| ObjectiveThis paper describes the distribution and dynamic change characteristics of salmonella in environmental sewage in Guangzhou from February 2022 to January2023,and then predicts the prevalence of salmonella infection in the population in Guangzhou.Genotyping database was established to provide theoretical data for future outbreak tracing and disease early warning.In addition,to understand the status quo and harm of salmonella drug resistance,reveal the resistance mechanism of Salmonella,and provide theoretical reference for clinical treatment of salmonella infection and prevention and control strategies of Salmonella infection.MethodFrom February 1,2022 to January 31,2023,samples were collected in Yuexiu District,Haizhu District,Baiyun District,Panyu District,Nansha District,Huadu District and Zengcheng District of Guangzhou.Serological identification,drug resistance phenotype,drug resistance genes and phylogenetic analysis of molecular typing were carried out.1.Serological identification of isolated strains was performed by slide agglutination method.2.The minimum inhibitory concentration of the isolates against 17 antibiotics was detected by microbroth dilution method,and the drug resistance phenotype and spectrum of the isolates were analyzed.3.PFGE technology was used for molecular typing and homology analysis of the isolated strains,and genetic characteristics of the strains were analyzed.4.Use whole genome sequencing technology combined with bioinformatics to detect drug-resistant genes.Multiple site sequence typing(MLST)and whole genome single nucleotide polymorphisms(wg SNPs)were used to analyze the bacterial community structure and phylogenetic relationships among strains.Results1.Salmonella detection in sewage showed that salmonella was detected in 156 out of 660 samples of sewage collected,and 246 strains of Salmonella were isolated,the detection rate of Salmonella was 23.64%.The total detection rate in March was the highest with 36.36%,followed by 32.73% in July and September,and 29.09% in August and October.The difference of detection rate in each season was statistically significant,with the highest detection rate in spring and autumn.The detection rates of salmonella were different in different places.The highest detection rates were found in restaurants and sewage treatment plants(35.71% and 33.97%,respectively),followed by markets and hospitals(22.62% and 21.43%,respectively).The detection rates of Salmonella were different in different districts.Baiyun District and Nansha District had the highest detection rates of 37.50% and 33.33% respectively,followed by Panyu District and Huadu District with 23.81% and 23.33% respectively.3.Serological identification results showed that 202 strains of Salmonella type I(enteric Salmonella subspecies),27 strains of Salmonella type II(enteric Salmonella Salam subspecies)and 1 strain of Salmonella type IV(enteric Salmonella Haotun subspecies)were identified,while 16 strains of Salmonella were not identified serotype.The dominant serotype was S.1,4,[5],12:i:-,accounting for 25.65%.Followed by Rosen and Derby,accounting for 8.70% and 4.78% respectively;Many rare Salmonella serotypes were detected,such as Agona,Budapest,Vilchot,etc.,accounting for less than 1%.4.PFGE study showed that Salmonella strains showed genetic polymorphism,showing highly sporadic epidemic characteristics.PFGE fingerprints had no obvious regional or time specificity,but the similarity of the same serotype was generally relatively high.Meanwhile,the similarity of the fingerprint of human salmonella and Salmonella in sewage was between 50% and 100%.5.The results of drug sensitivity test showed that the isolates had the highest resistance rate to ampicillin,tetracycline,streptomycin,chloramphenicol and cotrimoxazole,with the resistance rate reaching more than 80%.The intermediate rate of polymyxin E and ciprofloxacin was higher.Tigacycline was 100% sensitive,meropenem,ertapenem,ceftazidime/avibactam,and amikacin were all over 90%sensitive.Multiple drug resistance was serious and multiple drug resistance spectrum was diverse.6.Drug resistance genes had a high carrying rate and varied types,mainly consisting of aminoglycosides,βlactam,tetracycline,sulfonamides and other 13 kinds of drug resistance genes,and the overall coincidence rate between drug resistance phenotypes and drug resistance genotypes was good.Multiple pump protein genes associated with multiple drug resistance were detected.7.MLST typing and whole genome single nucleotide polymorphism analysis showed that ST34 was the dominant clonal prevalent,and ST typing was correlated with serotype.Local Salmonella strains have relatively clear phylogenetic clades,with a total of 11 clades,and different ST clones generally belong to different clades.Some isolates were closely related to human salmonella in Guangzhou and foreign isolates.Conclusions1.The overall detection rate of salmonella in sewage was high,mainly in spring and autumn,among which,the detection rate of Salmonella was the highest in sewage treatment plants and restaurants,Baiyun District and Nansha District,suggesting that there were large food safety risks in these months,places and regions.Supervision and publicity and education should be strengthened to prevent the outbreak of food-borne diseases caused by salmonella.2.There were many serotypes of salmonella in sewage,and the dominant serotype were S.1,4,[5],12:i:-,which can detect rare serotypes except reported cases and poultry,which was of great significance for the prevention and control of infectious diseases.Therefore,environmental sewage monitoring should be used as a routine monitoring method.3.Salmonella in sewage showed genetic polymorphism and highly sporadic prevalence,without local outbreaks.The PFGE fingerprints of salmonella in sewage were similar to those of Salmonella in human population,suggesting horizontal transmission of salmonella in human population and sewage.4.Salmonella in sewage had serious drug resistance and multiple drug resistance,and its drug resistance spectrum was diverse.The resistance mechanism mediated by mobile genetic elements such as drug resistance genes was the main cause of drug resistance and multiple drug resistance.5.Salmonella in sewage was cloned by ST34,which had an epidemic trend in Guangzhou sewage and was not easy to mutate.There was a correlation between ST type and serotype.6.Salmonella strains in sewage had a relatively clear phylogenetic clade,ST34 group S.1,4,[5],12:i:-probably evolved from the ST34 clone of Salmonella typhimurium,and the clones that were prevalent in human populations were still prevalent in Guangzhou. |
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