Modulating Antibiotic Resistance Of Bacteria By Non-antibiotics

The human as well as the economic costs of antibiotic resistance are already enormous as an increasing number of people are getting infected by resistant bacteria.Antimicrobial resistant infections currentlyaccount for approximately 50,000 deaths each year in Europe and the US alone and by 2050 these infections have been estimated to kill an extra 10 million people and 100 trillionevery year globally if nothing is done to prevent the growing antibiotic resistance.Currently,antibiotic consumption in China accounts for about half of the total amount of the world,in addition,the increasingly emergence of new "super superbugs" suggested that it is important that action is taken to conserve the existing antibiotics,provide new antibiotics anddevelop new treatment strategies.The aim of this study is to survey the status of distribution of antibiotic resistance bacteria in a large scale meat processing plant in China and to screen potential helper drugs.Then choose which with broad-spectrum antibiotic synergist performance of antibiotic drugs to further study the effects of non-antibiotics alone or combined with antibiotics on bacteria by method such as transcriptome.Furthermore,to identify their possible effect on conjugation,and finally investigate the the influence of helper drugs alone or combined with antibiotics on intestinal microbial flora through animal models.The study hypothesised that antimicrobial resistant bacteria change their metabolic and biosynthesis activity in an effort to adapt to therapeutic concentrations of helper grugs and/or antibiotic,and the helper grugs and/or antibiotic change the conjugation efficiency and intestinal microbial flora.If the hypothesis is successful,these changes will create an opportunity to specifically increase the susceptibility of antibiotic resistant bacteria by targeting such drug-induced phenotypic adaptations and inhabitation of antibiotic resistance transference using helper drugs.The first part of this thesis focused on investigating the prevalence of antibiotic resistance bacteria and resistance genes in China,and evaluating the potential role of the culturable bacteria in raw pork as a reservoir of resistance genes,which was carried out by random sampling of raw pork samples from a large scale pig slaughterhouse,and then by isolation and identification of different phenotype of strains,analyzing of phenotype and genotype of antibiotic resistance,locating the mobile genetic elements and finally examing the transference ability of the elements.The results of this study showed that it is quite easy for raw pork to be contaminated by various bacteria species and genus during processing,mainly by commensals,pathogens and spoilage organisms.It was deducible that the contamination sources of the raw pork were mainly from fecal and environmental sources from the bacteria species and genus isolated.Moreover,it is quite commom that the bacteria was found to exhibite different levels of resistance and carry antibiotic resistance genes,irrespective of resistant phenotypes.Mobile genetic elements in different bacterial species were easily transferred between different species.Various kinds of bacteria in pork can be reservoir of resistance genes and mobile genetic elements.Besides,a few new carries of resistance genes were identified in this study.The second part of this thesis screened the potential helper drugs by determination of the minimal inhibitory concentrations?MIC?and minimum bactericidal concentration?MBC?,as well as growth viability under different concentrations of three major categories,a total of eight kinds of non-antibiotics.Studies showed that phenothiazine and thiamethoxam tons,tricyclic antidepressants and selective serotonin reuptake inhibitors?SSRI?antidepressants have antibacterial activity both on Gram-positive bacteria and Gram-negative with different activities.Preliminary experiment showed that in vitro antibacterial activity of sertaline belonged to SSRI on E.coli was the highest.Sertraline can increase the susceptibility of E.coli to tetracycline,ciprofloxacin ad meropen.It showed synergistic effect with tetracycline,but also showed antagonism effect when combined with ciprofloxacin and meropen.Based on the above research,the third part of this thesis investigated the mode of action of non-antibiotics?sertraline?with broad-spectrum antibiotic synergist performance by methods such as transcriptome study.Results from this study showed that sertraline affect bacterial growth in a concentration-depend manner,and act synergistic with tetracycline in an E.coli mediating tetracycline resistance trough intracellular acidification,a shift from oxidation to fermentation and decrease in proton motive force,also sertraline combined with tetracycline affected global metabolic pathways,especially the transcriptional level of ribosomal and purine metabolism associated genes.The fourth part of this thesis further explored the effect of sertraline alone or combined with tetracycline on conjugation and resistance transference.Results of this study showed the sub-inhibitary concentrations?1/2 MIC?of sertraline combined with tetracycline treatment significantly reduced the conjugation rates which induced by tetracycline.Sertraline with sub-inhibitary concentration and tetracycline with low concentration has no observable effects on conjugation in gut of chicken.However,we found that sertraline alone or with tetracycline treatment significantly reduce the number of APEC O₂ in intestines of chicken.The results showed that the combination of sertraline with tetracycline treatment could not only help to reduce the use of antibiotics that would be used in treatment of pathogens infection,but also could reduce the potential impact of in vitro plasmid mediated resistant clonal expansion.The fifth part of this thesis aimed to explore the effects of sub-inhibitory concentration of sertraline alone or combined with tetracycline on intestinal microbial flora through animal model,which helps to deepen the understanding of gut microbes ecosystem,provides insight in understanding the influence of non-antibiotics on gut microbiome,as well as the development of new treatment strategies and reasonable limit the use of antibiotic compounds.The results showed that sub-inhibitory concentration of sertraline combined with tetracycline can affect the abundance and diversity of the microbial community more or less in both ileum and cecum,can specifically interfere with specific members of the microbial population,and resulted in differences in microbial communities in the ileum and cecum.Overall,the presented work revealed the status of prevalence of antibiotic resistance bacteria in meat product in China,provided valuable reference for studying the modulation mechanism of sertraline to tetracycline resistance and insight into understanding the influence of non-antibiotics on gut microbiome.These findings could be the stepping stone for development of helper drugs that are capable of increasing the susceptibility of bacteria to tetracycline and broaden the understanding of the relationship between gut microbiome and human health which would ultimately lead to the development of new treatment options.