单增李斯特菌LPXTG蛋白Lmo0880在感染致病中的作用

【目的】通过构建单核细胞增生李斯特菌(单增李斯特菌) LPXTG蛋白Lmo0880的基因缺失菌株和回补菌株,探究Lmo0880在细菌生长、细胞感染和宿主感染等方面发挥的作用。【方法】利用同源重组原理构建lmo0880的基因缺失株及回补株,比较野生株、缺失株和回补株在生长能力、细胞黏附与侵袭和胞内增殖能力等方面的差异,从而鉴定Lmo0880在单增李斯特菌感染宿主中的作用。【结果】缺失lmo0880基因后,单增李斯特菌在生长能力上无明显变化;对细胞的黏附能力无显著差异,但对细胞侵袭能力、胞内增殖能力、小鼠致病力和小鼠组织定殖能力显著降低。【结论】本研究阐明了单增李斯特菌LPXTG蛋白Lmo0880在细胞侵袭、胞内增殖和组织定殖等方面发挥的重要作用。     

DegU调控单核细胞增生李斯特菌感染宿主细胞及适应高温的机制研究

【目的】本研究旨在探究孤儿调节因子DegU在介导单核细胞增生李斯特菌(Listeria monocytogenes)宿主感染和高温环境适应性方面的调控机制。【方法】本研究以单增李斯特菌参考菌株EGD-e、degU基因缺失菌株ΔdegU和回补菌株CΔdegU为研究材料，通过细胞模型、实时荧光定量聚合酶链式反应和凝胶阻滞试验等方法探究DegU对单增李斯特菌感染宿主细胞和适应高温的调控机制。【结果】研究结果表明：缺失degU后，单增李斯特菌在Caco-2上的黏附和侵袭能力显著降低，在RAW264.7中的增殖能力显著降低，在L929中的空斑形成能力也显著降低；进一步通过实时荧光定量聚合酶链式反应检测degU基因缺失后引起的单增李斯特菌毒力因子转录水平变化，发现多个重要毒力因子转录水平均显著下调；该试验结果还发现与毒力相关的热应激基因clpE(受CtsR抑制的ATP依赖蛋白水解酶编码基因)转录水平显著升高，而在43℃高温条件下，clpE转录水平显著降低；进一步通过凝胶阻滞试验结果表明DegU能够与clpE的启动子直接结合。【结论】综上所述，degU基因缺失能够降低单增李斯特菌在宿主感染过程中的细...     

单增李斯特菌新疆分离株lmo0160基因克隆及序列分析

【目的】单增李斯特菌是一种重要的食源性致病菌,常引起人和动物致病。其细胞壁表面LPXTG基序蛋白在单增李斯特菌致病过程中发挥重要作用,根据参考株全序列预测的41个LPXTG基序蛋白中仍有部分蛋白功能未知。对单增李斯特菌新疆绵羊脑分离株LM90SB2的LPXTG基序蛋白Lmo0160的基因进行克隆及生物信息学分析,为功能验证提供基础。【方法】根据GenBank中收录的lmo0160序列设计特异性引物,利用PCR方法对新疆分离株的lmo0160基因进行扩增,将扩增产物克隆到pMD 19-T载体,进行PCR、双酶切鉴定及序列测定,并对基因核苷酸序列和蛋白序列进行分析。【结果】分离株LM90SB2的lmo0160序列全长为1 708 bp,包含1 428 bp的开放阅读框,共编码475个氨基酸;LM90SB2株lmo0160核苷酸序列与CFSAN008100株(4b型,美国)、CFSAN023463株(4b型,美国)、J2-064株(4b型,美国)、F2365株(4b型,奶酪,美国)和NTSN株(4b型,绵羊脑,中国扬州)相似性为99.0%-99.1%;与M7株(4a型,牛奶,中国浙江)相似性为97.2%,与Finland1998株(1/2a型,美国)、N53-1株(1/2a型,熟火腿,瑞士)、N1546株(1/2a型,鱼,丹麦)和EGD-e株(1/2a型,美国)相似性为87.2%-91.1%;其推导的氨基酸序列与上述菌株相似性为91.8%-99.4%。系统进化树显示,LM90SB2菌株的lmo0160基因与CFSAN023463、F2365和NSTN菌株亲缘关系较近,处于同一分支上,而与标准株EGD-e菌株亲缘关系较远。蛋白质二级结构预测表明,LM90SB2的Lmo0160蛋白为亲水性蛋白,无信号肽,不形成跨膜结构。蛋白结构域预测表明Lmo0160蛋白含有胶原蛋白结合域和Cna B结构域。【结论】克隆了LM90SB2的lmo0160基因,为进一步研究LM90SB2的lmo0160基因功能奠定了基础。     

一株ST477型单增李斯特菌的全基因组测序及inlA基因遗传多样性

【背景】单增李斯特菌是一种重要的条件致病菌,不同型别菌株在宿主范围和毒力等方面存在差异。内化素基因inlA在入侵宿主上皮细胞中具有重要作用。【目的】研究单增李斯特菌序列型(Sequence type,ST)为477菌株的基因组特征及内化素基因inlA的遗传多样性。【方法】使用相关软件对测序数据进行多位点序列分型(Mutilocussequencetyping,MLST)、单核苷酸多态性(Single nucleotide polymorphism,SNP)及基因inlA遗传多样性分析。【结果】MLST进化分析结果显示,分离自不同国家的菌株具有较近亲缘关系。以分离自中国食品的ST477型菌株为参考菌株,通过SNP分析表明,加拿大食品中的ST9型菌株发生的突变位点最少(91-93个)。7株复合克隆系(Clonal complex,CC)为9的菌株其inlA基因序列间核苷酸相似性为29.8%-100%。【结论】初步分析了ST477型别菌株的进化及基因组特征,同时研究了部分CC9克隆系菌株inlA基因突变情况,为研究ST477型别菌株的进化及单增李斯特菌的毒力提供基础数据。     

进口水产品中单增李斯特菌的分子流行病学特点

摘要：[目的] 探明进口水产品中单增李斯特菌的污染状况、致病性和分子特征。[方法] 针对2007年7月至2008年11月间从29个国家进口的1275批水产品,进行单增李斯特菌鉴定、谱系与血清型分析、小鼠毒力试验与多位点序列分析。[结果] 检出单增李斯特菌33批次（2.6%）,其中以4b型为主（65.2%）,而1/2a型、1/2b型与1/2c型仅分别占13.0%、17.4%与4.4%。这些分离株对小鼠均具有与强毒参考株相当的毒力。基于actA-hisJ-ribC-sigB的多位点序列分析可将32个菌株分为23个序列型,分辨力达0.97。其中3个序列型包含3个以上分离株,其中序列型9属于流行性克隆I。[结论] 进口水产品中单增李斯特菌污染率与国内水产品相近,但血清型分布以4b型为主,且有流行性克隆I检出,因此要加强对进口水产品中单增李斯特菌的监测。     

硫氧还蛋白Lmo1903介导单增李斯特菌抵抗氧化应激的生物学功能研究

【目的】以单增李斯特菌(Listeria monocytogenes, LM)硫氧还蛋白Lmo1903为研究对象,研究其在细菌环境适应过程中的抗氧化应激生物学作用。【方法】使用生物信息学方法分析Lmo1903的进化关系和关键活性位点,使用酶切连接的方法构建Lmo1903蛋白表达载体,获得纯化的重组蛋白,以胰岛素为底物分析其氧化还原酶学活性;同时制备鼠源多克隆抗体,分析其在细胞内的定位;采用核苷酸定点突变技术构建CX1X2C基序中的半胱氨酸点突变蛋白,分析关键位点半胱氨酸对Lmo1903酶活的影响;采用同源重组原理构建lmo1903基因缺失株Δlmo1903和回补株CΔlmo1903,研究lmo1903在单增李斯特菌生长、运动和抗氧化应激方面发挥的功能。【结果】生物信息学分析显示,Lmo1903含有CX1X2C基序,与枯草芽孢杆菌(Bacillussubtilis)的TrxA的亲缘关系较近,属于硫氧还蛋白家族成员,主要定位在细菌细胞质中,具有较强的还原酶学活性,突变CX1X2C基序中的半胱氨酸残基会显著降低Lmo1903的还原酶活能力。缺失lmo1903不影响单增李斯特菌的生长能力,但显...     

单核细胞增生性李斯特菌prfA基因缺失株的构建及其生物学特性

【目的】单核细胞增生性李斯特菌(Lm)是人兽共患李斯特菌病的病原菌,其致病性与调控因子PrfA蛋白作用下毒力基因的表达有着密切关系,本文初步探讨了PrfA蛋白对细菌毒力因子的调控作用。【方法】利用同源重组技术对血清型分别为1/2a和4b的LM4、F4636进行prfA基因的敲除,并构建其回复突变株,对获得的突变株LM4ΔprfA、F4636ΔprfA进行生物学特性研究。【结果】实验结果表明:两株缺失株的溶血活性丧失、回复突变株的溶血活性得到恢复,突变株还丧失磷脂酶活性,黏附和侵袭特性显著下降(P<0.05),对BALB/c小鼠的半数致死剂量提高了105个数量级。【结论】由此表明,PrfA蛋白对hly、plcB、inl家族基因的表达及细菌毒力具有重要的调控作用。prfA基因缺失株的构建为进一步研究PrfA蛋白的调控功能提供了材料,为研究其在Lm致病性中的作用奠定了基础。     

rmlB基因在单核细胞增生李斯特菌耐药性、生物被膜形成和毒力方面的作用

【目的】探究单核细胞增生李斯特菌(Listeria monocytogenes,Lm)rmlB基因在细菌耐药、生物被膜形成和毒力方面的作用。【方法】通过同源重组的方法敲除Lm染色体上的rmlB基因,比较野生株与rmlB缺失株在耐药性方面的差异;利用微孔板法观测rmlB缺失菌株生物被膜形成能力的变化;利用RT-PCR检测缺失菌株中主要毒力基因转录表达,并观察rmlB缺失对细菌溶血活性的影响。【结果】同野生菌株相比,rmlB缺失菌株对头孢菌素和杆菌肽等作用位点在细菌细胞壁和细胞膜的敏感性显著增加(P≤0.01),生物被膜形成能力显著降低(P≤0.01),细菌主要毒力基因hly的转录表达及溶血活性也发生显著降低(P≤0.01)。【结论】rmlB基因在Lm生物被膜形成和耐受作用位点位于细胞壁和细胞膜的抗生素及细菌毒力方面具有重要作用。     

单增李斯特菌二硫键形成蛋白DsbG介导酸耐受及鞭毛运动性调控北大核心

【目的】本研究旨在通过构建单增李斯特菌(Listeria monocytogenes)二硫键形成蛋白编码基因dsbG缺失株和回补株,探究该蛋白在酸耐受和鞭毛介导的运动性中发挥的生物学功能。【方法】利用同源重组方法构建单增李斯特菌dsbG缺失株和回补株,比较野生株和突变株在不同pH梯度培养基条件下的生长速率和存活率;通过实时荧光定量PCR方法,比较致死酸应激条件下野生株和缺失株酸耐受基因转录水平。通过半固体培养基、荧光定量PCR方法和鞭毛负染色透射电镜观察,比较野生株和突变株的运动能力、鞭毛相关基因转录水平变化和鞭毛形态差异。【结果】与野生株相比,dsbG缺失株的生长能力和速率差异不显著;在pH 3.5(盐酸和柠檬酸)培养条件下,存活率显著降低;精氨酸合成途径基因argD和argF转录水平分别下调2.4和3.7倍。同时,dsbG缺失株的运动能力减弱,且鞭毛形成相关的flaA、flgB和flgD等基因转录水平显著下调(分别为29.7、6.7和6.9倍),鞭毛形成能力减弱。【结论】本研究首次证实了单增李斯特菌二硫键形成蛋白DsbG能感应低pH应激,并形成耐受;证实了DsbG通过调控鞭毛相关基因的转录进而影响细菌的鞭毛形成和运动性。本研究有助于深入了解二硫键形成蛋白家族介导单增李斯特菌环境适应的分子机制,为食源性致病菌的防控提供理论基础。     

单核细胞增多性李斯特菌OpuCA蛋白介导抗氧化应激和宿主感染研究

【目的】本文旨在研究opuCA基因在单核细胞增多性李斯特菌(单增李斯特菌)生长过程及渗透胁迫下发挥的作用,探究opuCA基因参与细菌抗氧化应激和致病力的生物学功能,为阐明OpuCA蛋白介导细菌环境适应和宿主内感染的机制奠定基础。【方法】利用细菌同源重组方法获得opuCA缺失株及回补株后,通过分子生物学、感染生物学和激光共聚焦技术,研究野生株和突变株的生长能力、抗渗透应激能力、抗氧化应激能力、细胞粘附、侵袭以及胞内增殖能力。【结果】缺失opuCA基因后,李斯特菌体外生长能力并没有受到影响,但在渗透条件下生长能力减弱;opuCA缺失株在铜离子和镉离子中抗氧化应激能力降低,但在巯基特异性氧化剂肼应激中无明显变化;opuCA缺失株在细胞中的侵袭能力显著减弱,且缺失该基因导致细菌聚合actin能力下降,进而影响了细菌在胞间迁移。【结论】本研究首次证实了缺失opuCA基因能降低单增李斯特菌抗氧化应激能力和感染宿主能力,并且在渗透胁迫下细菌生长能力减弱,但具体的分子机制有待深入研究。本研究有助于深入理解单增李斯特菌OpuCA蛋白介导的细菌体外环境适应及宿主内感染的分子机制,为防控单增李斯特菌感染提供...     

Atypical Listeria monocytogenes serotype 4b strains harboring a lineage II-specific gene cassette

Listeria monocytogenes is the etiological agent of listeriosis, a severe food-borne illness. The population of L. monocytogenes is divided into four lineages (I to IV), and serotype 4b in lineage I has been involved in numerous outbreaks. Several serotype 4b epidemic-associated clonal groups (ECI, -II, and -Ia) have been identified. In this study, we characterized a panel of strains of serotype 4b that produced atypical results with a serotype-specific multiplex PCR and possessed the lmo0734 to lmo0739 gene cassette that had been thought to be specific to lineage II. The cassette was harbored in a genomically syntenic locus in these isolates and in lineage II strains. Three distinct clonal groups (groups 1 to 3) were identified among these isolates based on single-nucleotide polymorphism-based multilocus genotyping (MLGT) and DNA hybridization data. Groups 1 and 2 had MLGT haplotypes previously encountered among clinical isolates and were composed of clinical isolates from multiple states in the United States. In contrast, group 3 consisted of clinical and environmental isolates solely from North Carolina and exhibited a novel haplotype. In addition, all group 3 isolates had DNA that was resistant to MboI, suggesting methylation of adenines at GATC sites. Sequence analysis of the lmo0734 to lmo0739 gene cassette from two strains (group 1 and group 3) revealed that the genes were highly conserved (>99% identity). The data suggest relatively recent horizontal gene transfer from lineage II L. monocytogenes into L. monocytogenes serotype 4b and subsequent dissemination among at least three distinct clonal groups of L. monocytogenes serotype 4b, one of which exhibits restrictions in regional distribution.     

Iron acquisition systems for ferric hydroxamates, haemin and haemoglobin in Listeria monocytogenes

Listeria monocytogenes is a Gram-positive bacterium that causes severe opportunistic infections in humans and animals. We biochemically characterized, for the first time, the iron uptake processes of this facultative intracellular pathogen, and identified the genetic loci encoding two of its membrane iron transporters. Strain EGD-e used iron complexes of hydroxamates (ferrichrome and ferrichrome A, ferrioxamine B), catecholates (ferric enterobactin, ferric corynebactin) and eukaryotic binding proteins (transferrin, lactoferrin, ferritin, haemoglobin). Quantitative determinations showed 10-100-fold lower affinity for ferric siderophores (Km approximately 1-10 nM) than Gram-negative bacteria, and generally lower uptake rates. Vmax for [59Fe]-enterobactin (0.15 pMol per 10(9) cells per minute) was 400-fold lower than that of Escherichia coli. For [59Fe]-corynebactin, Vmax was also low (1.2 pMol per 10(9) cells per minute), but EGD-e transported [59Fe]-apoferrichrome similarly to E. coli (Vmax=24 pMol per 10(9) cells per minute). L. monocytogenes encodes potential Fur-regulated iron transporters at 2.031 Mb (the fur-fhu region), 2.184 Mb (the feo region), 2.27 Mb (the srtB region) and 2.499 Mb (designated hupDGC region). Chromosomal deletions in the fur-fhu and hupDGC regions diminished iron uptake from ferric hydroxamates and haemin/haemoglobin respectively. In the former locus, deletion of fhuD (lmo1959) or fhuC (lmo1960) strongly reduced [59Fe]-apoferrichrome uptake. Deletion of hupC (lmo2429) eliminated the uptake of haemin and haemoglobin, and decreased the virulence of L. monocytogenes 50-fold in mice. Elimination of srtB region genes (Deltalmo2185, Deltalmo2186, Deltalmo2183), both sortase structural genes (DeltasrtB, DeltasrtA, DeltasrtAB), fur and feoB did not impair iron transport. However, deletion of bacterioferritin (Deltafri, lmo943; 0.97 Mb) decreased growth and altered iron uptake: Vmax of [59Fe]-corynebactin transport tripled in this strain, whereas that of [59Fe]-apoferrichrome decreased 20-fold.     

Multilocus sequence typing of Listeria monocytogenes by use of hypervariable genes reveals clonal and recombination histories of three lineages

In an attempt to develop a method to discriminate among isolates of Listeria monocytogenes, the sequences of all of the annotated genes from the fully sequenced strain L. monocytogenes EGD-e (serotype 1/2a) were compared by BLASTn to a file of the unfinished genomic sequence of L. monocytogenes ATCC 19115 (serotype 4b). Approximately 7% of the matching genes demonstrated 90% or lower identity between the two strains, and the lowest observed identity was 80%. Nine genes (hisJ, cbiE, truB, ribC, comEA, purM, aroE, hisC, and addB) in the 80 to 90% identity group and two genes (gyrB and rnhB) with approximately 97% identity were selected for multilocus sequence analysis in two sets of L. monocytogenes isolates (a 15-strain diversity set and a set of 19 isolates from a single food-processing plant). Based on concatenated sequences, a total of 33 allotypes were differentiated among the 34 isolates tested. Population genetics analyses revealed three lineages of L. monocytogenes that differed in their history of apparent recombination. Lineage I appeared to be completely clonal, whereas representatives of the other lineages demonstrated evidence of horizontal gene transfer and recombination. Although most of the gene sequences for lineage II strains were distinct from those of lineage I, a few strains with the majority of genes characteristic of lineage II had some that were characteristic of lineage I. Genes from lineage III organisms were mostly similar to lineage I genes, with instances of genes appearing to be mosaics with lineage II genes. Even though lineage I and lineage II generally demonstrated very distinct sequences, the sequences for the 11 selected genes demonstrated little discriminatory power within each lineage. In the L. monocytogenes isolate set obtained from one food-processing plant, lineage I and lineage II were found to be almost equally prevalent. While it appears that different lineages of L. monocytogenes can share habitats, they appear to differ in their histories of horizontal gene transfer.     

Virulence Phenotyping and Molecular Characterization of a Low-pathogenicity Isolate of Listeria monocytogenes from Cow＇s Milk

A low-pathogenicity isolate of Listeria monocytogenes from cow＇s milk, as screened in mouse and chicken embryonated egg models, was examined for virulence-related phenotypic traits. Corresponding virulence genes （iap, prfA, picA, hly, mpl, actA, plcB, InlA and lnlB） were compared with L. monocytogenes reference strains 10403S and EGD to elucidate the possible molecular mechanisms of low virulence. Although L. monocytogenes H4 exhibited similar patterns to strain 10403S in terms of hemolytic activity, in vitro growth and invasiveness and even had higher adhesiveness, faster intracellular growth and higher phospholipase activity in vitro, it was substantially less virulent than the strain 10403S in mouse and chicken embryo models （50% lethal dose： 10^8.14 VS. 10^5.49 and 10^6.73 VS. 10^1.9, respectively）. The genes prfA, picA and mpl were homologous among L. monocytogenes strains H4, 10403S and EGD （〉98%）. Genes iap, hly, plcB, lnlA and lnlB of L. monocytogenes 10403S had higher homology to those of strain EGD （〉98%） than isolate H4. The homology of the gene hly between strain 10403S and isolate H4 was 96.9% at the nucleotide level, but 98.7% at the amino acid level. The actA gene of isolate H4 had deletions of 105 nucleotides corresponding to 35 amino acid deletions falling within the proline-rich region. Taken together, this study presents some clues as to reduced virulence to mice and chicken embryos of the isolate H4 probably as a result of deletion mutations of actA.     

Virulence Phenotyping and Molecular Characterization of a Low-pathogenicity Isolate of Listeria monocytogenes from Cow's Milk

A low-pathogenicity isolate of Listeria monocytogenes from cow's milk,as screened in mouseand chicken embryonated egg models,was examined for virulence-related phenotypic traits.Correspondingvirulence genes (iap,prfA,plcA,hly,mpl,actA,plcB,InlA and InlB) were compared with L.monocytogenesreference strains 10403S and EGD to elucidate the possible molecular mechanisms of low virulence.Al-though L.monocytogenes H4 exhibited similar patterns to strain 10403S in terms of hemolytic activity,invitro growth and invasiveness and even had higher adhesiveness,faster intracellular growth and higherphospholipase activity in vitro,it was substantially less virulent than the strain 10403S in mouse and chickenembryo models (50% lethal dose:10~(8.14) vs.10~(5.49) and 10~(6.73) vs.10~(1.9),respectively).The genes prfA,plcA andmpl were homologous among L.monocytogenes strains H4,10403S and EGD (>98%).Genes iap,hly,plcB,InlA and InIB of L.monocytogenes 10403S had higher homology to those of strain EGD (>98%) than isolateH4.The homology of the gene hly between strain 10403S and isolate H4 was 96.9% at the nucleotide level,but 98.7% at the amino acid level.The actA gene of isolate H4 had deletions of 105 nucleotides correspondingto 35 amino acid deletions falling Within the proline-rich region.Taken together,this study presents someclues as to reduced virulence to mice and chicken embryos of the isolate H4 probably as a result of deletionmutations of actA.     

携带新城疫病毒融合蛋白基因的重组减毒单核细胞增多性李斯特菌构建与鉴定

以鸡新城疫病毒F基因(NDV-F)为模式外源基因,通过基因切割-重叠延伸PCR法(SOE-PCR)将其插入到单核细胞增多性李斯特菌(Listeria monocytogenes)毒力基因hly的启动子和信号肽序列下游,并将该融合片段克隆入穿梭质粒pKSV7,随后将重组质粒电转李斯特菌进行同源重组。NDV-F基因的PCR扩增表明该重组菌构建成功,RT-PCR结果表明F基因在重组菌中得到了转录。比较了重组菌和野生型菌株的溶血性、黏附和侵袭力、对小鼠和鸡胚的毒力和生长特性以及重组菌的体内外稳定性,结果表明:hly基因中F片段的整合消除了单核细胞增多性李斯特菌溶血素基因的表达,其培养上清液没有溶血性,而野生型菌株的溶血价达24;细胞试验表明重组菌对细胞的黏附力和相对侵袭力均有不同程度的降低,而相对侵袭力与野生型菌株具有显著性差异(P<0.05);重组菌对小鼠及鸡胚的毒力(LD50)与野生型相比分别下降3.7和6.5个对数数量级;重组菌在BHI肉汤和小鼠体内连续5次后,仍然可以扩增出目的基因NDV-F,初步表明该重组菌较为稳定。     

The cell wall binding domain of Listeria bacteriophage endolysin PlyP35 recognizes terminal GlcNAc residues in cell wall teichoic acid

The cell wall binding domains (CBD) of bacteriophage endolysins target the enzymes to their substrate in the bacterial peptidoglycan with extraordinary specificity. Despite strong interest in these enzymes as novel antimicrobials, little is known regarding their interaction with the bacterial wall and their binding ligands. We investigated the interaction of Listeria phage endolysin PlyP35 with carbohydrate residues present in the teichoic acid polymers on the peptidoglycan. Biochemical and genetic analyses revealed that CBD of PlyP35 specifically recognizes the N-acetylglucosamine (GlcNAc) residue at position C4 of the polyribitol-phosphate subunits. Binding of CBDP35 could be prevented by removal of wall teichoic acid (WTA) polymers from cell walls, and inhibited by addition of purified WTAs or acetylated saccharides. We show that Listeria monocytogenes genes lmo2549 and lmo2550 are required for decoration of WTAs with GlcNAc. Inactivation of either gene resulted in a lack of GlcNAc glycosylation, and the mutants failed to bind CBDP35. We also report that the GlcNAc-deficient phenotype of L. monocytogenes strain WSLC 1442 is due to a small deletion in lmo2550, resulting in synthesis of a truncated gene product responsible for the glycosylation defect. Complementation with lmo2550 completely restored display of characteristic serovar 1/2 specific WTA and the wild-type phenotype.