Antimicrobial Resistance Investigation And Genome Sequencing Analysis Of Salmonella Enterica Serovar Weltevreden In Some Regions Of China

Salmonella is a worldwide distributed foodborne pathogen.Common infections can lead to enteritis and invasion-related diseases.As a common zoonotic pathogen,Salmonella has become one of the major threats to global food safety and public health.The Salmonella genus,which consists of Salmonella enterica and Salmonella bongori,contains 2,600 different serotypes.Enterica serovar Weltevreden(hereinafter referred to as S.Weltevreden)is considered to be a serotype originating from India.Previous studies have found that S.Weltevreden has distributed and been prevalent in some regions of Asia(Southeast Asia,etc.)for a long time.Due to its strong sustainable survival ability in water,S.Weltevreden is constantly detected in seafood,which is the primary cause of human enteritis diseases in coastal areas of Southeast Asia.S.Weltevreden may continue to be prevalent and transmitted to other countries through multiple routes of transmission,including ocean currents.S.Weltevreden has also been reported in poultry in recent years.At present,it has been reported that S.Weltevreden presents a regional epidemic trend along the southern coast of China,and is found in both seafood and poultry.Therefore,the systematic study of S.Weltevreden is of significance in veterinary public science.In addition,due to the widespread use of antibacterial drugs,there is a serious problem of antimicrobial resistance in clinical medicine and livestock farming.It is concerned that the continued detection of multiple drug-resistant Salmonella,particularly carbapenem-resistant and polymyxin-resistant Salmonella,could lead to the "embarrassing" dilemma of no drugs being available in the future.Therefore,it is very important to investigate the resistance of Salmonella and to explore the prevalence of the major resistance related genes.Although S.Weltevreden has been reported as a common non-typhoid Salmonella serotype in China(the main disease is intestinal disease),epidemiological studies on S.Weltevreden in China are still very limited,especially lack of studies on the association between animal related strains and human strains.In addition,genome-wide studies on food-borne pathogens such as Salmonella are still in the initial stage in China.Therefore,this study systematically collected S.Weltevreden isolates from major coastal areas in China to compare and study the prevalence distribution and antimicrobial resistance status of different origins and time periods.Through whole genome sequencing and bioinformatics analysis,the correlation between antimicrobial resistance phenotype and antimicrobial resistance genotype of S.Weltevreden isolates in China was further studied,and the dominant genotype,plasmid type,antimicrobial resistance genes and virulence related genes were explored.A total of 170 strains of S.Weltevreden from human,animal,environmental and aquatic sources collected from Shanghai,Zhejiang,Guangdong,Guangxi and Shandong provinces during 1999-2020 were included.All S.Weltevreden isolates were tested for the minimum inhibitory concentration(MIC)of 14 antibacterial drugs.The study found that among all the strains,sulfamethoxazole got the highest drug resistance rate 81.8%(139/170),followed by tetracycline 20%(34/170)and ceftriaxone 19.4%(33/170).In addition,17%(29/170)of the strains showed multiple antimicrobial resistance.Of concern,two strains of human origin were detected to carry the polymyxin-resistant gene MCR-1.1.Epidemiological data showed that the number of S.Weltevreden isolates increased significantly during last 20 years,and the proportion of drug-resistant strains and multi-resistant strains also showed a significant upward trend.Using Illumina second-generation sequencing technology,we sequenced the whole genome of 170 S.Weltevreden strains,and performed bioinformatics analysis,including serotype prediction,multi-sequence locus sequence analysis,antimicrobial resistance gene detection,plasmid type detection,virulence gene-related gene analysis.We found that the sequence type(ST)of all strains was ST365,and the most common drug-resistant gene and drug-resistant plasmid were aph(3")-lb and Inc FII(S),respectively.Notably,some strains of S.Weltevreden carried an important toxin gene,cdt B.We found that S.Weltevreden isolated from China contained 5 clusters with rich genetic diversity.It was found that drug-resistance related genes and plasmid types were correlated with different clusters.At the same time,we further studied the biological characteristics of S.Weltevreden,including its biofilm formation ability,mobility and virulency.It was found that its biofilm formation ability was strongest at 28 ?,while its mobility was strongest in the absence of oxygen.In conclusion,the prevalence of S.Weltevreden in China is on the rise,and the multi-drug resistant strains are mainly from poultry.Whole genome sequencing analysis indicates that the dominant genotype of S.Weltevreden in China was ST365,and there were at least five clusters with rich genetic diversity.This study suggests that we need to strengthen the continuous surveillance of S.Weltevreden and provide a scientific basis for the prevention and control of S.Weltevreden.