Bacteria Flashcards
What are flagella used for?
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
What is a biofilm?
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
What are fimbriae?
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
What is a bacterial cell wall made from ?
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
Describe the surface structure of a gram positive bacteria
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
Describe the surface structure of a gram negative bacteria?
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
What are acid fast bacteria?
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
Describe the structure of acid fast bacteria
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)
Describe the structure of spirochaetes
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
Name the six targets for antibiotics?
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
Describe the six mechanisms of antibiotic resistance
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
Define intrinsic and acquired antibiotic resistance and how they differ from one another
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).
What are here three mechanisms by which antibiotic resistance can be transferred between bacteria?
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.
Define what is meant by virulence and what three categories virulence factors can be grouped into?
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).
Define a transposon?
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
Define a plasmid?
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
What is a pathogenicity island?
Regions of bacterial genome that encode virulence factors
Found in pathogenic bacteria but not in bacteria of the same species which are not pathogenic
Define lysogeny?
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
How are bacterial toxins defined?
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
What are endospores?
Spores of bacteria
Formed inside bacteria and when released are highly infectious and resistant to the environment
Example tetanus
Name the various methods of bacterial attachment within host cells
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
What is quorum sensing?
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.
What are siderophores?
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
Name the various methods of bacterial spread within the host?
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
What is bacteraemia?
The presence of bacteria in the blood
What is the mononuclear phagocyte system?
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.
List two airborne bacterial infections
Diphtheria and whooping cough
Summarise the main points of diphtheria?
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
Summarise the main points of pertussis/whooping cough
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
List three arthropod-borne infections?
Bubonic plague
Lyme disease
Typhus
Summarise the main points of the bubonic plague
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
Summarise the main points of Lyme disease
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
Summarise the main points of typhus
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
List two direct contact bacterial infections
Staphylococcus and chlamydia
Summarise the main points of a staphylococcal infection
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
Summarise the main points of chlamydial infections
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
List three food or waterborne infections
Salmonella
travellers diarrhoea
staphylococcal food poisoning
Define a probiotic?
Probiotics are defined as Live microorganisms which, when administered in adequate amounts, confer a health benet on the host.
