in previous message:
> The mechanisms of growth promotion are still not exactly known.  Four hypotheses have been proposed to explain their action

Another explanation for the growth promoting effects of antibiotics is termed "hormesis." 

> The biochemical mechanisms by which hormesis works are not well understood. It is conjectured that low doses of toxins or other stressors might activate the repair mechanisms of the body. The repair process fixes not only the damage caused by the toxin, but also other low-level damage that might have accumulated before without having triggered the repair mechanism.

> In this work, the ability of sub-inhibitory concentrations of Tetracycline to induce hormetic response in a model organism was investigated. These data confirm that hormesis is common to many - if not all - living systems, including bacteria; they underline the relevance of a deepened knowledge of both the effects and the possible consequences of exposure to low doses of contaminants.  The overall lack of literature concerning hormetic response in bacteria does not allow to speculate too much about the underlying mechanisms.

> The sub-inhibitory doses of Tetracycline inducing the hormetic response are comparable to the concentrations commonly detected in antibiotic contaminated soils and waters (Sarmah et al. 2006; Brambilla et al. 2007; Migliore et al. 2007). The occurrence of the hormetic response at these concentrations opens new concerns about the effects of antibiotic environmental and food contamination. 

Migliore, L., Rotini, A., & Thaller, M. C. (2013). Low doses of tetracycline trigger the E. coli growth: A case of hormetic response. Dose-Response, 11(4), dose-response.

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