Abstract
AbstractPersisters are a small subpopulation of bacteria that survive a lethal concentration of antibiotic without antibiotic resistance genes. Isolation of persisters from normally dividing population is considered difficult due to their slow growth, low numbers and phenotypic shift i.e. when re-grown in antibiotic free medium, they revert to parent population. Inability to isolate persisters is a major hindrance in this field of research. Here we reject the ‘phenotypic shift’ phenomenon exhibited by persisters. Persisters, on the other hand, exhibit a heritable phenotype and can be easily isolated from a normally dividing population that allows their selective growth. Rather than a single subset, they comprise many distinct subgroups each exhibiting different growth rates, colony sizes, antibiotic tolerance and protein expression levels. Clearly, they are one of the sources of bacterial heterogeneity and noise in protein expression. Existence of persisters in normally dividing population can explain some of the unsolved puzzles like antibiotic tolerance, post-antibiotic effect and viable but non-culturable bacterial state. We hypothesize that persisters are aging bacteria.
Highlights
Persisters were first described by Joseph Bigger in 1944 when he found that a culture of Staphylococcus spp. was not completely sterilized by a lethal concentration of ampicillin [5]
When the surviving bacteria were grown in antibiotic free medium, they grew just like parent population which was again susceptible to ampicillin
Since the persisters reverted to original population on removal of antibiotics, they were considered as dormant bacteria that avoided killing by antibacterial agents [21]
Summary
Persisters were first described by Joseph Bigger in 1944 when he found that a culture of Staphylococcus spp. was not completely sterilized by a lethal concentration of ampicillin [5]. For isolating pure cultures of persisters, 50μl of overnight culture of E.Coli DH5α was added to 3 ml of fresh LB medium containing kanamycin at concentrations of 10, 20, 30, 40 and 50μg/ml and incubated at 370C for 48-60 hours at 240 r.p.m. When the culture reached an O.D. of approximately 0.5, 200 μl was withdrawn and centrifuged to remove the supernatant containing antibiotics.
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