Pseudomonas, Burkholderia and Stenotrophomonas

Overview

• Pseudomonas, Burkholderia and Stenotrophomonas species
  • Family pseudomonadacea contains 200 species.
  • The Genus pseudomonas is a large diverse group of aerobic oxidative GNRs. They were referred to as pseudomonads because of their morphologic similarity – commonly arranged in pairs of cells that resemble a single cell.
  • They derive energy from CHOs by oxidative (rather than fermentative) metabolism.
  • They are Strict aerobes (differentiates them from enterobacteriacea)
  • Pseudomonads are Opportunistic pathogens of plants, animals and humans.
  • Taxonomic classification has had numerous changes.
  • They are Ubiquitous, and primarily saprophitic. Meaning they habitat soil decaying organic matter, vegetation, water and have a predilection to moist environments.
  • In Hospital environment, pseudomonads are found in moist reservoirs (food, cut flowers sinks/drains, toilets, floor mops,respiratory therapy and dialysis equipment, disinfectant solution)
  • It is uncommon for carriage as part of the normal microbial flora but may colonize moist sites, IE. perineum, ear (otitis externa in divers) + axilla.
  • Pseudomonads are opportunistic pathogens esp. hospitalized patients and ambulatory or immunocompromised hosts. ****
  • They have a potency to develop innate resitance to many antibiotics.
  • Species that cause disease in humans include:
    • Pseudomonas aeruginosa
    • Pseudomonas fluorescence
    • Pseudomonas putida
    • Pseudomonas stutzeri
    • Burkholderia cepacia
    • Bulkholderia mallei
    • Bulkholderia pseudomallei
    • Stenotrophomonas maltophilia

Pseudomonas

• Briefly describe Pseudomonas spp
  • Pseudomonas are GN bacilli.
  • Motile with single or multiple polar flagella.
  • Obligate aerobes (different from enterobacteria), oxidase and catalase positive.
  • Unencapsulated, Non-spore forming, and fimbriated.
  • However strains isolated from cystic fibrosis (CF) patients have a prominent slime layer of alginate polymers (glycocalyx), which gives the colonies a very mucoid appearance (loose capsule) – the Slime layer is mediated by genes which are active in patients suffereing from chronic respiratory disease or in CF and when colonized.
  • Produces diffusible pigments (Pyocyanin, Pyorurin, Pyomelanin, Pyoverdin)
  • Can grow in H2O containing only traces nutrients (e.g. tap water) favor persistence in hospital environments.
  • Contamination of respiratory therapy and anesthetic equipment, IV fluids and even distilled H2O.
  • P.aeruginosa and B.cepacia can withstand disinfectants. – they have been found growing in soap solutions in antiseptics and in detergents.
  • They are susceptible to acid, silver salts, 2% alkaline, glutaraldehyde and disinfectants e.g. dettol and cetrimide, but also resistant to other common antiseptics or disinfectants.
  • Pseudomonas is known for its Broad antibiotic resistance – genome has largest known resistance island with > 50 resistance gene
  • O antigens is the somatic, group specific antigen and is heat stable.
    • Possesses 10 distinct group specific O antigens.
      • H antigen (heat labile).
• List the virulence factors of Pseudomonas aeruginosa, clinicopathologic features and laboratory diagnosis of Pseudomonas spp.
  • Cell wall components: pili ,flagella and alginate.
  • Toxins:
    • Exotoxin A
    • Exotoxin S
    • Exotoxin T
  • Enzymes and cytotoxic substances*:* Elastases, Leucocidin, Phospholipase C (PLC), Rhamnolipid, Proteases
  • Pigments:
    • Pyocyanin produces oxygen radicals
    • Pyoverdin acts as a siderophore)
• What population groups are at risk for infection with Pseudomonas aeruginosa
  • AIDS
  • Cystic fibrosis (normal ciliary clearance is impaired)
  • Neonates
  • Complement deficiency
  • Hypogammaglobulinemia
  • Neutropenia (<500/uL)
  • Patients with injury to the skin and mucocutaneous membranes (Burn injuries – as skin host defense destroyed, Urinary catheters, dialysis catheters, endotracheal tubes, IV lines, prosthetic vaVces, Intravenous Drug Users)
• Describe the pathogenesis of toxigenic and invasive diseases caused by Pseudomonas aeruginosa
  • Infection occurs where host defenses are compromised +/- skin or mucus membrane breach. Or when a relatively large inoculum is introduced directly into the tissues. ****
  • Attachment → colonization → local invasion → dissemination of systemic disease.
  • Mucoid polysaccharide capsule forms biofilm
  • Endotoxin causes fever and shock
  • Exotoxin A inactivates EF-2 inhibitng protein synthesis thus causing apoptosis
  • PLC degrades cell membranes,
  • Pyoverdin acts as a siderophore
  • Pyocyanin produces ROS
• Classify and list the Community Acquired Infections caused by Pseudomonas aeruginosa
  • Ear infections:
    • Otitis externa (mild disease is associated with simmers vs malignant diseases which is invasive and associated with different groups) ****
    • Chronic Otitis media.
  • Skin and nail infections:
    • Burn wounds
    • Chronic paronychia
    • Infected toe web
    • Toe web rot
    • Pseudomonas folliculitis
    • Pseudomonal cellulitis.
  • Eye infections
    • Endophthalmitis
    • Corneal ulcers.
  • Nosocomial infections
    • Wounds and burn infections (blue-green pus – verdoglobin or fluorescent pigment is detected in wounds and urine by UV light)
    • **Meningitis (**when introduced by Lumbar Puncture)
    • Pulmonary infections – necrotizing pneumonia in CF patients (diffuse bilateral broncopneumonia with microabscesses and necrosis) +/- burns + mechanically ventilated patients. ****
    • Endocarditis in IDUs.
    • UTIs in indwelling catheters, instrumentation and surgery of urinary tract.
    • Bone and joint infections
    • Post-op neurosurgical infections
    • Osteochondritis in patients with puncture wounds
    • Sepsis mostly from infections of lower Respiratory Tract, Urinary Tract, wounds and skin infections.
    • Ecthyma gangrenosum in sepsis – starts as hemorrhagic pustules that evolve into necrotic (black) ulcers
• What are the laboratory features of Pseudomonas aeruginosa
  • Identification: Beta hemolytic fluorescent greenish colour colonies on BA, sweet fruity smell, oxidase positive, presence of pigments, growth at 42*C, motile, non-fermenters and NLF on MAC.
  • Specimen include wounds, swabs, csf, blood, urine, depends on patient.
  • Culture: Grows best at 37C and 42C and needs aerobic conditions. Simple nutritional requirements. ****Emits a characteristic musty to fruity odour and pigment
    • NA: Large, opaque, translucent and irregularly round volonies
    • BA: Beta hemolytic, greenish colonies (ID)
    • MAC: NLF
    • Cetrimide Agar: demonstrates Bluee-green pigment,
  • Biochemical characteristics
    • Catalase: Positive
    • Oxidase: Rapidly positive (10-20s)
    • IMViC: IMVi negative, Citrate positive
    • Urease: Negative
    • Nitrate reduction: Positive
    • H2S: Negative
    • Pigment: Positive
    • TSI: K/K, no gas, no H2S
  • Serotyping: Epidemiological purposes
    • Pulse-Field Gel Electrophoresis
• Briefly describe the treatment and control of Pseudomonas spp. infection
  • Pseudomonas is MDR therefore susceptibility testing. FQs, Cipro (The only oral option) AGs (Genta, Tobra) Penicillins (Piperacilline), Carbapenems (Imi, Meropenem), Polymyxin B.
  • Always resistant to TMP-SMX unlike S.maltophilia which is usually susceptible to it and always resistant to carbapenems.
  • Injection of hyperimmuune globulins and granulocytes transfusion
  • AMR is via intrinsic resistance (low rate of antibiotic movement through outer membrane pores, rapid efflux of antibiotics due to intrinsic regulation of efflux pumps )
  • Acquired resistance (to AG and B-lactams, horizotal transfer of resistance genes via plasmids or other genetic elements and mutations)
  • Adaptive resistance (induced when Pseudomonas is exposed to environmental stimuli such as biofilms or specific antbiotics).
  • Infection control methods to prevent contamination of sterile equipment and nosocomial infections, isolation, avoid inappropriate broad spectrum, disinfection of pools and jacuzzis, monitor clinically relevant isolates to id epidemic strains.

Differentiate between Proteus and Pseudomonas. Citing their family, species, virulence factors, Diseases and lab characteristics

Burkholderia

• Briefly describe Burkholderia cepacia
  • Formerly called Pseudomonas cepacia.
  • Burkholderia cepacia is a GNR resembling Pseudomonas aeruginosa
  • It can colonize a variety of moist environmental surfaces and are opportunistic.
  • Important cause of chronic infections in patients with cystic fibrosis or with chronic granulomatous disease
  • Respiratory colonization = poor prognosis
  • Also causes UTIs and Septicemia

Sternotrophomonas

• Briefly describe Sternotrophomonas maltophilia
  • Formerly called Pseudomonas maltophilia.
  • Sternotrophomonas maltophila is a GNR resembling P.aeruginosa,
  • It is an Important cause of chronic infection in patients with cystic fibrosis.