Pseudomonas

• Objectives related to Pseudomonads


  • Know their general characteristics
  • Understand the characteristics, virulence factors and pathogenesis of infection caused by those organisms
  • Know the various methods for laboratory diagnosis of infections
  • Know the general principles of treatment, prevention and control of infection they caused
• Pseudomonas aeruginosa

  • Commonly present in moist environments in hospitals
  • Saprophytes causing disease in humans with abnormal host defense, especially in neutropenia
  • Gram negative, Motile, Rod-shaped occurring singly, in pairs, and occasionally in short chains
  • Obligate aerobe
  • Produces a sweet or grape-like or corn taco-like odor
  • Forms smooth round colonies with fluorescent greenish color
  • Forms mucoid colonies in patients with Cystic fibrosis due to overproduction of Alginate, an exopolysaccharide
  • Grows well at 37-42°C; oxidase positive
  • Does not ferment carbohydrates
• Pathogenesis of Pseudomonas aeruginosa

  1. Pathogenic if introduced into areas devoid of normal defenses, attaches and colonizes mucus membrane, invades locally, produces systemic disease

  2. Lipopolysaccharide plays a direct role in causing various symptoms

  3. Propensity to form biofilms in catheters greatly contributes to virulence
• Diagnostic Laboratory test for Pseudomonas aeruginosa

  Specimens obtained from various sources, Gram-negative rods seen, cultures in blood agar for specific diagnosis
• Pseudomonads

  • Gram negative, motile, aerobic rods
  • Produce water-soluble pigments
  • Classification based on rRNA/DNA homology and common culture characteristics
• Antigenic structures and toxins of Pseudomonas aeruginosa

  • Pili (fimbriae)
  • Exopolysaccharide, alginate
  • Enzymes like elastases, proteases, and two hemolysins
  • Exotoxin A
  • Exoenzymes S and T
  • Exoenzyme U
  • Exoenzyme Y
• Clinical findings of Pseudomonas aeruginosa infection

  • Infection of wounds and burns with blue-green pus
  • Meningitis introduced by lumbar puncture or during neurosurgical procedure
  • UTI introduced by catheters
  • Necrotizing pneumonia from contaminated respirators
  • Otitis externa among swimmers and invasive otitis externa in patients with diabetes
  • Ecthyma gangrenosum with skin necrosis often in sepsis
• Brucellae are obligate parasites
• Brucella canis infects dogs
• Brucella suis infects swine
• Brucellae are Gram-negative but stain irregularly
• P. aeruginosa causes mucoid colonies due to the formation of Alginate
• Brucellae have preferred hosts and can infect through ingestion, mucous membranes, and skin contact
• Erythritol is a growth factor for brucellae found in placenta and fetal membranes except in humans
• Brucellae are tiny gram-negative coccobacilli that are catalase positive and oxidase positive
• Brucellae produce small, convex, smooth colonies on enriched media in 2-5 days
• Cultures in blood agar are the specific test for diagnosis of P. aeruginosa infection
• Brucella melitensis infects goats and has multiple biovars
• P. aeruginosa infection can lead to Cystic Fibrosis
• Brucellosis, also known as Undulant fever or Malta fever, is a disease in humans characterized by an acute bacteremic phase followed by a chronic stage
• Brucellae cause different clinical findings depending on the species
• Brucella abortus infects cattle
• Brucellae are moderately sensitive to heat and acidity and are killed in milk pasteurization
• Brucellae are aerobic, non-motile, and non-spore forming
• Brucellae can be diagnosed through blood culture, biopsy material culture, and serum testing
• Specimens where organisms are most often isolated

  • Bone marrow
  • Blood
• Serology

  1. IgM antibody levels rise during the first week of acute illness, peak at 3 months, persists during chronic disease

  2. IgG rise after 3 weeks of onset, peak 6-8 weeks, remain high during chronic disease
• Agglutination test – IgG agglutinin titers above 1:80 indicate active infection
• Combined treatment with tetracycline and either streptomycin or gentamycin for 2-3 weeks or rifampicin for 6-8 weeks is recommended
• Limitation of spread and possible eradication of animal infection, pasteurization of milk and milk products, and reduction of occupational hazards wherever possible
• Brucellacapt– rapid ELISA – IgG, IgA, and IgM antibodies are detected
• Specimens where Francisella tularensis may be recovered

  • Lymph node aspirates
  • Bone marrow
  • Peripheral blood
  • Deep tissue
  • Ulcer biopsies
• Biosafety practices are required
• Penetration of the skin or mucous membranes or inhalation of 50 organisms can result in infection
• Treatment options for Brucella species

  • Tetracyclines
  • Rifampicin
  • Trimethoprim sulfamethoxazole
  • Aminoglycosides
  • Some quinolones
• Yersinia and Pasteurella


  Short, pleomorphic Gram-negative rods that can exhibit bipolar staining
• Streptomycin or Gentamycin for 10 days; resistant to all beta-lactam antibiotics due to beta-lactamase production
• Brucella species


  • Tiny gram-negative coccobacilli that are catalase positive and oxidase positive
  • A positive urease test is characteristic
• In patients with endocarditis or evidence of neurological disease, triple therapy with doxycycline, rifampicin, and an aminoglycoside is suggested
• For best results, treatment must be prolonged