persistent and chronic infections Flashcards
if antibiotics were 100% effective then all infections would
cleared
bacterial populations contain
peristers
persister cells
phenotypic variants that constitute approx 1% of cells in stationary phase and biofilm culture. They are multi drug tolerant and largely responsible for the inability of antibiotics to completely eradicate infections
when were persister cells first recognised
1940
presence of persists cells
may be important in the aetiology of many recalcitrant infectious diseases
when antibiotic are given
regular cells will decreases, until just persisters and resistant matts are left resistant mutants will continue to reproduce, whilst persister levels will never change
when antibiotics are removed
persister cells are able to regrow
why aren’t persistrcells resistant mutants
they won’t grow in the presence of antibiotics
persister cells are not
genetically different
formation of persister rapidly increases during
mid-exponential phase m several species, but the mechanism that underlies this remains a puzzle
since persister cells are genetically identical to susceptible bacteria
they are phenotypic variants of the wild type
how are persister cell isolated
by applying a lethal dose of antibiotics to a growing cult,.
after removal of antibiotics persisters can regrow and give rise to
antibiotic sensitive cells that are genetically identical to the original population
what indicates that the optimal individual strategy is not to enter into persistence
that fact that most E.coli cells in the stationary phase population are non persisters
why is presser state thought to be altruistic behaviour
since being persister is not optimal and benefits kind
persister cells in biofilms are able to
regrow after cessation of antibiotic therapy, whereas planktonic cells are not
an approach to treat persisters
to serially reduce the conc of antibiotics thereby generating fewer numbers of persisters with each round of treatment
how do we identify persisters from a population if they are non growing
- add antibiotics
- kill all non-persister cells
- will be left with just persister cell
Time consuming and microscopy is expensive
FACS
fluorescence activating cell sorting
FACS more
-seperates cells on size and colour- can show which populations show most fluorescence- the less fluorescent the more likely to be persistent.
the less fluorescent the
more likely to be persistent
how does FACS work
promotors will drive the transcription of GFP (edit promotes to make it active). Persister cels won’t produce GFP since they aren’t growing, therefore they can be seen in phase contrast (smaller), but will not fluoresce since they parent growing.
fluorescence dilution
FD can be used to track non-replicating persister in infected hosts. Bacterial cells are loaded with fluorescent protein, once induction is switched off, dilution of the pre-formed pool of fluorescent protein will report the extent of bacterial replication. The lack of FD is a mark for the absence of replication
Why is the lack of FD a marker for the absence of replication
if persister, it won’t be replicating, so fluoresce should stay the same conc. If normal, then the fluorescence should fade after every division, until no fluoresce
