Effect Of Antibiotics On The Growth And Resistance Of Escherichia Coli Under Different Nutritional Conditions

The massive use of antibiotics in production and life has led to problems such as reduced susceptibility of bacteria to antibiotics and increasingly serious contamination by drug resistance,which seriously endanger human health and ecological safety.Bacteria need to adjust their metabolism and survival strategies in order to adapt to various nutritional conditions,which involves a series of complex physiological activities such as energy metabolism,division and proliferation,and stress defense,which may change the growth and metabolic state of bacteria and further affect the bacterial toxicity and resistance of antibiotics in these processes.Therefore,in this paper,Escherichia coli（E.coli）was used as the test organism,and tetracycline hydrochloride（TH）,ciprofloxacin（CIP）and 2-methyltetrahydrofuran-3-one（MTHF）were used as test antibiotics to simulate changes in nutrient conditions in real environments by changing the type of broth（LB and MH broth）and concentration,and to carry out experiments on E.coli growth and single and mixed antibiotic-induced toxicity,mutation and splice transfer under different nutrient conditions,and to use independent action（IA）model and interactive effects were used to discriminate the combined mode of action between antibiotics and antibiotics,nutritional conditions and antibiotics.The main findings were as follows:1)Effect of nutritional conditions on E.coli growth and antibiotic toxicityCompared with MH broth,E.coli in LB broth had shorter retardation period,faster growth rate in logarithmic growth period and greater OD₆₀₀ in stable period,indicating that LB broth provided more favorable conditions for E.coli growth.The growth promotion effect of LB and MH broth on E.coli increased and then decreased as the broth concentration increased.In LB broth and 1.0-,1.4-and 2.2-fold MH broth,TH,CIP and MTHF consistently inhibited E.coli growth,and the inhibition increased with increasing antibiotic concentration.In 0.2-,0.4-and 0.6-fold of MH broth,all three antibiotics induced the Hormesis effect of low concentration promotion and high concentration inhibition in E.coli,and the maximum promotion rate reached 23.97%,24.67%and 7.93%,respectively,but the maximum promotion rate and promotion interval of Hormesis effect gradually decreased with the increase of MH broth concentration.Overall,the toxicity of antibiotics to E.coli under different nutritional conditions:CIP>TH>MTHF;the toxicity of all three antibiotics in LB broth was greater than that of MH broth,and the toxicity of TH,CIP and MTHF to E.coli gradually increased with the increase of broth concentration.2)Effect of antibiotics on E.coli resistance under different nutritional conditionsTH,CIP and MTHF could promote mutation and splice transfer of drug-resistant genes in E.coli,the maximum mutation frequency promotion rates were 313.63%,454.25%and118.89%,and the maximum splice frequency promotion rates were 76.58%,76.86%and41.57%,respectively.The promotion effect of the three antibiotics on E.coli mutation and splice transfer effect increased and then decreased with increasing antibiotic concentration,and finally changed to inhibition.MTHF-induced E.coli mutation and splice effect were lower than TH and CIP.The promotion of E.coli mutation and splice transfer effect by the three antibiotics in MH broth was greater compared with LB broth.The increase of broth concentration led to a gradual decrease of the promotion effect of the three antibiotics on E.coli mutation and splice transfer effect,and even showed a gradual deepening of the inhibition effect.3)Effects of mixed antibiotics on E.coli growth and resistance under nutritional conditions and interactive effectsThe IA model was used to discriminate the mode of combined effect between antibiotics and antibiotics.In LB and MH broth,as the concentration of mixed antibiotics（CIP and MTHF）increased,the combined toxic effect pattern of CIP and MTHF on E.coli was generally additive and synergistic,the combined effect pattern on E.coli mutagenesis effect was generally synergistic and then antagonistic,and the combined effect pattern on E.coli splice transfer effect was generally shifted from synergistic or additive to antagonistic.The interactive effects were used to discriminate the mode of combined action between altered nutrient conditions and antibiotic stress.The combined mode of action of decreasing broth concentration（0.2-,0.4-and 0.6-fold LB/MH broth）compared to 1.0-fold LB/MH broth and antibiotic stress on the inhibition of E.coli growth,promotion of E.coli mutation and splice transfer effects was generally antagonistic,synergistic and synergistic;increasing broth concentration（1.4-and 2.2-fold LB/MH broth）and antibiotic coercion were synergistic,antagonistic,and antagonistic,respectively.