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To clarify the ecological risks of antibiotics in aquatic environments regarding bacterial toxicity and resistance, norfloxacin (NOR) and ceftazidime sodium (CTX) were selected as test compounds. Characteristic parameters including EC50and lower concentrations inducing 10% mutation/conjugation transfer promotion rates were employed. Binary antibiotic mixtures were designed using the direct equipartition ray method to investigate their toxicity and resistance-inducing effects on Escherichia coli (E. coli). Results demonstrated hormetic effects in both individual and combined exposures, with maximum growth promotion, mutation promotion, and conjugation transfer promotion rates reaching 38.40%, 101.26%, and 28.73%, respectively. Compared with individual exposure, the maximum promotion rate of mixed antibiotics on E.coli growth and mutation was reduced, along with decreased relative safety concentrations for mutation and conjugation transfer. Higher NOR proportion in mixtures resulted in lower EC50 values, elevated maximum mutation/conjugation promotion rates, and reduced safety concentrations. The combined action patterns transitioned from additive/synergistic/synergistic to synergistic/antagonistic/antagonistic for toxicity/mutation/conjugation transfer effects respectively as concentrations increased. Higher NOR proportions diminished the maximum synergistic intensities for growth/mutation promotion and antagonistic intensity for conjugation transfer. The concentration ratio in antibiotic mixtures was identified as a critical factor for assessing bacterial toxicity and resistance risks in aquatic environments.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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