M5 Non-Fermenting GNB Flashcards
What are the general characteristics of non-fermenting gram negative bacilli (4)?
- Do not ferment glucose
- May or may not utilize glucose by oxidization.
- Oxidative metabolism.
- Some grow rapidly and most grow on MAC.
What is the most common genera for Non-fermenting GNB?
Pseudomonas spp.
What kind of environment does Psuedomonas spp. really like?
Moisture rich environments –> moisture loving.
What is the clinical significance of Pseudomonas aeruginosa (9)?
- Superficial skin infections
- Nail infections
- Ear infections - Otitis media, swimmers ear (externa)
- Eye infections
- Burn infections
- Osteomyelitis
- UTIs.
- Respiratory infections
- Sepsis.
What type of infections are caused by Pseudomonas aeruginosa in Cystic Fibrosis (CF) patients?
- Chronic infections
What does Pseudomonas aeruginosa do in CF patients (3)?
Pseudomonas aeruginosa causes biofilm formation:
1. ExoPolysaccharide polymer (alginate) - protects from adversity and enhances adhesion.
2. CF patients produce a thick & sticky bronchial secretion because of stasis of the lungs.
3. Mucin layer is resistant to antibiotics.
What virulence factors does Pseudomonas aeruginosa have?
- Pilli (attachment)
- ExoPolysaccharide polymer (Alginate) protects it from adversity and adhesion - antiphagocytic
- Pigments
- Extracellular products
a) Hemolysins
b) Pigments
c) Exotoxins (shock)
d) Proteases
Also it’s flagellum make it very motile.
What is the clinical significance of Pseudomonas fluorescens/putida/stutzeri?
- Patients in hospital with underlying disease
- They can cause infections on many sites but their significance has to be questioned and discussed
Are Pseudomonas fluorescens/ putida/stutzeri part of the normal human flora? If not, what?
Environmental, not part of the human normal flora
How are infections from Pseudomonas fluorescens/ putida/stutzeri transmitted? Virulence factors?
- Transmitted through medical devices & solutions
- Unknown virulence factors
What is the normal habitat of Acinetobacter spp.?
Environmental organism, and sometimes part of human normal flora
What is the clinical significance of Acinetobacter spp.?
- Opportunistic pathogen
- Nosocomial
- Ventilator acquired pneumonia
- Implicated in postwar infections “Iraqibacter”
What makes Acinetobacter spp. difficult to deal with in the hospital?
- Survives for a long period of time
- Resistant to antibiotics, drying, and disinfection
How does Acinetobacter spp. look like on BA and a gram stain?
- Purplish hue on BA, large healthy colonies
- “tricky” on Gram: plump cocco-bacilli (diplo-cocci-like) and sometimes underde-colorized
What divides the different Acinetobacter species in the lab?
Species divided based on saccharolytic or asaccharolytic
What is the clinical significance of Stenotrophomonas maltophilia?
- Nosocomial
a) Must correlate with clinical symptoms
b) Exogenous spread through ventilators
c) Immunosuppressed at increased risk - Broad ranges of infections including ocular, UTI, vascular, skin, mostly respiratory.
Is Burkholderia cepacia typically pathogenic and where is it normally found in general?
Burkholderia cepacia:
1. Generally non-pathogenic
2. Environmental, not normal flora
What disease does B. pseudomallei cause?
B. pseudomallei:
Causes “melioidosis”
presents usually as a pneumonia and spreads systemically to other organs resulting in abscess formation
What level of lab should work with B. pseudomallei?
Level 3/Risk Group 3
“A pathogen that usually causes serious human or animal disease but usually not spread by casual contact. These organisms have a high individual risk but low community risk”
From what patients is Burkholderia cepacia may be isolated from?
- Often isolated from CF
- Occasionally UTI’s and respiratory infections
What non-fermenting GNB bacteria can be found in diabetic ulcers?
Alcaligenes faecalis
What are some of the unique characteristics of Alcaligenes faecalis?
- “Fruity odor” on BA
- Nitrate reduction – (NEG)
- Asaccharolytic (incapable of hydrolyzing or breaking down sugar molecules)
- O/F = -/-
What is the clinical significance of Achromobacter xylosoxidans/denitrificans?
Nosocomial septicemia & others in compromised patients
What are the nitrate reduction and O/F results expected for Achromobacter xylosoxidans/denitrificans?
Nitrate reduction +
O/F = +/-
What results are expected Pseudomonas aeruginosa in terms of gram, BA morphology, oxidase, TSI and O/F tests?
- Gram: G-b
- BA: Green pigment, Metallic sheen. Fruity smell
- Oxidase +
- TSI K/NC
- O/F +/-
What non-fermenting organisms looks like a lavender-green-yellowish (not at 24 h), Fried egg, with an “ammonia” odor on blood agar (BA)?
Stenotrophomonas maltophilia
What are the results for MAC, oxidase, and DNase for Stenotrophomonas maltophilia?
MAC - NLF
Oxidase negative!
DNase +
What non fermenting organisms has colony morphology with a slightly raised appearance with a dirt like odor on blood agar (BA)?
Burkholderia cepacia
What is the gram, oxidase, and lysine results for Burkholderia cepacia?
G-b
Weak oxidase positive
Lysine decarboxylase +
For Burkholderia cepacia what needs to be used because it is weakly oxidase positive?
Need to use Tetramethylphenyldiaminedihydrochloride
What is the principle of the O/F (Oxidative/Fermentative) Test?
Media contains a high concentration of carbohydrate (dextrose, maltose, glucose, etc.) relative to peptones. Organisms ability to ferment or oxidize carbohydrates can be determined.
What is the procedure for the O/F test?
- Pick a colony from a 24 hour culture plate and inoculate 2 OF medium with a straight stab almost to the bottom of tube followed by a BA ck plate.
- Leave cap loose on 1 of the tubes.
- Cover one tube from the pair of inoculated tubes with a 1 cm layer of sterile mineral oil and tighten cap.
- Incubate both tubes at 35C in ambient air up to 5 days depending on the organism.
What are the O/F Tube results for oxidative, fermentative, and nonsaccharolytic?
Interpretation:
Oxidative: opened tube acid (yellow); closed tube alkaline (green)
Fermentative: opened tube acid (yellow); closed tube acid (yellow)
Nonsaccharolytic: opened tube alkaline (green or blue); closed tube alkaline (green or blue). Organisms do not use the carbohydrate oxidatively or fermentatively (inert).
What is the limitations with the O/F test for organisms such as Pseudomonas, Stenotrophomonas, or Burkholderia?
Incubation should be at 30°C. These organisms are more active at lower temperature.
What is the principle of the growth at 42C test and what is the main purpose of the test?
- Determine the ability of an organism to grow at 42°C
- Differentiates Pseudomonas spp. (aeruginosa grows at 42°C, others do not)
Positive = Pseudomonas aeruginosa ATCC 10145
Negative = E coli
It can be done on agar or broth (see growth or turbidity)
What is the principle of the Gelatin Liquefaction test and how is it performed?
- Determine the presence of the proteolytic enzyme gelatinase that liquefies gelatin.
- Incubate, then refrigerate, and read:
Positive = liquefaction of solidified media
Negative = complete solidification of media
What organism is Gelatinase positive?
Pseudomonas fluorescens
