PH1123 bacteria Flashcards
what is virulence ?
the degree or intensity of pathogenicity of an organism
what does the upper respiratory tract include ?
the sinuses, nasal passages, pharynx, and larynx.
where does the lower respiratory tract include ?
in the lungs or below the voice box.
what is a virulence factor ?
a microbial (bacteria, fungi, protozoa…) product that contributes to virulence
What is a common component in bacterial cell walls ?
peptidoglycan (murrain or glycopeptide)
= glycan + peptide bridges
What is glycan ?
glycan =N- acetyl muramic acid (NAM) and N - acetyl glucosamine (NAG).
what does the NAM of glycan attach to ?
- To each NAM is attached a tetrapeptide consisting of the amino acids l - alanine, d - alanine, d - glutamic acid and either lysine or diaminopimelic acid (DAP).
- This glycan tetrapeptide repeat unit is cross - linked to adjacent glycan chains, either through a direct peptide linkage or a peptide interbridge
what are the two main groups of bacteria and how do we differentiate between them ?
Gram - positive and Gram - negative, on the basis of a differential staining technique called the Gram stain. Essentially, the Gram stain consists of treating a film of bacteria dried on a microscope slide with a solution of crystal violet, followed by a solution of iodine; these are then washed with an alcohol solution. In Gram - negative organisms the cells lose the crystal violet – iodine complex and are rendered colourless, whereas Gram - positive cells retain the dye.
Gram negative – rendered colourless but when counter stained red
Gram positive – retain colour and when counter stained purple
Why does gram positive bacteria retain the stain better than gram negative
The cell wall is thicker
Gram negative bacteria is much thinner and can be inhibited by a capsule
Why does gram positive bacteria retain the stain better than gram negative
In Gram-positive, the low lipid concentration is important for the retention of the complex
iodine-crystal violet: the cells remain blue.
The cell wall is thicker
Gram negative bacteria is much thinner and can be inhibited by a capsule
what does the cell envelope usually consist of? (3)
- outer cell wall or peptidoglycan (gram +ve and -ve)
- cytoplasmic or plasma membrane (gram +ve and -ve)
- outer membrane (gram -ve only)
what is the chemical property of peptidoglycan? (2)
- chemically inert
- composed of sub-units found nowhere else in nature
what can the cell envelope of gram -ve bacteria produce?
- they can produce symptoms of disease (endotoxins)
where is the site of action of the most effective chemotheraputic antibiotics?
- cell wall peptidoglycan
what does the cell wall prevent?
- prevents osmotic rupture of the protoplast in dilute solutions
what is the protoplast?
- when no cell wall remains
what is the structure of peptidoglycan? (3)
- N-acetyl-muramic acid and N-acetyl glucosamine that alternate to form a high molecular weight polymer
- a chain of several amino acids is attached to each of the N-acetyl-muramic acid molecules
- multilayered network around the organism
what are the matrix materials found within the open meshwork? (3)
- chiefly polysaccharides
- immunology active substances which determine the antigenic specificity of certain organisms
- techoic acids which are highly acidic substances present only in the cell wall of gram +ve bacteria
what is the peptidoglycan cell wall a target for? (5)
- beta-lactams
- glycopeptides
- bacitracin
- D-cycloserine
- fosfomycin
what do the drugs that target the peptidoglycan cell wall do to it?
- they inhibit cell wall synthesis
what do beta-lactams and glycopeptides do to the cell wall? (2)
- the different beta- lactams target different enzymes (penicilin-binding enzymes)
- beta-lactams and glycopeptides interfere with the late stage of cell wall maturation (cross-linking)
what are examples of extended spectrum penicillins? (4)
- amoxicillin
- ampicillin
- carbenicillin
- piperacillin
what bacteria do extended spectrum penicillins target?
- gram negative bacteria
what is the purpose of the plasma membrane?
effective permeability barrier of the cell regulating the inflow and outflow of metabolites to and from the protoplast
what can pass through the plasma membrane? (2)
- it is semi permeable
- low molecular weight materials can penetrate to the inside of the cell
what are efflux proteins? (2)
- present in the cytoplasmic membrane (aka vomit pumps)
- gets rid of things the cells doesnt like (removal from cytoplasm
what does the outer membrane of gram -ve bacteria contain?
lipopolysaccharides
- one layer of phospholipids
how are bacterial ribosomes characterised?
- by their sedimentation properties when centrifuged at very high speeds in untracentrifuge
what size are bacteria ribosomes?
70S
what are the components of bacterial ribosomes? (2)
- ribosomal protein
- ribosomal RNA (rRNA)
what do plasmids play a role in in bacteria?
- transfer of genetic material between bacteria
what happens in binary fission?
- cell elongates and dna is replicated
- cell wall and plasma membrane begin to divide
- cross-wall forms completely around divided dna
- cell separates
what are the phases in bacterial growth? (4)
- lag phase
- log (exponential) phase
- stationary phase
- death phase
what is the lag phase? (4)
- population remains temporarily unchanged
- bacterial cell may be growing in volume or mass
- synthesizing enzymes, protein, rna etc.
what happens to the metabolic activity in the lag phase?
- increasing in metabolic activity
what is the stationary phase? (4)
- population growth is limited
- exhaustion of available nutrients
- accumulation of inhibitory metabolites or end products
- exhaustion of space
what is a chemostat? (2)
- bioreactor to which fresh medium is continuously added
- culture liquid is continuously removed to keep the culture volume constant
what do the chemostat do?
- control growth rate
- optimise population
at which phase are bacteria in whilst in a chemostat and why?
- always in the log (exponential) phase
- optimise growth of microorganisms
what are the chemical requirements for growth? (6)
- oxygen, sulphur and phosphorous
- energy source
- source of electrons
- nitrogen source
- carbon source
- ions
what are the optimum temperatures for the storage of pharmaceutical products? (3)
- deep freeze (-20); total parenteral nutrition and raw materials
- 8 to 12; reconstituted syrups and multi-dose eye drops
- 80; for WFI (regrowth of gram -ve and release of toxins)
what is the optimum pH for growth?
- 6.5 to 7.5
what is the viable count?
- referred as to the number of colony-forming units (cfu) rather than as number of bacteria
what might alter bacterial growth and the formation of colonies? (2)
- type of medium used
- conditions of incubation
when is the MPN (most probable number) method used?
- reserved for the enumeration of bacteria in situations where no other method is available
how do you do the MPN method of enumeration? (4)
- prepare a series of at least 3 subsequent tenfold dilutions of product
- from each level of dilution three aliquots of 1g or 1ml are used to inoculate
- three tubes with 9ml to 10ml of a suitable liquid medium
- incubate all tubes for five days at 30 to 35 degrees and record each level of dilution the number of tubes showing microbial growth
what are the different functions of pili? (6)
- adherence; to one another and foreign cells
- antigenic differences
- gene transfer; by conjugation
- attachment sites; for bacteriophages
- chemotaxis; may keep bacteria near the surface of liquids or where oxygen is most available
- virulence; enhances the ability of bacteria to cause disease
what is the role of the bacterial capsule? (3)
- virulence; prevents phagocytosis from macrophages
- protection ; contains water which protects bacteria against desiccation
- protection; exclude bacterial viruses and most hydrophobic toxic materials such as detergents
what are endospores?
- unique structure formed within the vegetative cell
what is the process of spore formulation? (2)
- sporulation
- it is not a reproductive process
what is the main role of spores?
- enable the survival of the bacterium (genetic material) during harsh conditions (lack of food, water, chemical and physical stress)
when are spores released?
- following the death of the bacteria
what is sterilization?
- a process that kill all micro-organisms including spores
what are the structure of bacterial endospores? (5)
- exosporium (hydrophobic) which sticks to surfaces
- spore coat
- cortex
- spore wall and membrane
- spore core (DNA and ribosomes)
what is germination?
- process by which a spore reverts into a (vegetative) bacterium
when can germination occur?
- when environmental conditions for bacterial growth is supported (food, water etc.)
- forced to occur using germinants
what happens during germination?
- outgrowing cell becomes susceptible to chemical and physical processes
what is stage one of germination? (4)
- cation is released
- Ca2+ - DPA release
- partial core hydration
- some loss of resistance
what is stage two of germination? (5)
- cortex hydrolysis
- further core hydration
- core expansion
- more loss of resistance
- loss of dormancy
what is the outgrowth stage of germination? (4)
- metabolism
- SASP degradation
- macromolecules synthesis
- escape from spore coats
Describe the process of bacterial germination?
Spore is activated.
Stage 1- partial core hydration and loss of resistance due to cation release.
Stage 2- cortex hydrolysis, further core hydration, loss of resistance and dormancy.
Stage 3- outgrowth, metabolism and escape from spore coat.
what is the result for a gram negative bacteria in gram staining and why? (3)
- the high lipid concentration found in the outer layer of the cell wall is dissolved
- this facilitates the release of the iodine-crystal violet complex
- the cell is left colourless
what antibiotics is the plasma membrane a target for? (4)
- polymyxins, colistin and daptomycin
- polymyxin B and colistin affects membrane permeability
- daptomycin affects membrane function
- antimicrobial peptides
what antibiotic inhibit the synthesis of nucleic acids? (4)
- quinolones (DNA gyrase which inhibits DNA replication and transcription)
- rifampicin (RNA polymerasewhich affects transcription)
- sulphonamides and trimethoprim (folic acid synthesis)
- nitrofurantoin and mitrodinazole (DNA interactions)
what is pili? (2)
- very fine, hair-lie surface filaments
- smaller than flagella (0.5μm)
what species of bacteria would you find (endo)spores? (2)
- Bacillus spp
- Clostridium spp
what is sterility assurance?
- ensure a process has killed all vegetative bacteria and spores
what is rickettsia? (4)
- intracellular parasites
- aerobic. small gram -ve bacteria
- non-motile, non-spore forming bacter
- highly pleomorphic bacteria
what is the rickettsia species carried by? (3)
- ticks
- lice
- fleas
what is the microbial structure of rickettsia? (4)
- peptidoglycan
- lipopolysaccharide
- no flagella or attachment proteins (ie no motility)
- surrounded by a loosely adherent slime layer
how does rickettsia enter the host cells? (3)
- attaches to the surface
- promotes their own entry by phagocytosis
- escape the phagosomes to the host cell cytoplasm
what are the prevention methods for rickettsia? (3)
- vaccination (limited due to a possible change with DNA vaccines)
- reduce exposure to tick-borne diseases
- appropriate sanitary hygiene
what type of bacteria is chlamydia?
- obligate intracellular bacteria
what does chlamydia lack?
- they lack the metabolic pathway to produce their own high-energy phosphate compounds
what is the microbial structure of chlamydia? (4)
- internal and external membrane similar to gram -ve bacteria
- no peptidoglycan layer
- lipopolysaccharide
- no flagella and non piliated
what are prevention methods of chlamydia? (3)
- safe sex
- not sharing sex toys
- appropriate sanitary hygiene
what is the structure of mycobacteria? (4)
- polypeptides and free lipids
- mycolate layer and arabinogalactan
- peptidoglycan
- cytoplasmic membrane
what is the cell wall of mycobacteria?
- highly hydrophobic
- basic layer; peptidoglycan linked to arabinogalactan wall esterified to mycolic acid structure
who are the people most at risk of developing tuberculosis? (5)
- close contact to infectious case
- those who have lived in places where TB is still common
- people who experience chronic poor health through lifestyle factors e.g. homelessness, alcoholism and drug abuse
- those who have weakened immune system by HIV etc.
- young children and very elderly people more susceptible
how long does a course of anti-TB drugs last and why? (2)
- at least 6 months
- the medicine is most effective against bacilli that are ‘awake’ and growing.
why are anti-TB drugs always prescribed in combination?
- to reduce risk of TB bacilli becoming resistant to one or more of them
how can drug resistance be developed to anti-TB medication? (2)
- if the medication isnt taken correctly
- eg wrong dose, intermittently, too short of a time etc.
what are the first line drug for TB? (4)
- isoniazid
- rifampicin
- pyrazinamide
- ethambutol
what is the classification of eukaryotic cells?
- a group of closely related organisms, which reproduce sexually to produce a fertile offspring
what is classification of bacteria based on? (3)
- based on the nucleotide sequence of rRNA
- present in all living cells as ribosomes are required to build protein
- rRNA sequence forms the basis for phylogeny (study of evolution of organisms)
what are the simple traditional methods of bacteria identification? (4)
- cultivation; growth requirement
- cultivation; selective agar
- biochemical profiling
- serological testing
what are the complex newer methods of bacteria identification? (2)
- nucleic acid techniques
- MALDI_TOFF
what is cultivation?
- bacteria grown in lab
- allows morphological characterisation
- spore production and flagella
- staining characteristics (eg gram staining)
- colony morphology
can just the cultivation method identify a bacteria and why?
- no as morphology alone can’t distinguish bacteria
- ne rod looks much like another
what does vogel johnson agar indicate?
- indicates S aureus
