Bacterial Structure and Physiology Flashcards
1
Q
How big are bacteria?
A
Generally: 1-2 um
The smallest bacteria overlap with viruses
2
Q
What is included in a cell envelope?
A
Minimum: Cell membrane and cell wall
Gram (+): Cell membrane and cell wall
Gram (-): Outer and inner membrane, thin cell wall, periplasm
3
Q
What is the difference between the outer and inner membranes in Gram (-) bacteria?
A
Outer membrane: Contains lipopolysaccharides (LPS) instead of phospholipids
- Lipid A
- Core polysaccharide
- O-antigen
Inner membrane: a phospholopid bilayer similar to the cytoplasmic membrane of gram (+) bacteria
4
Q
What are the functions of bacterial cell membranes?
A
- Permeability barrier with transport mechanisms
- Electron transport
- Export of membrane and secreted proteins
- Biosynthesis of cell wall components
- Partition of newly replicated chromosome into daughter cells during cell division
5
Q
What compound do most bacterial membranes NOT contain?
A
Sterols
Exception: wall-less organisms (mycoplasmas)
6
Q
What kinds of bacterial cell membranes contain sterols?
A
Mycoplasma
(These bacteria do not have cell walls)
7
Q
Which bacteria have an external cytoplasmic membrane but no cell wall?
A
Mycoplasma
8
Q
What are cocci?
A
Spherical
9
Q
What are bacilli?
A
Rods
10
Q
What are coccibacilli?
A
Short rods that appear to be spherical
11
Q
What are the three components of LPS?
A
- Lipid A
- Core polysaccharide
- O antigen (or O-specific side chain)
12
Q
What is Lipid A?
Where is it found?
What does it do?
A
Lipid A: a phosphorylated diglucosamine molecule with substituted fattey acids
Found in: Outer membrane of gram negative bacterial cell envelope; part of LPS
Function: contributes to the toxic effects of LPS
13
Q
What is core polysaccharide?
A
A region attached to lipid A consisting of 7-9 sugar residues
(Ketodeoxyoctonate and heptose are two unusual sugar residues found there)
14
Q
What is O-Antigen?
Where is it found?
What does it do?
A
O-Antigen: Repeating units of 3-5 sugar residues
Found in: Outer membrane of gram (-) cell envelope. Part of LPS. (However, not present in all gram (-) bacteria)
Function: Protective against complement-mediated lysis; it confers serum resistance
BUT: antibodies can recognize O-antigens, leading to clearance of the bacteria
15
Q
What component of LPS is toxic to humans?
A
Lipid A
16
Q
What is the unique component of bacterial cell walls?
A
Peptidoglycan
Also known as murein
17
Q
What are the functions of peptidoglycan?
A
- Gives bacterial cells their shape
- Protects cell against osmotic lysis
18
Q
What is the basic structure of peptidoglycan?
A
Long polymers of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) w/ alternating L-and D- amino acids
The polymers are crosslinked to each other to form 3D sheets
19
Q
What kinds of bacteria contain teichoic acid in their cell walls?
A
Gram positive
20
Q
What is teichoic acid?
Where is it found?
What does it do?
A
Teichoic Acid: Long polymers of glycerol phosphate or ribitol phosphate. Contains sugars and amino acids
Where found: Embedded in cytoplasmic membranes of gram (+) bacteria. Extends through cell wall
Function: makes the bacteria sticky! Teichoic acids function as adhesins on the bacterial surface
21
Q
Which enzymes are responsible for proper crosslinking of NAG/NAM chains?
A
Penicillin-binding proteins (PBPs)
22
Q
What class of proteins are penicillin-binding proteins?
A
Enzymes
23
Q
At low concentrations, how does LPS (aka endotoxin) affect the human host?
A
Effects that are protective of the host
- Fever
- Activates Complement
- Stimulates B cells and macrophages
- Activates acute phase response
24
Q
Describe the crosslinking process
A
PBPs link the third amino acids of some tetrapeptides to the terminal amino acids of other tetrapeptides
25
What are penicillin binding proteins responsible for?
Crosslinking NAG/NAM chains to form 3D sheets
26
Describe the gram staining process
1. Apply crystal violet
2. Apply iodine
3. Alcohol Wash
(Crystal violet and iodine **remain in gram (+) bacteria** and **wash out of gram (-) bacteria**)
4. Sarafin (couterstain; stains gram (+) bacteria red)
27
Which type of bacteria have a thick cell wall?
Gram-positive
28
Which type of bacteria have a thin cell wall?
Gram-negative
29
Which types bacteria are poorly visualized by Gram staining?
Mycobacteria, some spirochetes, and mycoplasma
Mycobacteria: cause TB, leprosy, other diseases
Spirochetes: Treponema pallidum causes syphilis
30
Why are myobacteria poorly visualized using Gram staining?
Special lipids in their cell envelops prevent them from taking up crystal violet/iodine dye
Use acid-fast, Ziehl-Neelsen, or Kinyoun staining instead
31
After gram staining, an unidentified bacterium appears purple.
What kind of bacterium is this?
What is causing it to appear purple?
Gram positive bacteria appear purple after gram staining due to retention of crystal violet/iodine dye
32
After gram staining, an unidentified bacterium appears red.
What kind of bacterium is this?
Why is it red?
Gram negative bacteria appear red because the take up the safarin counterstain
(After the crystal violet/iodine has been washed away by alcohol)
33
What staining porcess can detect mycobacteria?
Acid-fast, Ziehl-Neelsen, or Kinyoun staining
34
Why are some spirochetes (such as Treponema pallidum) poorly visualized using Gram staining?
The cell walls are too thin to be seen by standard light microscopy
Use dark-field microscopy instead
35
Why are Mycoplasma spp. poorly visualized by Gram staining?
They lack cell walls
36
At high concentrations, how does LPS (aka endotoxin) affect the human host?
High concentrations of endotoxin cause septic shock (aka endotoxic shock or gram (-) shock) due to systemic spread of gram (-) bacteria
This is characterized by...
* Hypotension
* Circulatory collapse
* Disseminated intravascular coagulation
* Multi-organ failure
* Death
37
What basic structures do the cell envelopes of Gram negative bacteria consist of?
Two lipid bilayer membranes - cytoplasmic (inner) and outer
Periplasm between the two membranes - consists of glucan structures (osmolarity) and thin peptidoglycan layer
38
How does endotoxin induce its effects?
Stimulates cytokine production by mononuclear cells
39
Describe the pathway inside the body that is activated by LPS
LPS stimulates cytokine production by...
1. **LPS** binds to **LPS-Binding Protein (LBP)**
2. **LPS-LBP** complex binds to **CD14** receptors on monocytes and macrophages
3. The **LPS-LBP-CD14** activates **TLR-4**
4. **TLR-4** stimulates the release of pro-inflammatory cytokines **IL-1 and TNF**
5. This causes:
1. Fever
2. Increased stickiness of endothelial cells (more leukocytes bind to the surface)
3. Stimulation of leukotrienes and prostaglandins
1. This causes a **secondary wave of cytokine production**, which can lead to concomitant effects and septic shock
40
Where is LPS found?
Outer leaftlet of outer membrane of gram negative bacteria
41
What is the function/utility of an O antigenic chain?
Antigenic and allows serotyping
42
What is the function of long O-side chains?
Protect against complement-mediated lysis and cause bacteria to be serum resistant
But can still be recognized by specific antibodies and then cleared
43
What causes bacteria to be serum resistant?
Long O-side chains
But can still be recognized by specific antibodies and then cleared
44
What causes bacteria to be serum sensitive?
Lack of long O-side chains
But are susceptible to complement mediated lysis
45
Describe the characteristics of septic shock
**HCDMD**
* Hypotension
* Circulatory collapse
* Diseminated intravascular coagulation
* Multi-organ failure
* Death
46
What causes septic shock?
High concentrations of LPS, typically due to gram (-) bacterial infections.
Note: Overwhelming gram (+) and fungal infections can also cause septic shock
47
What are the external structures of bacteria?
Capsules, flagella, pili
48
What are capsules made of?
Layers of organic polymers (usually polysaccharides, but can be a peptide) that form hydrophilic gels surrounding the cells of some bacteria
49
What are the functions of capsules?
* Prevent dessication
* Plauy a role in virulence of some pathogens by preventing engulfment by phagocytes
50
How do capsules prevent engulfment by phagocytes?
Prevent complement activation via the alternate pathway on the cell surface
51
What factor is important in reducing ability of phagocytes to engulf bacteria whose capsule prevents phagocytosis by phagocytes?
Absence/reduction of C3b bound to bacterial cell surface
52
In which bacteria is the capsule an important virulence determinant?
* **Streptococcus pneumoniae**
* **Neisseria meningitidis**
* **Haemophilus influenzae**
* Klebsiella pneumoniae
* Streptococcus agalactiae
* Some strains of Escherichia coli
* Bacillus anthracis
53
What diseases are encapsulated bacteria important in causing?
* Meningitis
* Bacteremia in people without a functional spleen
54
What are K antigens?
Capsules of certain bacteria used for serological typing
55
For which bacteria are capsular vaccines available?
Streptococcus pneumoniae, Haemophilus influenzae B, Neisseria meningitides A & C
56
What is the function of flagella?
Movement (chemotaxis)
57
What are flagella composed of?
Filament (made of multiple subunits of flagellin protein) attached to a flexible hook that connects basal body/apparatus in bacterial envelop
58
What is the function of the basal body of the flagella?
Motor that drives energy-dependent rotation of the filament
59
What are flagella designated for serotyping?
H antigens
60
The presence of flagella can be used to serologically distinguish and classify which bacteria?
Gram-negative enteric bacteria
Ex: Escherichia coli O157:H7 has type 7 flagella and type 157 O antigen
61
What is chemotaxis?
What component of bacterial structure used for chemotaxis?
What two sorts of movements does chemotaxis include?
Movement toward attractants and away from repellants
Uses flagella
Running (counterclockwise rotation of flagella) and tumbling (clockwise rotation of flagella)
62
What causes bacterial running?
Counterclockwise rotation of flagella
63
What causes tumbling of bacteria?
Clockwise rotation of flagella
64
Which two flagella interactions with host cells can lead to inflammatory responses?
* Binding to external toll-like receptor 5 (TLR-5)
* Binding to internal receptor NLRC4 (inflammasome)
65
What are pili/fimbraie?
Long thin filamentous structures found in the surface of bacterial cell
66
What are pili/fimbraie composed of?
Composed mainly of subunits of pilin
67
What is the function of pili/fimbraie?
How is this accomplished?
Mediating adherence of certain bacteria to cells and tissues of human host
Pili bind receptors consisting of surgar residues on glycolipids or glycoproteins in the host cell membrane
68
What factor related to pili accounts for the tissue specificity of many bacteria?
There are many different types of pili, each recognizing a different cell receptor
69
What is phase variation?
When certain pathogenic bacteria turn on/off production of particular surface proteins
70
What is antigenic variation?
Which group of bacteria utilizes antigenic variation?
What is the purpose of antigenic variation?
When bacteria make a surface protein but change its antigenic form
Neisseria spp. changes antigenic nature of pili by changing the type of pilin that is produced
Prevents detection of organism by host immune system
71
What does the bacterial cytoplasm consist of?
Proteins and RNA
72
What is the main biosynthetic activity of growing bacterial cells?
Protein synthesis
| (cytoplasm loaded with ribosomes)
73
Describe bacterial ribosomes
What subunits do they include?
70S ribonucleoprotein structures
50S subunit (includes 23S, 5S, 34 proteins)
30S subunit (includes 16S and 21 proteins)
74
Why are bacterial ribosomes an important target for antibiotics that inhibit bacterial protein synthesis?
Bacterial ribosomes (70S composed of one 50S and one 30S subunit) differ from eukaryotic ribosomes (80S composed of one 60S and one 40S subunit)
75
The gene sequence of which portion of bacterial ribosomes can be used to identify bacteria?
Which subunit is it found in?
Why can this be done?
16s rRNA gene sequence
Found in 30S subunit
The sequences of some regions of 16S rRNA gene are unique to various bacterial genera and species
76
How do broad-range PCR primers amplify the rRNA gene of previously unknown/unculturable bacteria from human tissue specimens?
They recognize 16S rRNA gene sequences common to all members of the bacterial domain
77
Describe the DNA of a typical bacterium
One double stranded circular molecule of 1-8 million base pairs (nucleoid)
Not surrounded by a membrane
Packed into cytoplasm in an irregular way
78
What are plasmids?
Why are they medically important?
Extrachromosomal DNA present as small circular molecules
Genes specify proteins that act as virulence factors or allow the organisms to resist antibiotics or heavy metals
79
What is the process bacteria use to multiply?
Describe the main steps involved
Asexual reproduction
1. Grow (after DNA replication)
2. Divide the cell at the middle into two daughter cells
3. Each daughter cell acquires one copy of chromosome at cell division
80
Describe the main steps of bacterial DNA replication
1. DNA polymerase replicates circular chromosome starting at oriC
2. DNA gyrases separate the initially linked daughter chromosomes
81
In what ways does bacterial transcription differ from eukaryotic transcription?
* Bacterial RNA polymerase is different
* Genes may be organized into operons (clusters of genes all transcribed from a single promoter onto a single mRNA molecule)
* Occurs in cytoplasm
* Performed concurrently w/ translation
82
Why is bacterial RNA polymerase a useful target for antibiotics?
Bacterial RNA polymerase differs significantly from eukaryotic RNA polymerase
83
What is an operon?
A cluster of genes that are all transcribed from a single promoter onto a single mRNA molecule
84
Where do transcription and translation occur in bacteria?
Both in the cytoplasm
85
Describe the temporal relationship between transcription and translation in bacteria
Transcription and translation can occur concurrently in bacteria
86
What is a spore?
A dormant form of bacterial cell that can survive for many years
Under favorable conditions, a spore germinates and forms vegetative cells that begin to grow
87
What stage do the Gram-positive bacilli have to be in for spores to develop?
Vegetative (dividing cells)
88
Which sorts of bacteria can form spores?
Which bacteria specifically?
Some Gram-positive bacilli
Clostridium and Bacillus
89
Why are spores hard to kill?
Spores are resistant to heat, UV radiation, drying, and chemical agents
90
How do many bacteria acquire iron from host molecules?
Secrete siderophopres (low molecular weight molecules) that remove iron from host molecules and allow it to be taken up by bacterial cells
(Exceptions: Neisseria meningitidis and Neisseria gonorrhoeae produce surface receptors that bind to lactoferrin and transferrin, then remove and internalize iron)
91
What are the two mechanisms bacteria can generate energy?
Fermentation and respiration
92
Describe the characteristics of fermentation
Generates energy by substrate-level phosphorylation
Organic compounds, such as glucose, service as electron donors and acceptors
Inefficient
Do not require oxygen
Produces endproducts, such as acids, that accumulate in culture medium
93
Describe the characteristics of respiration
Efficient generator of energy
Final electron acceptor is O2 for aerobic respiration and NO3- for anaerobic respiration
1. Electrons transported through a chain of carriers in plasma membrane to the final electron acceptor
2. Protons pumped from cytosol to external side of plasma membrane creating a protonmotive force
3. Protonmotive force harvested by ATP synthase to generate ATP from ADP (chemiosmosis)
94
What is the protonmotive force in respiration utilized for?
* Chemiosmosis: generating ATP from ADP via ATP synthase
* Flagellar rotation
* Uptake of some small molecules into the cell
95
Which bacteria contain cytochrome c?
What test can detect cytochrome c? What does it measure?
Pseudomonas aueroginosa and Neisseria spp.
Oxidase test: measures ability of bacteria to oxidize and change color of N,N-dimethyl-p-phenylenediamine
96
What are oxidase positive bacteria?
Bacteria containing cytochrome C
97
Which reactive and toxic substances does oxygen give rise to?
* Hydrogen peroxide (H2O2)
* Superoxide anion (O2-)
98
What is the function of superoxide dismutase?
Degrades superoxide
2O2- + 2H+ -\> H2O2 + O2
99
What is the function of catalase?
Degrades hydrogen peroxide to water and oxygen
H2O2 + H2O2 -\> 2H2O + O2
100
What are the characteristics of a strict aerobe?
* Grows with oxygen
* Does not grow without oxygen (cannot ferment)
* Contains superoxide dismutase and catalase
101
What are the characteristics of a strict anaerobe?
* Killed by oxygen
* Grows in absence of oxygen (ferments)
* Lacks superoxide dismutase and catalase
102
What are the characteristics of a facultative anaerobe?
* Respires with oxygen
* Ferments in absence of oxygen
* Contains superoxide dismutase and catalase
103
What are the characteristics of an indifferent (aerotolerant anaerobe)?
* Ferments in presence or absence of oxygen
* Contains superoxide dismutase and catalase
104
What methods can be used to identify bacterial pathogens?
* Staining of clinical specimens or after growth of bacterium on lab medium
* Determining metabolic and biochemical characteristics and antibiotic resistance after growing the organism
* Antibody tests in patient or laboratory assays
* PCR
* MALDI-TOF
* Whole genome sequencing
105
How fast is bacterial metabolism compared with human metabolism?
Bacterial metabolism is 10-100x faster than human metabolism
106
Describe the lag phase of bacterial growth
Bacteria are adapting to their new environment
They are making enzymes and intermediates to utilize the nutrients in the medium
They aren't significantly increaseing in number
107
Describe the exponential phase of bacterial growth
Bacterial are rapidly dividing via binary fission
They are increasing in number very quickly
108
Describe the stationary phase of bacterial growth
Numbers are constant or slightly decreasing
Growth is limited by nutrient exhaustion or toxic product accumulation
109
What is the minimum inhibitory concentration (MIC)?
The least amount of antibiotic that prevents bacterial **growth**
No new colonies can form
110
WhaAddt is the minimum bactericidal concentration (MBC)?
The least amount of antibiotic required to kill a predetermined portion of an inoculum (usually 99.9%) in a given amount of time
111
When would you want to use a selective media to grow bacteria?
When you are trying to culture a slower-growing bacteria
Example: you take a sputum sample and want to culture a slower-growing bacteria. You don't want the faster growing bacteria to out-compete and obscure the slow grower. You use a media that is selective for the slower bacteria
112
Why would you want to use sheep-blood agar?
To distinquish heolytic from non-hemolytic bacteria
113
Why would you use MacConkey agar?
MacConkey agar is selective for gram (-) rods
It is also differential for lactose fermentation
114
When would you want to use Bordet-Genou agar to grow bacteria?
When you are suspicious for Bordetella Pertussis
115
What is a transposable element?
* A DNA fragment that mediates its own movement from one location on a chromosome or plasmid to another
* A "jumping gene"
* These are important in the transfer of antibiotic resistance or creating mutation
* 2 types: Insertion Sequences (IS) and Transposons
116
What is a siderophore?
Siderophores remove **iron** from trensferrin and lactoferrin so it can be taken up by bacterial cells
117
What is an insertion sequence?
What is its structure?
The simplest transposable element
Structure:
* Inverted repeated base sequences (15-40 BP) at ends
* Genes encoding tranposases in the middle
118
What are transposases?
Enzymes that mediate tranposition
* Recognize inverted repeats
* Catalyze the cutting and resealing of DNA
* Allow movement of IS elements from one location to another
119
What is a transposon?
Larger transposable element
* Carries extraneous genes in addition to transposition genes
* May encode **antibiotic resistance** or **virulence determinants**
* Some consist of extraneous genes flanked by IS elements
* IS element = inverted repeats w/tranposase gene between
* Others just have inverted repeats of 30-40 BPs at each end
120
What is the difference between an insertion sequence and a transposon?
**Insertion sequences (IS)** only contain genes for tranposases
**Transposons** contain genes for transposase AND other genes that may encode antibiotic resistance or virulence determinants.
Note: Transposons may contain IS at each end
121
What are plasmids?
* Small, extrachromosomal, circular, double stranded DNA (basically a bably bacterial chromosome)
* Replicates independently of host chromosome
* They have their own initiations sites for DNA polymerase: oriP
* May carry and disseminate antibiotic resistance or virulance determinant genes
* 2 Types: nonconjugative and conjugative
122
What is a nonconjugative plasmid?
A plasmid that cannot mediate its own transfer.
Usually smaller
123
What is a conjugative plasmid?
A plasmid that can mediate its own transfer
- Usually larger
124
What is an R plasmid?
Why is it significant?
An R plasmid is a conjugative plasmid that carries genes for antibiotic resistance
If a bacterium acquires the R plasmid, it will gain antibiotic resistance
125
What virulence determinants of *Escherichia coli* are encoded by plasmids?
Enterotoxins (LT and ST)
126
What virulence determinants of *Shigella* spp are encoded by plasmids?
Type III secretion system that facilitates the invasion of epithelial cells
127
What virulence determinants of *Clostridium tetani* are encoded by plasmids?
Tetanus toxin
128
What is a bacteriophage?
A virus that infects bacteria. Also called a phage
2 types: **Virulent** and **Temperate**
129
How do bacteriophages infect bacteria?
Transduction
* The phage binds to specific receptors on the bacterium's surface
* The phage injects DNA or RNA
* The phage uses the host's replication machinery to replicate its nucleic acids
130
What is a virulent phage?
A virulent phage causes a **lytic infection**
The injected DNA or RNA takes over the replication system of the host and produces many new virons within the infected cell.
This causes the host bacterium to lyse, spilling the new virons out
131
What is a temperate phage?
Can cause a **lytic** or **lysogenic infection**
**Lytic** = host cell lyses
**Lysogenic** = quiescent;
* The infected bacterium grows and divides
* Passes on the phage (called prophage in host) to progeny.
* If the bacterium is stressed, more prophage DNA may be induced which can cause a **lytic** infection
* The prophage DNA may be integrated into the host chromosome
* The phrophage DNA may change the characteristics of the host in **phage conversion**
132
What is **phage conversion**?
**Phage conversion** is associated with infection by a temperate phage
* It confers new properties to the host, including virulence determinants, toxins, and/or antibiotic resistance
* It occurs when phage DNA that is integrated into the host chromosome takes part of the host DNA when is excised
* The excised phage carries some of this host DNA when it integrates into a new host chromosome
* The new host may now have additional characteristics
133
What is transformation?
Pieces of naked DNA from lysed bacterial cells are taken up by other bacterial cells and incorporated into their chromosomes
134
What are "naturally competent bacteria?"
Bacteria that are natrually able to take up DNA in transformation
135
Give 4 examples of naturally competent bacteria
* Streptococcus pneumoniae*
* Bacillus* spp
* Haemophilus influenzae*
* Nisseria* spp
136
What are artificially competent bacteria?
Why are they important?
Artificially competent bacteria are treated to induce transformation
They are important in lab research! E. Coli can be induced to become competent, which allows them to express genes that are important for research
137
Give an example of an artificially competent bacteria
E. Coli
Competence can be induced in E. Coli, allowing them to uptake DNA an express genes to create clones for research
138
What is transduction?
The mechanism that **bacteriophages** use for DNA transfer
2 types of transduction:
* Generalized
* Specialized
139
Describe generalized transduction
Host DNA is nonspecifically transferred from cell to cell
* Bacteriophages produce caspids that can package **any** fragment of DNA
* If host DNA fragments are present, they are packaged and injected into neighboring cells upon infection
* Can result in transfer of virulence determinant and/or antibiotic resistance genes
140
Describe specialized transduction
Carried out by phages that excise and package **phage DNA** that is integrated into the host cell chromosome
* Sometimes the phage will excise some of the host DNA that is adjacent to the phage DNA
* This host DNA now travels along with the phage DNA
* The amount and parts of host DNA that can be transferred are limited becasue the phage DNA only integrates into the host chromosome at specific places
141
Describe conjugation
Bacterial sex!
* Cell to cell contact
* Unidirectional transfer if DNA from donor to recipient
* Mediated by conjugative plasmids and ICEs
142
Describe conjugation of the F Plasmid
The F plasmid encodes conjugation machinery
* The F plasmid induces a sex pilus in the donor bacterial cell
* The sex pilus allows the donor to contact and bind to the recepient bacterial cell
* A copy of the F plasmid is transferred to the recipient via the sex pilus
* If the F plasmid has been integrated into the host chromosome, additional genes may travel along with it when it is excised
143
List the phases of bacterial growth
1. **Lag phase:** the bacterium is adpating to its new environment and making enzymes and intermediates needed to survive
2. **Exponential phase**: The bacteria are rapidly dividing via binary fission
3. **Stationary phase**: The bacteria are at a steady state or slightly decreasing; their replication is limited by nutrient availability or toxic product accumulation
144
How do plasmids and bacteriophages contribute to the virulence of certain pathogens?
Both may carry virulence genes that will be expressed by the bacteria that contain them
145
Can lytic bacteriophages every be useful to humans? How?
Lytic phages can be useful in treating certain bacterial infections in humans
The lytic phage infects the bacterium and causes it to lyse, thus killing the bacteria and potentially eradicating the bacterial infection
146
Would a beta-lactam antibiotic be useful against gram-positive or gram-negative bacteria?
Both; Both types of bacteria can be treated by beta-lactam antibiotics becasue both have peptidoglycan in their cell walls (although the layer is thinner in gram (-) bacteria)
147
What kinds of bacteria contain superoxide dismutase and catalase?
Obligate aerobes, facultative anerobes, aerotolerant anaerobe
148
What kinds of bacteria (in general) would **not** contain superoxide dismutase and catalase?
Obligate anaerobes
149
Which genetic exchange mechanism utilizes a sex pilus?
Conjugation
150
Which genetic exchange mechanism involves the uptake of naked DNA?
Transformation
151
What is an integron?
"Antibiotic resistance machines"
A genetic entity that captures exogenous gene cassettes and ensures their expression.
They are not mobile on their own, but they can be inserted into mobile elements, such as plasmids or transposons
152
What is the structure of an integron?
3 core components:
* Outward-oriented promoter
* Primary recombination site downstream of promoter
* A gene encoding an integrase (an integrase can insert gene cassettes into the integron)
When a gene cassette is insterted into an integron, the recombination site re-forms. More cassettes can be inserted; the cassettes are expresed as operons
153
What is a gene cassette?
A discrete unit of a singel gene
Most encode antibiotic resistance genes
