lec 7 - persisters Flashcards
most common chronic infection
tb
persister cells
dormant variants of bacterial cells
antibiotic resistant
responsible for chronic disease
add antibiotics at stationary phase
more persistent phenotypes seen emerging
altruistic behaviour
beneficial to recipient
cooperative behaviour
western blot
analytical technique used to monitor protein expression and detect specific proteins
uses probe and antibodies against the proteins
electrophoresis often used
stochastic fluctuation
formation of persister cells is a random process
what controls expression of persister genes
external evironment
identifying persisters
kill off susceptible population isolate persister cells dye cells red cell debris shows dead cells add antibiotics remove antibiotics - growth of persister cells seen
what part of the cells will show dye
intact cellular membranes
fluorescent activated cell sorting - FACS
separates cells on size and colour
smaller and less coloured cells are persister population - not expressing RNA
ribosomal RNA promoter
GFP downstream of promoter for ribosomal gene
healthy cells express this to make proteins
effect of up-regulation of toxin/antitoxin molecules
cell in growth arrest
toxin-antitoxin (TA) systems
2 linked genes combine
1 encodes a protein ‘poison’
1 encodes a corresponding ‘antidote’
constant non-activity of toxin, unless antitoxin is degraded
over expression of toxin
generation of more persister cells
quorum sensing
regulation of gene expression in response to fluctuations in cell-population density
essential for generating persister cells
persister cells are not genetically resistant
they are a sub-population of antibiotic-tolerant bacteria
growth of persister cells
slow growing or in growth arrest
have decreased metabolic activity
able to resume after lethal stress
why are persisters a public health concern
antibiotic resistance
treatment failure
asymptomatic persistent infections
can be caused by latent growth-arrested bacteria
are associated with relapses of acute symptomatic infections
symptomatic persistent infections
characterised by long period of clinical manifestations
repetitive use of antibiotics
-ve effects on health
deplete resident microbiota
increase antibiotic-resistant strains
why do infections persist
ineffective clearance by host
inability of immune system to detect a pathogen
formation of biofilms
can block complement-mediated and cell-mediated killing in many persistent infections
cefotaxime
causes many antibiotic-susceptible bacteria to die rapidly
results in large initial decrease in colony forming units (CFUs)
persister cells remain viable
if cells have an intermediate growth rate…
bacteria may be able to grow without being killed by the antibiotic
effect of mutations
can increase the lag time of bacteria or probability of persisters
therefore antibiotic resistance
factors enhancing persister cell formation
nutrient limitation
extreme pH
DNA damage
bacteria-rich environments e.g. biofilms/macrophages
bistability
explains how growing and growth arrested cells can live in the same clonal population
pore-forming toxins
can reduce proton motive force and decrease the rate of ATP synthesis within a cell
how do persister cells become tolerant to antibiotics?
through target inactivity due to a decrease in growth and metabolism or reduced drug uptake
persister cell regrowth
either all together
or spontaneously as soon as external stress is removed
conditional cooperativity
autoregulation of some toxin-antitoxin molecules where they can only form complexes at some ratios
