Antimicrobials are designed to eliminate microorganisms and are commonly prescribed as antibiotics (to kill bacteria), antifungals (to kill fungi), antivirals (to kill viruses), and antiparasitics (to kill parasites). For many individuals, the surviving cells from antimicrobial treatment initiate a cycle of ongoing infection and multidrug tolerance, with biofilms and persister cells playing a central role.
Biofilms are essentially slimy clusters of bacteria or other microorganisms that stick together and adhere to surfaces. They primarily consist of proteins and polysaccharides secreted by microorganisms (a common example of biofilm formation is dental plaque). Biofilms are believed to be responsible for most infections in the developed world and are naturally formed as a protective mechanism for the underlying microorganisms (Lewis, 2005).
Persister cells, which are enriched in biofilms, are also formed by microorganisms. Persisters are thought to be responsible for chronic, stubborn infections. When stressed, these cells enter a resting state "in which they become tolerant to nearly all antibiotics without undergoing genetic change" (Wood, 2017). Once antibiotics are discontinued and conditions become more favorable, these cells can re-establish infection, creating new populations of persisters that are just as susceptible as the original cells (Wood, 2017; Maarten Fauvart, 2011).
The findings of a 2017 study showed that pretreatment with rifampicin, tetracycline, or CCCP "converted an initial population of 0.01% persisters to up to approximately 80% persisters (a 10,000‐fold increase in persister cells)" (Wood, 2017), demonstrating that traditional antimicrobial treatment can promote persister cell proliferation.
References
Lewis, K. (2005, February). Persister cells and the riddle of biofilm survival. Biochemistry, pp. 70(2):327-336.
Maarten Fauvart, V. N. (2011, June 1). Role of persister cells in chronic infections: clinical relevance and perspectives on anti-persister therapies. Journal of Medical Microbiology, pp. 60: 699-709.
Wood, T. K. (2017, July 11). Strategies for combating persister cell and biofilm infections.