Protective Effects Of Organic Acids,Capric Acid And Bacillus Licheniformis On Piglets Infected With Escherichia Coli K88

The test is divided into two parts:an in vitro screening test with acidifiers and an in vivo piglets Escherichia coli K88 challenge trail.Experiment I:1.Four types of organic acids were selected to be used in the in vitro screening test.The MIC and MBC of the four organic acids to 5 types of common pathogens and 2 types of gastrointestinal Lactobacilli in piglets were determined,and one organic acid with strongest antibacterial ability was selected.Four kinds of organic acids and capric acid(medium-chain fatty acids)were combined in vitro and a combination of the most powerful combination was screened by valuing their antibacterial ability.The results of experiment I showed that:(1)Under near-neutral conditions:LMN had weaker bacteriostatic activity against Escherichia coli k88 among the four composite organic acids.LCN had weaker bacteriostatic activity against Staphylococcus aureus than the other three organic acids.The antibacterial activities of LC and LM were almost similar to the five pathogens.The bactericidal abilities of the four organic acids were so weak under near-neutral conditions that they could not kill pathogenic bacteria and Lactobacillus at 32 mg/mL,the highest concentration in the test.(2)Under low pH conditions:The antibacterial activities and bactericidal capacities of the four organic acids were stronger than near-neutral conditions,among which LC had the best antibacterial and bactericidal activity against the five pathogenic bacteria.The two Lactobacilli have stronger resistance to organic acids than pathogens.Overall,LC and LC+CRA were selected for experiment II.Experiment II:Escherichia coli K88 challenge test to piglets.30 three-dimensional hybrid weaned piglets(cocks)which have consistent genetic background,similar age and weight(7.9±0.5 kg),good mental state and healthy body were selected.TA total of 5treatments were performed in the trial:CON=negative control(basis diet);ATB=positive control(basis diet plus 50 mg/kg quinocetone,75 mg/kg chlortracycline,50 mg/kg kitasamycin);OA=basis diet plus 1%organic acid(64%formic acid,25%propionic acid,11%water);OA+CRA=basis diet plus 1%organic acid(64%formic acid,25%propionic acid,11%water)+0.2%capric;OA+PB=basis diet plus 1%organic acid(64%formic acid,25%propionic acid,11%water)+3.3×10~9 cfu/kg Bacillus Licheiformis.Each Treatment had 6 replicates with one piglet.The whole test lasts 23 days.The adaptation period last 6 days,the pre-feed period last 10 days and the formal trial period last 7 days.All the piglets were challenged after the pre-feed period.After 10 days of pre-feeding,the time when piglets were challenged orally with Escherichia coli K88 was regarded as the beginning of the formal test.Blood and fecal samples were collected and fecal scores were valued at 0h,9 h,24 h,48 h,96 h,and 168 h after challenge,and fecal droppings were scored.The rectal temperature was measured at 0 h,9 h,24 h,33 h,48 h,96 h,and 168 h after challenge.The results of the experiment II showed that:(1)After the Escherichia coli K88 challenge,the rectal temperature of piglets in CON group and OA+CRA group increased(P<0.05).At 9 h after challenge,rectal temperature in ATB group,OA group,OA+CRA group and OA+PB group was lower than NC Group(P<0.05).(2)After the Escherichia coli K88 challenge,the index of diarrhea in the 5 groups increased(P<0.05),and the index of diarrhea in CON group was higher than that in the other four groups(P<0.05).(3)After the Escherichia coli K88 challenge,the concentration of TNF-?in CON group,OA group and OA+CRA group increased(P<0.05).At 9 h after challenge,the concentration of TNF-?in CON group was higher than that in other four groups(P<0.05).(4)After the Escherichia coli K88 challenge,the concentration of IFN-?in CON group,OA+CRA group and OA+PB group increased(P<0.05).At 24 h after challenge,the concentration of IFN-?in CON group was higher than that in other four groups(P<0.05).the concentration of IFN-?in CON group,OA+CRA group and OA+PB group increased(P<0.05).(5)After the Escherichia coli K88 challenge,the concentration of IL-1?in CON group increased(P<0.05).At 24 h after challenge,the concentration of IL-1?in CON group was higher than that in OA+CRA group and CON group(P<0.05).At 48 h after challenge,the concentration of IL-1?in the ATB group and the OA group was lower than that in the CON group(P<0.05)and was lower in the PC group than that in the OA+CRA group(P<0.05).(6)After the Escherichia coli K88 challenge,the concentration of IL-6 in CON and OA+CRA groups increased(P<0.05).At 9 h after challenge,the concentration of IL-6 in ATB group,OA group and OA+PB group were lower than that in CON group(P<0.05).(7)After the Escherichia coli K88 challenge,the concentration of IL-12 in OA+CRA group(P=0.063)and the concentration of IgG in CON group trend to increase(P=0.061),the concentration of plasma IgG in OA+CRA group significantly increased(P<0.05).At 96h after challenge,the concentration of plasma IgG in CON group were higher than that in the other four groups(P=0.099).In a conclusion,LC,combination of LC and citric acid were screened by antibacterial,bactericidal and synergic antibacterial tests.Endogenous piglet Escherichia coli challenge test has verified:the addition of 1%organic acid could alleviate the inflammatory response caused by Escherichia coli K88 infection,and it could reduce the inflammation-induced fever and diarrhea,and the mitigating effect is equivalent to the addition of antibiotics.However,the combination of medium-chain fatty acids or probiotics could not make further improvements.