Chapter 1: Bacterial morphology, taxonomy, and Gram stain Flashcards
What are the 4 major shapes of bacteria?
1) Cocci - spherical
2) Bacilli - rods (short bacilli are called coccobacilli)
3) Spiral - comma, S, or spiral-shaped
4) Pleomorphic - lacking a distinct shape, like jello
What are the 7(+1) classic Gram-positive bugs that cause disease in humans?
1) Streptococcus, 2) Enterococcus
3) Staphylococcus
4) Bacillus
5) Clostridium
6) Corynebacterium
7) Listeria
(8) Mycobacteria (weakly Gram+)
What is the morphology of the classic Gram-positive bacteria? (hint: how do you remember the classification)
Of the Gram-positives, 3 are cocci and 4(+1) are rods. 2 are branching filamentous growth
What Gram-positive bacteria are cocci? (3)
1) Streptococcus
(2) Enterococcus
3) Staphlococcus
What Gram-positive bacteria are bacilli? (4+1)
1) Bacillus
2) Clostridium
3) Corynebacterium
4) Listeria
(5) Mycobacteria (weakly Gram+)
Which Gram-positive bacilli form spores? (2)
1) Bacillus
2) Clostridium
Which Gram-positive bacilli do not form spores? (2+1)
1) Corynebacterium
2) Listeria
(3) Mycobacteria
What is the morphology of Streptococcus?
Gram-positive cocci that form strips
What is the morphology of Enterococcus?
Gram-positive cocci that form strips
What is the morphology of Staphylococcus?
Gram-positive cocci that form clusters
What is the morphology of Bacillus?
Gram-positive rods that form spores
What is the morphology of Clostridium?
Gram-positive rods that form spores
What is the morphology of Corynebacterium?
Gram-positive rods
What is the morphology of Listeria?
Gram-positive rods
Which bacteria is weakly Gram-positive?
Mycobacteria
Mycobacteria are weakly Gram-positive. What is a better stain for mycobacteria?
Acid-fast stain
Acid-fast stain detects which bacteria? Why is it needed?
Mycobacteria, which is weakly Gram-positive.
What Gram-negative bacteria are cocci? (2)
1) Neisseria2) Moraxella
What Gram-negative bacteria are spirals? (1)
Spirochetes
Which bacteria are the spirochetes? (3)
1) Borrelia (Giemsa)
2) Leptospira
3) Treponema
What is the morphology of Neisseria?
Gram-negative diplococci
What is the morphology of Moraxella?
Gram-negative diplococci
What is the morphology of spirochetes?
Gram-negative spirals
Can spirochetes be detected by Gram-stain? Why or why not?
Spirochetes have a gram-negative cell wall but are too small to be seen with the light microscope.
How can you detect spirochetes?
Spirochetes must be visualized with a special darkfield microscope.Spirochetes have a Gram-negative cell wall but are too small to be seen with the light microscope.
Which bacteria is neither Gram-negative nor Gram-positive so does not Gram-stain? Why not?
Mycoplasma lack a cell wall, so they are neither Gram-positive nor Gram-negative.
What is the morphology of the Gram-negative bacteria? (hint: how do you remember the classification)
Of the Gram-negatives, 2 are cocci, 1 are spirals, 2 are pleomorphic, and the rest are rods.
Which Gram-negative bacteria are pleomorphic? (2)
1) Chlamydia (Giemsa)
2) Rickettsiae (Giemsa)
What is the morphology of mycoplasma?
Neither Gram-positive nor Gram-negative because they lack a cell wall.
What structure is composed of small circles of double-stranded DNA adjacent to bacterial DNA?
plasmid
What is bacterial DNA?
single circle of double-stranded DNA
What is the mechanism of action of erythromycin?
antibiotic that inhibits bacterial protein synthesis at the 50S subunit of the ribosome
What is the mechanism of action of tetracycline?
antibiotic that inhibits bacterial protein synthesis at the 30S subunit of the ribosome
What antibiotic inhibits bacterial protein synthesis at the 30S subunit of the ribosome?
tetracycline
What antibiotic inhibits bacterial protein synthesis at the 50S subunit of the ribosome?
erythromycin
Which bacteria do not Gram stain well? (6)
These Microbes May Lack Real Color
1) Treponema
2) Mycobacteria
3) Mycoplasma
4) Legionella
5) Rickettsia
6) Chlamydia
Why doesn’t Treponema Gram stain well?
it is a spirochete and too thin to be visualized
Why doesn’t mycobacteria Gram stain well?
high lipid content in cell wall
Treponema doesn’t Gram stain well. What is a better way to detect treponema? (2)
Darkfield microscopyFluorescent antibody staining
Mycobacteria doesn’t Gram stain well. What is a better way to detect mycobacteria?
Acid-fast stain : the carbolfuchsin detects the high lipid content in the cell wall
Why doesn’t mycoplasma Gram stain well?
It lacks a cell wall.
Why doesn’t Legionella Gram stain well?
It is predominantly intracellular.
Legionella doesn’t Gram stain well. What is a better way to detect Legionella?
silver stain
What bacteria can be detected by acid-fast stain?
Mycobacteria(and weakly Nocardia)
What bacteria can be detected by dark-field microscopy?
Treponemes (spirochetes)
What bacteria can be detected by silver stain?
Legionella
Why doesn’t Rickettsia Gram stain well?
it’s an intracellular parasite
Why doesn’t Chlamydia Gram stain well?
It’s an intracellular parasite, and lacks muramic acid in its cell wall
Which Gram-positive bacteria have morphology of branching filamentous growth? (2)
1) Actinomyces (anaerobic)
2) Nocardia (weakly acid-fast)
What is the morphology of Actinomyces?
Gram-positive branching filamentous growth
What is the morphology of Nocardia?
Gram-positive (acid-fast)
Which bacteria have unusual cell membranes and cell walls? (3)
1) Mycoplasma
2) Mycobacteria
3) Chlamydia
What is unusual about the cell membrane of mycoplasma?
Mycoplasma cell membrane contain sterols
The cell membrane of which bacteria contains sterols?
Mycoplasma
The cell wall of which bacteria lacks muramic acid and is therefore not sensitive to penicillin?
Chlamydia
Which bacteria lacks a cell wall?
Mycoplasma
What is unusual about the cell wall of mycoplasma?
Mycoplasma doesn’t have a cell wall.
What is unusual about the cell membrane of mycobacteria?
It contains mycolic acid
What bacteria contain mycolic acid in their cell membrane?
Mycobacteria
What is unusual about the cell wall of mycobacteria?
high lipid content
Which bacteria have a high lipid content in their cell wall and thus need to be detected by acid fast stain?
Mycobacteria
