To explore the in vitro and in vivo synergistic effect of paclitaxel in combination with co-listin against MDREscherichia coli(E.coli)and the corresponding mechanism of synergism,we measured the MICs of PTX alone and combination of PTX+antimicrobial drugs on E.coli and Staphylococcus aureus(S.aureus)by broth microdilution method.Then,checkerboard method was used to determine the FICI of PTX+COL combination,and the antibacterial synergies of PTX and COL was further explored through analyzing the membrane permeability and efflux pump ac-tivity.The MICs results showed that the MIC values of PTX alone against E.coli(G5,E25)and S.aureus S238 were＞1 024 mg/L and 512 mg/L,respectively.Meanwhile,we found that the anti-bacterial activity of COL against E.coli could be significantly enhanced(MIC decreased by 4 to 8 times)when used in combination with PTX.The checkerboard test showed that the FICI values of PTX combined with COL for E.coli(G5,E25)were 0.31 and 0.29,respectively,indicating a synergistic antibacterial effect on these strains.The FICI values of PTX combined with COL for E.coli G21,S.aureus(S237 and S238)were 0.51,0.75 and 0.53,respectively,indicating additive effects on these strains.In the mouse abdominal infection model,the combination group could ex-tremely significantly reduce the bacterial burden of E.coli in abdominal compared to the COL or PTX alone group(P＜0.001).The analysis of membrane permeability and efflux pump activity showed that PTX combined with COL significantly increased the inner and outer membrane per-meability of E.coli(G5 and E25),and markedly inhibited the efflux pumping activity of E.coli,when compared that of PTX and COL alone(P＜0.01).The above results indicated that the com-bination of PTX and COL could exert a synergistic in vivo and in vitro antibacterial effect on COL-resistant E.coli through increasing bacterial membrane permeability and inhibiting efflux pump activity.This study provides the theoretical foundation for the development of a novel combi-nation regimen for the treatment of MDR E.coli infection.

To explore the in vitro and in vivo synergistic effect of paclitaxel in combination with co-listin against MDREscherichia coli(E.coli)and the corresponding mechanism of synergism,we measured the MICs of PTX alone and combination of PTX+antimicrobial drugs on E.coli and Staphylococcus aureus(S.aureus)by broth microdilution method.Then,checkerboard method was used to determine the FICI of PTX+COL combination,and the antibacterial synergies of PTX and COL was further explored through analyzing the membrane permeability and efflux pump ac-tivity.The MICs results showed that the MIC values of PTX alone against E.coli(G5,E25)and S.aureus S238 were＞1 024 mg/L and 512 mg/L,respectively.Meanwhile,we found that the anti-bacterial activity of COL against E.coli could be significantly enhanced(MIC decreased by 4 to 8 times)when used in combination with PTX.The checkerboard test showed that the FICI values of PTX combined with COL for E.coli(G5,E25)were 0.31 and 0.29,respectively,indicating a synergistic antibacterial effect on these strains.The FICI values of PTX combined with COL for E.coli G21,S.aureus(S237 and S238)were 0.51,0.75 and 0.53,respectively,indicating additive effects on these strains.In the mouse abdominal infection model,the combination group could ex-tremely significantly reduce the bacterial burden of E.coli in abdominal compared to the COL or PTX alone group(P＜0.001).The analysis of membrane permeability and efflux pump activity showed that PTX combined with COL significantly increased the inner and outer membrane per-meability of E.coli(G5 and E25),and markedly inhibited the efflux pumping activity of E.coli,when compared that of PTX and COL alone(P＜0.01).The above results indicated that the com-bination of PTX and COL could exert a synergistic in vivo and in vitro antibacterial effect on COL-resistant E.coli through increasing bacterial membrane permeability and inhibiting efflux pump activity.This study provides the theoretical foundation for the development of a novel combi-nation regimen for the treatment of MDR E.coli infection.

The genotypes of extended spectrum β-laetamases(ESBLs) and AmpC β-lactamases produced by Enterococcus gallinarum isolated from chloebia gouldiae were determined to elucidate the evolution mechanism of the resistant genes.The minimum inhibitory concentrations (MICs) of 18 antibacterial drugs against the Enterococcus gallinarum were detected with two dilution method,and the ESBLs and AmpC β-lactamases from the bacterium were amplified by PCR using the primers of TEM,SHV,CTX-M,ACC,CIT,DHA,EBC,FOX and MOX,respectively.The PCR products were cloned and then the cloned fragments were sequenced to identify their genotypes and subtypes.The bacterium was proved to be a ESBL-producing and AmpC β-lactamase-producing bacterium,showing severe resistant to the other drugs,except the third and forth cephalosporins,carbopenems and fosfomycin.Compared with that of AJ847364 (TEM-116),the sequence of the TEM-type was characterized by two nucleotide mutations (512T→A and 695A→C),which led to two mutations of amino acids(17111e→Lys and 232Lys→Thr),showing that the detected TEM-type was a new genotype,the sequence of the AmpC β-lactamase was similar to that of EF078894 (ACT-like type)with a 97% homology.The genotype of ESBLs of Enterococcus gallinarum was a new TEM-type derived from the TEM-type ESBLs of klebstella pneumoniae isolated from the same avian.The genotype of AmpC lactamase was ACT-type,which probably concerned with β-1actam antibiotics used.