Ch. 22 - Nonfermenting Gram-Negative Rods

UNT Biol 3381

Pseudomonads

• Aerobic bacilli

• Ubiquitous in soil, decaying organic matter, and moist environments

• Problematic in hospitals

• Opportunistic pathogens

Pseudomonads General Characteristics:

• Prefer wet environments

• Not usually part of healthy human normal flora

• Rarely causes disease, despite producing various virulence factors

  • Fimbriae, adhesins, capsule, toxins, and enzymes

• Most are environmental organisms (including the hospital environment)

• Considered opportunistic and can colonize and infect immunocompromised individuals

• Often found as transient or colonizing flora of hospitalized individuals and become nosocomial pathogens

Pseudomonads Colony morphology

• Pigments and Distinct Odors.

• Growth at 42 degree C

• Motility

Pseudomonads Key Biochemical identification:

• Organism does not ferment carbohydrates

• Nonfermenters can be oxidase positive

• Nonfermenting gram-negative rods show poor growth on MacConkey agar

• Some have sweet, fruity odors and display unique colony morphologies and pigmentation

• Many are often multi-drug resistant

Pseudomonas aeruginosa Microscopic morphology:

• Long thin GNR (Enterobacteriaceae are usually short and plump)

• May be encapsulated

• Single polar flagellum

P. aeruginosa Colony morphology

• Often beta-hemolytic

• Rough, spreading colonies with ground glass appearance and

  serrated or jagged edges

• Aluminum foil or metallic sheen

• Blue-green pigment that diffused into the agar

  • Also red or brown pigment

  • Often sweet, fruity odor (grapelike or corn taco-shell-like)

  • May be mucoid

P. aeruginosa Pathogenesis, Disease and Treatment:

• Rarely causes disease

  • Despite producing various virulence factors

• Opportunistic infections in immunocompromised patients

  • Can colonize almost any organ or system

• Also infects the lungs of cystic fibrosis patients

  • Biofilm protects bacteria from phagocytosis

• Treatment is difficult due to drug resistance

P. aeruginosa Pathogenesis and Infectious Diseases:

• Respiratory infections

• Cystic fibrosis colonizer

• Bacteremia and septicemia

• “swimmers ear”

• Bacterial keratitis

• Urinary tract infections

• Necrotizing enterocolitis in infants

• Antibiotic-associated diarrhea

• Skin and soft tissue infections

  • Burn wound

  • Pyoderma with large sores

  • Dermatitis

  • Folliculitis

• Nosocomial infections due to the use of antibiotics to which

  P. aeruginosa is resistant

• Exogenous infections: infections brought about by organisms

  in the environment

• Endogenous infections: infections brought about by

  organisms which have colonized the host

P. aeruginosa Key biochemical reactions:

• Rapid ID:

  • NLF

  • Oxidase positive

  • Blue-green pigment

  • Grape-like odor

• Oxidizes glucose, fructose, and xylose but not lactose or sucrose

• Motility

• Fluoresces under UV light

Pseudomonas fluorescens (Fluorescent Group) Identification:

• Motile, aerobic, Oxidase positive, GNR

• Resemble P. aeruginosa

• Produce pyoverdine or fluorescein but not pyocyanin

• Isolated from respiratory tract specimens, pleural fluid, urine, CSF, feces, blood and other specimens

• Associated with abscesses, urinary tract infections, septicemia, and septic arthritis

• Nosocomial pathogen in immunosuppressed persons

Burkholderia General characteristics:

• Burkholderia cepacia complex

  • Motile, GNR

  • Environmental organism

  • Associated with cystic fibrosis patients

• Aerobic, flagellated betaproteobacterium

• Can decompose a broad range of organic molecules

• Assists in cleanup of contaminated environmental sites

• Used by farmers to reduce fungal infection of plant crops

• Opportunistic pathogen of cystic fibrosis patients

• Resistant to many antimicrobial drugs

Burkholderia Colonial morphology:

• SBA

  • Smooth and slightly raised

  • “dirt-like” odor

  • Some may have yellow or green pigment

• MAC

  • May be pink after 4-7 days incubation

  • Selective and differential

  • Burkholderia cepacia Selective agar (BCSA)