Staphylococcus aureus is a Gram-positive bacterium with strong pathogenicity. With the widespread use of antibiotics， its multi-drug resistance has gradually increased. Among them， methicillin-resistant S. aureus （MRSA） is one of the main pathogens of hospital and community infections. Antimicrobial peptides are short-chain peptides with good antibacterial effects and low drug resistance， which have been widely studied in recent years. This study summarizes the mechanism of action of antimicrobial peptides and related study on antimicrobial peptides against MRSA from different sources. It is found that the mechanisms of action of antimicrobial peptides include targeting bacterial cell membranes， bacterial cells， and bacterial cell walls， etc. Besides isolating antimicrobial peptides with anti-MRSA activity from animals， plants， and microorganisms， antimicrobial peptides can also be obtained through synthetic methods. Among them， GHa-derived peptides from animal sources， Ib-AMP4 from plant sources， Ph-SA from microbial sources， the synthetic peptide LLKLLLKLL-NH2， and so on， due to their effective antibacterial activity， rapid bactericidal speed， and low toxicity， are promising candidates for anti-MRSA drugs.

Objective To investigate the in vitro bacterial inhibitory activity and biofilm effect of the combination of tannic acid and imipenem on carbapenem-resistant Acinetobacter baumannii(CRAB),and provide a theoretical basis for the treatment of CRAB infections with tannic acid in combination with imipenem.Methods Collected 30 non-duplicated CRAB strains from clinical isolates of the First People's Hospital of Yibin from May to December 2022.The minimal inhibitory concentration(MIC)of tannic acid and imipenem on CRAB was detected separately by micro broth dilution method,and the effect of drug combina-tion was evaluated according to the fractional inhibitory concentration index(FICI).The effect of sub-inhibitory concentration of drugs on biofilm formation was observed by semi-quantitative adhesion assay.Changes in the microscopic morphology of mature biofilms under the effect of drugs were observed by scanning electron microscopy.Changes in the expression of biofilm-asso-ciated genes BaP,BfS,OmpA were detected by reverse transscription PCR(RT-PCR)after the administration of tannic acid and imipenem alone and in combination.Results The MICs of tannic acid and imipenem against 30 CRAB strains ranged from 32 to 256 μg/ml,and the FICI values of tannic acid combined with imipenem ranged from 0.625 to 1,which showed additive effects.Compared with the control group,tannic acid combined with imipenem could effectively inhibit the formation of biofilm and destroy the structure of mature biofilm,and the biofilm-related genes of BaP,BfS,OmpA and were expressed at a low level in the strains,and the differences were statistically significant(t=26.32,79.17,29.22,all P<0.05).Conclusion For CRAB,tannic acid in combination with imipenem showed additive effects.The anti-biofilm effect of tannic acid in combination with imipenem may be realized by inhibiting the expression of biofilm-related genes BaP,BfS,OmpA.

Objective To investigate the in vitro bacterial inhibitory activity and biofilm effect of the combination of tannic acid and imipenem on carbapenem-resistant Acinetobacter baumannii(CRAB),and provide a theoretical basis for the treatment of CRAB infections with tannic acid in combination with imipenem.Methods Collected 30 non-duplicated CRAB strains from clinical isolates of the First People's Hospital of Yibin from May to December 2022.The minimal inhibitory concentration(MIC)of tannic acid and imipenem on CRAB was detected separately by micro broth dilution method,and the effect of drug combina-tion was evaluated according to the fractional inhibitory concentration index(FICI).The effect of sub-inhibitory concentration of drugs on biofilm formation was observed by semi-quantitative adhesion assay.Changes in the microscopic morphology of mature biofilms under the effect of drugs were observed by scanning electron microscopy.Changes in the expression of biofilm-asso-ciated genes BaP,BfS,OmpA were detected by reverse transscription PCR(RT-PCR)after the administration of tannic acid and imipenem alone and in combination.Results The MICs of tannic acid and imipenem against 30 CRAB strains ranged from 32 to 256 μg/ml,and the FICI values of tannic acid combined with imipenem ranged from 0.625 to 1,which showed additive effects.Compared with the control group,tannic acid combined with imipenem could effectively inhibit the formation of biofilm and destroy the structure of mature biofilm,and the biofilm-related genes of BaP,BfS,OmpA and were expressed at a low level in the strains,and the differences were statistically significant(t=26.32,79.17,29.22,all P<0.05).Conclusion For CRAB,tannic acid in combination with imipenem showed additive effects.The anti-biofilm effect of tannic acid in combination with imipenem may be realized by inhibiting the expression of biofilm-related genes BaP,BfS,OmpA.

Objective To explore the clinical application of antibiotics Ceftazidime(CAZ) and Cefotetan(CTT)by analysis susceptibility and scatter of the CAZ adn CTT against Escherichia coli(ECO) and Klebsiella pneumoniae(KPN).Methods The drug sensitivity analysis of 1 311 strains of ECO and 898 strains of KPN isolated from 2012 to 2015 and the relationship between CAZ and CTT was analyzed by using the Whonet 5.6 software.Results The resistance rate of ESBL+ KPN to CAZ was 41.2％ and the rate to CTT was 14.1％,the difference was statistically significant(P<0.05).The resistance rate of ESBL+ ECO to CAZ was 34.6％ and the rate to CTT was 1.1％,the difference was statistically significant(P<0.05).The average value of MIC of CAZ was highest in group of ESBL+KPN,it was 6.39 μg/mL.And it was lowest in group of ESBL-KPN,it was 1.37 μg/mL.The average value of MIC of CTT was highest in group of ESBL+KPN,it was 6.8 μg/mL.And the lowest was in group of ESBL-KPN.The range of MIC of CAZ was 1-64 μg/mL,and the range of CTT was 4-64 μg/mL in all groups.The cross sensitivity of CAZ and CTT was more than 90.0％.The cross resistance was less than 5.0％.The cross sensitivity of CAZ and CTT was less than 70.0％ in ESBL+ group.And the cross resistance was up to 13.4％.Conclusion The cross resistance and cross sensitivity of the two antibiotics is very important in guiding clinical antibiotic selection or replacement.

Objective To study the limitation analysis of Staphylococcus spp Susceptibility Test Kit ATB STAPH 5 from Bi-oMerieux in clinical application and to propose remedy.Methods The coverage area and break point of antibiotics ATB STAPH 5 from BioMerieux were analysed by using CLSI M100-S23 as standard.Results The kit ATB STAPH 5 did not include chloromycetin,oxazolidinones and lipopeptide three antibiotics that were recommend by CLSI.The 16 kinds of antibi-otics break point in the kit ATB STAPH 5 were all not inconsistent or did not contain with the standard of CLSI M100-S23. It may lead to error drug sensitivity tests,false sensitive or false drug resistance.Conclusion Only using this kit ATB STAPH 5 for Staphylococcus spp ,it may occurre errors or mistakes.Other experiments must be corrected before the re-port.