Pseudomonas aeruginosa-Etiology, Pathogenesis and Treatment

Pseudomonas aeruginosa– Etiology, Pathogenesis, and Treatment

Introduction

  • There are diverse numbers of Pseudomonas species but P. aerugonisa is considered a clinically significant opportunistic pathogen.
  • P. aerugonisa are motile, aerobic, gram-negative rods,oxidase-positive,  its bacteriologic characterization is the production of water-soluble pigments, few strains appear mucoid in presence of dense polysaccharides capsule.

Growth & Metabolism:

  • It can be grown on simple media as it requires simple molecules like ammonia & CO2 for N2 and C requirements.
  • Can survive on a wide variety of temperatures ranging from 20-42 °C and also in high salt concentration.
  • In media,  confluent growth (merged colonies), has a metallic sheen appearance, also the fruity odor is emitted.
  • On blood agar, hemolysin is observed.
  • Pigments are produced that are blue. yellow and rust in color, It helps to differentiate from other gram -ve rods.
    • Blue pigment, Pyocyanin
    • Yellow pigment, Fluorescin (fluoresces under UV light)
    • Yellow-Green pigment, Pyoverdin
    • Reddish Brown pigment, Pyorubin
Gram Staining of Pseudomonas
Gram Staining of Pseudomonas

Pathogenesis

  • Virulence factors are associated with adhesins, toxins & enzymes which induce pathogenicity for Pseudomonas.
Virulence Factors  Components of Virulence factors Functions 

Adhesins

  • Flagella
  • Pili
  • Lipopolysaccharide(LPS)
  • Alginate
  • Flagella & Pili mediate motility
  • LPS induce endotoxin activity
  • Alginate, present in the capsule, protects from phagocytosis & antibiotics

Secreted Toxins and Enzymes

  • Exotoxin A (ETA)
  • Pyocyanin
  • Pyoverdin
  • LasA (serine protease) and LasB (zinc metalloprotease)
  • Alkaline protease
  • Phospholipase C (heat-labile hemolysin)
  • Exoenzymes S and T
  • ETA disrupts protein synthesis
  • Pyocyanin produces superoxide and hydrogen peroxide.
    • Stimulates interleukin-8 (IL-8)
  • Pyoverdin, a siderophore that binds iron
    • Secretion of other virulence factors including ETA.
  • Both LasA & LaB act synergistically to degrade elastin
    • Degrade complement components and inhibit neutrophil chemotaxis.
  • Alkaline protease induces tissue destruction.
  • Phospholipase C breaks
    down lipids and lecithin, initiate tissue destruction
  • Exoenzymes S and T facilitate bacterial spread, tissue invasion, and necrosis when the type III secretion system introduce the protein in the host cell

Epidemiology

  • Pseudomonas is ubiquitous in nature.
  • It can grow in a diverse range of temperatures (4-42° C) with a minimum requirement.
  • They are antibiotic-resistant due to porin mutation, which restricts the flow of antibiotic inside the cell; also produce enzymes to inactivates the antibiotics.
  • They are opportunistic pathogens, usually, cause infection in burn patients.

Clinical Diseases

Clinical Diseases caused by Pseudomonas

Pulmonary Infections

  • Infects lower respiratory tract, may cause asymptomatic colonization, tracheobronchitis (benign inflammation of bronchial), and necrotizing bronchopneumonia (severe form).
  • In cystic fibrosis patients, during Pseudomonas infections, mucoid strains are isolated.
  • Characteristics of invasive disease caused by P. aeruginosa infections include bilateral bronchopneumonia with the formation of microabscess & tissues necrosis.
    • The mortality rate is 70%.

Primary Skin and Soft-Tissue Infections

  • P. aeruginosa causes various types of primary skin infections.
  • Mostly recognized are burn wounds infections.
    • Bacteria colonize the burn wounds, cause localized vascular damage, tissue necrosis, and bacteremia in severe cases of burn patients.
    • The moist surface of the burn wound & failure in penetration of the neutrophils causes such infections.
    • Only topical antibiotic creams are used for treatment in these cases.
  • Folliculitis, caused by contaminated water( such as swimming pools, hot tubs) by Pseudomonas.
  • Also, cause fingernails infections and osteochondritis (Bone & cartilage inflammation) of the foot can occur after penetrating injury (for e.g, stepping on a nail).

Urinary Tract Infections

  • Cause in patients with long-term use of urinary catheters.

Ear Infections & Eye Infections

  • Can cause swimmer’s ears infection (external otitis), it is managed by topical antibiotics & drying agents.
  • In elderly & diabetic patients, P. aeruginosa can cause malignant external otitis, can invade the concealed tissues & damage cranial nerves & bones (fatal disease).
  • Trauma in the eyes or abrasion from contact lens can cause infection.
  • A more severe form like corneal ulcers can progress & can be fatal if not treated.

Bacteremia and Endocarditis

  • Bacteremia occurs in patients suffering from extensive burns, diabetes mellitus, neutropenia( absence of neutrophils ).
    • Originates from lower respiratory tracts, urinary tract, burn wound infections.
    • Skin lesions (ecthyma gangrenosum) may develop, it can become ulcerated, hemorrhagic(vascular destruction) & necrotic.
  • Endocarditis by pseudomonas is uncommon, but this condition is seen in intravenous drug abusers. ( Drug paraphernalia contaminated with waterborne organisms).
    • It involves the tricuspid valve of the heart.

Laboratory Diagnosis

  • Microscopy: Thin, gram-negative rods are observed arranged single or in pairs.
  • Culture media: Selective isolation media is used, such as Blood Agar & MacConkey agar, it is identified by flat colonies with spreading border, pigmentation, colony size, hemolysis, and by rapid biochemical tests ( especially cytochrome oxidase-positive test).
Colony Morphology of Pseudomonas; flat colonies and, green color is observed due to the production of pigments

Treatment

  • Antibiotic therapy is not that effective due to antibiotic-resistant.
  • Effective control practice of infections can be prevented by sterilizing equipment, such as dialysis machines & mechanical ventilation.

References and Sources

  1. https://quizlet.com/11628656/chapter-33-pseudomonas-and-related-bacteria-flash-cards/
  2. https://www.frontiersin.org/articles/10.3389/fmicb.2017.01566/full
  3. https://www.microbiologybook.org/Infectious%20Disease/Lower%20Respiratory%20Tract.htm
  4. https://www.infectiousdiseaseadvisor.com/home/decision-support-in-medicine/infectiousdiseases/
    endocarditis-ivda/
  5. https://link.springer.com/chapter/10.1007/978-1-4614-0242-8_6
  6. https://bio.libretexts.org/Bookshelves/Microbiology/Microbiology_(OpenStax)/15%3A_Microbial_Mechanisms
    _of_Pathogenicity/15.03%3A_Virulence_Factors
  7. https://dermnetnz.org/topics/spa-pool-folliculitis/

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