Are we really studying persister cells?

Reactive Oxygen Species Penetrate Persister Cell Membranes of Escherichia coli for Effective Cell Killing

“…The cell pellets were washed with 1× PBS at 3,500 × g for 2 min and re-suspended in 1 mL of 1× PBS twice. This procedure for developing persister cells was performed as described previously (Kwan et al, 2013 ; Kim et al, 2018a ), and many groups have used this approach (Song and Wood, 2020 ).…”

Combatting Persister Cells With Substituted Indoles

“…Since nearly all cells face nutrient limitations and need dormant states to weather this stress, it is reasonable that cells require elegant regulation for both persister cell formation and resuscitation. Critically, the PRDP model suggests the "phenotypic switch" for persistence is predicated on the number of ribosomes inactivated; hence, only a small subpopulation of stressed cells become persistent since they are the cells with a threshold level of ribosomes inactivated (Song and Wood, 2020a;Wood and Song, 2020); i.e., not all stationary cells are persisters since not all of these cells have a large enough percentage of ribosomes inactivated. The PRDP model is general in that it is applicable to how persister cells form from various stresses since RMF has been shown to increase persistence dramatically in E. coli for myriad stresses including (i) ampicillin (Song and Wood, 2020b), ciprofloxacin (Song and Wood, 2020b), netilmicin (Tkachenko et al, 2017), gentamicin (McKay and Portnoy, 2015), acid (El-Sharoud and Niven, 2007), osmotic stress (Shcherbakova et al, 2015), and nutrient limitation (Yamagishi et al, 1993;Bubunenko et al, 2007).…”

“…In contrast to persistence , which occurs in a small sub-population of cells, resistance occurs when mutations arise that allow growth in the presence of the antibiotic, and tolerance occurs when slow growth (e.g., stationary-phase cells) makes the entire population less susceptible to the antibiotic ( Kaldalu et al, 2016 ; Kudrin et al, 2017 ). We have tried to clarify these terms to reduce the confusion in the persister-related literature ( Wood et al, 2013 ; Kim and Wood, 2016 , 2017 ; Kim et al, 2018a ; Wood and Song, 2020 ) and tried to indicate how mistakes are being made in the persister literature by not waiting for a true plateau in the classic graph of the remaining viable cells during stress conditions that indicates the presence of persister cells (i.e., “biphasic” cell graph) ( Song and Wood, 2020a ). In addition, there is another term for the dormant state, “viable but non-culturable,” but we have demonstrated that the viable fraction of these cells is the same as persisters cells, at least for Escherichia coli and enterohemorrhagic E. coli (EHEC; Kim et al, 2018a ).…”

“…Since nearly all cells starve ( Song and Wood, 2018 ), persistence is likely a universal resting state of Bacteria and Archaea ( Song and Wood, 2020b ). Although persistence occurs to a small extent spontaneously ( Balaban et al, 2004 ), it primarily arises as a highly regulated response to the environment ( Dörr et al, 2010 ; Möker et al, 2010 ; Vega et al, 2012 ; Kwan et al, 2013 , 2015 ; Hu et al, 2015 ; Song and Wood, 2020a ; Wood and Song, 2020 ). This environmental response results in a small sub-population of stress-tolerant cells (∼1% or less) in biofilms and in stationary-phase cultures ( Lewis, 2007 , 2008 ).…”

“…Since nearly all cells face nutrient limitations and need dormant states to weather this stress, it is reasonable that cells require elegant regulation for both persister cell formation and resuscitation. Critically, the PRDP model suggests the “phenotypic switch” for persistence is predicated on the number of ribosomes inactivated; hence, only a small sub-population of stressed cells become persistent since they are the cells with a threshold level of ribosomes inactivated ( Song and Wood, 2020a ; Wood and Song, 2020 ); i.e., not all stationary cells are persisters since not all of these cells have a large enough percentage of ribosomes inactivated.…”