nonfermenting and oxidase positive gram-negative rods

Identify the most common non-fermenting gram-negative rods

Non-fermenting gram-negative rods
- diverse group of organisms, but they have some things in common
  - oxidase negative
  - grow well on MAC
  - either oxidize glucose or do not utilize glucose
- inhabit environmental niches including water and soil
- capable of survival on inanimate objects for long periods of time
- most commonly isolated:
  - Acinetobacter spp
  - Stenotrophomonas melophilia
Acinetobacter spp
- ICU and long-term care facilities
- produce a lipopolysaccharide capsule
- cause respiratory, genitourinary, and wound infections
- gram stain: plump coccobacilli that may appear gram positive
- routine media and incubation conditions
  - does not ferment lactose but colonies have a purple hue on MAC agar
- two groups:
  - saccharolytic spp
    - oxidize glucose
    - nonhemolytic
    - Acinetobacter baumannii - nosocomial infections
  - assacharolytic spp
    - do not utilize glucose
    - nonhemolytic
    - Acinetobacter lwoffii
Stenotrophomonas maltophilia
- infects the immunocompromised (CF, malignancy, mechanical ventilation, HIV)
- causes respiratory, genitourinary, and wound infections
- gram stain: short to medium sized straight rods
- routine media and incubation conditions
  - on BA, colonies have a lavender-green to light purple pigment or a greenish discoloration undergrowth
- oxidizes glucose and maltose
- often displays broad spectrum antibiotic resistance

Identify the most common oxidase positive gram-negative rods

GROUP 1 = all oxidase positive, oxidize glucose, grow on MAC

Burkholderia spp
- environmental inhabitants
- transmitted by human contact with contaminated medical devices or solutions encountered in hospital settings
- routine media and incubation conditions
- three groups:
  - B. cepacia
    - gram stain: medium straight rods
    - “dirt-like” odor on blood agar
    - dark pink/red colonies on MAC due to oxidation of lactose
  - B. pseudomallei
    - gram stain: small rods with bipolar staining
    - putrid odor on blood agar
    - dark pink/red colonies on MAX due to oxidation of lactose
  - B. mallei
    - gram stain: coccobacillus
Ralstonia spp
- environmental inhabitants
- transmitted through contaminated medical devices or solutions
- routine media and incubation conditions
  - may take up to 72 hours to produce visible colonies
- gram stain: medium straight rods
- rarely cause disease
  - R. pickettii
  - R. insidiosa
  - R. mannitolytica
Brevundimonas spp
- encountered primarily in water, soil, and on plants, including fruits and vegetables
- routine media and incubation conditions
  - B. vesicularis sometimes does not grow on MAC
- gram stain: medium straight rod
- rarely cause disease
  - B. vesicularis
  - B. diminuta
Pseudomonas spp
- Pseudomonas aeruginosa
  - opportunistic pathogen and uncommon member of normal human microbiota
  - produces endotoxin A, exoenzymes S and T, proteolytic enzymes and hemolysis
  - can survive harsh environmental conditions
  - displays intrinsic resistance to a wide variety of antibiotics
  - immunocompromised host
    - burns, puncture wounds, ear, eye, and respiratory infections (especially CF patients)
  - routine media and incubation conditions
    - metallic sheen and often beta-hemolytic on blood agar
    - “grape-like” or “fruity” odor
    - can grow in 42C (distinguishing factor)
  - gram stain: medium straight rod
- The rest of the organisms are primarily encountered in nature and rarely cause human disease
  - P. fluorescens
  - P. putida
  - P. stutzeri
  - P. mendocina
  - P. fulva

GROUP 2 = all oxidase positive, do not utilize glucose, grow on MAC

Alcaligenes spp
- environmental inhabitants
- transmitted through exposure to contaminated medical devices/solutions
- grow on routine media, but prefer 5% CO2
- feather-edged colonies usually surrounded by a zone of green discoloration
- “fruity” or “apple/strawberry” odor
- two species
  - A. faecalis - infects humans
  - A. aquatillis - not routinely isolated
Oligella spp
- habitat is unknown, but may colonize the distal urethra
- cause infections in the urinary tract - specifically catharized patients
- grow on routine media, prefer 5% CO2
- two species
  - O. ureolytica - urea positive and motile
  - O. urethralis - urea negative and non-motile
Achromobacter spp
- environmental inhabitants
- transmitted through exposure to contaminated fluids, soaps, and disinfectants
- grow on routine media, prefer 5% CO2
- species include:
  - A. piechaudii
  - A. xylosoxidans (CF patients)
  - A. denitrificans

GROUP 3 = oxidase positive, oxidize glucose, do not grow on MAC

Sphingomonas paucimobilis
- environmental habitant - waterborne contaminant
- grows on blood and chocolate agar but not MAC
- colonies will grow bright yellow on BA
- cultures performed on water to verify cleanliness

GROUP 4 = oxidase positive, ferment glucose, grow on MAC (also, primary habitat is water, not normal in human microbiota)

Aeromonas spp
- gram stain: gram-negative straight rods with rounded ends or coccobacillary
- facultative anaerobes
- occur singly, in pairs, or short chains
- found in freshwater or marine water with low salt content
- causes gastroenteritis, HUS, and kidney disease
- laboratory diagnosis:
  - no molecular or serological methods available for detection
  - grows well on blood, MAC, and chocolate
  - beta hemolytic
  - Aeromonas agar containing D-xylose
  - CIN
- clinical specimens:
  - A. hydrophilia
  - A. caviae
  - A. veronii
Vibrio spp
- family: Vibrionaceae
- gram stain: curved or comma-shaped rods
- require sodium for growth, motile
- found in marine water
- cause gastroenteritis, wound infections and bacteremia
- most notable pathogen:
  - V. cholerae
- Vibrio cholerae
  - causes the diarrheal disease Cholera
  - spread among people by fecal-oral route
  - virulence factors:
    - cholera toxin - causes mucosal cells to hyper secrete water and electrolytes into the lumen of the GI tract
      - causes rice water stools
    - toxin coregulated pili
    - zona occludens toxin
- laboratory diagnosis:
  - Cary Blair medium for stool samples
  - molecular methods for detection of cholera toxin
  - rapid antigen tests
  - direct examination - dark field microscopy
  - cultures
    - TCBS
    - MAC
    - SS
    - BA and CA
Chromobacterium violaceum
- facultative anaerobic and motile
- gram stain: curved, gram-negative rods with rounded ends
- found in soil and water
- causes wound infections - life threatening if not treated
- laboratory diagnosis:
  - PCR assay
  - grows on routine media
  - beta hemolytic
  - “Almond-like” odor
  - violet pigmented colonies
    - presumptive ID can be used for pigmented colonies
    - positive indole test and glucose fermentation for non-pigmented colonies

Identify the most common biochemical tests used to differentiate these organisms

Routine media
- MAC
- Blood agar/ chocolate agar
Special media
- CIN - Aeromonas spp
- TCBS - Vibrio spp

List common places these organisms are found and how they cause infection

Inhabit environmental niches
- Acinetobacter
- Stenotrophomonas maltophilia
- Burkolderia spp
- Ralstonia spp
- Pseudomonas spp
- Alcaligenes spp
- Achromobacter spp
- Sphingomonas paucimobilis
Water
- Brevundimonas spp
- Aeromonas spp
- Vibrio spp
- Chromobacterium violaceum
Human microbiota
- Oligella spp

Common infections/diseases these organisms cause

Nosocomial infections (respiratory/genitourinary/wound)
- Acinetobacter spp
- Stenotrophomonas maltophilia
- Burkolderia spp
- Ralstonia spp (rare)
Gastroenteritis
- Vibrio spp
- Aeromonas spp
UTIs
- Oligella spp