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CLS 753 > Micro - Gram Positive Rods > Flashcards

Micro - Gram Positive Rods Flashcards

1
Q

What two genera stain acid fast?

A

Mycobacterium

Nocardia

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2
Q

Two genera that spore endospores… What rapid test can help differentiate them and what are the test results?

A

Bacillus = catalase positive

Clostridium = catalase negative

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3
Q

The two important Bacillus species that cause disease are… What illness is each associated with?

A

Bacillus cereus = food poisoning

Bacillus anthracis = anthrax

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4
Q

What plate do Bacillus spp grow best on?

A

Blood agar

-do not grow well on selective plates

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5
Q

Bacillus anthracis colonies have this defining characteristic on a blood agar plate called…

A

“Ground-glass”, powdery, white

  • rapidly growing
  • flat
  • trailing edges coming out of colonies (“Medusa head”)
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6
Q

Bacillus anthracis colonies have this type of consistency when picked up with a loop…

A

“Sticky” consistency, like beaten egg whites

  • tenacious colonies
  • stays raised after being picked up with loop
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7
Q

What does B. anthracis look like gram stained?

A

Broad rods in long chains, gram positive

  • boxcar-shaped
  • blunt ends
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8
Q

What are some features that emerge in a B. anthracis gram stain as the culture ages (2)?

A

Cells decolorize easily as they age, looking gram-negative

Endospores form

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9
Q

B. anthracis possess this virulence factor… What type of stain should we do to see it?

A

Capsule

India ink

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10
Q

What is the term for a gram positive positive organism that stains and looks gram negative

A

Gram variable

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11
Q

How is B. anthracis usually transmitted to people?

A

From livestock, especially handling wool

  • zoonotic infection
  • anthrax aka woolsorters’ or ragpickers’ disease
  • also exposure from soil, lab
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12
Q

99% of anthrax is infection of this organ…

A

Skin

  • eschar (depressed black necrotic ulcer) formation
  • deadlier if spores are inhaled, systemic
  • GI if spores are ingested
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13
Q

One way to differentiate Bacillus cereus and Bacillus anthracis is to look at the type of hemolysis that each causes…

A

B. cereus = beta-hemolytic

B. anthracis = non-hemolytic

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14
Q

Another way to differentiate Bacillus cereus and Bacillus anthracis is to look at which organism is motile…

A

B. cereus = motile

B. anthracis = non-motile

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15
Q

As its name suggests, Corynebacterium are associated with this unique gram stain shape… It also display cells laying in parallel rows called…

A

Club-shaped
-“coryne” = Greek for club shaped

Palisades

  • Chinese letters
  • also V, L, U patterns
  • pleomorphic
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16
Q

Based on their 16S rRNA analysis, Corynebacteria resemble (2)…

A

Mycobacterium

Nocardia

  • acid fast organisms
  • lots of lipids on their cell walls
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17
Q

C. diphtheriae causes this to form in the throat…

A

Sticky pseudomembrane

  • bleeds when removed
  • blocks airway
  • asphyxiation or cardiac failure cause of death
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18
Q

What is the major virulence factor of C. diphtheriae? What is the gene that encodes this?

A

Diphtheria toxin

tox gene

  • not all strains of Corynebacterium diptheriae carry this gene
  • only toxin producing strains cause diptheria
19
Q

C. diptheriae causes two types of infections…

A

Respiratory

  • droplet transmission
  • swelling of neck
  • toxins cause severe myocarditis

Cutaneous
-nonhealing ulcers with dirty gray membrane

20
Q

The appearance of a “bull neck” is symptomatic for what type of disease? Caused by what type of bacteria?

A

Respiratory diphtheria

Corynebacterium diphtheriae

21
Q

Can people infected with C. diphtheriae be treated with antibiotics? Why or why not?

A

No

Toxin needs to be inactivated because they are attacking heart muscles. Treat with anti-toxin
-cultured in horses

22
Q

How are C. diphtheriae cultures collected and what culture specimens are sent to the lab (2)?

A

Throat swab

Nasopharyngeal swab

23
Q

What are the selective media to culture C. diphtheriae (2)? One of these two media can be ran in parallel with this other medium called…

A

Cystine-tellurite agar
OR
Tinsdale agar
-fosfomycin used to select for bacteria

Loeffler’s serum medium

24
Q

What do C. diphtheriae colonies look like on Tinsdale or Tellurite agar?

A

Black colonies with brown halos

-tellurite reductase and cystinase breakdown their substrates

25
Q

What do C. diphtheriae colonies look like on Loeffler’s serum medium?

A

Characteristic purple metachromatic granules inside cells

-grow overnight and stain with methylene blue

26
Q

What tests are done to determine if a toxogenic strain of C. diphtheriae is producing the diphtheria toxin (2)?

A

Immunodiffusion test

Guinea pig lethality test

27
Q

Erysipelothrix rhusiopathiae - how is it transmitted?

A

From animals

-zoonotic infection

28
Q

Although TSI slants are usually reserved for gram negative bacteria, culturing Erysipelothrix rhusiopathiae on a TSI slant gives this result…

A

H2S production

29
Q

What pattern does Erysipelothrix rhusiopathiae produce in a gelatin tube stab incubated at 22C for a day? What does this indicate about the organism?

A

Test tube brush cleaner around stab line

Organism is motile

30
Q

What kinds of infection does Erysipelothrix rhusiopathiae cause?

A

Skin infections (erysipeloid)

31
Q

How is Lactobacillus beneficial to the mucous membrane?

A

Produces lactic acid, decreasing pH of mucous membrane and makes condition unfavorable for pathogens to grow

  • normal vaginal and GI flora
  • in probiotics
32
Q

What is happening to Lactobacillus during a period of bacterial vaginosis?

A

Lactobacillus numbers decline and pH increase, allowing other organisms to overgrow
-polymicrobial

33
Q

What should we do with a vaginal discharge specimen to check for bacterial vaginosis? What kind of cell are we looking for?

A

Gram stain the vaginal discharge
-use Nugent scoring system

Clue cell

  • lack of Lactobacilli
  • overgrowth of many other organisms
34
Q

Bacterial vaginosis - a patient with this condition has a discharge pH of…

A

pH > 4.5

35
Q

How is the “whiff test” done for bacterial vaginosis?

A

Add 10% KOH onto discharge. Smell strong fishy odor

36
Q

A person must be positive for how many conditions to be diagnosed with bacterial vaginosis?

A

Any of these 3:

Milky discharge
pH > 4.5
Clue cells
No visible Lactobacilli
Positive whiff test
37
Q

How is Listeria monocytogenes usually transmitted?

A

In dairy products

  • unpasteurized or contaminated products
  • infected animals
38
Q

What growth condition is unique for Listeria?

A

Can grow at 4C

39
Q

Listeria is motile and moves about in a manner called… What peculiar feature is produced when Listeria is stabbed into a medium and incubated?

A

Tumbling motility

  • best at 28C, reduced at 37C
  • seen in wet mount

Thicker “umbrella head” near top of agar and fine thin line going into the gel

40
Q

What condition does a Listeria infection cause in a healthy person? In pregnant women?

A

Gastroenteritis

Stillbirth

41
Q

What specimen sample should we use to culture Listeria? What method do we use to isolate the bacteria?

A

Stool

Cold enrichment technique

  • inoculate in enrichment broth and incubate at 4C
  • all warm growing stool flora inhibited
  • do a subculture onto a blood agar plate and incubate at 37C everyday or every other day to maximize Listeria recovery
42
Q

Listeria and ___ are often confused because they are both beta hemolytic and look like short rods

A

Streptococcus, particularly group B

-both weak beta hemolytic

43
Q

What rapid test can be used to differentiate Listeria from Streptococcus and what are the results for each organism?

A

Listeria = catalase positive

Streptococcus = catalase negative

44
Q

Of the important gram positive rods, which ones are motile?

A

Bacillus cereus

Erysipelothrix rhusiopathiae

Listeria monocytogenes

CLS 753 (12 decks)

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