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Microbiology > Lab Study 2 > Flashcards

Lab Study 2 Flashcards

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1
Q

What are the clinically significant groupings of gram negative bacilli?

A

The clinically significant GNB can be divided in four groups

  1. Non-fastidious, fermentative, facultatively anaerobic, oxidase-negative bacilli-
    eg. the Enterobacterales or enteric bacilli
  2. Non-fastidious, obligately aerobic, non-fermentative bacilli (NFB) eg. Pseudomonas spp.= This module and Lab!
  3. Fastidious, haemophilic bacilli eg. the Haemophilus spp.= next Lab
  4. Others or unusual bacilli eg. GNB other than enteric bacilli like Aeromonas spp., Pasteurella spp., Vibrio spp.
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2
Q

What test provides a major clue that a gnb is a NFB?

A

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).

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3
Q

Why are single tube tests not done to I.D. NFB?

A

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.

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4
Q

Describe the colony morphology of Pseudomonas aeruginosa on BA plates?

A

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.

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5
Q

What characteristic differentiates Pseudomonas aeruginosa from the other common Pseudomonas spp.?

A

Growth at 42°C differentiates it from most other common Pseudomonas spp.

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6
Q

What pigments does Pseudomonas aeruginosa produce on MH or TSA plates?

A

Production of pigments on MH or TSA: bluish (pyocianin), green (pyoverdin), red (pyorubrin), brown (pyomelanin).

MH = Mueller-Hinton.

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7
Q

What areas of society does Acinetobacter spp. typically infect as a pathogen?

A

Acinetobacter spp.

Common nosocomial opportunistic pathogen (mainly ICU’s and long term care)

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8
Q

How does Acinetobacter spp. appear on a gram stain? What can it be mistaken for?

A

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!

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8
Q

How does Acinetobacter spp. appear on a gram stain? What can it be mistaken for?

A

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!

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9
Q

What does Acinetobacter spp. morphology on BA and MAC look like?

A

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.

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10
Q

What two groups are Acinetobacter spp. divided up into?

A

Divided in two groups:

  1. the saccharolytic (oxidize GLU) and
  2. 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).

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11
Q

Who and what does Stenotrophomonas maltophilia typically infect?

A

Common nosocomial opportunistic organism that specifically infects the respiratory tract in Cystic fibrosis patients and other immunocompromised patients.

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12
Q

What does Stenotrophomonas maltophilia gram stain look like?

A

Gram stain: short to medium straight GNB

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13
Q

Describe the morphology of Stenotrophomonas maltophilia on BA and a MAC plate?

A

Morphology on BA smooth, large glistening colonies with a lavender-green-yellowish pigment and slightly green under the colony; ammonia smell. NLF on MAC.

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14
Q

What two sugars does Stenotrophomonas maltophilia oxidize?

A

Stenotrophomonas maltophilia:

Oxidizes Glucose and maltose (malto-philia looves Maltose)

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15
Q

What other environmental Pseudomonoas spp. (not aeruginosa) organisms are also found in clinical specimens?

A

Mainly P. fluorescens, P. putida and P. stutzeri are environmental organisms less commonly found in clinical specimens than P. aeruginosa.

16
Q

What other useful tests can identify which Pseudomonoas spp. (not aeruginosa) organisms is found in clinical specimens?

A

Nitrate, xylose and gelatin are useful tests to differentiate them but more are needed.

17
Q

What is the morphology like for Alcaligenes faecalis and Achromobacter spp on a BA plate?

A

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.

18
Q

Does Alcaligenes spp. and Achromobacter spp. oxidize glucose?

A

No

19
Q

What other tests can be used to help I.D. Alcaligenes spp. and Achromobacter spp.?

A

Urea and nitrate help in their ID

20
Q

Are Alcaligenes spp. and Achromobacter spp. very clinically significant?

A

Environmental organisms that rarely infect humans by exposure to medical solutions or devices.

21
Q

What is the clinical significance of Burkholderia cepacia Complex?

A

Environmental organisms that tend to produce infections via colonization of medical devices and disinfectants in nosocomial environments.

22
Q

Describe what the morphology looks like for Burkholderia cepacia Complex on BA and MAC.

A

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

23
Q

What is the API 20NE identification system?

A

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.

24
Q

What is the purpose of the O/F test? How is it performed?

A

O/F Test –> Oxidation/Fermentation Test
Used to determine whether bacterium oxidize or ferment glucose.
A semi-solid medium is used which contains a carbohydrate (can be dextrose, glucose, maltose, etc.)

  1. Two tubes are inoculated with a straight wire.
    1 lid loose
    1 lid tight w/ mineral oil overlay
  2. Incubation 18-24 hrs at 35C.
25
Q

What is the purpose and limitations of the “Growth at 42C” test?

A

Growth at 42C
Purpose is to separate \Pseudomonas aeruginosa from other Pseudomonas spp.

Limitations are:

  1. Light inoculum is required.
  2. Tube must be incubated immediately after inoculation.
26
Q

What are the QC organisms for Growth at 42C test and its interpretation?

A

Growth at 42C:

Interpretation:
Pos: Turbidity throughout the tube or growth on the plate
Neg: No turbidity in tube or no growth on plate.

QC:
Pos: Pseudomonoas aeruginosa
Neg: Escherichia coli

27
Q

If the morphology/growth characteristics, gram stain and oxidase suggest a possible Pasteurella what is the best next ID test?

A

API 20NE

(although that is not what we did in lab, only for time sake).

28
Q

What is the purpose of the satellitism test?

A

Satellitism Test:

Test is used to presumptively identify Haemophilus spp. to the genus level.

29
Q

What is the principle of how the satellitism tests works?

A

Many bacteria and yeasts synthesize and secrete NAD (V factor) during growth on bacteriologic media. Staphylococcus spp. are such organisms.

Therefore, Haemophilus spp. that requires V factor would not normally grow on a BA plate, but if near Staphylococcus spp. it may grow as pinpoint colonies around the colonies of Staph. The BA provides the X factor and S.aureus provides V factor.

30
Q

How do you perform the satellitism test?

A

Satellitism Test:

  1. Pick a colony with sterile wire & inoculate onto blood agar.
  2. Streak plate to 4 quadrants.
  3. Using an inoculating loop, pick a colong of S. aureus & draw a line from 3rd to 1st quadrant.
  4. Incubate the plate in CO2 at 35C for 24 hours.
  5. Observe for the pinpoint moist, gray colonies adjacent to the Staph.
31
Q

How do you interpret the satellitism test?

A

If only growth near the Staph. Streak –> X and V dependent or just V

If growth on blood agar (all over) –> X factor dependent only

32
Q

In brief, what is the principle of the X and V factor test?

A

To identify common isolates of Haemophilus by using X, V, and X&V factor discs. The disks that show growth around them indicate the factors needed for growth. The disks w/o growth around them indicate factors are still missing to enable the organism to grow.

33
Q

What can cause false identification in a X and V factor test?

A

If media is picked up that may have residual hemin or NAD on the agar, it could lead to some growth and result in false identification.

34
Q

What plate would you use for a X and V Factor Test?

A

Mueller Hinton or TSA

Organism is plated onto a simple agar (MH,TSA that does not contain factors).

35
Q

What is the purpose of the MUB test?

A

MUB (Butyrate Esterase) Test
Test is used in conjunction with cultural characteristics on blood agar, gram reaction and oxidase, the butyrate test is useful for the definitive I.D. of Moraxella catarrhalis.

Rapid test to detect enzyme butyrate esterase.

36
Q

What is the principle of the MUB (Butyrate Esterase) Test? How is it interpreted?

A

If the substrate bromo-chloro-indolyl butyrate is hydrolyzed by butyrate esterase a blue coloured indigo compound is formed.

Pos: Blue to blue/black colour
Neg: No colour change

37
Q

What is the principle and interpretation of the Oxidation-Fermentation (O/F) Test?

A

A closed and open tube containing carbohydrate (can be glucose, maltose, sucrose, lactose, mannitol or xylose), is inoculated and incubated and when the bacteria utilizes the carbs either oxidatively or fermentatively, and ACID end products are produced.

The end product is detected by the indicator bromothymol blue, which turns yellow in an acid environment.

Oxidative: Open (Yellow), Closed (Green) --> +/-
Fermentative Open (Yellow), Close (Yellow) --> +/+
Non-saccharolytic (or asaccharolytic): Open (Green), Closed (Green) --> -/-

E.g. of Understanding:
+/- Glucose is oxidized but not fermented
+/+ Glucose is oxidized and fermented
-/- Glucose is not used at all

Microbiology (13 decks)

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