lecture 8) antibiotics Flashcards
describe bacteriostatic modes of action
total and viable cell count plateau out on addition of antibiotic
doesnt kill any cells
describe bacteriocidal mode of action
kills viable cells
total cells plateau on addition of antibiotics; cells are still there but they are unable to divide as they are dead
describe bacteriolytic mode of action
total and viable cell counts completely deplete as dead cells diasppear
give an example of a bacteriostatic antibiotic
fluoroquinolines
why are fluoroquinolines an example of bacteriostatic antibiotic?
they inhibit protein synthesis
why can fluoroquinolines be considered a bacteriocidal antibiotic too?
they can damage DNA
why is there a motivation to discover more essential cell processes?
antibiotics normally target essential cellular processes therefore by finding more essential cell processes they could be potential targets for new antibiotics to combat the issue of antibiotic resistance
what do bacteriostatic antibiotics target?
cellular processes eg protein synthesis
what do bacteriolytic antibiotics target?
cell synthesis eg ABs that cause lysis forming pores in cell membrane/wall
what are macrolides?
they are a class of antibiotic
what is the binding site of a macrolide on a bacterial cell?
a large ribosomal subunit in the upper part of the nascent peptide
what is the large ribosomal subunit in the upper nascent peptide responsible for?
it is an exit tunnel for proteins to pass through
what is the mode of action of a macrolide?
binds to the large ribosomal subunit in the upper part of the nascent peptide, blocking the exit tunnel for proteins therefore proteins wont be able to leave the ribosome therefore translation is inhibited
growth arrest
what is the primary target of fluoroquinolines?
DNA gyrase
what is another name for DNA gyrase?
topoisomerase II
what is the function of DNA gyrase?
involved in the binding of DNA
also fragments DNA which isnt ideal
what is the secondary target of fluoroquinolines?
topiosomerase IV
describe the structure of topiosomerase II
heterotetramer
name the subunits in topiosomerase II
2 ParC subunits
2 ParE subunits
the protein that encodes for ParC subunits is homologous to what subunit of DNA gyrase?
subunit A
the protein that encodes for ParE subunits is homologous to what subunit in DNA gyrase?
subunit B
what is topiosomerase responsible for in DNA?
the decantation and relaxation of DNA
assists with segregation of replicating chromosomes/plasmids in bacteria
if topiosomerase was inhibited, what would be the outcome in bacteria?
decantation and relaxation of DNA and segregation of replication chromosomes/plasmids would be inhibited
describe the fluoroquinoline mode of action on bacteria
they inhibit DNA gyrase aka topiosomerase II that is involved in the relaxation and decantation of DNA and the segregation of chromosomes and plasmids
these processes wont happen if DNA gyrase is inhibited
how do fluoroquinolines get into gram positive and gram negative bacteria?
passively diffuse into gram positives
via outer membrane porins in gram negatives
what are the newer fluoroquinolines like?
broader spectrum
better activity against gram positives
describe cephalosporins
broad spectrum
semi synthetic
Beta lactam
where do cephalosporins come from?
derived from mould cephalosporins
what are cephalosporins chemically related to?
penicillins
what type of cells do penicillins work on?
actively dividing cells
what is the mode of action of penicilins?
in cell wall synthesis carbohydrate linkages break
penicillins prevent the peptide bonds from linking
what is the consequence of penicillins mode of action?
preventing the linkage of the peptide bonds means the cell wall will be weaker
bacterial cells will die due to osmotic shock
describe the mode of action of beta lactam antibiotics
interfere with cell wall synthesis
what type of antibiotics are beta lactams?
bactiolytic
what are carbapenamases?
aggressive beta lactams
what type of bacteria are resistant to carbapenamase? how are they resistant?
enterobacteria eg e coli
enzymatic breakdown of carbapenamase
what is the risk of using one antibiotic a lot?
lots of use = more likelihood of resistance
what do novel antibiotics aim to target and why?
broad range of targets in bacterial pathogens so they can be used for more than one condition
why would it be a bad idea to target essential cellular processes?
we know that bacteria will develop a resistance mechanism for these bacteria as they want to live so will find a way to prevent this antibiotic from attacking them
name the 5 stages of infection
adsorption to specific receptor
DNA injection
redirection of host metabolism to phage DNA replication and phage DNA protein synthesis
assembly and packaging of phage particles
bacterial cell lysis and phage progeny release
describe the process of adsorption to receptor in the first stage of infection
phage attachment is specific
describe the two types of receptors for adsorption in the first stage of infection
surface components (some bacteria have generated enzymes that degrade the EPS therefore covering the receptor) sex pillus for male specific F+ phages
how does the lytic phage inject its DNA into the host?
after degrading peptidoglycan and forming pores in the cell wall, lytic DNA is transferred into cell
phage DNA hijacks hosts machinery
what is responsible for bacterial cell lysis and phage progeny release?
phage protein inhibitors responsible for host cell lysis and virion burst to environment
give some examples of phage protein inhibitors
lysins
holins
mureins
name a technique used to analyse bacteriophages killing cells
plaque assays
what is the difference between lysis and lysogeny?
lysogeny is the integration of the bacteriophage nucleic acid into the host’s bacterial genome
lysis is the packaging and release of the phage
how are lysis and lysongey interchanged?
genetic switch
give 2 advantages of lytic phages
specific
cheap
give 2 disadvantages of lytic phages
narrow spetrum
bacterial resistance
describe what would be the case when using individual phages
narrow spectrum
higher pretreatment costs (pretesting and phage bank)
1 phage isnt as good of a antimicrobial
describe a less complex cocktail of phages
potential requirement for development of a diverse range of individual cocktails (cocktail bank)
not as narrow spectrum
to decrease resistance a diverse range needs to b developed
describe more complex cocktails
greater ease of use
potentially greater complexity in manufacture and outcomes
more broad spectrum
describe typical commercial antibiotics
they have a greater impact on normal microbiota
more unknown physiologies during their development
describe the balance needed in antibiotics
need it to be not too low so as its too narrow spectrum and therefore not killing enough of the bacterial strains and it being too broad and therefore killing some of the natural microbiota
what is the collateral damage if antibiotics?
dysbiosis ie disturbing the gut microbiome
describe an alternative phage strategy
use the phage to deliver a protein that interferes with an essential process rendering the bacteria more susceptible to antibiotics
what is the SOS response?
a programme elicited from bacteria in response to detection of DNA damage
how could you inhibit the SOS response to make the bacteria more susceptible to antibiotics?
engineer bacteriophage to inject DNA into host cell
engineer a protein called Xa3 which will be turned on during SOS response
Xa3 will inhibted SOS response making bacteria more susceptible to antibiotics
what is the CRISPR associated system (Cas)?
a defence strategy employed by bacteria
what can be targetted when phage deliver Cas to the bacteria?
essential proteins on plasmid/DNA
toxin antitoxin system which would prevent persister cell formation
phage could also be used to mediate effects on bacteria
what is the baseline level of expression of toxin antitoxin systems?
degradation of the toxin mediated by going into growth arrest
give a general overview of antivirulence strategies
inhibit specific mechanisms that promote infection and that are essential to persistence
what would antivirulence strategies offer in terms of mutations?
reduced selection pressure for drug-resistant mutations
what would virulence specific therapeutics avoid?
dysbiosis as they are more specific treatments that antibiotics preventing disturbance to the gut microbiota
what is the most common cause of HCAIs and UTIs?
UPEC (uropathogenic escherichia coli)
how does UPEC invade the host?
invades with pili on the surface that facilitates interaction with host
what are IBCs?
intracellular bacterial communities
how do IBCs cause infection?
replicate, burst, spread
what type of cells are included in IBCs?
facet cells
in what manner do type I and II pilli binds to europlakin on facet cells?
carbohydrte dependent manner
lectin binding domain
what is a pilicide?
agent that removes pili on UPEC deeming it unable to cause infection
why is quorum sensing important for virulence?
signal communication between cells to activate the transcription of genes to code for more virulent cells
one cell wont cause an infection but multiple will therefore QS makes more virulent cells to cause disease
what is used in the identification of inhibitors?
reporter strains
name the autoinducer in QS of gram positive bacteria
AIP (autoinducing peptide)
name the signalling molecule in QS of gram negative bacteria
AHL (N- aceyl homoserine lactones)
how would you prevent QS in gram positive bacteria?
inhibit the production of AIP deeming it unable to cause infection
how would you prevent QS in gram negative bacteria?
block the AHL receptor making it unable to cause infection
why might QS not be direct enough?
in order to prevent infection the pathogen and its communities must be alive not just the AV factor as there can be cross talk between the cells
why type of toxin does cholera release?
AB toxin (exotoxin)
what is the name of the protein that causes the toxic effects of cholera?
ToxT
what is virstatin?
a small molecule that inhibits ToxT transcription therefore preventing infection
what is responsible for the expression of ToxT?
transcription factor in V. cholerae
what is the possible collateral damage when inhibiting the ToxT gene in V. cholerae?
the transcription factor could encode for other genes
what is an alternative to targetting the transcription factor of ToxT in V. cholerae?
receptor mimics - make something that looks like the receptor but has a higher affinity for the toxin than the actual receptor so the toxin binds to it preventing infection
what was discovered to inhibit secretion systems that didnt lack potency and a clear mode of action?
ATPase YscN which is essential for T3SS in Y. pestis
what secretion systems in gram negative bacteria inject effect molecules into host cell and cause disease?
type 3 and 4
give an example of 2 bacteria that use type 3/4 secretion systems to inject their effector molecules into the host cell
salmonella and heliobacter pylori
what are T3SS related to?
flagella (how bacteria move)
what are T4SS related to?
conjugation pillus (how bacteria mate)
how would you inhibit the activity of T3 and 4SS in flagella and conjugation pillus?
ATP dependent processes therefore if you prevent the ATPase no ATP will be produced so the secretion systems wont be able to work and wont be able to cause infection
this is tricky because the ATPase may be generating ATP for other processes
what is a synergistic drug?
when 2 or more drugs are used and they work together to produce a response that would be more potent if they were used in isolation
what is the impact of synergistic drugs on subpopulations?
suppresses drug resistant subpopulations more than a single drug therapies
what is the consequence of suppressing drug resistant subpopulations?
eliminates competitors of the drug resistant strains so they will grow more rapidly therefore increasing the population density
