Bacterial Structure and Physiology Flashcards
1
Q
Describe conjugation of the F Plasmid
A
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
2
Q
What is the difference between an insertion sequence and a transposon?
A
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
3
Q
What is an integron?
A
“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
4
Q
What is an R plasmid?
Why is it significant?
A
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
5
Q
Which bacteria contain cytochrome c?
What test can detect cytochrome c? What does it measure?
A
Pseudomonas aueroginosa and Neisseria spp.
Oxidase test: measures ability of bacteria to oxidize and change color of N,N-dimethyl-p-phenylenediamine
6
Q
Where do transcription and translation occur in bacteria?
A
Both in the cytoplasm
7
Q
Which sorts of bacteria can form spores?
Which bacteria specifically?
A
Some Gram-positive bacilli
Clostridium and Bacillus
8
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
9
Q
What are capsules made of?
A
Layers of organic polymers (usually polysaccharides, but can be a peptide) that form hydrophilic gels surrounding the cells of some bacteria
10
Q
When would you want to use a selective media to grow bacteria?
A
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
11
Q
Describe the crosslinking process of peptidoglycan synthesis
A
PBPs link the third amino acids of some tetrapeptides to the terminal amino acids of other tetrapeptides
12
Q
Which bacteria have an external cytoplasmic membrane but no cell wall?
A
Mycoplasma
13
Q
What is transduction?
A
The mechanism that bacteriophages use for DNA transfer
2 types of transduction:
- Generalized
- Specialized
14
Q
What are flagella designated for serotyping?
A
H antigens
15
Q
Describe the lag phase of bacterial growth
A
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
16
Q
When would you want to use Bordet-Genou agar to grow bacteria?
A
When you are suspicious for Bordetella Pertussis
17
Q
What class of proteins are penicillin-binding proteins?
A
Enzymes
18
Q
What are bacilli?
A
Rods
19
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
20
Q
What causes septic shock?
A
High concentrations of LPS, typically due to gram (-) bacterial infections.
Note: Overwhelming gram (+) and fungal infections can also cause septic shock
21
Q
What kind of infection is caused by a virulent phage?
A
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
22
Q
How does endotoxin induce its effects?
A
Stimulates cytokine production by mononuclear cells
23
Q
After gram staining, an unidentified bacterium appears red.
What kind of bacterium is this?
Why is it red?
A
Gram negative bacteria appear red because the take up the safarin counterstain
(After the crystal violet/iodine has been washed away by alcohol)
24
Q
List the phases of bacterial growth
A
- Lag phase: the bacterium is adpating to its new environment and making enzymes and intermediates needed to survive
- Exponential phase: The bacteria are rapidly dividing via binary fission
- Stationary phase: The bacteria are at a steady state or slightly decreasing; their replication is limited by nutrient availability or toxic product accumulation
25
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
26
What are K antigens?
Capsules of certain bacteria used for serological typing
27
What is the unique component of bacterial cell walls?
Peptidoglycan
Also known as murein
28
What are the characteristics of an indifferent (aerotolerant anaerobe)?
* Ferments in presence or absence of oxygen
* Contains superoxide dismutase and catalase
29
What kinds of bacteria contain superoxide dismutase and catalase?
Obligate aerobes, facultative anerobes, aerotolerant anaerobe
30
How do capsules prevent engulfment by phagocytes?
Prevent complement activation via the alternate pathway on the cell surface
31
What is O-Antigen?
Where is it found?
What does it do?
**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
32
What are the two mechanisms bacteria can generate energy?
Fermentation and respiration
33
What is transformation?
Pieces of naked DNA from lysed bacterial cells are taken up by other bacterial cells and incorporated into their chromosomes
34
Describe the stationary phase of bacterial growth
Numbers are constant or slightly decreasing
Growth is limited by nutrient exhaustion or toxic product accumulation
35
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
36
What is the function of catalase?
Degrades hydrogen peroxide to water and oxygen
H2O2 + H2O2 -\> 2H2O + O2
37
Why is bacterial RNA polymerase a useful target for antibiotics?
Bacterial RNA polymerase differs significantly from eukaryotic RNA polymerase
38
What kinds of bacterial cell membranes contain sterols?
Mycoplasma
| (These bacteria do not have cell walls)
39
What are the characteristics of a strict anaerobe?
* Killed by oxygen
* Grows in absence of oxygen (ferments)
* Lacks superoxide dismutase and catalase
40
What causes bacterial running?
Counterclockwise rotation of flagella
41
For which bacteria are capsular vaccines available?
Streptococcus pneumoniae, Haemophilus influenzae B, Neisseria meningitides A & C
42
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
43
What is the function of superoxide dismutase?
Degrades superoxide
2O2- + 2H+ -\> H2O2 + O2
44
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
45
How big are bacteria?
Generally: 1-2 um
The smallest bacteria overlap with viruses
46
Which type of bacteria have a thick cell wall?
Gram-positive
47
What compound do most bacterial membranes NOT contain?
Sterols
Exception: wall-less organisms (mycoplasmas)
48
What are the characteristics of a facultative anaerobe?
* Respires with oxygen
* Ferments in absence of oxygen
* Contains superoxide dismutase and catalase
49
Give 4 examples of naturally competent bacteria
* Streptococcus pneumoniae*
* Bacillus* spp
* Haemophilus influenzae*
* Nisseria* spp
50
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)
51
What is a conjugative plasmid?
A plasmid that can mediate its own transfer
- Usually larger
52
What is a bacteriophage?
A virus that infects bacteria. Also called a phage
2 types: **Virulent** and **Temperate**
53
Why are spores hard to kill?
Spores are resistant to heat, UV radiation, drying, and chemical agents
54
What are coccibacilli?
Short rods that appear to be spherical
55
What causes bacteria to be serum sensitive?
Lack of long O-side chains = susceptible to complement mediated killing = serum sensitive
(but avoids antibodies)
56
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
57
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)
58
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
59
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
60
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
61
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
62
Describe the temporal relationship between transcription and translation in bacteria
Transcription and translation can occur concurrently in bacteria
63
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
64
What is core polysaccharide?
A region attached to lipid A consisting of 7-9 sugar residues
(Ketodeoxyoctonate and heptose are two unusual sugar residues found there)
65
Which genetic exchange mechanism involves the uptake of naked DNA?
Transformation
66
What is a siderophore?
Siderophores remove **iron** from trensferrin and lactoferrin so it can be taken up by bacterial cells
67
Which type of bacteria have a thin cell wall?
Gram-negative
68
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
69
What is the function of flagella?
Movement (chemotaxis)
70
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
71
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
72
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
73
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
74
What is a nonconjugative plasmid?
A plasmid that cannot mediate its own transfer.
Usually smaller
75
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)
76
What is an operon?
A cluster of genes that are all transcribed from a single promoter onto a single mRNA molecule
77
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
78
What are the external structures of bacteria?
Capsules, flagella, pili
79
What are penicillin binding proteins responsible for?
Crosslinking NAG/NAM chains to form 3D sheets
80
What is the function of the basal body of the flagella?
Motor that drives energy-dependent rotation of the filament
81
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**
82
What is a gene cassette?
A discrete unit of a singel gene
Most encode antibiotic resistance genes
83
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
84
What diseases are encapsulated bacteria important in causing?
* Meningitis
* Bacteremia in people without a functional spleen
85
What stage do the Gram-positive bacilli have to be in for spores to develop?
Vegetative (dividing cells)
86
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
87
What component of LPS is toxic to humans?
Lipid A
88
Which reactive and toxic substances does oxygen give rise to?
* Hydrogen peroxide (H2O2)
* Superoxide anion (O2-)
89
What staining porcess can detect mycobacteria?
Acid-fast, Ziehl-Neelsen, or Kinyoun staining
90
Why would you use MacConkey agar?
MacConkey agar is selective for gram (-) rods
It is also differential for lactose fermentation
91
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)
92
At low concentrations, how does LPS (aka endotoxin) affect the human host?
Effects that are **protective of the host**
* Fever
* Activates Complement
* Stimulates B cells and macrophages
* Activates acute phase response
93
Describe conjugation
Bacterial sex!
* Cell to cell contact
* Unidirectional transfer if DNA from donor to recipient
* Mediated by conjugative plasmids and ICEs
94
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
95
What is phase variation?
When certain pathogenic bacteria turn on/off production of particular surface proteins
96
What kinds of bacteria contain teichoic acid in their cell walls?
Gram positive
97
What is the difference between the outer and inner membranes in Gram (-) bacteria?
**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
98
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
99
What are the functions of peptidoglycan?
* Gives bacterial cells their shape
* Protects cell against osmotic lysis
100
What is teichoic acid?
Where is it found?
What does it do?
**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
101
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
102
What is included in a cell envelope?
Minimum: Cell membrane and cell wall
Gram (+): Cell membrane and cell wall
Gram (-): Outer and inner membrane, thin cell wall, periplasm
103
Which genetic exchange mechanism utilizes a sex pilus?
Conjugation
104
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
105
Where is LPS found?
Outer leaftlet of outer membrane of gram negative bacteria
106
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
107
What are the characteristics of a strict aerobe?
* Grows with oxygen
* Does not grow without oxygen (cannot ferment)
* Contains superoxide dismutase and catalase
108
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
109
What are pili/fimbraie composed of?
Composed mainly of subunits of pilin
110
What are oxidase positive bacteria?
Bacteria containing cytochrome C
111
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
112
What causes bacteria to be serum resistant?
Long O-side chains
But can still be recognized by specific antibodies and then cleared
113
Which enzymes are responsible for proper crosslinking of NAG/NAM chains?
Penicillin-binding proteins (PBPs)
114
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
115
What are pili/fimbraie?
Long thin filamentous structures found in the surface of bacterial cell
116
What is the minimum inhibitory concentration (MIC)?
The least amount of antibiotic that prevents bacterial **growth**
No new colonies can form
117
What is Lipid A?
Where is it found?
What does it do?
**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
118
What are "naturally competent bacteria?"
Bacteria that are natrually able to take up DNA in transformation
119
What virulence determinants of *Shigella* spp are encoded by plasmids?
Type III secretion system that facilitates the invasion of epithelial cells
120
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
121
Describe the exponential phase of bacterial growth
Bacterial are rapidly dividing via binary fission
They are increasing in number very quickly
122
Why would you want to use sheep-blood agar?
To distinquish heolytic from non-hemolytic bacteria
123
What are the functions of capsules?
* Prevent dessication
* Plauy a role in virulence of some pathogens by preventing engulfment by phagocytes
124
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
125
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)
126
What is the main biosynthetic activity of growing bacterial cells?
Protein synthesis
| (cytoplasm loaded with ribosomes)
127
How fast is bacterial metabolism compared with human metabolism?
Bacterial metabolism is 10-100x faster than human metabolism
128
What is the function/utility of an O antigenic chain?
Antigenic and allows serotyping
129
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
130
What virulence determinants of *Escherichia coli* are encoded by plasmids?
Enterotoxins (LT and ST)
131
Why are Mycoplasma spp. poorly visualized by Gram staining?
They lack cell walls
132
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
133
What kinds of bacteria (in general) would **not** contain superoxide dismutase and catalase?
Obligate anaerobes
134
What causes tumbling of bacteria?
Clockwise rotation of flagella
135
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
136
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)
137
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
138
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
139
What are cocci?
Spherical
140
What are the three components of LPS?
* Lipid A
* Core polysaccharide
* O antigen (or O-specific side chain)
141
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
142
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
143
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
144
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...
* Hyptension
* Circulatory collapse
* Disseminated intravascular coagulation
* Multi-organ failure
* Death
145
Describe the characteristics of septic shock
**HCDMD**
* Hypotension
* Circulatory collapse
* Diseminated intravascular coagulation
* Multi-organ failure
* Death
146
What virulence determinants of *Clostridium tetani* are encoded by plasmids?
Tetanus toxin
147
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)
148
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)
149
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
150
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
151
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
152
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
