Effect of virus-induced destruction of villous epithelium on intestinal secretion induced by heat-stable Escherichia coli enterotoxins and prostaglandin E1 in swine

Villous atrophy and crypt hyperplasia were induced in the jejunal epithelium of thirteen 3-week-old pigs by inoculation with transmissible gastroenteritis virus. The responses (changes in net fluid movement) induced in ligated intestinal loops of these pigs by intraloop injections of prostaglandin E1 (PGE1) or Escherichia coli broth culture filtrates containing either or both E coli heat-stable enterotoxins (STa and STb) were compared with the responses induced by these preparations in littermates not inoculated with virus. Villous atrophy was associated with a marked decrease in response to preparations containing STa, STb, or STa + STb, but the response to PGE1 was undiminished. These results were consistent with the reports of others that the response to cyclic adenosine monophosphate-mediated secretogogues (PGE1) is a function of crypt epithelium; however, the present results also suggest that the secretory response to STa and to STb is dependent on the integrity of the villous epithelium. In the present study, loss of villous epithelium was associated with loss of response to STa and STb, but not to PGE1.     

Effects of Escherichia coli heat-stable enterotoxin b on small intestinal villi in pigs, rabbits, and lambs

Culture supernates from two strains of E. coli were placed into different ligated intestinal sections (loops) of each animal. The two bacterial strains were identical except that one contained a plasmid carrying the heat-stable toxin b (STb) gene, while the other did not. Morphometric techniques were used to assess villous epithelial surface areas and mucosal volumes in both intestinal segments exposed to STb-positive (test) and to STb-negative (control) supernates. In pigs whose intestines were exposed to STb-positive supernatants for 2 hours, both villous epithelial surface area and mucosal volume were significantly smaller in test loops than in control loops (P less than 0.02). In test loops of pigs incubated for 1 hour, and in test loops of lambs incubated for 2 hours, there was a decrease in villous epithelial surface area which approached the test for significance but did not meet it (0.05 less than P less than 0.10). Rabbit test loops did not differ from rabbit control loops in either villous epithelial surface area or mucosal volume. Histological examination of the tissues from all three species revealed epithelial changes in porcine and ovine tissues only. In porcine and ovine tissues, epithelium at villous tips was seen to be cuboidal or squamous, or even to be absent. Villi with similarly altered epithelium were seen in control loops, but were seen much more frequently in test loops. These epithelial changes were seen as early as 30 minutes of incubation in pigs. Intestinal tissues from these pigs were examined by transmission electron microscopy, but no difference between test and control tissues was seen.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of jejunal loop location on the activity of Escherichia coli heat-stable enterotoxin in 4- to 5-week-old pigs

Heat-stable enterotoxin (STa) from Escherichia coli strain 431 was injected into the jejunum of 4 pigs from each of 3 litters, using a ligated intestinal loop assay (with loops beginning 1 m caudad to the pylorus). The jejunum was divided into 4 contiguous areas, with 4 loops in each area. Doses of 0, 10, 100, or 1,000 ng of purified toxin (10 ng/mouse unit) were injected into the loops within an area, using a 4 X 4 Latin square design. Fluid accumulation in the loops increased (P less than 0.05) with increasing concentrations of STa in pigs in all litters, but the magnitude of the response varied across litters. Fluid responses to the STa varied in the different areas of the jejunum, with pigs in 2 litters having a decrease (P less than 0.05) in the response to STa in the caudal areas. These data quantitate the variability within the different areas of the jejunum of the young pig.     

Transmissible Gastroenteritis in Feeder Swine: Clinical, Immunofluorescence and Histopathological Observations

Eight feeder swine (four to six months of age) were inoculated orally with 200,000 to 500,000 pig infectious doses (PID) of the Purdue strain of transmissible gastroenteritis (TGE) virus. Biopsies obtained from their small intestines were examined histopathologically and by fluorescent antibody tissue section technique at intervals that included 24, 48, 72 and 96 hours postexposure, and similar examinations were carried out at necropsy 168 hours postexposure. Evidence of virus infection was demonstrated in all segments of the small intestine except the upper duodenum and the viral antigen was found only in the cytoplasm of the absorptive cells covering the villi. Although six of the eight pigs failed to show clinical signs of TGE, typical microscopic lesions of villous atrophy with replacement of columnar absorptive cells by cuboidal cells were observed in seven pigs, and TGE virus antigen was demonstrated in the intestinal cells of four of eight pigs during the first week postexposure. The infection was usually mild to moderate and focal in the pigs without clinical signs of the disease and more severe and extensive in the pigs with clinical signs of the disease variable in severity. It was concluded that TGE virus probably replicated in all feeder swine exposed, and that the presence or absence of clinical signs of TGE in these pigs was related to the severity and extent of the villous atrophy and columnar cell replacement induced in their small intestines.     

Age-dependent resistance to transmissible gastroenteritis of swine. III. Effects of epithelial cell kinetics on coronavirus production and on atrophy of intestinal villi.

Coronavirus titers in small intestine, degree of villous atrophy and apparent rates of regeneration of intestinal villi were compared in newborn, 3-week-old and adult pigs for 1 week after they were exposed to the transmissible gastroenteritis virus of swine. The response within the newborn group was homogeneous, resulting in high virus titers, maximal villous atrophy and comparatively slow regeneration. In general, virus titers were lower, villous atrophy was less severe and regeneration more rapid in both older groups than in the newborn pigs. However, the response varied greatly in the older groups. The 3-week-old group was divided into two populations. The major population had low virus titers and developed partial villous atrophy, whereas the minor population had marked villous atrophy and virus titers comparable to those of the newborn pigs. These observations support the hyposthesis that the accelerated replacement of villous epithelium in the small intestine of pigs during the first 3 weeks contributes to the innate age-dependent resistance to transmissible gastroenteritis. The accelerated replacement of villous epithelial cells in older pigs contributes to resistance in two ways. The increased proliferative capacity of crypt epithelium results in a more rapid regeneration of atrophic villi; and the comparatively young villous absorptive cells resulting from accelerated replacement produce less virus per cell than the older ones of the newborn pig.     

Transmissible Gastroenteritis in Feeder Pigs: Observations on the Jejunal Epithelium of Normal Feeder Pigs and Feeder Pigs Infected with TGE Virus

Light and electron microscopy findings in the jejunal mucosa of the normal feeder pig and feeder pigs infected with transmissible gastroenteritis (TGE) virus are reported. Villi in the mid jejunum of the normal feeder pig were elongated, finger shaped and covered with a layer of columnar absorptive cells with a well developed and regular brush border. Severe lesions of villous atrophy were present in all jejunal segments of feeder swine killed 96 hours post infection with TGE virus. Atrophic villi were covered by flat to cuboidal cells with a poorly developed brush border in some areas. In other segments, cells varied in appearance from sub-columnar to columnar type of near normal appearance.

The ultrastructure of the jejunal absorptive cells in the normal feeder pig was found to be similar to that described for the jejunal cells of other adult mammals. There were no significant indications of high pinocytotic activity. The epithelial cells covering the atrophic villi of TGE infected pigs had a fine structure similar to that described for the crypt cells, ranging in appearance from very immature to moderately differentiated cells. Microvilli were very short, decreased markedly in number and irregular in arrangement. The terminal web was poorly developed. Strands of rough endoplasmic reticulum were markedly diminished and an increase in free ribosomes was noted. The significance of these observations in explaining pathogenesis of TGE in feeder pigs is discussed.

     

Intestinal responses to enterotoxigenic Escherichia coli heat-stable toxin b in non-porcine species

The Escherichia coli heat-stable enterotoxin (STb) is the most prevalent toxin associated with diarrheagenic E coli isolates of porcine origin. Unequivocal biological activity of this toxin has been observed only in swine intestine. In this study, when endogenous protease activity was blocked with soybean trypsin inhibitor, intestinal secretion was stimulated by STb in jejunal loops of rats, mice, calves, and rabbits. Compared with pigs, rats, mice, and calves, rabbits were relatively insensitive to STb. These data demonstrate that the activity of STb is not a species-specific toxic activity; there is species variation in sensitivity to STb, and some common laboratory animals may have potential to be used to measure biological activity of STb.     

Prevalence of virulence genes in Escherichia coli strains recently isolated from young pigs with diarrhea in the US

Enterotoxigenic Escherichia coli (ETEC)-associated post-weaning diarrhea (PWD) is economically one of the most important diseases for the swine industry. Porcine ETEC strains typically express K88 or F18 fimbria and heat-labile (LT) and/or heat-stable (STa, STb) enterotoxins. However, recent studies indicate that EAST1 toxin, adhesin involved in diffuse adherence (AIDA-I) and porcine attaching and effacing-associated factor (paa) may also be expressed by ETEC strains associated with diarrhea. To better understand the virulence factors of E. coli strains that cause PWD, we applied PCR to screen for K88, F18, F41, 987P and K99 fimbrial genes; LT, STa, STb, Stx2e and EAST1 toxic genes; and AIDA-I, paa and EAE adhesin genes in E. coli strains recently isolated from young pigs with PWD in the US. Of 304 E. coli isolates from diarrheic pigs submitted for testing, 175 (57.6%) strains possessed fimbrial genes: K88 (64.6%), F18 (34.3%), F41 (0.57%), K99 (0.57%), 987P (0); toxin genes: LT (57.7%), STb (72.6%), STa (27.4%), STx2e (17.4%), EAST1 (35%); and adhesin genes: AIDA-I (26.9%), paa (60%), EAE (1.1%). All toxin genes except the EAST1 toxin gene, were almost exclusively associated with K88+ or F18+ isolates, and most of these isolates carried multiple toxin genes. The non-fimbrial adhesin paa was found present in over half of the K88+ isolates. A total of 129 (42%) isolates carried no fimbrial genes, including 66 (21.7%) isolates that did not have any of the above virulence genes. These results suggest a broad array of virulence genes associated with PWD in pigs.     

Effects of intraluminal glucose on intestinal secretion induced by heat stable and heat labile Escherichia coli enterotoxin, cholera toxin and theophylline.

Glucose, l-alanine, l-aspartate, l-methionine and glycine enhanced net fluid and electrolyte absorption in acute isolated loops of the proximal jejunum of weanling swine. The effect of glucose on intestinal secretion induced by heat stable and heat labile Escherichia coli entero-toxin, cholera toxin and theophylline was examined in both the proximal and distal jejunum of weanling swine. In the proximal jejunum glucose enhanced the rate of net fluid and electrolyte absorption. This increase was accompanied by an increase in unidirectional dosium absorption. In loops exposed to either heat stable or heat labile enterotoxins, glucose significantly decreased the rate of net fluid and electrolyte secretion. The magnitude of glucose enhancement in loops exposed to heat stable and heat labile enterotoxins was similar to adjacent control loops. However, glucose enhancement did not occur in loops exposed previously to cholera toxin or concurrently to theophylline. Therefore, cholera toxin and theophylline may inhibit substrate dependent sodium absorption in the proximal jejunum. In the distal jejunum glucose enhancement did occur but the rate of enhancement was less than in the proximal jejunum. In this region glucose enhancement was not evident in loops exposed to either theophylline, heat stable, heat labile or cholera toxin.     

In vitro effects of a mixture of Escherichia coli heat-stable enterotoxins on chloride flux in everted jejunal sacs of male pigs

In vitro effects of a mixture of Escherichia coli heat-stable enterotoxins (STa and STb) on isolated jejunum of 3-week-old male pigs were studied, using everted intestinal sac techniques. Heat-stable enterotoxins increased chloride secretion and chloride absorption in everted intestinal sacs. The increase of secretory flux was greater than that for absorptive flux. Vasoactive intestinal peptide (6 x 10(-9) M) increased chloride secretion, but had no effect on chloride absorption. Neither vasoactive intestinal peptide nor pilocarpine (10(-5) M) had additive effect to ST. Secretory effects of ST were not blocked by atropine (2 x 10(-5) M), clonidine (10(-6) M), or morphine (4.2 x 10(-6) M).     

Fimbriae and enterotoxins associated with Escherichia coli serogroups isolated from pigs with colibacillosis

A comprehensive study of 223 Escherichia coli isolates from pigs with colibacillosis included determination of O serogroups, detection of heat-labile enterotoxin, heat-stable enterotoxin (STa and STb), and identification of K88, K99, 987-P, F-41, and type 1 fimbriae. The incidence of the various E coli types among isolates of pigs of different ages was also determined. Escherichia coli bearing K88 fimbriae accounted for 48% of all isolates studied, were most often of serogroup O157, O149, or O8, and usually produced labile toxin alone or in combination with STa or STb. These E coli were commonly isolated from pigs in each age group studied (0 to 5 days, 6 to 10 days, 11 to 24 days, and greater than 24 days). Escherichia coli bearing 987-P accounted for 30% of the isolates, were most often of serogroup O141 or O20, and usually produced STa. Escherichia coli bearing K99 accounted for 13% of the isolates, usually were of serogroup O101 or O8, and almost always produced STa. Escherichia coli bearing 987-P or K99 were most often isolated from pigs less than 6 days of age. Fimbriae F-41, when identified, were usually on E coli of serotype O101:K99. Although infrequently found, type 1 fimbriae were on E coli of most of the serogroups identified in this study.     

Prevalence of the enteroaggregative Escherichia coli heat-stable enterotoxin 1 gene and its relationship with fimbrial and enterotoxin genes in E. coli isolated from diarrheic piglets.

A total of 720 Escherichia coli strains isolated from diarrheic piglets on 756 swine farms were screened for the presence of the enteroaggregative E. coli heat-stable enterotoxin 1 (EAST1) gene by polymerase chain reaction (PCR). Escherichia coli strains that carried EAST1 genes were also tested by PCR for the presence of 4 fimbriae (F4, F5, F6, F41), 2 heat-stable enterotoxins (STa and STb), and 1 heat-labile enterotoxin (LT) gene. One hundred sixty-four (22.7%) of the 720 E. coli isolates carried genes for EAST1. Of these 164 isolates, 62 (37.8%) carried EAST1 genes only, 11 (6.7%) carried genes for at least 1 of the fimbrial adhesins, 51 (31.1%) carried genes for at least 1 of the enterotoxins, and 40 (23.8%) carried genes for at least 1 of the fimbrial adhesins and enterotoxins. Forty-six percent of strains that carried EAST1 genes carried STa genes, and 16% of strains that carried EAST1 genes carried F4. The isolation rate of enterotoxigenic E. coli strains carrying genes for EAST1 gene was 63%. The 6 major genotypes observed in this study (in decreasing order) were EAST1+, EAST1+STa+, EAST1+STa+STb+, EAST1+STa+F5+, EAST1+STa+F4+, and EAST1+STb+F4+. EAST1 is widely prevalent among diarrheagenic strains of E. coli and may represent an important virulence determinant in the pathogenesis of enteric colibacillosis of preweaned pigs.     

Functional significance of histologic alterations induced by Escherichia coli pig-specific,mouse-negative,heat-stable enterotoxin (STb)

In contrast to cholera enterotoxin and other Escherichia coli enterotoxins, a pig-specific, heat-stable E. coli enterotoxin (ST_b) causes morphologic lesions (loss of villous epithelial cells and partial villous atrophy). These lesions reflect a loss of absorptive cells and thus suggest that ST_b causes impaired absorption as well as inducing net secretion. The present studies assess functional significance of morphologic changes induced by ST_b. Net fluid movement, mucosal surface area, sucrase activity and the electrical response induced by alanine were measured in swine jejunal loops exposed to E. coli culture filtrates with and without ST_b. Net fluid secretion (-11.1±1.1 ml) occurred in some ST_b loops (secretors) and net absorption (2.7±0.3 ml) in others (nonsecretors), but net absorption occurred in all control loops (4.9±0.2 ml). The mucosal surface area of St_b loops was about 20% less than that of controls (P<0.01). Sucrase activity was also lower (about 15%) in ST_b loops than in control loops (P<0.01). The electrical response induced by alanine in mucosa from nonsecreting ST_b loops did not differ from that induced in mucosa from control loops. However, the response to alanine in mucosa from secreting ST_b loops was reduced about 70% from that in mucosa from nonsecreting ST_b loops or from control loops (P<0.05). It is concluded that reduced sucrase activity is a functional correlate to villous atrophy induced by ST_b, that ST_b impairs alanine absorption in some loops (secretors), and that the impaired alanine absorption is independent of the decreased surface area caused by St_b. Because the impaired alanine absorption occurred independent of the decreases in surface area, it is suggested that the secretory response to ST_b is associated with an impairment of active absorption of alanine.     

Rapid identification of virulence genes in enterotoxigenic Escherichia coli isolates associated with diarrhoea in Queensland piggeries

OBJECTIVE: To identify virulence genes in enterotoxigenic E coli (ETEC) isolates associated with diarrhoea in neonatal, 1 to 3 week-old and weaned pigs in southeast Queensland. DESIGN: Multiplex PCR and serotyping were applied to E coli isolates obtained over a 5-year period (1998-2002) from cases diagnosed at Toowoomba Veterinary Laboratory. PROCEDURE: A total of 126 isolates from 25 different Queensland piggeries were tested for haemolytic activity on 5% sheep blood agar and by multiplex PCR for the presence of five commonly recognised fimbrial (F4, F5, F6, F41 and F18) and three enterotoxin genes (STa, STb, LT). A subset of 62 representative isolates were serotyped by slide agglutination. For comparative purposes, multiplex PCR was also performed on the DNA of 31 ETEC isolates from 9 serotypes originating from piggeries in southern New South Wales. RESULTS: A total of 113 (89.7%) of the isolates from Queensland possessed ETEC virulence genes, including 14 of 15 isolates from neonatal pigs (93.3%), 18 of 23 isolates from 1 to 3 week old pigs (78.3%) and 81 of 88 isolates from weaned pigs (92.1%). F4:STa:STb:LT (serotype O149) was the most prevalent pathotype in neonatal and 1-3 week old pigs and F4:STa:STb:LT (serotype O149) and F18:STa:STb:LT (serotype O141) were most prevalent in weaned pigs. In comparison, isolates obtained from neonatal pigs from New South Wales belonged to a more diverse range of pathotypes and serotypes. CONCLUSION: Multiplex PCR was a rapid and specific method for detecting the presence of ETEC virulence genes in porcine E coli isolates. For isolates obtained from cases of suspected colibacillosis in Queensland, growth of a heavy pure culture of haemolytic E coli was a sensitive prognostic indicator of the presence of ETEC virulence genes in the isolate. ETEC pathotypes and serotypes remained stable in Queensland piggeries over the five-year study period and appear to have changed little over the last three decades.     

Genotypic prevalence of the fimbrial adhesins (F4, F5, F6, F41 and F18) and toxins (LT, STa, STb and STx2e) in Escherichia coli isolated from postweaning pigs with diarrhoea or oedema disease in Korea

A PCR was used to determine the genotypic prevalence of five fimbrial adhesins (F4, F5, F6, F41 and F18), two heat-stable enterotoxins (STa and STb), the heat-labile enterotoxin (LT), and the shiga toxin 2e (Stx2e) in 230 isolates of Escherichia coli from postweaning pigs with diarrhoea or oedema disease. Ninety-four (40.9 per cent) of the isolates carried genes for at least one of the fimbrial adhesins or toxins. Genes for the F18 fimbrial adhesin were detected in 18.3 per cent, and genes for F4, F6, F5 and F41 were detected in 10.0 per cent, 4.3 per cent, 1.7 per cent and 0.8 per cent of the isolates, respectively. Genes for STa, STb and LT were detected in 25.7 per cent, 15.2 per cent and 8.7 per cent of the isolates, respectively. Genes for Stx2e were detected in 36 (15.6 per cent) of the isolates, and among them 24 also contained the gene for F18ab and four also contained the gene for F18ac.     

Prevalence of genotypes for fimbriae and enterotoxins and of O serogroups in Escherichia coli isolated from diarrheic piglets in Korea.

Polymerase chain reaction for 4 fimbriae (F4, F5, F6, F41), 2 heat-stable enterotoxins (STa, STb), and 1 heat-labile enterotoxin (LT) were performed on 400 Escherichia coli isolates to determine their genotype prevalence among enterotoxigenic E. coli isolates from preweaned pigs with diarrhea in the Republic of Korea. A total of 200 of the 400 E. coli isolates were also selected for characterization of the O serogroup. Of these 200 isolates, serogroup could be determined in 139 (69.5%) but not in 61 isolates (30.5%). Isolates of serogroup O101 were the most common, followed in descending order by 08, 020, 0162, 0141, and 0149. Ninety-seven (24.3%) of the 400 E. coli isolates carried genes for at least 1 of the entertoxins or fimbrial adhesins. Of these 97 isolates, 27 carried genes for at least 1 of the fimbrial adhesins and entertoxins. Sixty-six percent of the isolates that carried fimbrial adhesin genes carried genes for at least 1 of the enterotoxins, and 71% of the isolates that carried enterotoxin genes carried genes for at least 1 of the fimbrial adhesins. Genes for the F6 fimbriae were detected in 6% of the E. coli isolates, and F4+, F41+, and F5+ genes were detected in 4.3%, 3.3%, and 2% of the isolates, respectively. Genes for STa, STb, and LT were detected in 10%, 8.5%, and 4.3% of the isolates, respectively. The 6 major genotypes observed in this study (in decreasing order) were F6+, STb+, F41+, STa+STb+, F6+STa+, and STa+.     

Scanning electron microscopic observations on the intestinal villi in growing White Leghorn and broiler chickens from 1 to 30 days of age

1. To obtain intestinal morphological data demonstrating the faster growth rate in broiler (BR) than in White Leghorn (WL) chickens, villi of the duodenum, jejunum and ileum were examined from 1 to 30 d of age by scanning electron microscopy. 2. At the first day after hatching, villi of each intestinal segment showed a finger-like shape in both breeds. Villi developed to a plate-like shape in the duodenum, a wave-like shape in the jejunum and a tongue-like shape in the ileum at 30 d of age via the common plate-like villi at 10 d of age. The fundamental villous shape and arrangement seem to be accomplished by 10 d of age; two types of obliquely elongated plate-like villi showed a zigzag arrangement, adjoining at an angle of 40 degrees to 60 degrees like an oblique T-shape. It is suggested that such a villous arrangement would be more effective for nutrient absorption by inducing a long zigzag flow of ingesta. 3. Compared with WL, even at the first day after hatching BR had many more developed epithelial cell protrusions over the whole apical surface of the duodenal villi. In WL the protrusions were not so apparent and located only in the central area of the villous tip. Furthermore, at 10 d of age BR showed more developed and larger villi, many wider microvilli at the apical portion of villi and more active extrusions of epithelial cells from the tip of the duodenal and jejunal villi. 4. These morphological characteristics of villi in early life in BR suggest a greater absorptive surface area and a more active intestinal function, permitting the faster growth rate of BR immediately after hatching.     

Genotypic prevalence of the adhesin involved in diffuse adherence in Escherichia coli isolates in pre-weaned pigs with diarrhoea in Korea

A total of 1002 Escherichia coli strains isolated from pre-weaned pigs with diarrhoea on 1114 swine farms were screened for the presence of the adhesin involved in diffuse adherence (AIDA) gene by polymerase chain reaction (PCR). Escherichia coli isolates that carried AIDA genes were also tested by PCR for the detection of five fimbriae (F4, F5, F6, F18 and F41), heat-stable (STa, STb) and heat-labile (LT) enterotoxin, enteroaggregative E. coli heat-stable enterotoxin 1 (EAST1), and Shiga toxin 2 oedema disease (Stx2e) genes. Twenty-three (2.3%) of the 1002 E. coli isolates carried the gene for AIDA. Among 23 isolates shown to carry genes for AIDA, three carried the AIDA gene as the only shown virulence factor. Other isolates carried other virulence factor genes in addition to AIDA. Four isolates carried genes for at least one of the fimbrial adhesins and enterotoxins. Sixteen isolates carried genes for enterotoxins only. The AIDA may represent an additional virulence determinant in pre-weaned pigs with diarrhoea.     

海安县猪水肿病的流行病学与病原特性研究

对江苏省海安县2003年5月～2004年5月各乡镇猪水肿病的发病和死亡情况进行了流行病学调查，发现猪水肿病在海安地区呈零星散发性发生，发病率为0.31％～1．84％，死亡率为0．07％—0．56％，病死率为16．0％～35．0％。水肿病主要侵害仔猪，育成猪也偶有发生，一般以气温比较高的季节多发。同时从疑似猪水肿病的病料中分离到12株大肠杆菌，经O血清型鉴定，5株为0139，2株为O45，O55、O93，O9、O101、O119各1株。经多重PCR检测毒素基因(STa，STb、LT、SLT-2e)和大肠杆菌粘附素单抗(F4、F5、F6、F41、F18)检测茵毛，共6个分离株带有SLT-2e基因，其中O139分离株5株，055分离株1株，其余6株均带STb基因。12个分离株中，单独表达F18菌毛的4株(O1392株，O45、O119各1株)，F5 F411株(O93)，F41 F181株(O139)，F5 F41 F182株(均为O139)。经药敏试验，多数分离株对壮观霉素和新霉素高度敏感。     

Liposomes targeted to deliver antisecretory agents to jejunal mucosa.

The B subunit of cholera toxin has been covalently attached to the surface of liposomes made from a mixture of phosphatidylethanolamine, phosphatidylcholine and cholesterol. Adenylate cyclase inhibitors and chloride conductance inhibitors were encapsulated within the liposomes. These "targeted" liposomes were used to study the combined effects of this novel delivery system, and a limited number of possible antisecretory agents, on net fluid flux into the pig jejunum. A state of net secretory fluid flux was induced in isolated jejunal loops in weanling pigs by adding theophylline or cholera toxin to the lumen of the isolated loops. There was no reduction in net fluid secretion when liposome suspensions without encapsulated secretory inhibitors were added to fluid in the lumen of loops treated with theophylline. There was also no reduction in net fluid secretion when miconazole, alpha-phenylcinnamate or 5 nitro-2-(3-phenethylamino)benzoate were encapsulated within targeted liposomes added to isolated jejunal loops. The net fluid flux induced by exposure of jejunal loops to theophylline was significantly reduced by adding targeted liposomes containing 2'-deoxy-3'-AMP. The reduction involved a reversal of net secretory fluid flux to an absorptive value. The net fluid secretory response to treatment of loops with cholera toxin was also inhibited by treating loops with targeted liposomes containing 2'-deoxy-3'-AMP. However, the reversal of secretion was less complete for secretion induced by cholera toxin than for secretion induced by theophylline. The reduced antisecretory efficacy versus cholera toxin was not improved by encapsulating higher concentrations of 2'-deoxy-3'-AMP.(ABSTRACT TRUNCATED AT 250 WORDS)