Bacteria

Question 0

What are flagella used for?

Answer 0

Movement in liquid or semiliquid environments
Used to attach to other cells
The number of flagellum can be used as a diagnostic technique for identifying bacterium

Question 1

What is a biofilm?

Answer 1

A colony of bacteria which grows on a surface.
Their properties are different to those bacteria grown in culture which has implications in the treatment and prevention

The upper layer of the biofilm is called a capsid, protein layer/polysaccharide or slime layer or glycocalyx and it protects the bacteria beneath
A capsid prevents the bacteria from being phagocytosed as it is too slippery
Provides protection from detergents and from drying out

Question 2

What are fimbriae?

Answer 2

Found on gram negative bacteria
Fine hairlike structures
Used in adhesion
Also known as pili
A sex pillus is used for reproduction via conjugation
Fimbriae are distinguished by their morphology, receptor specificity and antigenic composition
2 main types depending on whether they are inhibited by the sugar d-mannose

Question 3

What is a bacterial cell wall made from ?

Answer 3

Peptidoglycan
Composed of two complex monosaccharides - NAM and NAG which alternate to form a polysaccharide chain
Several chains lie in parallel to each other and are attached via cross links
Cross linking between NAM and NAG gives great strength to the wall
The amino acids making NAM are unique to bacteria as the are in d form as opposed to l form

Question 4

Describe the surface structure of a gram positive bacteria

Answer 4

Can have up to 40 layers of peptidoglycan in the cell wall which are cross linked to each other
Peptidoglycan can make up as much as 90% dry cell mass
Also contains teichoic acid and lipoteichoic acid
Teichoic acid attaches to NAM
lipoteichoic acid attaches to the plasma membrane
Their function is unclear but hey are possibly stabilising
They project from the surface and are the cells main surface antigens
The bacterial cell is negatively charged due to these acids

The periplasmic space contains enzymes, metabolites and other substances being transferred in and out of the cell
It is highly viscous and is found between the plasma membrane and the cell wall

Question 5

Describe the surface structure of a gram negative bacteria?

Answer 5

Only 1-2 layers of peptidoglycan
Cell is surrounded with an outer membrane which contains porins which allow the passage of molecules
Attached to the peptidoglycan layer by lipoproteins
Different composition to the inner membrane it contains lipopolysaccharides (LPS) as opposed to phospholipids

Question 6

What are acid fast bacteria?

Answer 6

Some bacteria can not be gram stained
They need to be heated along with the stain
Once stained they cannot be unstained with acid
They are therefore called acid fast

Example mycobacterium which cause leprosy and treponemes which cause syphilis

Question 7

Describe the structure of acid fast bacteria

Answer 7

Gram positive bacteria as they only one membrane which is surrounded by a peptidoglycan layer

The peptidoglycan layer is covalently linked to a layer of arabinogalactan which is a polymer formed of arabinose and galactose monomers
Some of the arabinose molecules are also attached to mycolic acid which makes the bacteria waxy

This covalently bonded complex of peptidoglycan-arabinogalactan-mycolic acid can also non-covalently link with Lipo-arabinomannan (LAM)

Question 8

Describe the structure of spirochaetes

Answer 8

Long rod shape bacteria which are wound into spirals
Gram negative bacteria as they have an outer membrane called a sheath which sits outside the thin peptidoglycan layer
They are able to move through viscous fluid and on solid surfaces
Movement is achieved due to flagella which do not project from the cell itself, it is wound around the cell and allow it to move with a corkscrew motion

Question 9

Name the six targets for antibiotics?

Answer 9

Bacterial wall synthesis

Bacterial protein synthesis at the ribosome

Bacterial RNA polymerase

Folic acid biosynthesis

Damage to bacterial membranes

Bacterial DNA processing, by binding to topoisomerase enzymes

Question 10

Describe the six mechanisms of antibiotic resistance

Answer 10

Reduced antibiotic uptake - loss of porin channels prevent the uptake of some antibiotics

Increased antibiotic efflux - pumps which remove antibiotics from the cell

Enzymes that destroy or alter antibiotics making them useless

Over production of antibiotic target molecules which the swamp he antibiotics and make their efforts diminished

Metabolic bypass - where he target is an enzyme and the bacteria produces a new enzyme therefore bypassing he target molecules which is effected by the antibiotics

Alteration of the target - same sad above but the target molecule is not involved in metabolism

Question 11

Define intrinsic and acquired antibiotic resistance and how they differ from one another

Answer 11

Intrinsic resistance is normal for that genus or species (e.g. the bacterium lacks the drug target or the drug cannot gain access to the target).

Acquired resistance arises by mutation of intrinsic genes (in the chromosomal DNA) or acquisition of a resistance gene (e.g. horizontal transfer on a
plasmid or transposon).

Question 12

What are here three mechanisms by which antibiotic resistance can be transferred between bacteria?

Answer 12

Conjugation: cell to cell contact resulting in direct transfer of plasmid DNA.

Transfection: transfer of DNA via a bacterial-specic virus (bacteriophage).

Transformation: uptake of DNA released from dead or dying bacteria.

Question 13

Define what is meant by virulence and what three categories virulence factors can be grouped into?

Answer 13

Virulence refers to the ease at which an organism can cause damage to host tissues or cause disease

The three categories for virulence factors are:

Substances that aid bacterial nutrition (acting on the bacterium)

Those that facilitate spread (acting on the host)

Those that mediate attachment (acting on both host and bacterium).

Question 14

Define a transposon?

Answer 14

Mobile genetic element
Short genetic sequence flanked by inverted repeats which allow the transposon to enter or leave DNA sequences by recombination
If a gene is between the inverted repeats then it can travel between cells
The transposon can also leave behind a copy of itself

Question 15

Define a plasmid?

Answer 15

Self replicating double stranded DNA which usually carry genes
Can initiate its own replication
May be able to integrate into the genome of bacteria and therefore transfer the genes that it is carrying - recombination
Such genes could code for antibiotic resistance

Question 16

What is a pathogenicity island?

Answer 16

Regions of bacterial genome that encode virulence factors

Found in pathogenic bacteria but not in bacteria of the same species which are not pathogenic

Question 17

Define lysogeny?

Answer 17

Lysogeny occurs whine a bacteriophage does not replicate and move to another bacterium but instead integrates into the bacterium genome
Known as lysogenic infection
Infected bacteria are known as lysogens
If the bacteriophage carries genes which encode virulence factors the lysogen may become pathogenic

Question 18

How are bacterial toxins defined?

Answer 18

They are either endotoxins or exotoxins

Exotoxins are proteins and unstable at high temperatures
Can have a variety of effect on the host cell including - some by binding to cell surface receptors and initiating transmembrane signalling - other damage the host cell membrane by either creating pores or disrupting the membrane - others target intracellular components. These are called A-B models which are composed of different subunits which are responsible for A- releasing the toxic effects on the cells and B - attaching to the host cell to allow entry of A

Endotoxins - are components of the outer cell membrane of the bacterial cell which are released suing cell division and lysis
They are composed of lipopolysaccharides which have a lipid a component which stimulates the release of cytokines from macrophages thereby inducing an inflammatory response. The polysaccharide component activates the compliment system (immune response) resulting in fever and shock

Question 19

What are endospores?

Answer 19

Spores of bacteria
Formed inside bacteria and when released are highly infectious and resistant to the environment
Example tetanus

Question 20

Name the various methods of bacterial attachment within host cells

Answer 20

Some express adhesins which are polysaccharide molecules which bind to host cell receptors/glycoproteins which differ from cell to cell

Fimbriae are used for attachment and the types of fimbriae expressed can be altered so as to alow attachment to different hosts

Haemagglutinins are surface glycoproteins which can bind to red blood cells and epithelium of the respiratory tract

Flagella can be used as adhesins

Fibronectin is a surface protein on the host cell which can act as a receptor for bacterial attachment
Often found in mucosal tissue. Thought to be defensive mechanism as it’s attachment results in it removal from the body

Question 21

What is quorum sensing?

Answer 21

Bacteria use quorum sensing to establish the numbers of their population. They sense the amount of signalling molecules which they all release and delay their spread until numbers are high enough so they can overwhelm the immune response.

Question 22

What are siderophores?

Answer 22

Siderophores are iron binding proteins which have a higher binding affinity for iron in comparison to the cells of the host therefore acquiring iron which is an essential nutrient for the bacteria
Some bacteria also have receptors for siderophores allowing them to bind other bacterial siderophores therefore having a selective advantage by obtaining other bacterial iron

Question 23

Name the various methods of bacterial spread within the host?

Answer 23

Spread via biofilms - movement through fluids on the epithelium
Spread via the skin - itching and movement of the fingers/hands which moves the bacterium from place to place
Spread via cells - bacterium can enter cells via phagocytosis and infect cells of the immune system as they are working to eradicate the bacteria
Spread via invasion - bacteria can produce a variety of degrading enzymes which can break through the extracellularly matrix and connective tissue
Spread via transport system - bacteria can travel in the blood and lymph system where they can be transported all over the body. Bacterial products can also be spread via these methods, such as exotoxins
Spread via the nervous system - unusual to travel via the nervous system but the leprosy bacterium travels via Schwann cells of the peripheral nervous system

Question 24

What is bacteraemia?

Answer 24

The presence of bacteria in the blood

Question 25

What is the mononuclear phagocyte system?

Answer 25

The mononuclear phagocyte system is a collection of phagocytic macrophages, found in the blood and tissues, that trap and eliminate particles
foreign to the body.

Question 26

List two airborne bacterial infections

Answer 26

Diphtheria and whooping cough

Question 27

Summarise the main points of diphtheria?

Answer 27

Airborne bacterial infection
Starts as a sore throat
Affects the respiratory tract
Secretes a toxin which damages the respiratory epithelium causing a pseudomembrane to form
Can cause asphyxiation and heart/kidney failure due to the toxin
A-B model structure
Treated with penicillin and erythromycin which prevent peptidoglycan synthesis and causes cell death respectively
Children are most susceptible
People can carry the disease after they have been treated and become carriers

Question 28

Summarise the main points of pertussis/whooping cough

Answer 28

Bacterial disease of the respiratory tract
Transmitted by droplet infection
Causes excessive mucus production
Death of ciliated epithelial cells preventing the removal of the bacteria and mucous
Various toxins produced
Binds to the respiratory epithelium by filamentous Haemagglutinin (FHA)
Antibiotics are relatively ineffective if not treated early but can reduce the effects of the symptoms

Question 29

List three arthropod-borne infections?

Answer 29

Bubonic plague
Lyme disease
Typhus

Question 30

Summarise the main points of the bubonic plague

Answer 30

The pathogen responsible is a rodent pathogen
Occurred during the Black Death due to e fleas feeding on rats which subsequently bit humans
Can also be passed from human to human via the respiratory tract meaning the it does not stay a zoonose
Causes massive swelling of the lymph nodes near the bite site
The pathogen binds to the host cell and introduces plasmids encoding bacterial toxins into the cell cytoplasm - encoded by the yop virulon
These bacterial proteins prevent phagocytosis by the immune system of the host
Symptoms are high fever, vascular damage and haemorrhage, black skin
Bacteria can be treated with tetracycline

Question 31

Summarise the main points of Lyme disease

Answer 31

Pathogen of deer and mice, transferred to humans via ticks which have previously bites infected animals.
Redness occurs around bite and flu like symptoms occur
Months later a secondary stage can cause inflammation of the heart and joints
A third stage can occur years later and in the form of a neurodegenerative disease similar to Alzheimer’s

Question 32

Summarise the main points of typhus

Answer 32

Linked to unsanitary conditions and is spread to humans via the scratching of faeces contaminated skin
Causes very high fever, rash, headaches and chills
The bacterium is the closest relative to mitochondria
Can be treated by tetracycline and doxycycline
There is a vaccine which provides lifetime immunity

Question 33

List two direct contact bacterial infections

Answer 33

Staphylococcus and chlamydia

Question 34

Summarise the main points of a staphylococcal infection

Answer 34

The most common cause of skin infections in humans
Infections usually involve the production of pus
There are pathogenic and non pathogenic forms of this bacterium. Pathogenic form produce an enzyme called coagulase which is involved in fibrin clot formation. The bacteria can form a fibrin coat which enables them to hide from the immune response
Also produce catalase which breaks down hydrogen peroxide into water. This prevents the degradation of the bacteria in phagosomes.
Also produces protein A which is a surface protein binds to host antibodies.
Releases two exotoxins - toxin A and toxin B which have a pathogenic effect by causing the skin to sheer off leading to scalded skin syndrome
Usually treated with beta lactam antibiotics such as methicillin but the bacteria are growing resistant -MRSA

Question 35

Summarise the main points of chlamydial infections

Answer 35

Three species of this bacteria are pathogenic to humans
Resemble viruses as they rely on the host for ATP however they are able to synthesise their own macromolecules
Can cause eye and genital infections
Enters the cell via endocytosis and forms a reticulate body which goes on to divide and produce progeny.

Treated with tetracycline antibiotics

Question 36

List three food or waterborne infections

Answer 36

Salmonella
travellers diarrhoea
staphylococcal food poisoning

Question 37

Define a probiotic?

Answer 37

Probiotics are defined as Live microorganisms which, when administered in adequate amounts, confer a health benet on the host.