Lecture 8 - Intervention and Prevention Flashcards
What are the three types of vaccine?
- The pathogen killed
- Live attenuated strain (disabled)
- Antigenic components of pathogen
What is the disadvantage of using the killed pathogen?
Killing can change antigenic structure of proteins
How can you make a live attenuated strain?
Use a mutant that cannot survive long with out a certain product you give it while it is in the lab
What kind of proteins are used as vaccines?
- Only ones that are expressed during host infection cycle
- Must be antigenic
- Immune system has to see them (outer membrane proteins are good for this)
- Inactivated toxins (toxoids)
What carbohydrates can be used as vaccines?
- O-antigen (LPS) on gr- bacteria
- capsule
What structure does the LPS take? (from membrane)
Lipid A tail
Core
O antigen repeat
What does the O antigen repeat consist of?
Sugars - galactose, mannose, aboquose
Repeated 20-50 times
How can you assess drugs?
Live imaging by adding lux gene into bacteria and use Xenogen machine to detect light
Whats the problem with using carbohydrates as vaccine?
They are normally not very antigenic and must find a way to couple it to a protein
How many serogroups does Neisseria meningitidis have and what is the different between them?
five
carbohydrate identity
What is the vaccine for four of the serogroups of Neisseria m?
Capsular polysaccharide
Why is the vaccine for serogroup B of Neisseria different to the rest?
It’s capsule has polysialic acid which is like human cells.
This is poorly immunogenic and risks autoimmunity
What is the vaccine for Serogroup B of Neisseria what is it made from?
4CMenB 1 adhesin H binding protein Heparin binding protein 2 additional antigens
What is reverse vaccinology?
Start with the pathogen and use genomics to look for cell surface markers (signal sequence - hydrophobic stretch) and see what the immune response may recognise
What steps are involved in reverse vaccinology (particularly 4CMenB)
- 2000 proteins identified to be surface
- purified protein tested for potential to induce bactericidal antibodies
- purified protein used to immunise mice
- antibody response analysed by ELISA
- prioritised based on ability to induce protection against a diverse collection of strains (5)
What is an example of vaccination that has not gone to market and why could it be?
FimH vaccine
FimH has a lot of antigenic variation so may not be effective
How has M. tubercolosis’ antibiotic resistance changed?
From 2000 to 2011 it’s resitance to any first line drug increased by 84%
Multidrug resitance increased by 189% since 2000.
What are the 3 main targets of current antibiotics?
Cell wall synthesis
Ribosome
DNA gyrase/topoisomerase
What is DNA gyrase?
Helps in DNA supercoiling where the helicase separates it
Which antibiotics target the ribosome and what part of it?
Chloramphenicol - 50S
Tetracycline - 30S
What do beta lactams inhibit and what are two examples of them?
Inhibit transpeptidation
Ampicillin and pennicillin
What do glycopeptides inhibit and what is an example of one?
Inhibit transglycosylation
Vancomycin
How do glycopeptides work?
bind to cell wall subunit and prevent incorporation into peptidoglycan
How do beta-lactams work?
inhibit enzymes (PBPs) required for cross linking of chains which is the last step of cell wall synthesis
What are metabolite analogs and give 2 examples,
Antibiotics that inhibit synthesis of nucleic acid precursors
Sulfonamides
Trimethoprim
How do sulfonamides work?
Competitive inhibitor with PABA for enzyme to make folic acid
Humans must take up folic acid so is not toxic
How does trimethoprim work?
It is a structural analog of folic acid so inhibits enzyme.
Has a higher affinity for bacterial enzyme than human so not toxic
How do you test bacteria for resistance to concentrations of antibiotic?
An E-test strip has dilutions of drugs down it
MIC (minimum inhibitory concentration) is measured on lowest concentration of no growth
What are the 4 mechanisms of antibiotic resistance?
Modifying antibiotic target
Limiting antibiotic in cell (reduced penetration or increased efflux)
enzymatic inactivation
Bypass pathway (another way to make product)
How have bacteria generated resistance to beta-lactams? (2 ways)
Produce beta-lactamase to degrade Alter PBP (pencillin binding protein) so beta-lactam can not interact with it
How have bacteria generated resistance to Vancomycin?
Altered target (peptidoglycan) D-ala-A-ala changed to D-ala-D-lactate
What are two ways a strain acquires resistance? (genetic)
Horizontal gene transfer
Mutations
What is a mechanism for multidrug resistance?
An efflux pump upregulated
Why did Brockhurst (2012) use genomics to look at multidrug resistance in Salmonella?
In Africa many strains of S. gastroenteritis were starting to look like invasive S. typhi
What did Brockhurst (2012) show had happened to confer multidrug resistance in this strain of Salmonella?
Transposon lead to clonal replacement and expansion of pSLT virulence plasmid.
Gene deletion from gastroenteritis and acquisition of chloramphenicol resistance.
What is a feature of persisters?
Large heterogeneity (lots of different ways to become resistant)
What disease can be caused by antibiotics and how?
Clostridium difficile causing diarrhoea.
Antibiotics kill off healthy microbiome so C. difficile grows and produces toxin
What some other ideas for stopping disease?
Affect virulence process - block or inactivate toxins
Block development of pathogenic phenotype (eg quorum sensing)
What did Hentzner and Giskov find in 2003?
Furanone treated P. aeruginosa biofilms are less tolerant to tobramycin.
However in 2013 found 3/8 strains not affected
What are the stages of clinical trials?
Lab studies
Human safety - 10s of people
Expanded safety - 100s
Efficacy and safety - 1000s
