The Hormetic Effect Of Typical Antibiotics To Bacteria And Resistance Mechanistic Exploration

Indiscriminate use of antibiotics in many fields leads to the organisms exposed to the threat of antibiotics with the characteristics of “low dose and mixed existence” in a long term,which poses potential risks to the ecosystem and human health.The antibiotics can induce stimulation and inhibition effect to physiological indicators of bacteria in low and high concentration,respectively.The combination of multiple antibiotics will produce different joint toxic actions with the change of exposure dose and time,which brings more unknown threats to the ecological environment.Meanwhile,the pathways and mechanisms of bacterial drug resistance caused by antibiotic is still remain unclear.Therefore,we chose the Aliivibrio fischeri(A.fischeri)and Escherichia coli(E.coli)as the tested organisms,chose sulfanilamides(SAs),tetracycline(TH),erythromycin(ERY),chloramphenicol(CHL)and potential substitutes of antibiotic(QSIs,quorum sensing inhibitors)as the chemicals,the hormetic effects and joint toxic action of antibiotics were explored,the main contents and achievements are as follows:(1)The hormetic effect of antibiotics on A.fischeri were determined,and the underlying mechanism was investigated.The toxic effects of 12 SAs,TH,B3 O,and C30 on the bioluminescence of A.fischeri were determined.The results show:(1)SAs,B3 O,C30 and TH induce hormetic effects on the bioluminescence of A.fischeri from 12 h,in which the intensity and concentration of the hourly maximum stimulation both increase gradually with exposure time;(2)there are only inhibitory effects of ERY and CHL on the bioluminescence of A.fischeri within the range of test concentration in 1-24 h.Based on molecular docking and QSAR modeling,the mechanism of hormetic effect of SAs on the bioluminescence was explored.The detailed mechanism is as follows:SAs can stimulate the expression of Lux R protein(a key protein in the quorum sensing system of A fischeri)in low concentration,leading to stimulate the bioluminescence of A fischeri;and SAs in the high concentration can compete with PABA to binding DHPS to inhibit bacterial growth,eventually leading to inhibit the bioluminescence of A.fischeri.By referring to the literatures,we summarized the mechanism of stimulation and inhibition of other antibacterial agents to the bioluminescence of A.fischeri.Our study provides a reference to the mechanistic investigation of hormetic effect.(2)The combined toxicities of the binary mixtures of antibiotics on the bioluminescence of A.fischeri were determined.The independent action(IA)model was chose to judge the joint toxic action of the mixtures,the regularity and potential mechanism of the “cross-phenomenon” change with exposure time wase exploredThe dose-response curves of the combined toxicities of SAs and other 5antibacterial agents on the bioluminescence of A.fischeri were determined,and the IA reference model was used to obtain the predictive dose-response curves.We found the actual dose-response curve of the mixtures cross the predictive dose-response curve,expressed the joint toxic action of the mixture varied with exposure dose,which was named as cross-phenomenon,through thorough analysis,we found the joint toxic action of all the test mixtures exhibit a time-dependent regularity changing from synergism to the cross-phenomena of synergism in the low-concentration region,addition in the mid-concentration region and antagonism in the high-concentration region with exposure time.Furthermore,the regularity of time-dependent cross-phenomena was confirmed to be caused by the hormetic effect of components in different exposure time.This study provides a reference on the assessment of the joint toxic action and environmental risk of mixtures.(3)The resistance mechanism of bacteria was explored based the hormetic effect of antibioticThe hormetic effect of(sulfamethoxypyridazine,SMP)on the growth of E.coli was determined.A method to determine the concentration of indole produced by E.coli was established.The results show: the bacteria can repair and regulate the damage caused by antibiotic by increasing energy consumption before the growth was inhibited by SMP;when SMP express inhibition to growth of E.coli,the bacteria can cope with the antibiotic pressure by producing indole and regulating the expression of antibiotic resistant genes.Our study provides a reference to explore of the mechanism of bacterial resistance under the hormetic effect.This study facilitate us to understand the possible negative effects of antibiotics comprehensively,befitting to evaluate the potential environmental risks of antibiotics accurately and even setting the environmental protection policies.