Lab Study 2 Flashcards
What are the clinically significant groupings of gram negative bacilli?
The clinically significant GNB can be divided in four groups
- Non-fastidious, fermentative, facultatively anaerobic, oxidase-negative bacilli-
eg. the Enterobacterales or enteric bacilli - Non-fastidious, obligately aerobic, non-fermentative bacilli (NFB) eg. Pseudomonas spp.= This module and Lab!
- Fastidious, haemophilic bacilli eg. the Haemophilus spp.= next Lab
- Others or unusual bacilli eg. GNB other than enteric bacilli like Aeromonas spp., Pasteurella spp., Vibrio spp.
What test provides a major clue that a gnb is a NFB?
Most NFB grow very well on a TSI (or KIA) slant but do NOT acidify the butt (‘no change’ or K/K).
In contrast, nearly all species within the other 3 groups either fail to grow on TSI or if they grow, acidify the butt of the tubed medium (ferment glucose).
Why are single tube tests not done to I.D. NFB?
Possible, but many of the tests take longer to produce reactions –> 48 - 72 hours and requires many tests to get a good complete I.D.
Describe the colony morphology of Pseudomonas aeruginosa on BA plates?
BA is medium-large, grey, beta-hem, often spready, flat, with a metallic sheen, and a very typical grape-like smell (yummy!).
They also produce a pigment, that tends to show on BA a bit later.
What characteristic differentiates Pseudomonas aeruginosa from the other common Pseudomonas spp.?
Growth at 42°C differentiates it from most other common Pseudomonas spp.
What pigments does Pseudomonas aeruginosa produce on MH or TSA plates?
Production of pigments on MH or TSA: bluish (pyocianin), green (pyoverdin), red (pyorubrin), brown (pyomelanin).
MH = Mueller-Hinton.
What areas of society does Acinetobacter spp. typically infect as a pathogen?
Acinetobacter spp.
Common nosocomial opportunistic pathogen (mainly ICU’s and long term care)
How does Acinetobacter spp. appear on a gram stain? What can it be mistaken for?
Gram stain: plump GN coccobacilli that tend to resist decolorization (might appear Gram-positive).
Their plump rounder look might make them easily mistaken for GN diplococci (Neisseria spp.), and if purple, for Gram positive cocci.
It is important to correlate Gram with plate morphology!
How does Acinetobacter spp. appear on a gram stain? What can it be mistaken for?
Gram stain: plump GN coccobacilli that tend to resist decolorization (might appear Gram-positive).
Their plump rounder look might make them easily mistaken for GN diplococci (Neisseria spp.), and if purple, for Gram positive cocci.
It is important to correlate Gram with plate morphology!
What does Acinetobacter spp. morphology on BA and MAC look like?
Morphology on BA smooth, opaque, raised, similar to Enterobacteria but smaller.
On MAC, they are NLF but might have a purple tone that might be mistaken for LF.
What two groups are Acinetobacter spp. divided up into?
Divided in two groups:
- the saccharolytic (oxidize GLU) and
- asaccharolytic (do not oxidize GLU) ones.
There are more than 30 species and some of them really hard to ID by species, so ID systems tend to group them together (e.g.: Acin. baumannii/calcoaceticus Complex Group as the saccharolytic non-hem common type, A. lwoffi as asaccharolytic non-hem and A. haemolyticus as beta hem).
Who and what does Stenotrophomonas maltophilia typically infect?
Common nosocomial opportunistic organism that specifically infects the respiratory tract in Cystic fibrosis patients and other immunocompromised patients.
What does Stenotrophomonas maltophilia gram stain look like?
Gram stain: short to medium straight GNB
Describe the morphology of Stenotrophomonas maltophilia on BA and a MAC plate?
Morphology on BA smooth, large glistening colonies with a lavender-green-yellowish pigment and slightly green under the colony; ammonia smell. NLF on MAC.
What two sugars does Stenotrophomonas maltophilia oxidize?
Stenotrophomonas maltophilia:
Oxidizes Glucose and maltose (malto-philia looves Maltose)
What other environmental Pseudomonoas spp. (not aeruginosa) organisms are also found in clinical specimens?
Mainly P. fluorescens, P. putida and P. stutzeri are environmental organisms less commonly found in clinical specimens than P. aeruginosa.
What other useful tests can identify which Pseudomonoas spp. (not aeruginosa) organisms is found in clinical specimens?
Nitrate, xylose and gelatin are useful tests to differentiate them but more are needed.
What is the morphology like for Alcaligenes faecalis and Achromobacter spp on a BA plate?
Alcaligenes faecalis is typically feathered-edged on BA, dry, with greening of agar and fruity odor.
Achromobacter spp are small, convex and glistening on BA.
Does Alcaligenes spp. and Achromobacter spp. oxidize glucose?
No
What other tests can be used to help I.D. Alcaligenes spp. and Achromobacter spp.?
Urea and nitrate help in their ID
Are Alcaligenes spp. and Achromobacter spp. very clinically significant?
Environmental organisms that rarely infect humans by exposure to medical solutions or devices.
What is the clinical significance of Burkholderia cepacia Complex?
Environmental organisms that tend to produce infections via colonization of medical devices and disinfectants in nosocomial environments.
Describe what the morphology looks like for Burkholderia cepacia Complex on BA and MAC.
Morphology on BA, smooth, slightly raised, dirt-like odor, NLF on MAC but might look pink because of oxidation of lactose after a few days
What is the API 20NE identification system?
API NE is a strip consisting of 20 microtubes containing dehydrated substrates. The substrates are inoculated / rehydrated by the addition of a dense bacterial suspension of the test organism.
The metabolic activity of the inoculated bacteria on the substrates results in visual colour change detected by pH changes or by the addition of specified reagents.
The assimilation tests are inoculated with a minimal medium, bacterial growth occurs only if the organism is able to utilize the substrate in the microtube.
