Effect Of Lysozyme On Preventing And Treating Rabbit Colibacillosis

Rabbit colibacillosis,also known as the mucous enteritis,is an intestinal disease caused by pathogenic Escherichia coli(E.coli)and its toxins.The morbidity and mortality of this disease are very high in 3-month-old kits.Farmers used numerous antibiotics to control it,but the abuse of antibiotics led to antibiotics residues and the occurrence of antimicrobial-resistant bacteria.Lysozyme is a new biotechnological feed additive.It can kill bacteria without causing antimicrobial resistance and harming animals.These studies were conducted in vitro and in vivo to verify the effect of lysozyme on preventing and treating rabbit colibacillosis.Bacteriostatic test in vitro:An enteropathogenic Escherichia coli(EPEC)strain with eaeA gene obtained from the institute of animal husbandry and veterinary science was used in the test.The concentration of lysozyme products was determined by turbidimetric method,and the results showed it was 0.049%in the powder product and 0.0889 ?g/ml in the liquid product.The strain was cultured in tryptone soya broth(TSB)with serially diluted lysozyme,and the result showed the minimum inhibitory concentration(MIC)of lysozyme is 6.223×10-4 ?g/ml.Log-phase E.coli cultures were treated with 10%lysozyme,1%lysozyme and 0.1%lysozyme respectively and examined under transmission electron microscopy.The result demonstrated that the inhibitory effect of lysozyme was significant because the cell wall of E.coli was destroyed and the contents flowed out after treatments.The study of therapeutic effect of lysozyme on colibacillosis is divided into three parts:intraperitoneal toxicity test,the effect of lysozyme treatment on rabbit intestinal flora,blood antioxidant index and immune index,and clinical treatment experiment.Intraperitoneal toxicity test:45 rabbits aged 30 days were divided into Control Group,Infection Group and Treatment Group.The Infection Group and Treatment Group were induced with 1ml 1.4×109CFU/ml of E.coli by peritoneal injection.Rabbits in the Control Group were injected with lml physiological saline.The Treatment Group was treated with 1ml of lysozyme(0.0889?g/ml)once a day for 3 days.Determine the white blood count(WBC)values of the rabbits before and 5 days after injection.The results showed that the WBC values in the Infection Group increased significantly after injection,the WBC values in the Control Group and the Treatment Group changed little before and after the injection.The death rate of the Infection Group was 40%,the death rate of the Treatment Group was 20%,and the curative effect of lysozyme treatment was obvious.The effect of lysozyme treatment on rabbit intestinal flora,blood antioxidant index and immune index:24 rabbits aged 30 days were divided into Control Group,Infection Group,Lysozyme Group and Antibiotic Group,orally inoculate with 1×1010 CFUs E.coli daily for 3 days.Lysozyme treatment group rabbits were continuously treated with 1 ml liquid lysozyme product,and antibiotic treatment group rabbits were continuously treated with 1 ml ciprofloxacin lactate.Measure the blood antioxidant indexes(SOD and MDA)and blood immune index(IgG and IgA)of rabbits in each group.Samples of cecal contents were collected and sequenced,and the flora polymorphism was analyzed.The results of blood antioxidation and immune blood immune index have no obvious difference,flora analysis results for lysozyme is similar to ciprofloxacin,can effectively kill the bacteria,but also have a great impact on the normal intestinal flora.Clinical treatment study:One hundred and Eighty diseased rabbits were divided into three groups with each 60 rabbits according to symptom level.The experimental groups were treated with different medicine including lysozyme,ampicillin and norfloxacin respectively.In the lysozyme group,all the rabbits were fed with medicine mixed forage.The results showed that effective rate of lysozyme group was up to 93.3%.The effect of lysozyme treatment is remarkable.The study of preventive effect of lysozyme on colibacillosis:seventy-two 20-day-old rabbits were equally divided into 4 groups with similar average weight as Control Group;Infection Group;Lysozyme Group;and Infection + Lysozyme Group.Rabbits in control group and infection group were fed basal diet and other rabbits were fed basal diet added lysozyme.Infection group and Infection + Lysozyme group rabbits were continuously inoculated with 1×1010 CFUs E.coli via mouth for 3 days at the 21st day of the experiment.The results showed that weight gain and feed conversion ratio were significantly increased by lysozyme.Moreover,lysozyme demonstrated a strong preventive effect on experimentally E.coli infection.