In vitro and in vivo antibacterial activity of shrimp chitosan against some intestinal bacteria

ABSTRACT:   The effects of shrimp chitosan with deacetylation degrees (DD) of 50%, 70% and 95% (DD50, DD70, DD95) on the growth of the intestinal bacteria were investigated in vitro in the laboratory media, and in vivo by an oral feeding test using hamsters as the animal model. The antibacterial activities of these chitosan products against one strain of pathogenic Clostridium perfringens and 13 strains of probiotics, including seven strains of Lactobacillus , and six strains of Bifidobacterium were evaluated. In vitro , the antibacterial activities of DD95 and DD70 were much higher than that of DD50. The strains of probiotics were more resistant to chitosan than the pathogen of C .  perfringens . The minimal lethal concentration for DD95 against C. perfringens was 250 p.p.m., whereas the survival percentages for most probiotics tested were above 90% for DD95 at 500 p.p.m. The animals were fed on either a control diet, or diets containing powdered chitosan instead of 5% cellulose in the control diet for 4 weeks. The cecal bacterial counts of total aerobes, total anaerobes, lactobacilli, bifidobacteria and clostridia were similar for the control and experimental groups. The reasons for the differences in the antibacterial activity in vitro and in vivo are discussed.     

Bacterial degradation of antibiotic residues in marine fish farm sediments of Uranouchi Bay and phylogenetic analysis of antibiotic-degrading bacteria using 16S rDNA sequences

ABSTRACT:   Antibiotic residues in marine sediments of fish farms negatively influence microbial ecologic systems. The microbial degradation of antibiotic residues was experimentally examined in the marine sediments of Uranouchi Bay, to which one of five antibiotics was added. After incubation reducing physical factors, ampicillin, doxycycline, oxytetracycline, and thiamphenicol were significantly degraded, while josamycin maintained most of the initial amounts. The isolates resistant to ampicillin, josamycin, oxytetracycline, or thiamphenicol degraded each antibiotic in wide ranges of degrees, whereas the isolates degrading doxycycline were not obtained. Microbial degradation may contribute to the disappearance of ampicillin, doxycycline, oxytetracycline, and thiamphenicol in the fish farm. In contrast, the disappearance of josamycin would depend on physical factors, but the bacteria degrading josamycin at least exist in the marine sediments. Phylogenetic analysis using 16S rDNA sequences demonstrated that the antibiotic-resistant isolates formed several clusters in the Gram-positive bacterial group, the Flavobacterium–Cytophaga–Bacteroides group, and the proteobacteria subdivisions. The antibiotic-resistant bacterial population would be composed of various species including ubiquitous coastal bacterial groups. Several species of antibiotic resistant bacteria show antibiotic degradation activities, and appear to contribute to the disappearance of antibiotics in Uranouchi Bay.     

Cortisol stimulates intestinal fluid uptake in Atlantic salmon (Salmo salar) in the post-smolt stage

The fluid uptake rate of the posterior intestine of salmonids increases during the parr-smolt transformation. Intestinal fluid uptake in post-smolt Atlantic salmon was investigated after treatment with cortisol and growth hormone (GH), alone or together. Two replicate experiments were conducted in August 1991 and August 1992. Cortisol was emulsified in vegetable shortening and vegetable oil (1:1) and implanted into the peritoneal cavity. GH was administered as intraperitoneal injections in a saline vehicle on days 0 and 2. On days 5 and 6, plasma cortisol levels, gill Na⁺,K⁺-ATPase activity, andin vitro measurements of fluid transport rate (J_v) across the posterior intestine were measured. Implants of cortisol elevated the plasma cortisol levels within a physiological range, and resulted in elevated gill Na⁺,K⁺-ATPase activity, as expected. The fluid uptake rate across the posterior intestine was roughly doubled by cortisol treatment. GH treatment did not affect intestinal fluid transport, gill Na⁺,K⁺-ATPase activity, or plasma cortisol concentrations. The seawater-adapting increase in the rate of fluid uptake by the posterior intestine of smolting salmon is probably stimulated by elevated plasma cortisol concentrations.     

Antimicrobial activity in bacteria isolated from Senegalese sole, Solea senegalensis, fed with natural prey

Intestinal bacteria in marine fish may produce antimicrobial substances which inhibit pathogenic bacteria. The aim of this study was to determine the influence of a change of fish diet on the antimicrobial activity of the culturable aerobic gut microflora of Senegalese sole, Solea senegalensis. Pre‐adult 15‐month‐old fish previously fed on an artificial diet, were fed polychaetes (Hediste diversicolor), which form part of the natural diet of Senegalese sole. Samples were taken0, 3 and 6 weeks after start of the experiment from the stomach, small and large intestine of the fish. The bacterial strains isolated from these samples were sub‐cultured to pure cultures and stored at ?80°C. Several biochemical tests were run to obtain some basic phenotypic characteristics of the isolated strains. Amplification and sequencing of 16S rDNA fragments were used to identify the majority of the bacterial strains isolated. The identification by use of this molecular approach gave results in agreement to the phenotypic characterization. Feeding with polychaetes significantly increased (P<0.05) the numbers of presumptive Vibrio isolates in the gut. The number of bacterial strains with antimicrobial activity, as determined by two in vitro approaches, was significantly (P<0.05) increased by feeding with polychaetes.     

益生菌健康功能的研究进展

益生菌是活的微生物,当摄入足够数量时,对宿主起有益健康的作用。益生菌的健康作用逐步被科学验证,包括调节肠道菌群、抑制有害细菌、消炎、抗过敏、提高机体免疫力等,但益生菌发挥健康作用的机理却尚未定论。目前,普遍认为益生菌发挥健康作用可能有3种途径:调节肠道微生态环境、调节机体免疫、改善定殖抗性。本文重点针对益生菌的特征、选择标准、健康作用机制进行了综述。     

日粮中添加酵母β-葡聚糖对早期断奶犊牛体内大肠杆菌数量的影响

本试验分别通过体外和体内试验比较了酵母β-葡聚糖与杆菌肽锌对大肠杆菌数量的影响。结果显示：体外试验中,当培养基基础pH为6和7时,单独添加酵母β-葡聚糖培养3 h后大肠杆菌数仍显著低于对照组（P＜0.05）,当基础pH为8时,培养6 h后培养基中大肠杆菌数仍显著少于对照组（P＜0.05）;体内试验中,口服大肠杆菌（O141︰K99）攻毒后,添加酵母β-葡聚糖与杆菌肽锌组ADG比对照组分别提高了30.38%和30.81%（P＜0.05）,各处理组F/G均显著优于对照组（P＜0.05）,同时,各处理组犊牛粪便指数显著低于对照组（P＜0.05）,各处理组犊牛攻毒后12 h和24 h时直肠中大肠杆菌数量显著降低（P＜0.05）。试验结果表明,在日粮中添加75 mg/kg酵母β-葡聚糖能缓解由大肠杆菌K99攻毒所导致的生长性能下降,并能在一定程度上替代或减少抗生素的使用。     

酵母培养物水溶物对离体草鱼肠道黏膜细胞生长及细胞膜完整性的影响

本试验以酵母培养物水溶物为试验材料,添加于离体草鱼肠道黏膜细胞培养液中,研究酵母培养物水溶物在不同浓度、不同作用时间下对细胞生长及细胞膜完整性的影响。采用单因子试验设计,设1个对照组及5个酵母培养物水溶物组(YC-1~5组),各组均设96个重复,每个重复为1个培养孔。对照组的培养液中不添加酵母培养物水溶物,YC-1~5组的培养液中酵母培养物水溶物的浓度分别为10、25、50、100、200 mg/L。结果表明:培养液中添加50~200 mg/L酵母培养物水溶物对细胞形态无损伤,100~200 mg/L酵母培养物水溶物在添加后3 h时显著增强细胞活性(P<0.05),50 mg/L酵母培养物水溶物在添加后6 h时显著增强细胞活性(P<0.05)。与对照组相比,3 h时各酵母培养物水溶物组培养液中乳酶脱氢酶(LDH)活力均没有显著变化(P>0.05),6 h时YC-4、YC-5组显著降低(P<0.05),9 h时YC-3、YC-4、YC-5组显著降低(P<0.05),12 h时YC-2、YC-3、YC-4、YC-5组显著降低(P<0.05)。各时间点(3、6、9、12 h)各酵母培养物水溶物组培养液中谷丙转氨酶(GPT)、谷草转氨酶(GOT)活力与对照组相比均没有显著变化(P>0.05),但在6~9 h时GPT活力均低于对照组。由此得出,培养液中添加10~200 mg/L酵母培养物水溶物能促进离体草鱼肠道黏膜细胞的生长,保护细胞膜的完整性,其发挥保护作用的适宜浓度为50~200 mg/L。     

早期断奶应激对仔猪肠黏膜屏障功能的影响及其监测与修复

在养猪生产中,常用日增重来衡量断奶仔猪的健康和生长性能,而影响断奶仔猪日增重的主要因素是断奶时所面临的大量应激(饲粮改变、母仔分离、环境变化等)。断奶应激会使仔猪肠道发生组织形态学和生理学上的变化,如肠绒毛萎缩、隐窝增生、肠黏膜通透性增强等,这些变化会引起仔猪消化和吸收功能下降或免疫机能降低,最终导致腹泻和生长性能下降。本文针对早期断奶应激引起的仔猪肠黏膜结构和屏障功能的变化作一简要综述,总结了一些可以作为评价肠黏膜结构和功能的一些标记物,并列举了饲粮中可用来缓解断奶应激损伤的一些饲料原料或添加剂,以期为仔猪生产和断奶应激的研究提供参考。     

乳酸菌对猪肠道屏障功能的调节作用及其机制

乳酸菌作为最重要和安全性最高的益生菌来源已被广泛关注,而乳酸菌调控人和动物肠道屏障功能已成为研究的热点,大量的体内外研究表明乳酸菌发挥益生作用的主要机制是通过调节肠道屏障功能实现的.相对于啮齿动物而言,乳酸菌在猪上的应用研究报道很多,对肠黏膜屏障功能的作用研究较少.这些研究尚未触及到乳酸菌作用机制的本质.猪肠道环境的复杂性,使得对乳酸菌调节肠道屏障功能机制的深入认识比较困难.近年来,基因组学、蛋白质组学和代谢组学的发展,为从体内试验的角度解析乳酸菌的确切作用机制提供了新的认识和研究手段.本文综述了乳酸菌对猪肠道屏障功能的调节作用,以期能帮助对乳酸菌的深入认识和科学应用.     

葡萄糖氧化酶对仔猪生长性能、粪便菌群和血清指标的影响

本试验主要研究在饲粮中添加葡萄糖氧化酶(GOD)对仔猪生长性能、粪便菌群以及血清生化指标和激素含量的影响。试验选用健康的35日龄仔猪112头,随机分为2个组,每个组4个重复,每个重复14头猪。对照组饲喂基础饲粮,试验组饲喂在基础饲粮基础上添加100 g/t GOD的试验饲粮,试验期35 d。结果表明:GOD组仔猪平均日增重和平均日采食量显著高于对照组(P<0.05),料重比显著低于对照组(P<0.05);GOD组仔猪粪便中沙门氏菌数显著低于对照组(P<0.05);对照组和GOD组间仔猪的血清生化指标(葡萄糖、白蛋白、球蛋白含量和蛋白系数)未出现显著性差异(P>0.05);GOD组三碘甲状腺原氨酸、甲状腺素和生长激素含量显著高于对照组(P<0.05)。试验结果表明,在饲粮中添加100 g/t的GOD可有效改进仔猪肠道健康,提高血清中相关激素含量,改善仔猪生长性能。