Study On The Effect Of Physical And Chemical Factors During Food Processing On The Drug Resistance Of Salmonella Enterica Serovar Typhimurium And Related Mechanisms

Antibiotic resistance in Salmonella enterica serovar Typhimurium(S.Typhimurium)has become a critical safety hazard in food.The sublethal environmental stresses during food processing will make Salmonella adapt to genotype and phenotype to respond to environmental pressure,thereby reducing the impact of pressure and increasing cell viability,triggering changes in antibiotic resistance,and causing safety hazards to food safety and human health.The generation and transmission mechanism of drug resistance in S.Typhimurium has become a research hotspot.Most of the current research focuses on the gene level,which requires a more comprehensive explanation of the mechanism of drug resistance in molecular biology and biochemistry.In this paper,two wild-type strains of chicken processing isolates(CPI)and pig breeding isolates(PFI),and ATCC 14028 standard strains(14028s)were used as the research object to study the growth and decline of drug resistance of S.Typhimurium after physical and chemical environmental stress in the process of processing.Based on metabolomics and transcriptomics,the response of drug resistance changes in gene level and metabolism level after stress was analyzed,so as to provide guidance for meat processing and provide valuable reference for the study of drug resistance mechanism.The main contents are as follows:The drug resistance of Salmonella under different p H and temperature stress was studied,and the effects of acid-base environment on extracellular Adenosine-triphosphate(ATP)and membrane surface morphology were explored.The results showed that acid and alkaline stresses(p H 5.0,p H 6.0,p H 8.0,p H 9.0)reduced the resistance of S.Typhimurium to eight antibiotics;meanwhile,the resistance of meropenem(MERO)increased.The minimal inhibitory concentration(MIC)of MERO was increased 16-to 64-fold.With acid or alkaline stress,the extracellular ATP content increased,and the scanning electron microscopy(SEM)result clearly revealed the appearance of wrinkles and holes on the outer membrane of S.Typhimurium.These observations imply changes in membrane permeability,which may decrease the antibiotic resistance of S.Typhimurium.Cold(-20?,4?)or heat(55?)stress increased the resistance of S.Typhimurium to tetracycline,cefotaxime,ceftazidime,nalidixic acid,azithromycin,and ampicillin;the MIC increased 2-to 4-fold.The antibiotic resistance only changed when cold and heat stresses occurred over a certain period of time and remained unchanged when the stress persisted.Objective to study the resistance changes and metabolic profile of the standard strain ATCC 14028 s after disinfectant stimulation.This study selected sodium hypochlorite(SH,1?g/m L),chlorhexidine(CH,2 ?g/m L),benzalkonium chloride(BC,8 ?g/m L)and cetyl pyridine chloride(CTPC,8 ?g/m L)respectively stress of S.Typhimurium ATCC14028 s,stress strain after the determination of disinfectant resistance and antibiotic resistance.The results showed that the resistance of Salmonella to four kinds of disinfectants was almost unchanged after stress,but the resistance to some antibiotics changed significantly.The resistance of Salmonella strains to ciprofloxacin and ampicillin increased significantly after stress of CH and SH,the MIC increased 2-to 4-fold;the resistance to gentamicin decreased,the MIC decreased2-fold.The resistance to ciprofloxacin,tetracycline and gentamicin of strains stressed by BC and CTPC was increased,the MIC increased 4-fold.Metabolism results showed that the minimum inhibitory concentration of BC and SH stress down-regulated the metabolites of pantothenic acid,glycine and glutamate in the cell,which had a huge impact on the pathways related to amino acid metabolism and energy metabolism.The mechanism of ATCC 14028 s resistance change after acid stress was studied.Objective to understand the physiological mechanism of antibiotic resistance under acid stress by transcriptomics and metabolomics.Metabolomics and transcriptomics analysis indicated that acidic stress-induced S.Typhimurium utilized an energy-saving strategy by up-regulating the purine metabolic pathway and enhancing the TCA cycle to accelerate energy metabolism(metabolites xanthosine,adenine,citric acid,succinic acid,ATP,and the gua C gene were upregulated).Bacterial chemotaxis was weakened(genes tcp,che A,che W,and trg and metabolite D-Ribose were down-regulated)and bacterial membrane synthesis ability was decreased,explaining the decreasing resistance of 14028 s to antibiotics,azithromycin,sulfamethoxazole,and streptomycin.Acidic stress leads to damage or severe reduction of porins,impeding the ability of carbapenems to enter the bacteria through the outer membrane system(OM),resulted in the increased resistance of Salmonella to MERO.Transcriptomics analysis revealed that Salmonella up-regulated the omp F gene to compensate for porin damage under acid treatment.