Microbiology - Bacteria Intro

Front 1

What color will gram-positive organisms appear under the microscope? Gram-negative?

Back 1

Gram positive = Blue
Gram negative = Red

Mnemonic: I'm positively BLUE over you!
No (negative) RED commies!

Front 2

What is the peptidoglycan layer composed of?

Back 2

The peptidoglycan layer or cell wall is composed of repeating disaccharides with 4 amino acids in a side chain extending from each disaccharide.

Front 3

What is the enzyme that catalyzes the formation of the stable cross-linked structure? Why is it important clinically?

Back 3

The enzyme that catalyzes the formation of this linkage is called transpeptidase and is located in the inner cytoplasmic membrane.
The antibiotic penicillin binds to and inhibits this enzyme.

Front 4

How many layers do gram-negative cell envelopes have? What are those layers?

Back 4

Gram-negative cells have 3 layers.
1) Inner cytoplasmic membrane
2) Thin peptioglycan layer
3) Outer membrane with lipopolysaccharide (LPS)

Front 5

What are some differences between gram-positive and gram-negative cells?

Back 5

Gram-positive cells have 2 layers while gram-negative cells have 3 layers. Gram-negative cells have endotoxin (LPS), a periplasmic space between layers, and porin channels. Gram-positive cells are vulnerable to lysozyme and penicillin attack while gram-negative cells are not.

Front 6

What are the clinically significant gram-positive bugs?

Back 6

The 2 cocci bugs
1) Streptococcus
2) Staphylococcus
The 2 rods that produce spores
3) Bacillus
4) Clostridium
The 2 rods that do not form spores
5) Corynebacterium
6) Listeria

Front 7

What is notable about the gram-positive bug Listeria?

Back 7

It is the only gram-positive bug that has endotoxin. All other bacteria that contain endotoxin are gram-negative.

Front 8

What is the only gram-negative cocci?

Back 8

Neisseria

Front 9

What is the only group of spiral-shaped organisms?

Back 9

Spirochetes

Front 10

What organisms are neither gram-positive or gram-negative?

Back 10

Mycoplasma (Do not have a cell wall)

Front 11

What are the three enzymes some bacteria possess to break down oxygen radicals?

Back 11

Catalse
Peroxidase
Superoxide dismutase

Front 12

Why are pili important for virulence?

Back 12

Pili can serve as adherence factors (in which case they are called adhesins). Pili allow the bacteria to bind to vells and cause disease.

Front 13

What tests are used to visualize capsules under the microscope?

Back 13

India ink stain: Stain is not taken up by the capsule, so the capsule appears as a transparent halo around the cell.
Quellung reaction: Antibodies bind to the capsules, capsules swell with water and can be seen microscopically.

Front 14

How do facultative intracellular organisms survive within white blood cells?

Back 14

These bacteria inhibit phagosome-lysosome fusion, thus escaping the host's deadly hydrogen peroxide and superoxide radicals.

Front 15

What are some examples of facultative intracellular organisms?

Back 15

Listeria monocytogenes
Salmonella typhi
Yersinia
Francisella tularensis
Brucella
Legionella
Mycobacterium

Front 16

Why are pili important for virulence?

Back 16

Pili can serve as adherence factors (in which case they are called adhesins). Pili allow the bacteria to bind to vells and cause disease.

Front 17

What tests are used to visualize capsules under the microscope?

Back 17

India ink stain: Stain is not taken up by the capsule, so the capsule appears as a transparent halo around the cell.
Quellung reaction: Antibodies bind to the capsules, capsules swell with water and can be seen microscopically.

Front 18

How do facultative intracellular organisms survive within white blood cells?

Back 18

These bacteria inhibit phagosome-lysosome fusion, thus escaping the host's deadly hydrogen peroxide and superoxide radicals.

Front 19

What are some examples of facultative intracellular organisms?

Back 19

Listeria monocytogenes
Salmonella typhi
Yersinia
Francisella tularensis
Brucella
Legionella
Mycobacterium

Front 20

What are the differences of exotoxins and endotoxins?

Back 20

Exotoxins are proteins excreted from cells, while endotoxins are normally found in the outer membrane and sheds off (especially during lysis).

Endotoxin is only present in gram-negative bacteria, with the exception of Listeria monocytogenes.

Front 21

What occurs in transformation?

Back 21

Naked DNA fragments from one bacterium, released during cell lysis, bind to the cell wall of another bacterium. The recipient bacterium must be competent, which means that it has structures on its cell wall that can bind the DNA and take it up intracellularly. The DNA can then incorporate itself into the recipient's genome.

Front 22

How does a bacteriophage infect bacteria?

Back 22

Transduction occurs when a virus that infects bacteria (bacteriophage) carries a piece of bacterial DNA from one bacterium to another.
Adsorption: phage binds by its tail fibers to specific receptors on the bacterial cell surface
Penetration: phage injects DNA into bacterium
Injected DNA takes over host bacteria's RNA polymerase for transcription of phage DNA to mRNA. Bacterial cell lyses.

Front 23

What occurs in generalized transduction?

Back 23

Virulent phages are involved in generalized transduction.
After phage penetration and transcription, replication, and translation of capsids and enzymes, the original bacterial DNA is repressed and eventually destroyed. Sometimes pieces of bacterial DNA are left intact and can accidentally be packed into the phage cap. This phage cap can now inject the piece of bacterial DNA that it is carrying into another bacterium.

Front 24

What occurs in specialized transduction?

Back 24

Specialized transduction occurs with temperate phages. phage DNA becomes incorporated into the bacterial chromosome. If the prophage becomes active, prophage DNA is spliced out of the bacterial chromosome and is then replicated, translated, and packed into a capsid. Sometimes an error in splicing can cause a piece of bacterial DNA that lies at one side of the prophage to be incorporated into the phage. This may result in a transfer of that piece of bacterial DNA to another bacteria.

Front 25

How does conjugation work?

Back 25

For conjugation to occur, one bacterium must have the F plasmid. Bacteria that carry F plasmids are called F(+) cells. In conjugation, an F(+) donor cell will pass its F plasmid to an F(-) recipient cell, making it an F(+) cell. This is done via a sex pilus.

Front 26

What is a Hfr cell?
What can happen with Hfr cells?

Back 26

Sometimes the extra-chromosomal F plasmid becomes integrated in the bacterial chromosome. The bacteria becomes a Hfr cell (High frequency of chromosomal recombinants).

1. The F plasmid that is now together with the entire bacterial circular DNA undergoes conjugation with an F(-) cell. The entire bacterial chromosome will transfer from the Hfr cell to the recipient.

2. The integrated F plasmid in the Hfr cell may be excised at a different site from that of integration. This may result in an F plasmid that now also contains a segment of chromosomal DNA. This plasmid is called F' (F prime).

Front 27

What are transposons?

Back 27

Transposons are mobile genetic elements. These pieces of DNA can insert themselves into a donor chromosome without having DNA homology.