Research On The Prevention And Control Of Salmonella Kentucky On A Large Scale Dairy Farm

Salmonella is an important zoonotic intestinal pathogen in the world.As a contact transmission infectious pathogen,it usually causes dairy cows diarrhea clinically.Sepsis,intestinal and reproductive system diseases are all potential clinical manifestations of Salmonella infection in cattle.Among them,reproductive system diseases only attract attention in sexual maturity female cattle,while intestinal diseases can occur in susceptible cattle at any age.Salmonella can potentially infect cows for a long time and intermittently excrete bacteria,causing contamination and transmission,which can easily harm human health by contaminating dairy or beef products.As the source of dairy production,it is necessary to monitor Salmonella in cattle farms to improve the food safety index of China.This study conducted Salmonella monitoring on a large-scale dairy farm in Jiangsu Province over a long period of time.On December 2021,S.Kentucky was isolated from 77.8%of calf feces.Some calves experienced intestinal diseases such as diarrhea and bloody feces.In order to identify the source and key links of contamination of S.Kentucky in the farm,seven different sampling plans were designed,with a focus on exploring the spread patterns of S.Kentucky in the farm.Combined with laboratory testing and on-site research,prevention and control suggestions for S.Kentucky were proposed,ultimately solving the problem of Salmonella prevalence in the dairy farm.During the period from December 2021 to July 2022,a total of 720 different samples were collected from the farm,and 144 strains of S.Kentucky were isolated,with a total isolation rate of 20%.They were mainly isolated from calving sheds(87.8%)and lactating sheds(12.2%),but no S.Kentucky was isolated from special and adult sheds.Out of 192 fecal samples,68 strains(35.4%)of S.Kentucky were isolated,and 273 bedding samples were obtained,74 strains of S.Kentucky were isolated,with a separation rate of 27.1%.160 feed samples,no S.Kentucky isolated.Among other environmental samples,only 2 strains of S.Kentucky were isolated from calf drinking water samples,with a separation rate of 3.6%.Antibiotic resistance test of S.Kentucky isolates found that all strains were resistant to ampicillin,nalidixic acid,ciprofloxacin,streptomycin,cefazolin,cefothiazide,tetracycline,gentamicin,and compound sulfamethoxazole,showing multiple drug resistance.Select 12 S.Kentucky isolates from different batches and sample types for whole genome sequencing analysis.The results showed that the difference in SNPs between the 12 sequencing strains was less than 5,indicating that the contamination was caused by the clonal transmission of the same strain of ST 198.2-1 S.Kentucky in the field.The isolated strains were closely related to a human isolate PC8212 from Germany and JC6095 from Belgium,with SNPs differences of≤15.All isolates carry 12 resistance genes,including blaCTX-M-9,aph(3")-Ⅰb,aph(3)-Ⅰa,aph(6)-Ⅰd,aac(3)-Ⅰd,aadA7,sull,qacE,strA,strB,tet(R),and tet(A),endowing the isolates with resistance to β-Drug resistance phenotype of lactam,sulfonamide,tetracycline,and aminoglycoside antibiotics.Attention should be paid to the hazards such as increased drug resistance caused by long-term cloning and transmission of S.Kentucky.Epidemiological data show that 97.7%of S.Kentucky isolates come from bedding-related samples,indicating that bedding circulation is a key prevention and control point for S.Kentucky pollution in this field.In order to effectively prevent and control the spread of S.Kentucky,eight different types of disinfectants were tested for their efficacy against S.Kentucky.The results showed that the use of four disinfectants,namely Glutaral and Deciquan Solution,Anritsu disinfectant,Compound Glutaraldehyde,and Compound Bromogeramide,had a certain bactericidal effect on S.Kentucky.In addition,the quaternary ammonium salt disinfectant tolerance gene qacE was found in all sequencing strains.Therefore,it is recommended that compound glutaraldehyde be preferentially selected for environmental disinfection and sterilization in this field.Further investigation into the processing technology of pad materials in the field has found that the steps of"solid-liquid separation" and "aerobic fermentation" were key steps in killing microorganisms in the production line.It is recommended to increase the working temperature of the solid-liquid separation machine or add solid-liquid separation equipment to make the dry and wet separation of feces more thorough.At the same time,it is also recommended to extend the aerobic fermentation time and utilize the high temperature generated inside the stacked aerobic fermentation to more effectively kill pathogenic bacteria.Finally,it is also suggested that the site should carry out disinfection and sterilization for the water circulation system to eliminate the risk of Salmonella transmission caused by water circulation.After the above prevention and control measures,in February 2022,samples were collected from the production area mat samples for bacterial isolation.The results showed that in the wet mat samples,the isolation rate of S.Kentucky was 16.6%,while in the dry mat samples,the isolation rate of S.Kentucky was 0.One S.Kentucky strain was isolated from the aerobic fermentation surface sample collected on May 20,2022,in the production area;On July 20,2022,no S.Kentucky was isolated during monitoring.In general,there is a clonal relationship between different sample types of S.Kentucky isolates from different cattle houses in the farm,and there may be a horizontal transmission,vertical transmission,and cross-contamination.The use of compound glutaraldehyde for overall disinfection and sterilization and the optimization of key links in the bedding production cycle can achieve the effect of prevention and control of S.Kentucky.