Identification of the heat-labile hemolysin of Actinobacillus pleuropneumoniae serotype 1.

The heat-labile hemolysin of Actinobacillus pleuropneumoniae serotype 1 strain CM-5 was partially purified using ammonium sulfate precipitation and gel permeation chromatography. This partially purified material was subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis and blotted onto nylon filters. The filters were treated with convalescent pig serum and subsequently with CM-5 culture supernatant containing active hemolysin. A 104 kd peptide was identified as the hemolysin because it bound antibodies in convalescent pig serum which cross-linked active hemolysin. The same 104 kd protein when injected into a rabbit produced neutralizing antibodies to the CM-5 hemolysin in culture supernatant.     

Immunological characterization of breakdown peptides of the 104 kilodalton hemolysin of Actinobacillus pleuropneumoniae serotype 1

The 104 kilodalton (kDa) hemolysin of Actinobacillus pleuropneumoniae serotype 1, strain CM-5 was precipitated from RPMI-1640 culture supernatant using ammonium sulfate to 80% saturation. In immunoblots, a rabbit polyclonal antiserum against the 104 kDa hemolysin protein, recognized not only the original 104 kDa monomeric form of the hemolysin but other proteins in the crude antigen mixture ranging in molecular mass from 43 to greater than 125 kDa. The antiserum was able to crosslink these proteins to active hemolysin in RPMI-1640 culture supernatant resulting in bands of hemolysis in blood agar used in a contact assay. Corresponding to these bands of hemolysis, denatured peptides with molecular masses of 51, 85, 104 and greater than 125 kDa were excised and injected into rabbits. In immunoblots, the resultant antibodies recognized the injected peptide and the monomeric 104 kDa protein. However, only the rabbit antisera produced against the 104 and 125 kDa proteins contained antibodies which neutralized the active 104 kDa hemolysin in culture supernatant. These results indicate that (i) the 104 kDa protein hemolysin can exist in a higher molecular weight aggregate (greater than 125 kDa) but can also break down to peptides which have molecular masses smaller than the 104 kDa parent molecule and (ii) while several epitopes are present in the hemolysin molecule, there seems to be a restricted number of antigenic determinants responsible for inducing neutralizing antibodies and these seem to reside only in the 104 kDa parent molecule. This may have consequences, in terms of vaccine development, for the control of pleuropneumonia in swine herds.     

Production and characterization of monoclonal antibodies against Actinobacillus (Haemophilus) pleuropneumoniae serotype 2

Four hybridoma cell lines producing monoclonal antibodies (MAbs) against Actinobacillus (Haemophilus) pleuropneumoniae were established by fusion of mouse myeloma and spleen cells obtained from mice immunized with a serotype 2, strain SH-15. Enzyme-linked immunosorbent assay-inhibition tests with antigens obtained from 12 serotype strains of A. pleuropneumoniae and 9 other gram-negative bacteria showed that all the MAbs bound to only serotype 2 strains of A. pleuropneumoniae. The epitopes recognized by the MAbs were located on a carbohydrate moiety of lipopolysaccharide (LPS) of the organism, which was sensitive to periodate oxidation. In immunoblotting analyses of LPS obtained from A. pleuropneumoniae serotype 2, all the four MAbs reacted specifically with the characteristic ladder bands of LPS detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. These results suggest that O-antigen side chains of the LPS are one of the antigenic determinants responsible for the serotype-specificity of A. pleuropneumoniae.     

Serological characterization of Haemophilus pleuropneumoniae (Actinobacillus pleuropneumoniae) strains and proposal of a new serotype: serotype 9

Ten strains of H. pleuropneumoniae isolated from 10 herd outbreaks of pleuropneumonia were studied by means of the slide agglutination test, the indirect haemaggluitiniation (IHA) test and by gel diffusion. The strains were antigenically homogeneous and serologically distinct from serotypes 1 through 8. It is therefore proposed to refer these strains to a new serotype: serotype 9, with strain CVJ 13261 as the type strain.In addition to the serotype-specific capsular antigens, capsular antigen of serotype 1 (strain 4074) could be demonstrated in the 10 strains by means of gel diffusion analyses.In cross protection studies it was shown that the antigenic determinants shared by serotypes 9 and 1 were unable to yield a sufficient protection against disease. Thus, parenteral immunization with a killed 6-h culture of serotype 9 did not afford an acceptable protection against challenge with serotype 1 since only 3 of the 5 vaccinates were protected. The reverse experiment showed that parenteral immunization with serotype 1 only protected 1 out of 4 vaccinates.     

猪胸膜肺炎放线杆菌蛋白酶的分离纯化及特性分析

将血清7型猪胸膜肺炎放线杆菌(APP)山东分离株接种含0.2%NAD的LB液体培养基,37℃培养48 h后,经硫酸铵盐析、DEAE-纤维素离子交换层析、葡聚糖凝胶分子筛层析,从其培养上清液中分离纯化了1种蛋白酶.SDS-聚丙烯酰胺凝胶电泳显示,APP蛋白酶含有相对分子质量约为45 000的亚单位.以酪蛋白为底物测得该酶的最适PH值为7.5.最适温度为45℃;该酶对热有一定的稳定性,80℃加热30 min仍保留部分活性;乙二胺四乙酸(EDTA)可抑制其活性,而苯甲基磺酰氟(PMSF)对其无影响.     

Immunological properties of Actinobacillus pleuropneumoniae hemolysin I

The 105 kDa hemolysin I protein from Actinobacillus pleuropneumoniae serotype I type strain 4074 (HlyI) was shown by immunoblot analysis to be the predominant immunogenic protein if convalescent field sera or sera from pigs experimentally infected with A. pleuropneumoniae serotype 1 were used. SDS gel- and immunoblot-analysis using total culture, washed cells or culture supernatant showed that HlyI is essentially secreted and is not found attached to the bacteria. Proteins in the 105 kDa range that react strongly with anti-HlyI antibody, are produced by all serotypes and are presumed to be their hemolysins. Sera from pigs experimentally infected with each of the 12 serotypes strongly reacted with HlyI. In addition, some sera from pigs that were confirmed to be negative for A. pleuropneumoniae, also reacted with HlyI as well as with related proteins from Actinobacillus rossii and Actinobacillus suis. These two species produce proteins in the 105 kDa range which cross-react strongly with HlyI. They could be the source of the immunological reactions of the A. pleuropneumoniae-negative sera with HlyI. However, no cross-reactions could be found between HlyI and the Pasteurella haemolytica leukotoxin, the Escherichia coli alpha-hemolysin or related proteins from various hemolytic E. coli strains isolated from pigs. The immunological cross-reactions of HlyI with related proteins from A. rossii, A. suis and possibly from other bacterial species may create uncertainty in interpretation if HlyI is used as the antigen in serodiagnosis of A. pleuropneumoniae.     

Serological characterization of Actinobacillus pleuropneumoniae serotype 2 strains by using polyclonal and monoclonal antibodies

The antigenic differences between strains of serotype 2 of both biotypes I and II of Actinobacillus pleuropneumoniae were studied by using several serological techniques. Monoclonal antibodies (MAbs) against A. pleuropneumoniae biotype I serotype 2 were produced by fusion of spleen cells of BALb/c mice immunized with whole-cell (WC) suspension with SP2/O-Ag14 murine myeloma cells. Desirable MAbs were selected by enzyme-linked immunosorbent assay (ELISA) using WC as antigen. MAbs MK-7 and MK-10 identified multiple bands of lipopolysaccharide in Western-blot. Treatment of WC with proteinase K and sodium periodate indicated that both MAb binding sites were carbohydrates in nature. In both ELISA and Western-blot, MAbs MK-7 and MK-10 recognized only biotype I serotype 2 isolates. Neither MAb MK-7 nor MK-10 reacted with reference strains of remaining serotypes of A. pleuropneumoniae and other Gram-negative bacteria tested. The results obtained with various serological tests showed that strains of serotype 2 biotype I shared antigenic determinants with strain N-282 of serotype 2 biotype II, but not with strain N-273 of serotype 1 biotype II. It is suggested that data obtained from this study may be helpful in the development of specific serotyping and serodiagnostic reagents of A. pleuropneumoniae strains.     

Isolation of Actinobacillus pleuropneumoniae serotype 2 by immunomagnetic separation

In Denmark porcine pleuropneumonia is most frequently caused by Actinobacillus pleuropneumoniae serotype 2 (60%). Isolation of A. pleuropneumoniae from nasal cavities or tonsils from carrier animals is complicated due to the mixed bacterial flora present. An immunomagnetic separation technique (IMS) using immunomagnetic beads (Dynabeads((R))) was developed for isolation of A. pleuropneumoniae serotype 2 from pure cultures and from heterogeneous suspensions. Different coating and washing procedures were evaluated in pure and mixed cultures using polyclonal (PAb) and monoclonal antibodies. The highest reisolation yield was achieved when the beads were coated with 1.5 microg PAb IgG/10(7) beads. After washing the beads for four times 9-24% of the bacteria could be reisolated depending on the amount of IgG attached to the beads and the number of beads used. The recovery was increased to 19-61% when only two washing steps were performed. The IMS was further evaluated using dilutions of A. pleuropneumoniae with added Pasteurella multocida (10(9) CFU/ml). After two washing steps 15% of the A. pleuropneumoniae cells and no P. multocida was reisolated. A detection limit of 10 CFU/ml was found in this heterogeneous suspension. No significant difference was observed when comparing the recovery of A. pleuropneumoniae from pure culture, from mixed cultures and from artificially inoculated tonsils. From 12 pigs inoculated with an aerosol of A. pleuropneumoniae serotype 2 the bacterium could not be detected from the nasal cavity or tonsils by cultivation or PCR 6 weeks later. By using IMS A. pleuropneumoniae serotype 2 could be reisolated from the tonsils of three pigs. The IMS method represents a valuable tool for isolation of A. pleuropneumoniae from tissue samples.     

Serological characterization of Actinobacillus pleuropneumoniae strains and proposal of a new serotype: serotype 12

Until now 11 serotypes of Actinobacillus pleuropneumoniae have been described (Nicolet 1971, Gunnarsson 1980, Nielsen 1982, Rosendal & Boyd 1982, Nielsen & O’Connor 1984, Nielsen 1985, Kamp 1986). Recently a hitherto unrecognized serotype was isolated from 9 Danish outbreaks of pleuropneumonia in pigs. The origin of the strains is given in Table 1. From 3 herds the unrecognized serotype was found in 2 to 3 pigs submitted for necropsy at different times. The present study describes the serological properties of the 13 isolated strains.     

猪传染性胸膜肺炎放线杆菌血清2型PCR程序优化及分子鉴定

猪接触性传染性胸膜肺炎（porcine contagious pleuropneumonia,PCP）又称坏死性胸膜肺炎,是由胸膜肺炎放线杆菌引起的一种高度接触传染性、致死性呼吸道传染病。以急性出血性纤维素性肺炎和慢性纤维素性坏死性胸膜炎为主要特征。各种年龄、性别的猪对本病均易感,急性者死亡率高,慢性者常能耐过。猪传染性胸膜肺炎放线杆菌有15个血清型,不同血清型之间没有或仅有较弱的交叉保护作用,这给猪传染性胸膜肺炎放线杆菌的诊断防治和免疫预防带来了很大的困难。因此建立一种快速血清型分子鉴定方法尤为重要。为了快速、简便的建立猪传染性胸膜肺炎放线杆菌血清型分子鉴定的方法,本研究所从临床发病疑似病例猪肺脏和气管中分离到的放线杆菌,首先经过血清型鉴定,确定部分血清型为2型,为了确定血清型鉴定的准确性,在此基础上,采用分子鉴定的方法,对这些菌株进行鉴定,确定分离到的11株菌为猪胸膜肺炎放线杆菌血清2型。这为猪传染性胸膜肺炎放线杆菌血清型分子鉴定及防治提供了理论依据,为今后临床血清型定型提供了一种简便方法。     

PCR specific for Actinobacillus pleuropneumoniae serotype 3

Serotypes 3 and 8 of Actinobacillus pleuropneumoniae, the aetiological agent of porcine pleuropneumonia, have been reported to predominate in the UK. Direct serotyping of isolates of the organism is typically determined by the immunological reactivity of rabbit serum to its surface polysaccharides, but the method has limitations, for example, cross-reactions between serotypes 3, 6 and 8. This study describes the development of a serotype 3-specific pcr, based on the capsule locus, which can be used in a multiplex format with the organism's specific gene apxIV. The pcr test was evaluated on 266 strains of A pleuropneumoniae and 121 strains of other organisms, including all the major respiratory bacterial pathogens of pigs. The test was highly specific and sensitive and should be useful for differentiating strains of serotypes 3, 6 and 8, and in seroprevalence and epidemiological surveys in regions where serotype 3 is prevalent, such as the UK.     

Production and characterization of monoclonal antibodies to Actinobacillus pleuropneumoniae serotype 5b.

Monoclonal antibodies specific for capsular polysaccharide (CPS) and lipopolysaccharide (LPS) of A. pleuropneumoniae serotype 5b were generated by hybridoma cells and selected by indirect ELISA of culture supernatants with purified and structurally defined LPS and CPS preparations and their synthetic conjugates. It was shown in this study that at least one monoclonal antibody, 3B4, presented 100% specificity and recognized all A. pleuropneumoniae serotype 5 field strains tested in a dot-ELISA assay.     

Identification and preliminary characterization of a 75-kDa hemin- and hemoglobin-binding outer membrane protein of Actinobacillus pleuropneumoniae serotype 1

The reference strains representing serotypes 1 to 12 of Actinobacillus pleuropneumoniae biotype 1 were examined for their ability to utilize porcine hemoglobin (Hb) or porcine hemin (Hm) as iron sources for growth. In a growth promotion assay, all of the reference strains were able to use porcine Hb, and all strains except 2 were able to use porcine Hm. Using a preliminary characterization procedure with Hm- or Hb-agarose, Hm- and Hb-binding outer membrane proteins (OMPs) of approximately 75 kDa were isolated from A. pleuropneumoniae serotype 1 strain 4074 grown under iron-restricted conditions. Matrix-assisted laser desorption ionization/time-of-flight (MALDI-TOF) analysis revealed a number of common tryptic peptides between the Hb-agarose- and Hm-agarose-purified 75 kDa OMPs, strongly suggesting that these peptides originate from the same protein. A database search of these peptide sequences revealed identities with proteins from various Gram-negative bacteria, including iron-regulated OMPs, transporter proteins, as well as TonB-dependent receptors. Taken together, our data suggest that A. pleuropneumoniae synthesizes potential Hm- and Hb-binding proteins that could be implicated in the iron uptake from porcine Hb and Hm.     

猪胸膜肺炎放线杆菌血清型的PCR鉴定

据胸膜肺炎放线杆菌（Actinobacillus pleuropneumoniae,APP）生物I型各血清型之间外毒素（apx）基因组结构差异,参考GenBank上已发表的4种毒素（apxⅠ/apxⅡ/apxⅢ/apxⅣ）的核酸序列设计了6对特异性引物,对APP的12个血清型进行多重PCR扩增,得出不同的特异性的扩增片段,得以准确鉴定APP生物I型中的9种血清型,但其中血清型2和8,血清型5、9和11仍未能区分。     

血清3型猪传染性胸膜肺炎放线杆菌的分离与鉴定

2005年3月,广东省惠州市某猪场发生了一起疑似猪传染性胸膜肺炎放线杆菌引起猪只死亡的病例,经细菌分离培养、生化鉴定、PCR、血清学鉴定,确诊该病原为血清3型猪传染性胸膜肺炎放线杆菌。     

猪胸膜肺炎放线杆菌的分离鉴定

采用巧克力琼脂平板从贵州省某养猪场发病猪体分离到3株细菌,经培养特性观察、生化特征检查和血清型鉴定,确定3株分离菌均为猪胸膜肺炎放线杆菌血清7型。经药敏试验显示,分离菌对氨苄西林、硫酸庆大霉素、丙氟哌酸、氟哌酸、头孢三嗪和四环素等药物高度敏感。     

Granulomatous lymphadenitis associated with Actinobacillus pleuropneumoniae serotype 2 in slaughter barrows

This study evaluated the occurrence of granulomatous lymphadenitis and its association with Actinobacillus spp. in 151 653 slaughtered pigs. Markedly enlarged pulmonary hilar, mediastinal, mandibular or hepatic lymph nodes were detected in 6 castrated males. The cut surfaces showed multifocal yellow-white lesions. Histologically, gram-negative bacilli were visible in the centers of the lesions with asteroid bodies, epithelioid cells, and multinucleated giant cells. Dense fibrous connective tissue surrounded these granulomatous lesions. Immunohistochemically, the organisms reacted with polyclonal antibodies against Actinobacillus pleuropneumoniae serotype 2 in all 6 barrows. The organism was isolated from the lymph nodes of all 6 animals. The results indicate that the granulomatous lymphadenitis was associated with A. pleuropneumoniae serotype 2 and the disorder had a tendency to occur in slaughter barrows.     

PCR-based identification of serotype 2 isolates of Actinobacillus pleuropneumoniae biovars I and II

A genetic typing method utilizing PCR for the identification of Actinobacillus pleuropneumoniae serotype 2 isolates has been developed based on the in vitro amplification of a 1.4 kb DNA segment of the serotype 2 capsular polysaccharide genes cps2AB. The assay was tested with all serotype reference strains and a collection of 92 different A. pleuropneumoniae strains of all 15 serotypes of both biovars I and II, originating from 18 different countries worldwide. The cps2 based PCR identified the serotype 2 reference strain and all 12 serotype 2 collection strains contained in this set. DNA was not amplified from the remaining A. pleuropneumoniae reference and collection strains, indicating the PCR assay was highly specific. Furthermore, the PCR method detected all 31 A. pleuropneumoniae serotype 2 field isolates from diseased pigs that were identified in parallel as serotype 2 by agar gel diffusion. The serotype 2 PCR assay proved to be highly specific and reliable for the identification of serotype 2 isolates of A. pleuropneumoniae.