Micro - Gram Positive Rods Flashcards
What two genera stain acid fast?
Mycobacterium
Nocardia
Two genera that spore endospores… What rapid test can help differentiate them and what are the test results?
Bacillus = catalase positive
Clostridium = catalase negative
The two important Bacillus species that cause disease are… What illness is each associated with?
Bacillus cereus = food poisoning
Bacillus anthracis = anthrax
What plate do Bacillus spp grow best on?
Blood agar
-do not grow well on selective plates
Bacillus anthracis colonies have this defining characteristic on a blood agar plate called…
“Ground-glass”, powdery, white
- rapidly growing
- flat
- trailing edges coming out of colonies (“Medusa head”)
Bacillus anthracis colonies have this type of consistency when picked up with a loop…
“Sticky” consistency, like beaten egg whites
- tenacious colonies
- stays raised after being picked up with loop
What does B. anthracis look like gram stained?
Broad rods in long chains, gram positive
- boxcar-shaped
- blunt ends
What are some features that emerge in a B. anthracis gram stain as the culture ages (2)?
Cells decolorize easily as they age, looking gram-negative
Endospores form
B. anthracis possess this virulence factor… What type of stain should we do to see it?
Capsule
India ink
What is the term for a gram positive positive organism that stains and looks gram negative
Gram variable
How is B. anthracis usually transmitted to people?
From livestock, especially handling wool
- zoonotic infection
- anthrax aka woolsorters’ or ragpickers’ disease
- also exposure from soil, lab
99% of anthrax is infection of this organ…
Skin
- eschar (depressed black necrotic ulcer) formation
- deadlier if spores are inhaled, systemic
- GI if spores are ingested
One way to differentiate Bacillus cereus and Bacillus anthracis is to look at the type of hemolysis that each causes…
B. cereus = beta-hemolytic
B. anthracis = non-hemolytic
Another way to differentiate Bacillus cereus and Bacillus anthracis is to look at which organism is motile…
B. cereus = motile
B. anthracis = non-motile
As its name suggests, Corynebacterium are associated with this unique gram stain shape… It also display cells laying in parallel rows called…
Club-shaped
-“coryne” = Greek for club shaped
Palisades
- Chinese letters
- also V, L, U patterns
- pleomorphic
Based on their 16S rRNA analysis, Corynebacteria resemble (2)…
Mycobacterium
Nocardia
- acid fast organisms
- lots of lipids on their cell walls
C. diphtheriae causes this to form in the throat…
Sticky pseudomembrane
- bleeds when removed
- blocks airway
- asphyxiation or cardiac failure cause of death
What is the major virulence factor of C. diphtheriae? What is the gene that encodes this?
Diphtheria toxin
tox gene
- not all strains of Corynebacterium diptheriae carry this gene
- only toxin producing strains cause diptheria
C. diptheriae causes two types of infections…
Respiratory
- droplet transmission
- swelling of neck
- toxins cause severe myocarditis
Cutaneous
-nonhealing ulcers with dirty gray membrane
The appearance of a “bull neck” is symptomatic for what type of disease? Caused by what type of bacteria?
Respiratory diphtheria
Corynebacterium diphtheriae
Can people infected with C. diphtheriae be treated with antibiotics? Why or why not?
No
Toxin needs to be inactivated because they are attacking heart muscles. Treat with anti-toxin
-cultured in horses
How are C. diphtheriae cultures collected and what culture specimens are sent to the lab (2)?
Throat swab
Nasopharyngeal swab
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…
Cystine-tellurite agar
OR
Tinsdale agar
-fosfomycin used to select for bacteria
Loeffler’s serum medium
What do C. diphtheriae colonies look like on Tinsdale or Tellurite agar?
Black colonies with brown halos
-tellurite reductase and cystinase breakdown their substrates
