Screening Of Drug-resistance Genes Of Serratia Liquefaciens Causing Cow Mastitis By NGS Technology

Dairy cow mastitis is the most common multiple disease of adult dairy cows.It can isolate a variety of bacteria,fungi,mycoplasma or algae from spontaneous cases.However,in many clinical cases of mastitis,the culture of milk bacteria is negative.Clinical mastitis in dairy cows is characterized by swelling,fever,pain or hard hair.Milk may form clot and sometimes blood.The research on the bacteria that causes cow mastitis is focused on E.coli,staphylococcus aureus,etc.And the study of Serratia is rare,so,this study was conducted on broad-spectrum resistant Serratia,using the OptiRead automated microbiological identification and drug susceptibility analysis system and the Ion torrent S5 sequencer.Genome sequencing was used to analyze the correlation between the gene phenotype and resistance phenotype of Serratia marcescens in Jilin province.During the study,300 milk samples from 15 dairy cattle farms in Jilin province were collected for bacterial isolation and Gram staining.Then the OptiRead automatic microbial identification and drug sensitivity analysis system were used to identify and drug sensitivity tests.144 gram-negative bacteria were isolated from 300 milk samples and identified by OptiRead automated microbiological identification system.18 strains were Serratia.Then 14 antibiotics of 8 classes was selected for drug susceptibility testing.Among them,3 strains of Serratia showed complete resistance.Other Serratia strains also had varying degrees of drug resistance,and the minimum resistant reached to 10 antibiotics.Extraction of gDNA from 3 fully resistant strains and construct library for next-generation sequencing(NGS).After sequencing and splicing the whole genome sequence of 3 strains liquefied marcescens was obtained.Separately compare sequences with drug resistance gene database CARD and arg-annot.The common drug resistance genes of the three strains are strA,strB,AAC(3),bla TEM,which are represents aminoglycosides,beta-lactam antibiotics;There are two strains of drug-resistant genes in common are Qnr,Sul2,Cat,DfrA,MrX,which are represents quinolones,sulfonamides,chloramphenicol,diaminopyrimidines,macrolide antibiotics.Through the NGS and sequence screening in the drug resistance gene database CARD and ARG-ANNOT,drug resistance gene types and gene sequences were obtained.The comparison of genotypes and drug resistance phenotypes provides a scientific basis for studying the drug resistance characteristics of S.liquefaciens and finding and discovering new drug resistance genes and drug resistance mechanisms.The drug mechanism has important social benefits for reducing bacterial resistance,preventing the abuse of antibiotics,and ensuring food safety.