Study On The Interaction Mechanism Between β-Lactam Antibiotics And Phosphorus-accumulating Organisms

The most widely used antibiotics at present,β-lactam antibiotics,which characterized by strong antibacterial activity and small adverse reactions,are widely applied and practical.As the main functional groups in the enhanced biological phosphorus removal process,phosphorus-accumulating organisms(PAOs)has the characteristics of releasing phosphorus in the anaerobic period and absorbing phosphorus in the aerobic period.In the study,Amoxicillin,aztreonam and cefoperazone are the selected antibiotics that applied in investigating the interaction mechanism of β-lactam antibiotics and PAOs.The effects of β-lactam antibiotics on PAOs were analyzed comprehensively from the impact of antibiotics on phosphorus removal rate,intracellular polymer,toxicity of PAOs,and researching the effect of PAOs on the fate of β-lactam antibiotics by changing content of antibiotics.PAOs entered the logarithmic growth phase after cultured with 6h.The phosphorus removal effect of PAOs is improved by amoxicillin and aztreonam,especially with the 10 mg / L amoxicillin and aztreonam,which promote the phosphorus removal rates of PAOs to 67.44% and 65.08%,respectively.To a certain extent,cefoperazone is able to inhibit the phosphorus removal efficiency and the inhibition is enhancing with the increase of antibiotic concentration.Sultan black staining is applied in dyeing the polyhydroxibutyrate(PHB)on the anaerobic phase,while DAPI staining,new Neisseria staining methods are used to dye the polyphosphates(poly-P)on the aerobic phase.Characteristic particle are observed in both control group(without addition of β-lactam antibiotics)and experimental group(amoxicillin,aztreonam,cefoperazone).Quantitative analysis shows that in the anaerobic stage,three kinds of β-lactam antibiotics could promote the synthesis of PHB,but amoxicillin and cefoperazone could inhibit the decomposition of poly-P that aztreonam has no significant effeet on it.In the aerobic stage,amoxicillin and aztreonam would prevent the decomposition of PHB,while cefoperazone can improve it.At the same time,all three kinds of beta lactam antibiotics can accelerate the synthesis of poly-P,however,the promoting effect of cefoperazone was significantly weaker than amoxicillin and aztreonam.The influence of PAOs on the fate of three kinds of β-lactam antibiotics was studied by sodium azide.It was found that the major factor affecting the degradation of amoxicillin is biosorption,and the biosorption is mainly occurred in the anaerobic stage.As for aztreonam and cefoperazone,when the concentration is 1mg/L,biodegradation is stronger than biological adsorption,while at 10mg/L exactly the opposite,and the effect of biodegradation and biosorption is similar at 5mg/L.The degradation rates of three kinds of β-lactam antibiotics were amoxicillin,amamoxan and cefoperazone in turn.The broth dilution method shows the minimum inhibitory concentration of amoxicillin on PAOs is 8μg/mL-16μg/mL,aztreonam is 4μg/mL-8μg/mL and cephalosporin is 0.5μg/mL-1μg/mL.Dose effect curve was plotted and 24 h half effect concentration of aztreonam,cefoperazone and amoxicillin are 0.701mg/L,0.098mg/L,10.905mg/L,respectively.The toxic effects of three kinds of β-lactam antibiotics on PAOs were as follows: cefoperazone > amamoxan > amoxicillin.