Objective To explore the activity and mechanism of polymyxin B combined with novel β-lactam/β-lac-tamase inhibitor combinations on biofilm of polymyxin B-resistant Pseudomonas aeruginosa and Klebsiella pneumo-niae.Methods The minimum inhibitory concentration(MIC),minimum biofilm inhibitory concentration(MBIC),and minimum biofilm eradication concentration(MBEC)of all antimicrobial agents were determined by micro-broth dilution method and MBECTM assay.The crystal violet staining method was adopted to evaluate the effect of poly-myxin B combined with cefepime/avibactam,ceftazidime/avibactam,meropenem/avibactam,aztreonam/avibactam,meropenem/vaborbactam,and imipenem/relebactam at sub-MIC doses on inhibition of biofilm formation and eradi-cation of mature biofilm.The best combination scheme for anti-biofilm activity was screened out,and anti-biofilm mechanism of this combination scheme was preliminarily explored with phenol-sulfuric acid method,bacterial motili-ty test,and quorum sensing inhibition test.Results The MBIC and MBEC of all antimicrobial agents were higher than MIC.The combination regimen based on polymyxin B could inhibit the formation of biofilms and eradicate ma-ture biofilm in Pseudomonas aeruginosa and Klebsiella pneumoniae.The combination of polymyxin B with cefepime/avibactam had the highest inhibition and eradication rates,ranging 67.99％-90.16％and 58.26％-63.86％,respectively.The combination of polymyxin B and cefepime/avibactam could inhibit the extracellular poly-saccharides of Klebsiella pneumoniae,with inhibition rates of 34.04％-61.10％,this combination could also re-duce the swimming and twitching motility diameters of bacteria.Cefepime/avibactam monotherapy on quorum sen-sing signaling molecules presented concentration dependent inhibitory effect,and when combined with polymyxin B,the inhibitory effect was consistent with that of monotherapy.Conclusion Polymyxin B and cefepime/avibactam may be potential scheme for clinical treatment for severe biofilm-associated infection caused by polymyxin B-resistant strains,and their mechanisms may be related to the inhibition of bacterial extracellular polysaccharides and motility.

Objective To explore the activity and mechanism of polymyxin B combined with novel β-lactam/β-lac-tamase inhibitor combinations on biofilm of polymyxin B-resistant Pseudomonas aeruginosa and Klebsiella pneumo-niae.Methods The minimum inhibitory concentration(MIC),minimum biofilm inhibitory concentration(MBIC),and minimum biofilm eradication concentration(MBEC)of all antimicrobial agents were determined by micro-broth dilution method and MBECTM assay.The crystal violet staining method was adopted to evaluate the effect of poly-myxin B combined with cefepime/avibactam,ceftazidime/avibactam,meropenem/avibactam,aztreonam/avibactam,meropenem/vaborbactam,and imipenem/relebactam at sub-MIC doses on inhibition of biofilm formation and eradi-cation of mature biofilm.The best combination scheme for anti-biofilm activity was screened out,and anti-biofilm mechanism of this combination scheme was preliminarily explored with phenol-sulfuric acid method,bacterial motili-ty test,and quorum sensing inhibition test.Results The MBIC and MBEC of all antimicrobial agents were higher than MIC.The combination regimen based on polymyxin B could inhibit the formation of biofilms and eradicate ma-ture biofilm in Pseudomonas aeruginosa and Klebsiella pneumoniae.The combination of polymyxin B with cefepime/avibactam had the highest inhibition and eradication rates,ranging 67.99％-90.16％and 58.26％-63.86％,respectively.The combination of polymyxin B and cefepime/avibactam could inhibit the extracellular poly-saccharides of Klebsiella pneumoniae,with inhibition rates of 34.04％-61.10％,this combination could also re-duce the swimming and twitching motility diameters of bacteria.Cefepime/avibactam monotherapy on quorum sen-sing signaling molecules presented concentration dependent inhibitory effect,and when combined with polymyxin B,the inhibitory effect was consistent with that of monotherapy.Conclusion Polymyxin B and cefepime/avibactam may be potential scheme for clinical treatment for severe biofilm-associated infection caused by polymyxin B-resistant strains,and their mechanisms may be related to the inhibition of bacterial extracellular polysaccharides and motility.

AIM: To establish a method for quantitation of cefepime and avibactam in M-H broth, and applicated in the in vitro dynamic PK/PD model. METHODS: The cefepime was also determined using the high-performance liquid chromatography method (HPLC), the avibactam was also determined using the liquid chromatography-mass spectrometry (LC-MS/MS), an in vitro dynamic PK/PD model was established to study the PK/PD relationship of cefepime/avibactam against carbapenem resistant Klebsiella pneumoniae (CRKP). RESULTS: The linear ranges of cefepime and avibactam were good at (0.5-20) and (0.1-25) μg/mL (r=0.999), and the lower limit concentrations were 0.5 and 0.1 μg/mL. The extraction recoveries of cefepime and avibactam in M-H broth were 88.0%-101.7% and 90.9%-95.2%, the relative standard deviation of intra-day precision and inter-day precision were less than 5.2%. The concentration-time curves were well simulated by the PK/PD model. All observed concentrations in each experiment were in the range of 20% of the targeted values. For the CRKP of MIC=8 μg/mL and MIC=16 μg/mL, the colony decreased to 2.783Log10 CFU/mL and 1.325Log10 CFU/mL at the cefepime/avibactam 2.5 g q8 h administration after 24 h. CONCLUSION: The determination method of cefepime and avibactam in broth established in this study has high sensitivity and good stability. For the CRKP with MIC≤8 μg/mL,cefepime/avibactam showed that good anti-CRKP activity under routine administration in vitro dynamic PK/PD model.