Table 2.

Definitions of terms used to describe different survival strategies of bacteria to cope with environmental, antimicrobial, or host-derived stress.

Term	Definition
Sporulation	When exposed to stress, some bacteria undergo asymmetric cell division to produce a metabolically inactive daughter cell, called a spore. Upon exposure to favorable environmental conditions, a fraction of the spore germinates and initiates rapid growth to restore the population. Sporulation is a specialized development program.
Dormant state	Bacteria are in a dormant state when they stop dividing and strongly, or even completely reduce their metabolic activity when exposed to stress. Under specific stimuli, these cells regain their activity and have the ability to divide again. This generic term includes different phenotypes (such as persistence and VBNC states).
Viable But Non Culturable state	Bacteria are in a VBNC state when they have transiently lost their ability to grow on routine growth medium on which they were previously able to grow. These bacteria exhibit low but detectable metabolic activity, maintain membrane integrity, express genes and produce proteins at low levels. They cannot be detected by colony forming units (CFU) on standard culture media. Under appropriate conditions, VBNC bacteria regain their ability to be culturable through a process called resuscitation.
Sublethal state	Bacteria are in a sublethal state when they have suffered damage to cell structures due to chemical or physical processes, but are not killed and have the ability to repair their damage under appropriate conditions. They can grow on culture media, however none-selective. Sublethally injured cells that remain metabolically active but cannot be resuscitated in culture media may enter the VBNC state.
Persistence state	Bacteria are in a persistence state when they enter a state of slow or no growth and are able to survive stress within an otherwise stress-sensitive clonal population. This is a general term that describes an adaptive and reversible process. This term is often associated with persisters.
Persisters	This term defines a subpopulation of bacteria that survive antibiotic treatment, without acquiring genetic changes that confer resistance. Persisters are refractory to antibiotic treatment in vitro or in the host due to low target activity or low antibiotic uptake.
Persistent infection	This clinical term refers to an infection that is not effectively eliminated by the host. Bacteria survive in the host’s tissues for a prolonged period of time despite the host’s immune defenses.
Latent infection	This clinical term refers to persistent asymptomatic infection. Latent infection occurs when a microbe persists in a host without disrupting homeostasis sufficiently to cause clinical symptoms or disease. Latency can be beneficial to both the host and the microbe, in a balance where the host avoids progressive damage from interaction with the microbe and the microbe secures a stable niche in which to survive. Latency can be deleterious to the host when a latent infection reactivates, causing symptomatic disease months or years after the initial infection.