Bacteria Flashcards
Describe the morphology of different bacteria.
Coccus (cocci) = 0.1-7m, round. Can be single, chains, pairs, 4s and 8s, and clusters.
Bacillus (bacilli) = 2-500m, sausage shaped. Such as, E.coli = 1-1.5m wide and 2-6m long. Can be single, pairs, chains, curved, helical, club-shaped and filamentous.
Coccobacillus – rugby ball shape
Pleomorphic
Describe bacterial cell composition.
Plasma membrane, nuclear region DNA in cytoplasm (no nuclear bound DNA), ribosome, mesosome, capsule, flagella, nucleoid, inclusion bodies.
What is the protoplast?
Protoplast = plasma membrane + cytoplasm + contents
What are the activities of bacteria cell membranes?
Hopanoids, proteins and carbohydrates:
- Boundary
- Semi-permeable
- Uptake/export
- Metabolism
What is the function of bacterial cell inclusion bodies?
Inclusion bodies (granules) – the energy and food storage granules containing glycogen, sulphur and polyphosphate (volutin, metachromatic).
What are the 2 different types of bacteria?
Gram positive
Gram negative
Describe the structure of gram positive bacteria.
Outside the plasma membrane there is a thick layer of peptidoglycan, which is essentially a sieve. These are held together by teichoic acids. Sieves then separate and are bound to the plasma membrane by the lipoteichoic acids.
Describe the structure of peptidoglycan.
A polymer made of N-acetylglucosamine and N-acetylmuramic acid. Permeable due to structure.
Describe the structure of gram negative bacterial cells.
Has single sieve/layer of peptidoglycan, which gives the cell its shape and structure. Has a second outer membrane outside. And outside this, there are lipopolysaccharides, polysaccharide chains that float like seaweed in the environment, which help to retain water.
Distinguish the properties of gram negative and gram positive bacterial cells due to their structures.
Gram negatives found often in the damper areas of the body. Gram positives are very good at surviving desiccation. Because they do not have the peptidoglycan, gram negatives are very good at retaining water, unlike gram positive, which are then found in places like the gut, as they are not good at retaining water.
What is the structure and function of gram negative cells’ lipopolysaccharide layer?
Helps to retain water and the polysaccharide chain also helps to prevent things like complement attack complexes getting close to the bacterial outer membrane and killing it.
It is called the O antigen sometimes and can be shed from the bacteria and into the circulation, activating immune response and a factor that activates a fever in response to sepsis. But is normally attached to the bacteria with a lipid core and defends the bacterium.
What are the possible external structures of bacterial cells?
Glycocalyx – capsules and slime layers
Fimbria – have pili 3-10nm in diameter and a few (micro)m in length
Flagellum – 20nm in diameter and 15-20(micro)m in length
What are bacterial endospores?
Dormant – metabolically inactive
Resistant – tough walls
What is the function of bacterial endospores?
Shrink up and desiccate and become very inactive and resistant as a survival mechanism. Makes them more resistant to infection or autoclaving. Can survive in the environment for hundred of years.
How are bacteria distinguished on a genus or species level?
- Gram positive or gram negative
- Cell size, shape and arrangement
- Presence or absence of capsules, spores, storage granules and flagella
How are bacteria distinguished on a species or strain level?
Serotyping: capsular Ag, Fimbrial Ag, Flagellar Ag, Cell wall Ag
Describe the process of carrying out a gram stain.
- Heat fixed smear
- Crystal violet – purple stain that gets in through the sieve like peptidoglycan gram positive and through the double membranes of the gram negatives.
- Iodine – gets to both cells and causes crystal violet to crystallise.
- Alcohol – dehydrates the peptidoglycan on the outside. Peptidoglycan sieves will shrink the cell and not allow the crystals out. In gram negative, the rei sonly 1 layer of peptidoglycan so the alcohol washes the crystals out the cell.
- Dilute fuchsin – will get into gram negatives and will stain them pink.
Why is studying bacterial multiplication and growth important?
Ability to grow in a laboratory for identification:
- Cell size, shape and colour
- Cell size, shape and arrangement
- Effect on medium – colour change and haemolysis
Biochemical tests for identification
Describe the appearance of haemolytic bacteria and staphylococcus aureus on agar.
Top left is haemolytic, as it is breaking down blood cells. Top right is staphylococcus aureus as its bright yellow and haemolytic, it is found on the skin and is gram positive.
How can bacteria be grouped by their nutritional requirements?
Simple needs – such as E.coli, for glucose, phosphate, sulphate and ammonium ions
Complex needs – fastidious. Growth factors for amino acids, fatty acids, vitamins, nucleotides. Such as haemophilus species – haemin and/or NAD
Unknown needs – such as Rickettsia species, intracellular parasites
What are the further nutritional requirements of bacteria?
pH – neutral and slightly alkaline
Temperature – mammals = 25-37˚C, cold blooded hosts = 25˚C, birds = 40˚C. Listeria species have growth at 4 ˚C
CO2 – from catabolism or environment – 0.03%
O2:
How can oxygen requirement vary between bacteria?
- Strictly/obligate aerobic
- Microaerophilic (smaller amounts of oxygen) – such as campylobacter species
- Facultatively anaerobic (can grow without oxygen but can with)– such as Enterobacteriaceae
- Strictly anaerobic – such as clostridium species
Why does oxygen kill microaerobic bacteria?
Produce hydrogen peroxide or superoxide radical. These will bleach and destroy the insides of cells that make them if they are not mopped up or destroyed by catalase or superoxide dismutase. Anaerobic cells produce lost of these so they can be destroyed before damage to the cell.
Campylobacter for example doesn’t produce a large amount of superoxide dismutase so cannot cope with the large amount of oxygen being metabolised.
How is energy acquired by aerobic bacteria?
Aerobic respiration
Detox system
How is energy acquired by microaerophilic bacteria?
Aerobic respiration
Detox system
How is energy acquired by facultative bacteria?
Aerobic respiration
Anaerobic respiration
Fermentation
Detox system
How is energy acquired by anaerobic bacteria?
Anaerobic respiration
Fermentation
What are the barriers of bacterial nutrient uptake?
Outer membrane
Plasma membrane
Not capsule or peptidoglycan
What are the mechanisms of nutrient uptake?
- Passive diffusion – concentration gradient
- Facilitated diffusion – concentration gradient and permeases
- Active transport – receptors, permeases and energetically expensive.
Why is iron uptake so important for bacteria?
Iron uptake – siderophores with Fe3+ binding proteins. Receptors for siderophores. Iron is the biggest limiting factor for bacterial growth and so bacteria need to take up iron to multiply.
What are faecal transplants?
Some bacteria cannot be grown in the gut so must be excreted in the faeces and stomach tubed, mixed with water, into the stomach. This is sued when there is overgrowth and so production of hydrogen, ethanol and propanol in the gut.
Name and describe the types of media that bacteria can be grown in.
- Nutritional simple
- Enriched (non-specific) – such as blood agar
- Selective – inhibition/suppression of other bacteria that may be present and/or specific enrichment of wanted bacteria. Such as MacConkeys bile lactose agar.
- Differential – visual differentiation of bacterial colonies. Such as blood agar and MacConkeys bile lactose agar
Describe MacConkeys bile lactose agar.
MacConkeys bile lactose agar can grow bacteria from the gut and it contains bile. Bile is what stops all other bacteria, except those that can survive bile, from growing. Has pH indicator and lactose, and so identifies bacteria that can ferment lactose, turning indicator pink. Those that can’t ferment, decarboxylase the amino acids and turn alkaline.
Describe the phases of bacterial growth.
Have a lag phase in order to adapt to environment and then exponential growth phase. Stationary phase where there is a limiting factor and then death.
How can growth rate differ between bacteria?
E.coli has a very quick exponential growth rate of 20 mins, so goes from 1 bacterium to 5xa0^21 in 24 hours. Mycobacterium bovis (TB) has a slow exponential growth rate of 24 hours, so would go from 1 to 2 bacteria in 24 hours.
What is the importance of knowing about bacterial growth?
- Bacterial identification
- Clinical infection control
- Vaccine production – production of different antigens at different stages of growth curve
Where do bacteria live?
Saprophytes – free living
Parasites – in or on animals. Probably the most successful.
What are the different relationships parasitic bacteria can have with the host?
Symbiotic – bacteria and host gain
Commensal – bacterial gain but no harm
Pathogenic – bacteria gain and cause harm. Not too much harm, as it cannot kill the host it survives off.
- Obligate pathogens
- Facultative pathogens
What are facultative pathogenic bacteria?
Facultative pathogens are opportunistic – normally harmless saprophytes/commensals but with altered host conditions, some have the facility to be pathogenic given this opportunity.
What are 2 possible sources of infection?
- Things that are obligate pathogens causes an exogenous infection as it comes from the environment and into the host. TB found in badgers and soil and causes disease in cattle.
- Animals own commensal flora re endogenous infections.
How is a new body site an opportunity for facultative pathogens?
For example, E.coli in the gut is harmless but gut surgery can release it into the peritoneal cavity, causing peritonitis. For example, staphylococcus aureus carried in the nose is harmless but can abscess if introduced through the skin or septicaemia if introduced into the blood system.
How is altered body site an opportunity for facultative pathogens?
Temperature, pH and commensal flora. Such as antibiotics for clostridium difficile caused antibiotic induced colitis in horses and humans. Clostridium perfringens can cause acute enterotoxaemia due to rapid nutritional change.
How is reduced defences an opportunity for facultative pathogens?
Due to extremes of age, malnutrition, immunosuppressive drugs, primary infection, stress (transport, crowding, temperature changes, wounding in trauma or parturition, fatigue, feed changes such as weaning). Shipping fever for example.
Describe shipping fever.
- Transporting calves
- Stress
- Hormonal effects (cortisol)
- Reduced immune defences
- Primary respiratory viral infection
- Damaged alveolar macrophages
- Susceptibility to secondary bacterial infections
- Pneumonia
What is needed in farm/practice and in the lab in order for diagnosis, treatment, control and prevention?
On the farm and in surgery, we need:
- Clinical specimen
- Clinical information
- Environmental information
In the lab, we need:
- To isolate bacteria
- Knowledge of relevant site commensals and facilitative pathogens
Define pathogenicity.
The ability of a bacterial species to cause disease.
Define virulence and virulence determinants.
Virulence – the degree of pathogenicity associated with a particular bacterial strain.
Virulence determinants – structural features and/or biochemical features causing bacteria to overcome or evade host defences.
How do bacteria invade the body?
- Multiply at skin or mucous membrane surface.
- Superficial invasion of skin or mucous membrane epithelium.
- Deeper invasion of body via blood or lymphatic systems.
How do bacteria evade complement attack?
- Hide from complement by hiding from trigger surface proteins an covers itself in host proteins, fibrin, to form a capsule.
- Triggers the cascade by avoids effects – steric/spatial hinderance of formation of the membrane attack complex
- Mutate and avoid antibody recognition
How else do bacteria hide from the body’s immune system?
- Hold on tight to epithelium to prevent uptake by macrophages and digestion
- Production of chemicals to repel phagocytes or inhibit their chemotaxis and prevent phagocyte activity (leukostatins) and kill phagocytes (leukocidins).
Give the stages of bacteria-host interaction.
- Contact host
- Enter host
- Invade host
- Survival in host
- Grow and multiply
- Spread to new hosts
How does the host control bacterial growth?
- Restriction of iron
- Bile in the intestine – ref MacConkey agar
- Oxygenation and the lysosome
What do bacteria need to do in order to multiply?
- Look like the host – fibrin
- Don’t look like yourself – mutate
- Hide inside the host – invade
- Rely on those around you – safety in numbers
Describe clusters of bacteria and what they form.
Cluster of bacteria: ones inside are protected and are protected so nutrients spread between bacteria and form quite complex ecosystems.
Describe the development of biofilm.
- Bacteria attach to the surface using fimbria.
- Make polysaccharides and capsular material.
- Other bacteria and yeast come and join.
- Grow big 3D structures with different bacteria in different places – anaerobic bacteria in the centre and aerobic at the outside.
- Bacteria can detach or large bits of biofilm can detach.
Where can biofilms form in different parts of the body?
- Staphylococcus/streptococcus attach, grow and block the heart valves
- Shedding streamers from mature biofilm causes distal blockages
- Dental plaque, oral surgery, bacteraemia and transient bacteraemia
- Catheters
- Joint replacements: produce a lot of acids so can have bone erosion
Describe biofilms at joint replacement sites.
- Early flora – skin bacteria
- Late flora – anaerobes
- Biofilm grows and costs implant
- Coating can prevent initial colonisation
How do bacteria develop resistance to disinfectants?
Bacteria produce polysaccharides. These are the glue, but also retard access of therapeutics/disinfectants to the bacteria. Some die on the outside so that more may live.
How do bacteria develop antibiotic resistance?
Beta lactamase production by some bacteria protects all other bacteria. These could be commensals but never looked for in commensals.
How can the balance between bacteria be altered?
- Prevent colonisation – stop bacteria getting into the blood and change catheters.
- Alter the bacteria present
- Can we alter the balance of bacteria in a mature intestine?
- Probiotics cannot get in unless a gap is made for them
What can be used to predict the site of a bacterial population?
Bacterial population or the likelihood of finding as bacterium at a site can be predicted by knowing metabolism.
How can bacteria enter at the skin?
Active penetration – enzymes such as brucella
Passive penetration – wounds, hair follicles and sweat glands
Via arthropod vectors – blood ducking insects
How can bacteria enter at all mucous membranes?
Mucinase (neurominidase) – a lot of bacteria have mucinase enzymes to digest the mucous at membranes.
Motility/chemotaxis – then need to be able to get to surface of cells so need to be motile and need chemotaxis (move up/down concentration gradients of nutrients) to move towards cell.
Iron-binding siderophores – need to then multiply, major factor that limits bacterial growth is iron, bacteria take up iron, as they need iron to multiply, and so multiply at the surface.
Adhesins – need to be able to adhere.
- Non-specific – hydrophilic and hydrophobic
- Specific – lipoteichoic acid, capsular material, fimbrial proteins
What is teeth plaque?
Bacterial capsular material
How can bacterial enter specific mucous membranes?
Respiratory tract (ciliated cells up to the larynx) – ciliostatic products (stop cilial function) and ciliotoxic products (kill cilia)
Urinary tract (urea) – urease production, which destroys urea: urea > ammonia and carbon dioxide
How do bacteria enter host cells via ‘sneaky invasion’?
- Adhesins attach to target cell
- Stimulate their own endocytosis. Inject proetins in host cell, causing host cell to pull them inside the cell.
- Intracellular survival - they then survive in a vacuole in the host cell and uptake nutrnets of the cell and hide from the immune system.
What is intracellular persistence of bacteria?
- Evades the immune system
- Provides nutrients
- Protected replication
- Persistence
- Epithelial cells and macrophages are major targets
- Entry by invasion, by endocytosis, or phagocytosis
- Endocytosis is more efficient than waiting to be phagocytosed – much longer incubation period, like TB
How does initial infection in epithelial cells spread to other parts of the body?
- Adhesins attach to target cell
- Stimulate endocytosis into an endosome (vesicle in the host cell that they live in)
- Host cell produces lysosomes to fuse with the endosome and kill bacteria
- Intracellular survival
- a) Bacterial enzyme, phospholipase, to escape endosome
b) bacterial surface components inserted into endosome membrane to block lysosome fusion
c) bacterial survival in endolysosome - Eventually transcytosis occurs and bacteria invade more deeply.
What consists of the bacterial genome?
Chromosomal DNA
Plasmid DNA
Transposons
What are the properties of bacterial chromosomal DNA?
- Principal DNA, encodes all key functions
- Nuclear regions
- 1 chromosome usually
- 1 copy
- Circular/double stranded
- Supercoiled
What are the properties of bacterial non-chromosomal DNA?
- Transmissible factors – transfer small parts of chromosomal DNA to other bacteria
- Resistance
What are plasmids and their function?
Extra-chromosomal circular DNA.
- Independent replication
- Usually auxiliary genes, but addition mechanisms exist – where if the bacterium loses the plasmid, it dies.
What are the different types of plasmids?
R = resistance
V = virulence
Col = colicin
F = fertility
D = degenerative
What are transposons?
‘Jumping genes’ or insertion sequences. The most primitive form of self-replicating organism. Different transposons have different inverted repeats.
Describe the action of transposons.
- Enzymes that insert themselves into the DNA and then cut themselves out again as bacteria replicated.
- Sticks to host DNA and interrupt things.
- When they cut themselves out, they take some host DNA with the, and so can end up shifting DNA between species.
What is the evolutionary purpose of transposons?
Evolutionarily, there is a small possibility that transposons transfer useful DNA that allows for bacterial adaptation.
What does bacterial genetic variation affect?
- Virulence
- Resistance to host defences
- Resistance to treatments
Describe the different genetic variations within the resident genome.
- Multiple genes
- Silent gene fragments
- Gene/promotor inversion
- Transposon activity
- Spontaneous (uninduced) mutations
What is recombination?
- Associated with free DNA and uptake of free DNA – transformation
- Associated with bacteriophage DNA (phage conversion), viruses that affect bacteria – generalised and specialised transduction
- Associated with cell-to-cell contact – conjugation
Describe the process of transformation.
- Cell death and lysis
- Plasmids and chromosomal fragments released as free DNA
- Uptake by other bacteria
- Plasmids act alone and start functioning in the new bacteria – this is how antibiotic resistance is spread throughout a population.
- Chromosomal fragments integrate into chromosome. Sometimes tick to genome and cuts out an essential portion causing cell death.
What is phage conversion?
A minority of bacterial virulence determinants, such as some toxins and surface antigens, are actually encoded by bacteriophage DNA and not host DNA. The phenotypic expression of such phage products during lysogeny is termed phage conversion.
Describe the lytic bacterial lifecycle.
- Phage DNA enters host cell
- Host mechanisms shut down under phage control
- Phage DNA replication and protein capsid production
- Progeny phage assembled
- Host cell lyses and new phage particles released
Describe the lysogenic lifecycle.
- Phage DNA enters host cell
- Site specific integration of phage DNA into host chromosome or a plasmid
- Silent prophage replicates with host DNA
- On stimulus prophage excision occurs followed by phage entering lytic life cycle. Transfer of genes between bacteria.
What is transduction?
Associated with the replicative life cycle – lytic and lysogenic phage.
Prophage excision/cutting error – associated with lysogenic phage only.
What are packaging errors?
Packaging error – phage picks up host DNA mistake. Rare events.
- Phage DNA packaged = specialised transduction
- Host DNA only = generalised transduction
What is conjugation?
- Plasmids are very common and this is how they are transferred between bacteria.
- They have no sexual preference.
- Promiscuous males: plasmid have wide host range and can cross the species and genus barriers.
- Makes tube that whips around outside the cell and attaches to another bacteria and this is how the DNA is transferred between the 2.
