The Effect Of A New Cephalosporin Compound NAC-19 Against Methicillin-resistant Staphylococcus Aureus

Staphylococcus aureus(S.aureus)an opportunistic pathogen,is a high priority pathogen in the global assessment of antibiotic resistance in the World Health Organization.It can provoke a range of diseases including sepsis,pneumonia,endocarditis,toxic shock syndrome and implant associated biofilm infections.Among them,methicillin-resistant Staphylococcus aureus(MRSA)strains exhibited higher pathogenicity,high infection rate and mortality compared to methicillin-sensitive Staphylococcus aureus(MSSA).Antibiotic therapy has been considered the primary treatment strategy for S.aureus infection,and its widespread application has greatly improved the prognosis of patients with S.aureus infection.For the past 70 years,no drug has proved to be cheap and effective in treatment of fatal diseases as antibiotics.With the rise of multidrug-resistant bacteria,old antibiotics have become powerless,and most large pharmaceutical companies have withdrawn from antibiotic research.Therefore,new strategies are needed to treat infections caused by methicillin-resistant Staphylococcus aureus,such as the development of new antibiotics,antibacterial synergists,and new vaccines.In this study,we evaluated the in vitro antibacterial activity of 10 newly synthesized cephalosporin antibiotics through the minimum inhibitory concentration(MIC),determined their MIC against 60 Gram-positive bacteria and 60 Gram-negative bacteria,and finally screened out the compound NAC-3 and NAC-19 exhibits excellent antibacterial activity in vitro.Further determination of the minimum inhibitory concentration of NAC-3 and NAC-19 against 20 clinical isolates of Staphylococcus aureus and Escherichia coli,once again proved that they still showed good inhibitory concentration against clinically isolated Staphylococcus aureus,but its antibacterial effect on Gram-negative bacteria is general.Both compounds have good antibacterial effect on MRSA in vitro,whether it also has protective activity in vivo,we further established a systemic infection model in mice,the results showed that NAC-19 and NAC-3 have a good protection against systemic infections in mice caused by MRSA strain USA300 and clinically isolated Staphylococcus aureus SA1B2 B,SA28.Among them,the therapeutic effect of NAC-19 is significantly better than that of NAC-3 and the commonly used clinical antibiotics cefepime and latamoxef.Based on the above experimental results,the new cephalosporin compound NAC-19 was selected as the research object to further study the effect of MRSA.NAC-19,a methoxycephalosporins semi-synthetic antibiotic with cephalosporin C as a precursor material,has strong resistance to ?-lactamase due to the presence of cephalosporin C mother nucleus.NAC-19 has a strong antibacterial effect on aerobic and anaerobic bacteria that can produce ?-lactamase.The minimum inhibitory concentrations of NAC-19 against methicillin-sensitive Staphylococcus aureus(MSSA)ATCC 29213 and methicillin-resistant Staphylococcus aureus(MRSA)USA300 were 0.5 ?g/mL and 8 ?g/m L,respectively.Moreover,we observed that NAC-19,a rapidly bactericidal agent with activity against MRSA and a longer post-antibiotic effect by in vitro.We further evaluated the in vivo antibacterial effect of NAC-19 and established mouse neutrophil-induced thigh infection models,mouse pneumonia protection models caused by MRSA strains respectively.The results showed that NAC-19 demonstrated potent in vivo effect on thigh infection and mouse pneumonia caused by S.aureus USA300.At present,the combined use of drugs is considered to be an effective strategy to effectively use the existing medical resources,reduce the dosage of drugs,reduce the side effects of drugs,and prevent the emergence of bacterial resistance.Sortase a(srtA)is an important virulence factor of Staphylococcus aureus.Early experiments found that isovitexin can effectively inhibit the SrtA-mediated adhesion of Staphylococcus aureus in vitro.We further evaluated the protective effect of the combination of isovitexin and NAC-19 on Staphylococcus aureus induced pneumonia in mice.The results showed that the combination of NAC-19 and isovitexin can significantly reduce the pathological damage and inflammatory response of the lung tissue of mice with S.aureus infectious pneumonia,reduce the lung bacterial load,and significantly improve the survival rate of mice.In order to confirm its antibacterial activity,the combined antimicrobial mechanism of NAC-19 and isovitexin was finally analyzed.The results showed that isovitexin could specifically bind to SrtA,thereby interfering with the adhesion and invasion of bacteria to epithelial cells,and exerting a significant antibacterial effect cooperate with NAC-19 in vivo.In summary,the new cephalosporin compound NAC-19 exhibited excellent antibacterial activity in vitro and in vivo against MRSA infections.In addition,isovitexin is used as a SrtA inhibitor in combination with NAC-19,which reduced the amount of drugs and showed excellent antibacterial activity.NAC-19 may be excellent candidates for novel against S.aureus infections and it provides a new strategy for alleviating the problem of multidrug resistance and has important clinical application value.