Persister cells Lewis, Kim
Annual review of microbiology,
01/2010, Volume:
64
Journal Article
Peer reviewed
Persisters are dormant variants of regular cells that form stochastically in microbial populations and are highly tolerant to antibiotics. High persister (hip) mutants of Pseudomonas aeruginosa are ...selected in patients with cystic fibrosis. Similarly, hip mutants of Candida albicans are selected in patients with an oral thrush biofilm. These observations suggest that persisters may be the main culprit responsible for the recalcitrance of chronic infectious disease to antimicrobial therapy. Screening knockout libraries has not produced mutants lacking persisters, indicating that dormancy mechanisms are redundant. Toxin/antitoxin (TA) modules are involved in persister formation in Escherichia coli. The SOS response leads to overexpression of the TisB toxin and persister formation. TisB is a membrane-acting peptide that apparently sends cells into dormancy by decreasing the proton motive force and ATP levels. Stress responses may act as general activators of persister formation. Proteins required for maintaining persisters may represent realistic targets for discovery of drugs capable of effectively treating chronic infections.
It is a given that new antibiotics are needed to combat drug-resistant pathogens. However, this is only a part of the need-we actually never had antibiotics capable of eradicating an infection. All ...pathogens produce a small subpopulation of dormant persister cells that are highly tolerant to killing by antibiotics. Once an antibiotic concentration drops, surviving persisters re-establish the population, causing a relapsing chronic infection. Persisters are especially significant when the pathogen is shielded from the immune system by biofilms, or in sites where the immune components are limited-in the nervous system, the stomach, or inside macrophages.Antibiotic treatment during a prolonged chronic infection of P. aeruginosa in the lungs of patients with cystic fibrosis selects for high-persister (hip) mutants. Similarly, treatment of oral thrush infection selects for hip mutants of C. albicans. These observations suggest a direct causality between persisters and recalcitrance of the disease. It appears that tolerance of persisters plays a leading role in chronic infections, while resistance is the leading cause of recalcitrance to therapy in acute infections. Studies of persister formation in E. coli show that mechanisms of dormancy are highly redundant. Isolation of persisters produced a transcriptome which suggests a dormant phenotype characterized by downregulation of energy-producing and biosynthetic functions. Toxin-antitoxin modules represent a major mechanism of persister formation. The RelE toxin causes dormancy by cleaving mRNA; the HipA toxin inhibits translation by phosphorylating elongation factor Ef-Tu, and the TisB toxin forms a membrane pore, leading to a decrease in pmf and ATP.
The superior–inferior (SI) axial shoulder view is an important part of shoulder imaging. It provides a true orthogonal view to the anterior–posterior (AP) shoulder projection and is a supplementary ...view to the lateral scapula view. When positioned correctly, the glenohumeral joint is visualised with the superior and inferior aspects of the glenoid superimposed to demonstrate the true relationship between the glenoid and humerus. Positioning for the SI axial view is challenging. Often the glenoid is not superimposed on resulting images, and the glenohumeral relationship cannot be assessed accurately. Some positioning texts do not demonstrate the SI axial view, opting instead for the inferior–superior (IS) view. When the SI axial view is included, bony landmarks are not provided to assist medical imaging technologists (MITs) with accurate positioning. This paper outlines a proposed modification using bony landmarks that can assist MITs in positioning their patients for this important view and obtain diagnostic images that demonstrate the glenoid in true profile.
The superior‐inferior (SI) axial shoulder view is an important part of shoulder imaging. When positioned correctly the gleno‐humeral joint is visualised with the superior and inferior aspects of the glenoid superimposed to demonstrate the true relationship between the glenoid and humerus. This paper outlines a proposed modification using bony landmarks that can assist MITs in positioning their patients for this important view and obtain diagnostic images that demonstrate the glenoid in true profile.
We are experiencing an antimicrobial resistance (AMR) crisis, brought on by the drying up of the antibiotic discovery pipeline and the resulting unchecked spread of resistant pathogens. Traditional ...methods of screening environmental isolates or compound libraries have not produced a new drug in over 30 years. Antibiotic discovery is uniquely difficult due to a highly restrictive penetration barrier and other mechanisms that allow bacteria to survive in the presence of toxic compounds. In this Perspective, we analyze the challenges facing discovery and discuss an emerging new platform for antibiotic discovery. The penetration barrier makes screening conventional synthetic compound libraries largely impractical, and actinomycetes, the main source of natural product compounds, have been overmined. The emerging platform is based on understanding the rules that guide the permeation of molecules into bacteria and on advances in microbiology, which enable us to identify and access attractive groups of secondary metabolite producers. Establishing this platform will enable reliable production of lead compounds to combat AMR.
The spread of resistant bacteria, leading to untreatable infections, is a major public health threat but the pace of antibiotic discovery to combat these pathogens has slowed down. Most antibiotics ...were originally isolated by screening soil-derived actinomycetes during the golden era of antibiotic discovery in the 1940s to 1960s. However, diminishing returns from this discovery platform led to its collapse, and efforts to create a new platform based on target-focused screening of large libraries of synthetic compounds failed, in part owing to the lack of penetration of such compounds through the bacterial envelope. This article considers strategies to re-establish viable platforms for antibiotic discovery. These include investigating untapped natural product sources such as uncultured bacteria, establishing rules of compound penetration to enable the development of synthetic antibiotics, developing species-specific antibiotics and identifying prodrugs that have the potential to eradicate dormant persisters, which are often responsible for hard-to-treat infections.
Bacteria induce stress responses that protect the cell from lethal factors such as DNA-damaging agents. Bacterial populations also form persisters, dormant cells that are highly tolerant to ...antibiotics and play an important role in recalcitrance of biofilm infections. Stress response and dormancy appear to represent alternative strategies of cell survival. The mechanism of persister formation is unknown, but isolated persisters show increased levels of toxin/antitoxin (TA) transcripts. We have found previously that one or more components of the SOS response induce persister formation after exposure to a DNA-damaging antibiotic. The SOS response induces several TA genes in Escherichia coli. Here, we show that a knockout of a particular SOS-TA locus, tisAB/istR, had a sharply decreased level of persisters tolerant to ciprofloxacin, an antibiotic that causes DNA damage. Step-wise administration of ciprofloxacin induced persister formation in a tisAB-dependent manner, and cells producing TisB toxin were tolerant to multiple antibiotics. TisB is a membrane peptide that was shown to decrease proton motive force and ATP levels, consistent with its role in forming dormant cells. These results suggest that a DNA damage-induced toxin controls production of multidrug tolerant cells and thus provide a model of persister formation.
Bacteria can survive antibiotic treatment without acquiring heritable antibiotic resistance. We investigated persistence to the fluoroquinolone ciprofloxacin in Escherichia coli. Our data show that a ...majority of persisters to ciprofloxacin were formed upon exposure to the antibiotic, in a manner dependent on the SOS gene network. These findings reveal an active and inducible mechanism of persister formation mediated by the SOS response, challenging the prevailing view that persisters are pre-existing and formed purely by stochastic means. SOS-induced persistence is a novel mechanism by which cells can counteract DNA damage and promote survival to fluoroquinolones. This unique survival mechanism may be an important factor influencing the outcome of antibiotic therapy in vivo.
Tuberculosis continues to be a major public health problem in many parts of the world. Significant obstacles in controlling the epidemic are the length of treatment and the large reservoir of ...latently infected people. Bacteria form dormant, drug-tolerant persister cells, which may be responsible for the difficulty in treating both acute and latent infections. We find that in Mycobacterium tuberculosis, low numbers of drug-tolerant persisters are present in lag and early exponential phases, increasing sharply at late exponential and stationary phases to make up ~1% of the population. This suggests that persister formation is governed by both stochastic and deterministic mechanisms. In order to isolate persisters, an exponentially growing population was treated with d-cycloserine, and cells surviving lysis were collected by centrifugation. A transcriptome of persisters was obtained by using hybridization to an Affymetrix array. The transcriptome shows downregulation of metabolic and biosynthetic pathways, consistent with a certain degree of dormancy. A set of genes was upregulated in persisters, and these are likely involved in persister formation and maintenance. A comparison of the persister transcriptome with transcriptomes obtained for several in vitro dormancy models identified a small number of genes upregulated in all cases, which may represent a core dormancy response.
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