Bacterial Cell Structure

Question 1

What bacteria use the capsule for adherence?

Answer 1

Streptococcus mutans

Streptococcus salivarius

Staphylococcus epidermidis

Question 2

Which bacteria use capsule for immune system avoidance?

Answer 2

Bacillus anthracis

Neisseria meningitidis

Streptococcus pneumoniae

Question 3

What is a biofilm?

Answer 3

bacteria can form multicellular communities in which the entire community surrounded by big capsule; whole thing is called biofilm.

typically individual cells find surface and attach; under right conditions bacteria begin to produce capsule material and become encapsulated in large amounts of protein or DNA; large colonies all encapsulated in a matrix.
some bacteria will prod. enzymes to degrade matrix and allow bacterium to escape

Question 4

What might explain a situation when drug therapy fails or disease recurrence in the absence of apparent reinfections?

Answer 4

Biofilms

If they do not form a biofilm, bacteria are exposed to host defenses and environmental stresses, and attach poorly to surfaces.

Cell-cell communication via pheromones causes matrix synthesis.

Eventually, the matrix surrounds the entire community, which is collectively called a biofilm.

Biofilm characteristics: Adherence, controlled release of bacteria from the biofilm, immune system avoidance, alteration of bacterial growth kinetics, activation of bacterial stress and defense responses, alteration of drug pharmacokinetics. Many if not most bacteria can form biofilms.

Question 5

What are some common sites of biofilms in the human host?

Answer 5

gum disease
catheter contamination
implant contamination (can establish on clinical device or surgically implanted materials)

Biofilms can be sites of continuous (and possibly cryptic) dissemination of pathogenic bacteria and, therefore, reinfection.

(infections of catheter or device can result in re-infection; travel to other place in body where wouldn’t suspect infection)

Question 6

What are some common sites of biofilms in the human host?

Answer 6

gum disease
catheter contamination
implant contamination

Biofilms can be sites of continuous (and possibly cryptic) dissemination of pathogenic bacteria and, therefore, reinfection.

Question 7

Urinary catheter infections and CF pneumonia are both examples of…

Answer 7

human infections involving biofilms

Question 8

A drug’s ADME has been altered unexpectedly when introduced to host? What might cause this?

Answer 8

biofilms

Biofilm characteristics: Adherence, controlled release of bacteria from the biofilm, immune system avoidance, alteration of bacterial growth kinetics, activation of bacterial stress and defense responses, alteration of drug pharmacokinetics. Many if not most bacteria can form biofilms

Question 9

Are there physiological (rather than just pathological) examples of biofilms?

Answer 9

The microbiota are likely present in biofilms throughout the GI tract

Question 10

Where are biofilms most prominent in humans?

Answer 10

In human, biofilms are most prominent in the proximal colon and appendix. Biofilm levels decline toward the distal colon.

Question 11

What might account for the differences in biofilm presence in proximal colon/appendix vs distal colon?

Answer 11

Possibly, the interactions between biofilms and IgA differ between the proximal and distal colon. If some feature of IgA allows it to better bind bacteria in the distal colon, this could inhibit bacterial deposition at that site.

bacteria in association w mucosa and w IgA …some present at mucosa, some bound to IgA and prevented from binding from lumen bc bound to IgA; so you see here that many more are present in the lumen as a result of binding to IgA

so diff abilities of IgA to bind to bacteria and prevent them from attaching to mucosa is controlling the density of bacteria along the GI tract… this is one host mechanism that can bolster density of bacteria along GI tract

Question 12

What is the clinical relevance of the flagellum?

Answer 12

Flagellum-dependent swimming can be required for disease.

The immunological response to flagella can be a diagnostic tool (serotyping).

Flagella can be organelles of attachment.

Question 13

Of what function is the HAP2 cap at tip of flagella?

Answer 13

diversity of ways they can cause disease!

helical propeller; propeller extends outwards many microns. tip of flagellum has cap bolted on tip…

ETEC flagella replace the cap with an adhesin.

ETEC attach to host cells via the flagella

Question 14

What is another word for pili?

Answer 14

fimbrae

Question 15

What is the role of pili?

Answer 15

Pili (fimbrae). Have adhesive molecules at their tips, which promote specific interactions with host cells. Some bacteria can switch these tip molecules to facilitate adherence to diverse host tissues.

distinct; thinner and smaller than flagellum, at tips they contain adhesins which are specific for binding to other molecules

Question 16

What is the difference between gram negative and gram positive?

Answer 16

gram neg. have outer membrane of LPS and thinner peptidoglycan layer

gram positive have no outer membrane; have thicker peptidoglycan exterior; teichoic acid and lipteichoic acid (specialized molecules imp. for pathogenesis and diagnosis)

Question 17

What is the difference between gram negative and gram positive?

Answer 17

gram neg. have outer membrane of LPS and thinner peptidoglycan layer

gram positive have no outer membrane; have thicker peptidoglycan exterior; teichoic acid and lipteichoic acid

Question 18

Classify the following as gram +/-

Teichoic acid
LPS
Leipoteichoic acid

Answer 18

Teichoic acid +
Lipteichoic acid +
LPS -

Question 19

What does the envelope consist of?

Answer 19

The envelope consists of an inner membrane, a cell wall (the peptidoglycan)
and, in the case of Gram - envelopes, an outer membrane.

Question 20

What does the inner membrane consist of; what is its purpose?

Answer 20

The inner membrane is common to both Gram - and Gram + envelopes. It
consists of a lipid bilayer comprising phospholipids and proteins.

The inner membrane serves to selectively transport molecules in and out of the
cell, and serves as the site of many biochemical reactions.

Question 21

What are some examples of peptidoglycan being toxic?

Answer 21

Gonococci, B. pertusis (endotoxin), S. aureus (activates complement, causing inflammation).

Question 22

How is peptidoglycan degraded?

Answer 22

Degraded by lysozyme (in tears, saliva).

Question 23

What component of bacterial structure gives the cell its shape?

Answer 23

The cell wall or peptidoglycan is found in both types of envelope and is unique to
bacteria. It is composed of sugar chains with attached short peptides. The chains
are cross-linked together by bonds between the peptides. The result is a strong meshwork that surrounds the cell and gives it shape.

Question 24

Outer leaflet called LPS on gram negative bacteria; the outer membrane is relatively impermeable compared to inner membrane. What structure will allow for transport through?

Answer 24

porins

barrel like structure through which molecules can pass and thus avoid extreme hydrophobicity of outer membrane

Question 25

How does outer membrane differ from inner?

Answer 25

The outer membrane is unique to the Gram - envelope. Like the inner
membrane, it is a bilipid layer, but the outer leaflet has lipopolysaccharide (LPS) molecules instead of phospholipids.

The outer membrane is a strong barrier to most molecules that might enter the cell. Porins are structures unique to the outer membrane that allow passive entry and exit of small molecules.

Question 26

Explain the major components and purpose of LPS.

Answer 26

LPS has three major components:

A lipid portion (lipid A)

a polysaccharide portion (core polysaccharide)

O antigen polysaccharide side chain.

Lipid A makes LPS highly toxic resulting in endotoxic shock, and the O antigen polysaccharide side chain, being the major surface antigen of Gram- cells, provides an important antigenic marker.

Question 27

Explain the major components and purpose of LPS.

Answer 27

LPS has three major components: A
lipid portion (lipid A), a
polysaccharide portion (core polysaccharide) and the O antigen polysaccharide side chain. Lipid A makes LPS highly toxic resulting
in endotoxic shock, and the O antigen polysaccharide side chain,
being the major surface antigen of Gram- cells, provides an important
antigenic marker.

Question 28

What is the clinical significance of multidrug efflux system?

Answer 28

Clinically significant multidrug resistance is usually associated with a relatively impermeable outer membrane. Strongly selected for in hospitals

(trans-envelope channel; not a porin)

Question 29

What is found within the cell interior?

Answer 29

ribosomes nucleoid plasmids

Question 30

Describe the bacterial chromosome. How does it differ from eukaryotes?

Answer 30

The nucleoid is the bacterial chromosome. It is not enclosed in a
membrane, unlike the chromosomes of the eukaryotes.

Often, additional genetic information is encoded on pieces of DNA that are separate from
and autonomous of the chromosome called plasmids.

Question 31

Describe the bacterial chromosome.

Answer 31

The nucleoid is the bacterial chromosome. It is not enclosed in a
membrane, unlike the chromosomes of the eukaryotes.

Often, additional genetic information is encoded on pieces of DNA that are separate from
and autonomous of the chromosome called plasmids.

Question 32

Describe a mechanism by which bacteria can confer resistance to antibiotics using an intracellular structure.

Answer 32

Frequently, plasmids encode determinants of virulence such as
antibiotic resistance factors and the molecules that comprise the pilus.

They can be easily transmitted between cells, and their spread is
facilitated by over use of antibiotics.

Question 33

How does sporulation differ from vegetative (or normal) cell growth?

Answer 33

normally bacteria grow by vegetated cell growth; septum forms in middle and you get identical daughter cells and one reenters cycle

sporulation- asymmetric… now you get compartment formed in cell and variety of things lead to hardening of that compartment; and you have a spore which is metabolically resistant to any type of stress; surround cell lyses and releases spore in environment

Question 34

What types of conditions will activate the sporulation process?

Answer 34

sporulation- asymmetric… now you get compartment formed in cell and variety of things lead to hardening of that compartment; and you have a spore which is metabolically resistant to any type of stress;

surround cell lyses and releases spore in environment… can convert back to growing cell in process called germination when nutrient is present in environment; (so starvation typically activates this process and the reappearance of food activates germination process;

cell sheds its protective armor; expands metabolism and will expand cell volume and now this cell is vegetative cell

Question 35

Describe the role of spore formation in gastrointestinal disease caused by Clostridium difficile.

Answer 35

• spores ingested
• spores transit the GI tract
• spores germinate in the small intestine
• vegetative cells colonize the large intesting, and produce toxin, causing disease

ingestion of spores which go into GI tract and germinate in upper portion in small intestine and convert into veg. cells which colonize the colon and implant in colonic mucosa and produce toxins… have veg. growth and toxin production in the mucosa.

Question 36

How does spore formation in C diff and C perfringens differ?

Answer 36

make toxins during sporulation (C. perfringens) and others only after germination (C. difficile, B. anthracis)

In some cases, the production of a spore by a stressed cell will directly
result in disease (as in Clostridium perfringens) and in other cases, the spores must convert back to a normal growing cell (germination) before they cause disease symptoms (as in Bacillus anthracis).

Question 37

How does B. anthracis use spores? When does it produce toxin?

Answer 37

B. anthracis (causing anthrax) also uses the spore to enter the host, and produces toxin only after/upon germination (like C. diff)

Question 38

How does B. anthracis use spores? When does it produce toxin?

Answer 38

B. anthracis (causing anthrax) also uses the spore to enter the host, and produces toxin only upon germination (like C. diff)

Question 39

What would be the implications for a cell type that only possessed an inner membrane? Give an example.

Answer 39

Mycoplasma- A very simple cell type that has only an inner membrane, of special composition. Because it lacks the peptidoglycan, it can have a variety of shapes.

mycoplsama varying from cell to cell, some spherical, some divits, some have stalk like extensions. morphological variation bc these bacteria lack peptidoglycan (key function of peptidoglycan det. cell shape)

this organism lacks peptidoglycan; has just inner membrane so as a result its structure varies from cell to cell; so these bacteria are insensitive to anti-peptidoglycan drugs like lysozyme…they can also pass through filters that normally exclude bacteria; so they can be potent sources of contamination where liquids are being kept clean via filters

Question 40

What would be the implications for a cell type that only possessed an inner membrane? Give an example.

Answer 40

Mycoplasma- A very simple cell type that has only an inner membrane, of special composition. Because it lacks the peptidoglycan, it can have a variety of shapes.

mycoplsama varying from cell to cell, some spherical, some divits, some have stalk like extensions. morphological variation bc these bacteria lack peptidoglycan (key function of peptidoglycan det. cell shape)

Question 41

Describe the mycobacterial envelope. Is this bacteria gram +/-? Describe how it may evade the immune system.

Answer 41

Sugars on the mycobacterial cell surface are thought to mimic host sugars and, as a result, engage macrophage receptors that facilitate uptake and sequestration into a safe intracellular compartment. These sugars may also stimulate anti-inflammatory responses on macrophage and dendritic cells.

surface glycolipids
MAPc (mycolic acid, arabinogalactan and peptidoglycan) then lipid bilyaer

this is just example of gram positive envelope that has specialized molecules on its surface that are not found in majority of cases

Question 42

Describe the mycobacterial envelope.

Answer 42

Sugars on the mycobacterial cell surface are thought to mimic host sugars and, as a result, engage macrophage receptors that facilitate uptake and sequestration into a safe intracellular compartment. These sugars may also stimulate anti-inflammatory responses on macrophage and dendritic cells.

surface glycolipids
MAPc (mycolic acid, arabinogalactan and peptidoglycan) then lipid bilyaer

this is just example of gram positive envelope that has specialized molecules on its surface that are not found in majority of cases