## 1 Introduction
### S. aureus in Biofilms and Resistance and Tolerance Mechanisms
(iv) Dispersal, where a detachment of some cells from biofilms into planktonic cells, colonizing new tissue or surfaces [1; 51; 62; 68; 70; 77], or cells tolerate antibiotics more than the planktonic cells [79]. Biofilms usually comprise multispecies bacterial communities (and other microorganisms), making it implausible that a single antibiotic quenches these diverse bacterial communities [55; 56; 72; 80]. These multispecies bacterial communities are encased within an envelope (EPS matrix) and interact mostly cooperatively within the matrix and with cells of other organisms and the environment [71]. Bacterial subpopulations within the biofilm could suffer starvation or switch phenotypically after stress exposure to antibiotic treatment into slow- or non-growing persisters (persister cells). These persisters tolerate antibiotics [46; 54; 67; 70; 71; 73; 79; 81; 82] and elicit recurrent infections [53; 83], as seen in Figure 2. Interestingly, persisters could also present in small proportions of non-stressed populations as an insurance mechanism to escape lethal stressors' attack. This insurance mechanism stems from the fact that metabolically inactive non-growing cells demonstrate enhanced tolerance to antibiotics comparedwith their replicating counterparts [83; 84; 85]. Despite the stochastic development of persisters, the tendency to form them remains a genetically controlled trait [82; 83; 85]. This trait is controlled via HipBA (the _hip_ is a high persister mutant), constituting a toxin-antitoxin (TA) locus in the workhorse model organism, Escherichia coli. Throughout normal bacterial replication, protein toxins are bound to their antitoxins (protein or RNA), inhibiting toxin activity. Throughout the persister scenario, toxins are liberated, inhibiting DNA replication and mRNA cleavage that inhibits global bacterial protein transcription and translation [85; 86]. The escalating question here is: would the same TA module signaling pathway control the development of persisters in _S. aureus_? Consistent with the TA module signaling pathway in _E. coli_, [PERSON] et al. [87] have also found that guanosine pentaphosphate, (p)ppGpp, was the pacemaker driving the formation of tolerant persisters in _S. aureus_ via inhibiting GTPases. The inhibition of GTPases reduces the growth and amount of mature 70S ribosomes of cells and increases the antibiotic tolerance of cells. Surprisingly, [PERSON] et al. [88] noted that the deletion of TA modules (i.e., no increased production of (p)ppGpp) did not affect the level of the produced persisters in _S. aureus_. The unexpected finding was that persisters emanated from a stochastic process of bacterial entrance into the stationary phase and associated with a decrease in the intracellular level of adenosine triphosphate, losing energy and developing antibiotic tolerance. Persisters also have the following hallmark features. (i) The biphasic killing curve is a heterogenous non-uniform killing rate of bacteria that describes the rapid killing of most bacterial within 25 min. The remaining cells are killed after a longer time, up to 6 h [76; 82; 85]. (ii) The production of susceptible progeny cells to antibiotics is similar to their progenitors if they resume growth without antibiotics [76; 79; 89; 90], as seen in Figure 2. (iii) The third hallmark feature is the heterogeneity of persisters exemplified via their bet-hedging stochastic formation. The concept 'bet-hedging' is an evolutionary strategy, depending on the phenotypic heterogeneity that facilitates the survival and tolerance of persisters against hefty stressful conditions [83]. In light of the biofilm broader view, biofilms possess less susceptibility to antibacterial agents and infected hosts' immune systems than their planktonic (free-living) counterparts [1; 53; 55; 56; 62; 91]. Biofilms are mostly untreatable except by surgical removal of the infected medical implant [53; 64; 65; 67; 80] or sharp debridement of wounds [55; 56; 68; 69].