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1.
The Brachyspira (formerly Serpulina) species rrl gene encoding 23S ribosomal RNA (rRNA) was used as a target for amplification of a 517bp DNA fragment by polymerase chain reaction (PCR). The primers for PCR amplification had sequences that were conserved among Brachyspira 23S rRNA gene and were designed from nucleotide sequences of Brachyspira hyodysenteriae, Serpulina intermedia, Brachyspira innocens and Brachyspira pilosicoli available from the GenBank database. Digestion of PCR-generated products from reference and field isolates of swine intestinal spirochetes with restriction enzymes Taq I and Alu I revealed five restriction fragment length polymorphism (RFLP) patterns. Each RFLP pattern corresponded to previously established genetic groups including B. hyodysenteriae (I), S. intermedia/B. innocens (II), Brachyspira murdochii (III), B. pilosicoli (IV) and B. alvinipulli (V). The 23S rRNA PCR/RFLP provided a relatively simple genotypic method for identification of porcine pathogenic B. hyodysenteriae and B. pilosicoli.  相似文献   

2.
A cross-sectional study was conducted on a commercial egg-producing farm with a history of wet litter. A total of 600 fresh caecal faecal samples were obtained from under cages of laying hens in three sheds each containing flocks of approximately 5400 hens. Samples were cultured for intestinal spirochaetes, and growth on the primary isolation plate was observed under a phase contrast microscope and subjected to PCRs specific for the intestinal spirochaetes Brachyspira intermedia and Brachyspira pilosicoli. Spirochaete isolates obtained in pure culture were assessed for their ability to cause haemolysis on blood agar and to produce indole, and were typed using pulsed field gel electrophoresis (PFGE). A 1250 base pair portion of the 16S rRNA gene of three B. intermedia and five unidentified isolates was sequenced, and the sequences compared with those of other Brachyspira species. Overall, 121 (20.2%) of the faecal samples contained spirochaetes as determined by growth on the plate and microscopy. Using PCR on the primary growth from these positive samples, 43 (7.2% overall) were shown to contain B. intermedia, 8 (1.3%) to contain B. pilosicoli, and 70 (11.7%) were PCR negative. Only 24 isolates of B. intermedia and five isolates of unknown species were obtained in pure culture. Comparative analysis of the 16S rRNA gene sequence identified the non-B. intermedia isolates as belonging to the proposed species "Brachyspira pulli". PFGE analysis of the B. intermedia strains identified them as having four major banding patterns. Individual patterns were found in hens from different flocks, suggesting cross-transmission of strains between flocks. No environmental sources of infection were identified. The youngest flock had a significantly lower level of colonisation with B. intermedia than the flock of intermediate age (P = 0.004), suggesting that following initial infection of individual young hens on this farm there was amplification and transmission of infection amongst members of the flock.  相似文献   

3.
Avian intestinal spirochaetosis (AIS) is an infection of the caeca and/or colo-rectum of laying and meat breeder hens caused by anaerobic intestinal spirochaetes of the genus Brachyspira. AIS can result in a variety of symptoms, including delayed and/or reduced egg production, and increased faecal water content. The two most commonly reported Brachyspira species involved in AIS are Brachyspira pilosicoli and Brachyspira intermedia, and their detection and identification can be difficult and time consuming. In the current study a two-step nested duplex PCR (2S-N-D-PCR) was developed for the detection of these two species, using DNA extracted from washed chicken faeces. In the first step, a duplex PCR (D-PCR) amplifying Brachyspira genus-specific portions of the 16S rRNA and NADH oxidase (nox) genes was undertaken on the washed faeces. In the second step, a nested D-PCR was used that amplified species-specific portions of the 16S rRNA gene of B. pilosicoli and the nox gene of B. intermedia from the amplicons produced in the first step. The 2S-N-D-PCR was rapid and specific, and could be used to detect approximately 10(3) cells of each spirochaete species per gram of washed faeces. When tested on 882 chicken faecal samples from infected flocks, it detected 4-5% more positive faecal samples than did the standard method of selective anaerobic culture followed by individual species-specific PCR assays conducted on the growth on the primary plate. The application of this new technique should improve diagnostic capacity, and facilitate further studies on AIS.  相似文献   

4.
Multilocus enzyme electrophoresis (MLEE) was used to identify, examine genetic relationships and look at disease associations of a collection of 53 intestinal spirochaete isolates previously recovered from the faeces of adult hens on 14 farms in Qld, Australia. The MLEE results were compared with those previously obtained using species-specific PCR amplifications. The isolates were divided into five Brachyspira species groups by MLEE: Brachyspira murdochii (n=17), B. intermedia (n=15), B. pilosicoli (n=14), B. innocens (n=2) and "B. pulli" (n=1). Three new MLEE groups each containing single isolates also were identified. The results of the PCR assay for B. pilosicoli were concordant with the MLEE results, but the 23S rDNA-based PCR for B. intermedia had failed to detect 8 of the 15 isolates. The B. innocens/B. murdochii nox-based PCR had correctly identified all the isolates of B. murdochii, but did not identify either of the two B. innocens isolates. Using MLEE, isolates from two farms (14%) were identified as B. murdochii, whilst the pathogenic species B. intermedia and B. pilosicoli were present in hens from eight (57%) and five (36%) farms, respectively, and were identified together in four (29%) farms. All seven of the farms with production problems or wet litter were colonised with B. intermedia and/or B. pilosicoli. Six farms had multiple spirochaete isolates available for examination. Two broiler breeder farms both had five isolates of B. pilosicoli that shared the same MLEE electrophoretic type (ET), whilst one laying hen farm had three isolates of B. intermedia that all belonged to the same ET. Hence on each of these farms a predominant strain of a pathogenic species was present. On the other farms isolates of the same species were more diverse and belonged to different ETs. These results show that the epidemiology of intestinal spirochaetal infections in broiler breeder and laying hen flocks can vary considerably between farms, although the reasons for these differences were not established.  相似文献   

5.
The distribution of many genes encoding virulence and virulence life-style (VL-S) factors in Brachyspira (B.) hyodysenteriae and other Brachyspira species are largely unknown. Their knowledge is essential e.g. for the improvement of diagnostic methods targeting the detection and differentiation of the species. Thus 121 German Brachyspira field isolates from diarrhoeic pigs were characterized down to the species level by restriction fragment length polymorphism analysis of the nox gene and subsequently subjected to polymerase chain reaction detecting VL-S genes for inner (clpX) and outer membrane proteins (OMPs: bhlp16, bhlp17.6, bhlp29.7, bhmp39f, bhmp39h), hemolysins (hlyA/ACP, tlyA), iron metabolism (ftnA, bitC), and aerotolerance (nox). For comparison, B. hyodysenteriae reference strains from the USA (n=7) and Australia (2) were used. Of all genes tested only nox was detected in all isolates. The simultaneous presence of both the tlyA and hlyA/ACP was restricted to the species B. hyodysenteriae. The hlyA infrequently occurred also in weakly hemolytic Brachyspira. Similarly to tlyA and hlyA all B. hyodysenteriae strains contained the ferritin gene ftnA which was also found in two Brachyspira intermedia isolates. OMP encoding genes were present in B. hyodysenteriae field isolates in rates of 0% (bhlp17.6, bhmp39h), 58.1% (bhlp29.7), and 97.3% (bhmp39f). Since the study revealed a high genetic heterogeneity among German B. hyodysenteriae field isolates differentiating them from USA as well as Australian strains, targets for diagnostic PCR were limited to the nox gene (genus specific PCR) as well as to the species specific nox(hyo) gene and the combination of hlyA and tlyA which allow to specifically detect B. hyodysenteriae.  相似文献   

6.
Rapid identification of porcine Brachyspira species is required in order to differentiate pathogenic from non-pathogenic species. The aim of our study was to compare a recently described genetic method based on polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP), nox RFLP-PCR assay, and three species-specific PCRs described previously in the literature with a 16S rRNA gene RFLP-PCR discriminatory reference assay (16S RFLP-PCR) for the identification of Brachyspira spp. of swine origin. In this study, 20 porcine spirochaetal strains were identified and compared to 33 reference strains by 16S RFLP-PCR and nox RFLP-PCR and three species-specific PCRs. RFLP-PCR methods showed concordant results for 47 strains and discordances for 6 strains (2 differently identified and 4 not revealed by nox RFLP-PCR). In our hands species-specific PCRs showed concordant results with 16S and nox RFLP-PCR for 43 strains and discordances for 10 strains (2 differently identified and 8 not amplified). The same results observed testing the 20 field-isolated spirochaetes were obtained for the corresponding porcine faecal samples. The detection limit was 10(2) -10(3) cells/g of faeces for 16S rRNA gene PCR and 10(4) cells/g of faeces for nox PCR. In our experience nox RFLP-PCR appeared successful for the speciation of B. hyodysenteriae reserving 16S RFLP-PCR for all other pathogenic and non-pathogenic Brachyspira species. Among the species-specific PCR assays tested only that for B. pilosicoli was useful in our hands.  相似文献   

7.
Avian intestinal spirochaetosis (AIS) is a disease complex affecting adult laying and breeding chickens associated with infection by anaerobic intestinal spirochaetes of the genus Brachyspira. Options for control of AIS are limited, as few effective antimicrobial agents are registered for use in laying chickens. One of the two most commonly encountered pathogenic species in AIS is B. intermedia, and the aim of the current study was to determine whether a B. intermedia bacterin vaccine would help control AIS caused by this species. An autogenous bacterin was prepared from B. intermedia strain HB60 and given twice intramuscularly at a 3-week interval to 12 laying chickens housed in individual cages. Twelve non-vaccinated control chickens were placed in adjacent cages in the same room. Two weeks after the second vaccination all the chickens were experimentally challenged with B. intermedia HB60 by crop tube. Subsequently faeces were cultured for spirochaetes every 2-3 days, faecal water content and chicken weight were measured weekly, and egg numbers and weights were recorded daily. Serum was taken prior to both vaccinations, at the time of challenge and at euthanasia. The chickens were killed 6 weeks post-challenge. The vaccinated chickens showed seroconversion to the vaccine, but antibody levels declined significantly post-infection. In comparison, the non-vaccinated chickens showed seroconversion post-infection. The reason for the reduction in the antibody levels in the vaccinated chickens after infection was not explained. At some point all the chickens excreted spirochaetes in their faeces, and the duration of excretion was not different between vaccinated and non-vaccinated chickens. There were no differences in faecal water content, chicken weights, egg production, or gross and microscopic caecal lesions between vaccinated and non-vaccinated chickens. In conclusion, an autogenous bacterin vaccine did not prevent infection with B. intermedia in laying chickens.  相似文献   

8.
Anaerobic intestinal spirochaetes of the genus Brachyspira are known to colonise dogs, but relatively little is known about their prevalence, distribution or pathogenic potential. One species, Brachyspira pilosicoli, is thought to cause diarrhoea in dogs, as well as in other animals and humans. To investigate the prevalence and distribution of infection, faecal samples from 49 puppies from six pet shops in the suburbs of Perth, Western Australia were subjected to selective culture for anaerobic intestinal spirochaetes. Growth from the primary plates was also harvested, the DNA extracted and a polymerase chain reaction (PCR) amplification of a portion of the 16S rRNA gene of B. pilosicoli applied. Weakly beta-haemolytic intestinal spirochaetes (WBHIS) grew on plates from 20 of the dogs (40.8%). Seven plates (14.2%) yielded PCR positive amplification for B. pilosicoli. Seven WBHIS isolates were obtained in pure culture, and two of these were shown to be B. pilosicoli by PCR. Application of multilocus enzyme electrophoresis to the seven isolates confirmed that the two PCR positive isolates were B. pilosicoli, whilst the other five belonged to a group previously designated "Brachyspira canis". All the "B. canis" isolates came from healthy puppies, suggesting that this WBHIS is a commensal. Three of the seven puppies with PCR evidence of B. pilosicoli had diarrhoea, but the sample size was small and the association between colonisation and diarrhoea was not statistically significant. Pet shop puppies are commonly infected with intestinal spirochaetes, and may act as a reservoir of B. pilosicoli for other animals and humans.  相似文献   

9.
Feral pigs are recognized as being a potential reservoir of pathogenic microorganisms that can infect domestic pigs and other species. The aim of this study was to investigate whether feral pigs in Western Australia were colonized by the pathogenic enteric bacteria Lawsonia intracellularis, Brachyspira hyodysenteriae and/or Brachyspira pilosicoli. A total of 222 feral pigs from three study-populations were sampled. DNA was extracted from faeces or colonic contents and subjected to a previously described multiplex PCR for the three pathogenic bacterial species. A subset of 61 samples was cultured for Brachyspira species. A total of 42 (18.9%) of the 222 samples were PCR positive for L. intracellularis, 18 (8.1%) for B. hyodysenteriae and 1 (0.45%) for B. pilosicoli. Four samples were positive for both L. intracellularis and B. hyodysenteriae. Samples positive for the latter two pathogens were found in pigs from all three study-sites. A strongly haemolytic B. hyodysenteriae isolate was recovered from one of the 61 cultured samples. Comparison of a 1250-base pair region of the 16S rRNA gene amplified from DNA extracted from the isolate and five of the B. hyodysenteriae PCR positive faecal samples helped confirm these as being from B. hyodysenteriae. This is the first time that B. hyodysenteriae has been detected in feral pigs. As these animals range over considerable distances, they present a potential source of B. hyodysenteriae for any domesticated pigs with which they may come into contact.  相似文献   

10.
A polymerase chain reaction assay, amplifying a 1027 base pair portion of the 23S rDNA gene, was evaluated for identification of the intestinal spirochaete Serpulina intermedia. A total of 34 strains of S. intermedia isolated from pigs and chickens and 195 strains of other related species were tested. The optimised assay correctly identified all the S. intermedia strains, but generated 11 false positive reactions, giving a test sensitivity of 100% and a test specificity of 94.3%. The false positive reactions were generated from strains of four different species of intestinal spirochaetes, and the product was of the original predicted size. This suggests that the primer sites selected on the 23S rRNA gene were not completely specific for S. intermedia. Pulsed-field gel electrophoresis was then developed to investigate diversity amongst the S. intermedia strains. All strains tested had distinct DNA banding patterns using Mlu1, although three isolates from chickens on the same farm appeared closely related. The collection exhibited considerable genetic diversity, and strains from pigs and chickens were distributed in clusters throughout the dendrogram produced. The most closely related porcine and avian strains shared only 62% similarity.  相似文献   

11.
Sixty-nine intestinal spirochetes isolated from pigs and poultry in eastern Australia were selected to evaluate the effectiveness of a species-specific PCR-based restriction fragment length polymorphism (RFLP) analysis of the Brachyspira nox gene. For comparative purposes, all isolates were subjected to species-specific PCRs for the pathogenic species Brachyspira hyodysenteriae and Brachyspira pilosicoli, and selected isolates were examined further by sequence analysis of the nox and 16S ribosomal RNA genes. Modifications to the original nox-RFLP method included direct inoculation of bacterial cells into the amplification mixture and purification of the PCR product, which further optimized the nox-RFLP for use in a veterinary diagnostic laboratory, producing sufficient product for both species identification and future comparisons. Although some novel profiles that prevented definitive identification were observed, the nox-RFLP method successfully classified 45 of 51 (88%) porcine and 15 of 18 (83%) avian isolates into 5 of the 6 recognized species of Brachyspira. This protocol represents a significant improvement over conventional methods currently used in veterinary diagnostic laboratories for rapid specific identification of Brachyspira spp. isolated from both pigs and poultry.  相似文献   

12.
The prevalence of infections with different Brachyspira species was assessed in 202 pigs with various chronic herd problems using different methods. Twenty-seven pigs (13.4%) were positive for Brachyspira spp. with at least one of the methods used. The highest number of positives was identified with mucosal scraping-PCR (23), followed by PET-PCR (22) and bacteriological-biochemical analysis (15). With the exception of three cases of B. pilosicoli infections, only weakly pathogenic Brachyspira species were identified. The majority was B. murdochii, followed by B. innocens and B. intermedia. Concurrent infections with two or more Brachyspira species were common and accounted for 37.1% of the total. Presence of weakly haemolytic Brachyspira was associated with wasting and diarrhoea in a number of cases. This investigation shows that infections with weakly haemolytic Brachyspira spp. may contribute to colonic pathology in pigs with chronic herd problems and that mixed infections seem to occur more frequently than previously noticed.  相似文献   

13.
对21株分离自河南及山西地区的鸡杆菌的16SrRNA基因序列进行研究,以此分析分离株的进化关系并确定其在鸡杆菌属中所属的具体种。采用PCR方法扩增其16SrRNA基因序列,然后克隆测序。用DNAStar软件对21个菌株的序列及GenBank中已公布的鸡杆菌属相关菌株序列进行同源性比较,结果发现21株分离株之间的核苷酸序列同源性为96．0oA～100％,同鸭源鸡杆菌F279（Gallibacteriuman atis F279）（AF228002）的同源性为95．3％～99．3％,同输卵管炎鸡杆菌F150（Gallibacterium salpingitidis F150）（EU424000）的同源性为88．3％～91．5％,同虎皮鹦鹉鸡杆菌F450（GallibacteriummelopsittaciF450）（EU339196）的同源性为90．3％～93．3％,同海藻糖发酵鸡杆菌52-S3-90（Gallibacteriumtrehalosi fermentans52-s3—90）（EU339199）的同源性为88．2％～91．4％,同多杀性巴氏杆菌CCUG179（P．multocida CCUG17977）（AF294411）的同源性为85．5％～88．8％,对21株细菌的序列同以上菌株的16SrRNA基因序列进行遗传进化树分析,显示21株细菌同鸭源鸡杆菌F279（AF228002）构成一个单独的大分支。结果表明,所有分离株均属于鸭源鸡杆菌,首次大量报道了来源于河南、山西省不同地区的鸡杆菌的16SrRNA基因序列,为鸡杆菌分类的研究提供了参考。  相似文献   

14.
Babesia canis has generally been considered the only large Babesia to infect dogs. In this study, we used PCR to detect and characterize B. canis canis isolated from naturally infected dogs in Poland by amplifying and sequencing a portion of the 18S ribosomal RNA (rRNA) gene. Venous blood samples were collected from 76 Babesia-symptomatic dogs. A 559-bp fragment of the B. canis canis 18S rRNA gene was amplified by PCR. The PCR products were then digested with HincII restriction enzyme, and isolates were classified according to whether they were cut (group A) or not (group B) by this endonuclease. Sequencing of the PCR products from the isolates led to the identification of seven sequence variants (four in group A, and three in group B). Sequences were compared with GenBank sequences, and alignments showed that all B. canis canis isolates from Europe may be classified into groups A or B as defined in our study.  相似文献   

15.
There is no ring test for quality assessment available in Europe for diagnostics and antimicrobial susceptibility testing of the fastidious, anaerobic bacteria of the genus Brachyspira. Therefore, an international ring test for Brachyspira spp. was performed once a year during 2002-2004. Two sets of coded samples were prepared and distributed on each occasion. One set comprised six swabs dipped in pig faeces spiked with Brachyspira spp. intended for diagnostics. The other set comprised two pure strains intended only for susceptibility testing. All methods used were in-house methods. The species used were Brachyspira hyodysenteriae, Brachyspira pilosicoli, Brachyspira innocens, Brachyspira murdochii and Brachyspira intermedia. In most cases, the correct Brachyspira spp. were detected. However, the results showed that Brachyspira spp. could be difficult to identify, especially if two Brachyspira spp. were mixed or if the concentration of Brachyspira in faeces was low. Additionally, some laboratories reported Brachyspira growth in control samples that were not seeded with any spirochaetes. The lowest detection level was 10(2) bacteria/ml faeces for both B. hyodysenteriae and B. pilosicoli. The susceptibility tests performed showed that disc diffusion was not recommendable for Brachyspira spp. Extended antimicrobial dilution series gave most congruent results. The diversity of the results highlights the importance of ring tests for a high quality of diagnostics and antimicrobial susceptibility tests for Brachyspira spp. This is the first ring test described for Brachyspira spp.  相似文献   

16.
This study aimed to obtain information about the types of spirochaetes colonising urban dogs in Thailand, and to investigate their pathogenic potential in a day-old chick model of intestinal spirochaetosis. Spirochaetes were isolated from the faeces of six of 47 (12.8%) healthy dogs and 11 of 104 (10.6%) dogs with diarrhoea. Their biochemical properties and 16S ribosomal DNA sequences were analysed. Four isolates were identified as Brachyspira pilosicoli, three resembled "Brachyspira pulli", nine clustered with "Brachyspira canis" and one was similar to Brachyspira intermedia. Canine isolates of B. pilosicoli, "B. canis" and "B. pulli", and control strains of Brachyspira hyodysenteriae, B. pilosicoli and Brachyspira innocens colonised experimentally infected day-old chicks. The chicks did not develop diarrhoea, but were significantly lighter than the non-infected group and those infected with B. innocens after 21 days (P<0.05). Using immunohistochemistry, spirochaetes were observed covering the surface epithelium and in the crypts of chicks in all three groups challenged with the canine isolates. Variable histopathological changes were seen, with the greatest inflammatory cell infiltration into the lamina propria occurring in the group infected with "B. pulli". Canine "B. canis", "B. pulli" and B. pilosicoli isolates may have pathogenic potential.  相似文献   

17.
Using three reference strains of Brachyspira hyodysenteriae (B204, B234, B169), one B. pilosicoli (P43/6/78), one B. murdochii (56-150), one B. intermedia (PWS/A), one B. innocens (B256) and ten Korean isolates, PCR-RFLP analysis of DNA encoding 23S rRNA was performed to establish a rapid and accurate method for characterizing porcine intestinal spirochetes. Consequently, B. hyodysenteriae and B. pilosicoli revealed different restriction patterns; however, the other three species shared the same pattern. These findings are not consistent with a prior report. Differences in 23S rRNA gene sequences, between two B. murdochii strains, 56-150 and 155-20, were observed. These results indicate that 23S rRNA PCR-RFLP could be used as an identification method for pathogenic Brachyspira spp. (B. hyodysenteriae and B. pilosicoli) as well as an epidemiological tool for characterizing spirochetes isolated from swine.  相似文献   

18.
Brachyspira infections are significant causes of enterocolitis in pigs. In order to differentiate pathogenic species (Brachyspira (Br.) hyodysenteriae, Brachyspira pilosicoli) from less pathogenic or non-pathogenic species (Brachyspira intermedia, Brachyspira innocens, Brachyspira murdochii) in paraffin-embedded tissue samples a polymerase chain reaction (PCR) protocol allowing identification of Brachyspira at species level in archival material was developed. This approach was complemented by sequencing of the PCR amplification products. All seven cases presented with clinical and morphological Brachyspira-associated enterocolitis. Br. hyodysenteriae was not identified in any of the cases, while Br. pilosicoli was identified in a single case in conjunction with Br. murdochii. One case each was found positive for Br. innocens and Br. intermedia. Interestingly, the majority of cases presented as single or double infections with Br. murdochii. In some of the pigs other pathogens, like porcine circovirus-2 or Lawsonia intracellularis were present. These observations point at the possibility that under certain conditions even Brachyspira species of low pathogenicity can multiplicate extensively and lead to Brachyspira-associated enterocolitis.  相似文献   

19.
Different Brachyspira (B.) species colonize the porcine intestinal tract, some of which are pathogens of significant clinical and economic importance. In 2002 we published a novel molecular method for differentiation of Brachyspira species from pigs based on the amplification of the nox-gene and the generation of species-specific restriction patterns (nox-RFLP) using the enzymes BfmI and DpnII (Rohde et al., 2002). We applied this method for identification in addition to biochemical testing in doubtful cases until 2008. Since 2009 we have used it as the first line method of identification. The current study documents the results of examining 2050 Brachyspira isolates collected from January 2009 to December 2011. In addition to identifying isolates with previously described patterns, four novel restriction fragment length patterns were observed, and isolates with these patterns could be assigned to the species B. intermedia and the B. innocens/murdochii complex on the basis of their phenotypic properties and by nox-sequence analysis. In 2007 a potentially new Brachyspira species, "B. suanatina", was described in Swedish pigs (R?sb?ck et al., 2007). From the published nox-gene sequence it could be expected that this Brachypira species should show a new restriction pattern making nox-RFLP a suitable technique for identification of "B. suanatina". In this study the new restriction fragment length pattern could be demonstrated in one of the strains described by R?sb?ck et al. (AN4859/03). Nevertheless, no isolates with this new pattern corresponding to "B. suanatina" were identified amongst the 2050 Brachyspira isolates examined from northern Germany.  相似文献   

20.
The objective of this study was to assess whether nucleotide substitutions in the 16S rDNA sequence of selected Brachyspira hyodysenteriae isolates could explain differences in doxycycline minimal inhibitory concentrations (MICs). The main part of the 16S rRNA gene was sequenced and compared for 19 isolates with different doxycycline MICs. A mutation in the 16S rRNA gene at the position corresponding to 1058 in Escherichia coli has been shown to cause tetracycline resistance in other bacteria. In the B. hyodysenteriae sequences a G1058C mutation was found for all isolates with increased doxycycline MICs whereas all susceptible isolates had the wild type sequence.  相似文献   

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