Replicon typing of F18 fimbriae encoding plasmids of enterotoxigenic and verotoxigenic Escherichia coli strains from porcine postweaning diarrhoea and oedema disease

The presence of fimbrial adhesin F18 is frequently found in enterotoxigenic Escherichia coli (ETEC) and verotoxigenic E. coli (VTEC) strains responsible for diarrhoea and oedema disease of weaned pigs. The F18 adhesin occurs in two antigenic variants: F18ab is characteristic of VTEC while F18ac is more typical for ETEC. F18 encoding plasmids of 17 phenotypically characterized porcine E. coli isolates (10 ETEC, 6 VTEC and 1 ETEC/VTEC) were tested with a DNA probe for F18 fimbrial adhesin and with replicon probes for the RepFIa, RepFIb and for the RepFIc family of basic replicons. In all the cases, the F18 probe hybridized to only one plasmid band of size higher than 42MDa. All F18 plasmids were determined to be unireplicon plasmids belonging to the RepFIc replicon family of the F incompatibility complex. There was no difference between F18ac plasmids of ETEC and F18ab plasmids of VTEC strains in terms of replicon type or subtype. However, the size of F18ab plasmids of the VTEC strains varied between 42 and 98MDa, in contrast to F18ac plasmids of ETEC strains (constantly approximately 98MDa).     

Identification of Escherichia coli O157:H7-strains from pigs with postweaning diarrhoea and amplification of their virulence marker genes by PCR

Escherichia coli isolated from pigs with postweaning diarrhoea were examined by PCR for the presence of the O157 rfb gene responsible for the biosynthesis of E coli O157 lipopolysaccharide. Among the 372 isolates tested, 38 (10.2 per cent) were of the O157 serogroup, but none of these possessed the H7 determinant. Further analysis of the E coli O157 isolates revealed that seven of them had the genes responsible for the production of Shiga toxin 1 and eaeA intimin, four other strains had genes responsible for the production of Shiga toxin 2, and four other strains were positive for the enterohaemolysin gene.     

Investigation of the relationship between SLA-1 and SLA-3 gene expression and susceptibility to Escherichia coli F18 in post-weaning pigs

Porcine post-weaning diarrhea and edema disease are principally caused by Escherichia coli strains that produce F18 adhesin. FUT1 genotyping and receptor binding studies divided piglets into E. coli F18-resistant and -sensitive groups, and the roles of SLA-1 and SLA-3 were investigated. SLA-1 and SLA-3 expression was detected in 11 pig tissues, with higher levels of SLA-1 in lung, immune tissues and gastrointestinal tract, and higher levels of SLA-3 also in lung and lymphoid tissues. Both genes were expressed higher in F18-resistant piglets, and their expression was positively correlated in different tissues; a negative correlation was observed in some tissues of F18-sensitive group, particularly in lung and lymphatic samples. Gene ontology and pathway analyses showed that SLA-1 and SLA-3 were involved in 37 biological processes, including nine pathways related to immune functions. These observations help to elucidate the relationship between SLA class I genes and E. coli F18-related porcine gastrointestinal tract diseases.     

Dietary inclusion of multispecies probiotics to reduce the severity of post-weaning diarrhea caused by Escherichia coli F18+ in pigs

This study was aimed to determine the efficacy of multispecies probiotics in reducing the severity of post-weaning diarrhea caused by enterotoxigenic Escherichia coli (ETEC) F18⁺ on newly weaned pigs. Thirty-two pigs (16 barrows and 16 gilts, BW = 6.99 ± 0.33 kg) at 21 d of age were individually allotted in a randomized complete block design with 2 × 2 factorial arrangement of treatments. Pigs were selected from sows not infected previously and not vaccinated against ETEC. Pigs were fed experimental diets for 25 d based on 10 d phase 1 and 15 d phase 2. The factors were ETEC challenge (oral inoculation of saline solution or E. coli F18⁺ at 2 × 10⁹ CFU) and probiotics (none or multispecies probiotics 0.15% and 0.10% for phase 1 and 2, respectively). Body weight and feed intake were measured on d 5, 9, 13, 19, and 25. Fecal scores were measured daily. Blood samples were taken on d 19 and 24. On d 25, all pigs were euthanized to obtain samples of digesta, intestinal tissues, and spleen. The tumor necrosis factor alpha (TNFα), malondialdehyde (MDA), peptide YY (PYY), and neuropeptide Y (NPY) were measured in serum and intestinal tissue. Data were analyzed using the MIXED procedure of SAS. The fecal score of pigs was increased (P < 0.05) by ETEC challenge at the post–challenge period. The ETEC challenge decreased (P < 0.05) jejunal villus height and crypt depth, tended to increase (P = 0.056) jejunal TNFα, increased (P < 0.05) ileal crypt depth, and decreased (P < 0.05) serum NPY. The probiotics decreased (P < 0.05) serum TNFα, tended to reduce (P = 0.064) jejunal MDA, tended to increase (P = 0.092) serum PYY, and increased (P < 0.05) jejunal villus height, and especially villus height-to-crypt depth ratio in challenged pigs. Growth performance of pigs were not affected by ETEC challenge, whereas the probiotics increased (P < 0.05) ADG and ADFI and tended to increase (P = 0.069) G:F ratio. In conclusion, ETEC F18⁺ challenge caused diarrhea, intestinal inflammation and morphological damages without affecting the growth performance. The multispecies probiotics enhanced growth performance by reducing intestinal inflammation, oxidative stress, morphological damages.     

Colonization factor different from K88, K99, F41 and 987P in enterotoxigenic Escherichia coli strains isolated from postweaning diarrhoea in pigs.

A novel common colonization factor was detected in enterotoxigenic strains of Escherichia coli isolated from intestinal contents of piglets affected with postweaning diarrhoea. This factor was antigenically distinct from the previously described K88, K99, F41, 987P, CFAI, CFAII and Att25 fimbrial antigens. E. coli strains possessing this factor adhered to the pig intestinal brush borders and one strain, used in experimental infection in weanlings, colonized the intestinal epithelium and induced diarrhoea. Examination of 212 toxigenic strains of E. coli isolated from weanlings revealed the presence of the novel common colonization factor in 83 strains, belonging to serogroups O25, O108, O138, O141, O147 and O157. The antigen K88 was detected in 47 strains belonging to serogroups O8, O141, O147 and O149.     

The age-dependent expression of the F18+ E. coli receptor on porcine gut epithelial cells is positively correlated with the presence of histo-blood group antigens

F18(+)Escherichia coli have the ability to colonize the gut and cause oedema disease or post-weaning diarrhoea by adhering to specific F18 receptors (F18R) on the porcine epithelium. Although it is well established that a DNA polymorphism on base pair 307 of the FUT1 gene, encoding an alpha(1,2)fucosyltransferase, accounts for the F18R phenotype, the F18R nature is not elucidated yet. The aim of the present study was to investigate the correlation between the presence of H-2 histo-blood group antigens (HBGAs) or its derivative A-2 HBGAs on the porcine gut epithelium and F18(+)E. coli adherence. A significant positive correlation was found between expression of both the H-2 (r=0.586, P<0.01) and A-2 (r=0.775, P<0.01) HBGAs and F18(+)E. coli adherence after examination of 74 pigs aged from 0 to 23 weeks. The majority of the genetically resistant pigs (FUT1M307(A/A)) showed no HBGA expression (91.7%) and no F18(+)E. coli adherence (83.3%). In addition, it was found that F18R expression levels rise with increasing age during the first 3 weeks after birth and that F18R expression is maintained in older pigs (3-23 weeks old). Taken together, these data suggest that, apart from H-2 HBGAs, A-2 HBGAs might be involved in F18(+)E. coli adherence.     

Pre-harvest factors influencing the acid resistance of Escherichia coli and E. coli O157:H7

The effects of pH, acetate, propionate, or butyrate concentration, and diet on acid resistance of fecal Escherichia coli and E. coli O157:H7 were determined by in vitro and in vivo experiments. The pH tested was from 4.0 to 8.0, and the VFA concentrations tested were 0 to 100 mM. The E. coli O157:H7 used was strain 505B. In an in vivo study, cattle were fed a grain-based diet, then either not switched or switched to a grain-based diet with 3% added calcium carbonate or two fiber-based diets (soybean hulls or hay). Acid resistance was expressed as viability after acid-shock at pH 2.0 for 1 h and 4 h for fecal E. coli and E. coli O157:H7, respectively. Enumeration methods used were multitube fermentation, agar plate, and petri-film methods. The E. coli O157:H7 was not found in continuous culture inocula or in vivo samples. The viability of fecal E. coli decreased linearly (P < 0.01) as the culture pH increased, and viability of E. coli O157:H7 was highest (P < 0.01) when cultivated at pH 6.0. The viability of fecal E. coli and E. coli O157:H7 showed quadratic responses (P < 0.05) as acetate and butyrate concentrations increased at pH 7.2, with maximal acid resistance at 20 and 12 mM, respectively. As propionate concentration increased, the acid resistance was not different (P > 0.05) for fecal E. coli. Acid resistance of E. coli was induced by acetate and butyrate, even though the environmental pH was near neutral. Similar results were measured in the in vivo study, where viability after acid shock was more dependent on VFA concentration than on pH. Increasing the dietary calcium carbonate concentration also increased (P < 0.05) acid resistance of fecal E. coli. Results from these studies demonstrated that culture pH and VFA affect acid resistance of E. coli.     

Protection against neonatal Escherichia coli diarrhoea in pigs by vaccination of sows with a new vaccine that contains purified enterotoxic E. coli virulence factors F4ac, F4ab, F5 and F6 fimbrial antigens and heat-labile E. coli enterotoxin (LT) toxoid

The efficacy of a new vaccine against neonatal Escherichia coli diarrhoea in piglets containing purified F4ab, F4ac, F5 and F6 fimbriae and detoxified heat-labile toxin (LT) was tested in challenge experiments by the method described by the European Pharmacopoeia (3rd edn, EDQM, Council of Europe, Strasbourg, France). A group of 11 young sows from a herd without E. coli problems was vaccinated 6-8 and 2-4 weeks prior to expected farrowing and another group of nine young sows were non-vaccinated controls. Escherichia coli antibody titres were determined in serum samples taken from the sows before first vaccination and before farrowing and in colostrum samples. The newborn piglets were allowed to suckle colostrum from their mother immediately after birth. The piglets were marked with individually numbered ear tags. Approximately 12 h after birth, 118 piglets from vaccinated sows and 79 piglets from non-vaccinated control sows were challenged by oral instillation of 5 ml of a freshly prepared culture of one of the challenge strains [O8:K87:F4ab (LT+) or O149:K91:F4ac (LT+) or O9:K30:F5 or O9:K103:F6 respectively]. The challenge cultures contained as a mean 6.8x10(9) CFU/ml. After challenge the piglets were observed for 7 days and mortality and morbidity were recorded. Vaccinated sows developed significant levels of antibody titres in colostrum and serum. Control sows stayed at a low/seronegative level. The protective efficacy was excellent because 66.7-87.5% of the piglets from vaccinated sows remained without clinical signs after challenge. Only 0.0-28.0% of the piglets from non-vaccinated sows remained healthy and more than 47.1% of the piglets in this group died after challenge. It is concluded that the new vaccine is very effective in protection of piglets against neonatal E. coli diarrhoea.     

Desperately seeking diarrhoea: outbreak of haemolytic uraemic syndrome caused by emerging sorbitol-fermenting shiga toxin-producing Escherichia coli O157:H-, Germany, 2009

Infection with sorbitol-fermenting Shiga toxin-producing Escherichia coli O157:H- (sf STEC O157:H-) is rare, but emerging in Europe. The pathogen is typically isolated from paediatric patients with life-threatening haemolytic uraemic syndrome (HUS). It is unclear whether this observation primarily reflects the pathogen's virulence or its complex laboratory diagnosis, not routinely conducted in diarrhoeal patients. In summer 2009, four boys living in the same suburb in Germany developed diarrhoea-associated HUS: three were infected by sf STEC O157:H- and one died. We conducted two analytical epidemiological studies, an extensive search for diarrhoeal cases in potentially exposed groups, and an environmental investigation. Outbreak cases were residents of the suburb diagnosed with HUS, sf STEC O157:H- infection, or both between 24 July 2009 and 25 August 2009. Overall, we ascertained eight cases with a median age of 4 years (range: from 8 months to 9 years). Stool screening of 220 persons led to the identification of only four additional cases: two asymptomatic carriers and two diarrhoeal cases. HUS was strongly associated with visiting a local playground in July, particularly on 16th July (odds ratio = 42.7, P = 0.002). No other commonality, including food, was identified, and all environmental samples (n = 24) were negative. In this localized non-foodborne outbreak, the place of likely infection was a local playground. Sf STEC O157:H- infection apparently limits itself rarely to diarrhoeal illness and progresses frequently to HUS. Therefore, detection of and response to this hypervirulent pathogen primarily relies on HUS surveillance.     

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.     

Escherichia coli in the rumen and colon of slaughter cattle,with particular reference to E. coli O157

The distribution of Escherichia coli O157 and of total E. coli was surveyed in the digestive tract of cattle under 30 months of age, slaughtered between August 1999 and May 2000 in three abattoirs in southern England. Samples were taken from the dorsal and ventral rumen wall, the rumen contents, the colon wall and colon contents, and from faeces or caudal rectal contents. Gut wall samples were processed by vortex-mixer to release loosely adherent bacteria, and by Stomacher to release firmly attached bacteria. E. coli O157 was detected by immunomagnetic separation followed by growth on selective culture media. The numbers of E. coli were higher in the colon than the rumen, and most were located in the digesta phase, rather than associated with the gut wall. The number of E. coli found in the gut and in faeces decreased during the winter months. E. coli O157 was detected more frequently in the colon than in the rumen, but the majority of detections(7/8) were in samples of rumen wall.     

Escherichia coli O157:H7 and other Shiga toxin-producing E. coli in white veal calves

The aims of the study were to determine the prevalence of enterohemorrhagic Escherichia coli O157:H7 (EHEC O157) and other Shiga toxin-producing E. coli (STEC) in feces of white veal calves in an operation in Ontario, to evaluate exposure of the calves to EHEC O157, and to investigate the milk replacer diet and antimicrobial resistance as factors that might influence the prevalence of EHEC O157. Feces from three cohorts of 20-21 calves were collected weekly for 20 weeks and processed for isolation of EHEC O157:H7 and detection of STEC by an ELISA. Exposure to EHEC O157 was also investigated by measuring IgG and IgM antibodies to the O157 lipopolysaccharide (O157 Ab) in sera by ELISA. The prevalences of EHEC O157 were 0.17% of 1151 fecal samples and 3.2% of 62 calves, and for STEC were 68% of 1005 fecal samples and 100% of 62 calves. Seroconversion to active IgG and IgM O157 Ab responses in some calves was not associated with isolation of EHEC O157. The milk replacer contained low levels of antibodies to EHEC antigens and without antimicrobial drugs, it did not inhibit the growth of EHEC O157 in vitro. Two E. coli O157:H7 that were isolated were totally drug sensitive whereas 60 commensal E. coli isolates that were examined were highly resistant. Antibodies in milk replacer that might be protective in vivo, and susceptibility to antimicrobial agents in the milk replacer may contribute to the low prevalence of EHEC O157 in white veal calves.     

Association between ceftiofur use and isolation of Escherichia coli with reduced susceptibility to ceftriaxone from fecal samples of dairy cows

OBJECTIVE: To estimate the association between ceftiofur use and the isolation of Escherichia coli with reduced ceftriaxone susceptibility from fecal samples of dairy cow populations. ANIMALS: 1,266 dairy cows on 18 farms in Ohio. PROCEDURES: Individual fecal samples from all cows in the study herds were tested for Escherichia coli with reduced ceftriaxone susceptibility. Herd antimicrobial use policy and antimicrobial treatment records were also obtained. Plasmid DNA from these isolates was tested for the presence of the AmpC beta-lactamase gene (blaCMY-2). Minimum inhibitory concentrations to a standard panel of 16 antimicrobial drugs were determined by use of a broth microdilution system. RESULTS: Herds for which ceftiofur use was reported were more likely to have cows from which reduced susceptibility E coli was isolated than herds that did not report ceftiofur use (odds ratio, 25.0). However, at the individual cow level, no association was found between recent ceftiofur treatment and isolation of reduced-susceptibility E coli (adjusted odds ratio, 1.01). No observed linear relationship was found between the percentage of cows from which E coli with reduced ceftriaxone susceptibility was isolated and the percentage of cows in the herd recently treated with ceftiofur. CONCLUSIONS AND CLINICAL RELEVANCE: Our observation of a herd-level but not an individual cow-level association between ceftiofur use and isolation of E coli with reduced ceftriaxone susceptibility from fecal samples suggests that interventions to reduce the spread of antimicrobial resistance genes in agricultural animals will be most effective at the herd level.     

Prevalence of Salmonella, Campylobacter, and Escherichia coli on ostrich carcasses and the susceptibility of ostrich-origin E. coli isolates to various antibiotics

There has been limited research on the prevalence of foodborne pathogens such as Escherichia coli O157:H7, Salmonella, and Campylobacter on ostrich carcasses. Likewise, few studies have been done in ostriches to determine the antimicrobial susceptibilities of common bacteria, like E. coli. In this study, ostrich carcasses were sampled from eight slaughterhouses in Ohio and one in Indiana. Although results demonstrated no E. coli O157:H7 from the carcasses sampled, 91% (116/128) of the dressed carcasses sampled had E. coli present. One carcass sample (1/152) was positive for Salmonella. Campylobacter were detected in 10% (19/191) of the carcasses. Antimicrobial susceptibility testing on 93 carcass E. coli isolates showed resistance to erythromycin (99%), neomycin (65%), netilmicin (2%), oxytetracycline (22%), streptomycin (2%), and trimethoprim (3%). All isolates were resistant to bacitracin, lincomycin, penicillin, and vancomycin. For the large intestinal sampling, 149 of the 217 (69%) samples had E. coli present. Fifty of these 149 samples had E. coli levels ranging from 10(2) to 10(5) colony-forming units/g feces. Campylobacter were isolated from 6 of 201 (3%) samples. No Salmonella colony was detected. Antimicrobial susceptibility testing on 131 intestinal E. coli isolates showed resistance to erythromycin (98%), neomycin (66%), netilmicin (34%), oxytetracycline (34%), streptomycin (40%), and trimethoprim (13%). All isolates were resistant to bacitracin, lincomycin, penicillin, and vancomycin.     

Escherichia coli O115 forms fewer attaching and effacing lesions in the ovine colon in the presence of E. coli O157:H7

Escherichia coli O115 has been isolated from healthy sheep and was shown to be associated with attaching-effacing (AE) lesions in the large intestine. Following previous observations of interactions between E. coli O157 and O26, the aim of the present study was to assess what influence an O115 AE E. coli (AEEC) would have on E. coli O157 colonisation in vitro and in vivo. We report that E. coli O115- and O157-associated AE lesions were observed on HEp-2 cells and on the mucosa of ligated ovine spiral colon. In single strain inoculum, E. coli O115 associated intimately with HEp-2 cells and the spiral colon in greater numbers than E. coli O157:H7. However, in mixed inoculum studies, the number of E. coli O115 AE lesions was significantly reduced suggesting negative interference by E. coli O157. Use of the ligated colon model in the present work has allowed in vitro observations to be extended and confirmed whilst using a minimum of experimental animals. The findings support a hypothesis that some AEEC can inhibit adhesion of other AEEC in vivo. The mechanisms involved may prove to be of utility in the control of AE pathovars.     

Escherichia coli strains from edema disease: O serogroups, and genes for Shiga toxin, enterotoxins, and F18 fimbriae

The objectives of the research were to determine the presence of the gene sequences for Shiga Toxin 2e (Stx2e), enterotoxins (ST-I, ST-II and LT-I), and F18 fimbriae in 144 Escherichia coli strains isolated from pigs with edema disease; to assess the ability of stx2e(+) strains to produce Stx2e; and to determine the O serogroups of the E. coli strains. Presence of the genes was determined by polymerase chain reaction (PCR), production of Stx2e was assessed by cytotoxicity for Vero and Hela cells, O serogroups were identified by agglutination with specific antisera. Of the 144 strains tested, 99 were stx2e(+) by PCR, but only 45 of these were Stx2e(+) in the cell culture assays. Among the 99 stx2e(+) strains, PCR detected the genes for F18ab, ST-I, ST-II, LT-I in 76, 40, 31 and 16 strains, respectively. Forty-one of the 99 sxt2e(+) strains belonged to O group 139; the rest did not belong to the classical edema disease O serogroups. It is likely that the enterotoxins, whose genes were detected at high frequency, are responsible for diarrhea seem in pigs with edema disease in Brazil.     

Dermatitis in broilers caused by Escherichia coli: isolation of Escherichia coli from field cases, reproduction of the disease with Escherichia coli O78:K80 and conclusions under consideration of predisposing factors

A dermatitis in broiler chickens, especially on the caudal back, thighs and around the cloaca is observed more frequently in the last years. The skin is swollen at sites of inflammation and a fibrineous plaque extends between muscle and subcutis. No clinical signs are visible in the living flock but the disease causes economical losses because of degrading and rejection of carcasses. Studies of literature and own field observations suggest that Escherichia (E.) coli is involved in the development of the dermatitis. The following serotypes were isolated from field cases: O78:K80 (3X), O2:K56 (2X), O127:K63 (3X), O9:K57 (1X), O140 (2X); two isolates could not be identified. The reproduction of the dermatitis was successful by infection via feather follicles with E. coli O78:K80. The density of broilers kept on farms may contribute to the outbreak of dermatitis by violation of the skin followed by infection of the injuries. Massage of the infected sites by close contact of birds and insufficient hygiene may support the development of the disease.     

Anti-capsular antibodies activate killing of Escherichia coli O8:K87 by the alternate complement pathway in porcine serum

Enterotoxigenic Escherichia coli (ETEC) strains that produce K88 (F4)+ fimbria are important causes of diarrhea and post-diarrheal septicemia in swine. ETEC O8:K87, a serotype represented by a number of these strains, is typically serum resistant. Strain-specific antibodies are known to activate alternative C pathway-mediated killing of other serum-resistant E. coli [Hill, A.W., Shears, A.L., Hibbitt, K.G., 1978. The requirement of specific antibody for the killing of E. coli by the alternate complement pathway in bovine serum. Immunology 34, 131-136], but their antigenic targets have not been determined. We tested the hypothesis that anti-K87 antibodies activate alternative pathway-mediated killing of ETEC O8:K87. Pigs were immunized with ETEC O8:K87 strain 2534-86 cells or purified K87 polysaccharide. Post-, but not pre-immunization sera killed 2534-86 cells, and absorption with 2534-86 cells or by K87 affinity chromatography eliminated bactericidal activity. Complementation of absorbed serum with anti-K87 antibodies restored bactericidal activity, confirming the ability of these antibodies to activate C-mediated serum killing. Serum from age-matched, non-vaccinated control pigs also killed 2534-86. This activity was eliminated by absorption with 2534-86 cells, but not K87 affinity chromatography, indicating that specific non-capsular antibodies are also able to activate C-mediated killing. In all cases, Mg-EGTA-treated serum was as effective as non-treated serum in killing, suggesting that bactericidal activity was mediated predominantly if not exclusively via the alternative C pathway.     

Genetic diversity among Escherichia coli O149:K91 strains isolated from pigs with diarrhoea determined by randomly amplified polymorphic DNA analysis.

The genetic relatedness among 72 Escherichia coli strains of serotype O149:K91 isolated from pigs with diarrhoea was investigated by randomly amplified polymorphic DNA (RAPD) analysis. Fimbrial and toxic virulence markers of the isolates were also tested. Amplification with primer 1254 resulted in three different RAPD types whereas primer 1290 generated one RAPD profile only. Based on the RAPD and fimbrial/toxin types the strains were classified into five distinct groups.     

大肠杆菌F18ac菌毛F亚单位基因的克隆与序列分析

根据已经发表的F18ab菌毛F亚单位(FedF／ab)的基因(fedF／ab),设计一对引物,利用PCR技术从表达F18ac菌毛的大肠杆菌2134P株、8199株、8813株中分别扩增到一段序列,并克隆至pGEM—T载体,获得重组质粒T8813F、T8199F、T2134PF。琼脂糖凝胶电泳、序列测定及分析表明,该3个序列大小均为903bp,与fedF／ab大小一致且具有较高的同源性(99．4％),推导的FedF／ac氨基酸序列与FedF／ab同源性为98．3％。数据表明该实验所克隆的序列均为F18ac菌毛F亚单位(FedF／ac)的基因(fedF／ac)。