other types of antibiotics.