微生物学报  2018, Vol. 58 Issue (1): 51-62
http://dx.doi.org/10.13343/j.cnki.wsxb.20170022
中国科学院微生物研究所,中国微生物学会,中国菌物学会
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文章信息

栗冬梅, 宋秀平, 金圣浩, 刘起勇, 代解杰. 2018
Dongmei Li, Xiuping Song, Shenghao Jin, Qiyong Liu, Jiejie Dai. 2018
中国部分地区实验猕猴巴尔通体感染状况及其遗传特征
Prevalence and genetic characteristics of Bartonella quintana in macaque populations of China
微生物学报, 58(1): 51-62
Acta Microbiologica Sinica, 58(1): 51-62

文章历史

收稿日期:2017-01-11
修回日期:2017-03-19
网络出版日期:2017-03-29
中国部分地区实验猕猴巴尔通体感染状况及其遗传特征
栗冬梅1 , 宋秀平1 , 金圣浩2 , 刘起勇1 , 代解杰3     
1. 中国疾病预防控制中心传染病预防控制所, 传染病预防控制国家重点实验室, 感染性疾病诊治协同创新中心, 北京 102206;
2. 河北省鼠疫防治所, 河北 张家口 075000;
3. 中国医学科学院医学生物学研究所, 云南 昆明 650118
摘要[目的] 五日热巴尔通体(Bartonella quintana)由体虱在人群中传播,可引起多种人类疾病包括战壕热。为进一步搜集猕猴是五日热巴尔通体自然宿主的证据,本研究调查了国内4个地区实验用猕猴五日热巴尔通体的感染状况,对菌株遗传特征进行了分析。[方法] 采集猕猴全血和血清样品各550份,用于菌株分离、核酸和血清IgG抗体检测。应用6个管家基因扩增及测序方法进行菌株鉴定、系统发育及核苷酸多态性分析;应用随机扩增多态性DNA标记(Random amplified polymorphic DNA,RAPD)技术分析不同宿主来源菌株RAPD指纹图谱差异;应用间接免疫荧光法(Indirect immunofluorescence assay,IFA)检测血清中抗五日热巴尔通体IgG抗体水平。[结果] 从550只猕猴中分离到8株五日热巴尔通体菌株,带菌率为1.5%;直接PCR检测550份全血核酸的总感染率为8.2%。普通猕猴血清阳性率为19.0%,感染水平明显高于食蟹猕猴(5.6%)。五日热巴尔通体与汉赛巴尔通体RAPD指纹图谱的带型完全不同,猴源和人源五日热巴尔通体菌株Fuller带型基本一致。不同宿主来源菌株核苷酸多态性分析显示,猴源菌株之间差异小,其与人源菌株差异较大。[结论] 中国猕猴五日热巴尔通体感染水平较高,普通猕猴自然感染率及抗体水平明显高于食蟹猕猴,猴源与人源菌株的基因型有明显差异。
关键词: 五日热巴尔通体     猕猴     战壕热     遗传多态性     非人灵长类    
Prevalence and genetic characteristics of Bartonella quintana in macaque populations of China
Dongmei Li1 , Xiuping Song1 , Shenghao Jin2 , Qiyong Liu1 , Jiejie Dai3     
1. State Key Laboratory of Infectious Disease Prevention and Control, Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, National Institute for Communicable Disease Control and Prevention, Chinese Center for Disease Control and Prevention, Beijing 102206, China;
2. Institute of Plague Prevention and Control of Hebei Province, Zhangjiakou 075000, Hebei Province, China;
3. Institute of Medical Biology, Chinese Academy of Medical Sciences and Peking Union Medical College, Kunming 650118, Yunnan Province, China
Received 11 January 2017; Revised 19 March 2017; Published online 29 March 2017
*Corresponding author: Qiyong Liu, E-mail:liuqiyong@icdc.cn
Jiejie Dai, E-mail:djj@imbcams.com.cn
Supported by the National Natural Science Foundation of China (81141108)
Abstract: [Objective] Bartonella quintana, transmitted by the body louse (Pediculus humanis), is the etiologic agent of a variety of disease manifestations in humans including trench fever. To further confirm if macaques can be the natural reservoir of B. quintana, we studied the infections of B. quintana in the experimental macaque populations from the four regions in China and characterized the islolates of B. quintana originated from the macaques. [Methods] The samples of blood and serum collected from 550 macaques were used to isolate strains, detect the specific nucleic acid fragment and test IgG antibody. The molecular taxonomic characterization and nucleotide polymorphisms of the strains were analyzed based on the sequences of the six housekeeping genes using PCR, sequecing and phylogenetic analysis. The fingerprint pattern of random amplified polymorphic DNA (RAPD) were also used to discriminated the stains from the different hosts by the three random primers. The IgG antibody anti-B. quintana were detected using indirect iocmmunofluorescence assay (IFA). [Results] Totally, 8 strains of B. quintana were isolated from 5 females and 3 males from 250 rhesus macaques in Sichuan province, with 3.2% infection rate. Our molecular test, detecting 550 blood samples using qPCR with a total of 8.2% infection rate of B. quintana, showed that the prevalence of macaques from Sichuan was significantly higher than that of the macaques from the other areas. The seropositivity rate was 19.0% in the rhesus macaques which was higher than that of the cynomolgus macaques (5.6%) and there was no difference between males and females and among the different areas. The RAPD-figerprints of the strains from the rhesus macaques in Sichuan province have an identical 8-bands pattern and was discriminated from the pattern of B. henselae. While the fingerprint of the human str. Fuller of B. quintana showed a 6-bands pattern. According to the nucleotide polymorphism analysis, the strains of B. quintana from different hosts show obvious genetic diversity. There was a higher diversity between the monkey strains and the human strains and a smaller difference among the monkey strains. [Conclusion] There are high prevalence of B. quintana in the macaques population in China. The natural infection rate and antibody level in the rhesus macaques were significantly higher than that of the cynomolgus macaques. The genotype of the strains originated from the macaques is different from that of the strains from human. We demonstrated that the macaques are the natural reservoir of B. quintana.
Key words: Bartonella quintana     macaque     trench fever     genetic polymorphism     nonhuman primates    

五日热巴尔通体(Bartonella quintana)是一种营养条件要求苛刻、难培养、革兰氏阴性、兼性细胞内寄生的需氧小杆菌,归属于α-变形菌纲(Alphaproteobacteria)、根瘤菌目(Rhizobiales)、巴尔通体科(Bartonellaceae)和巴尔通体属,经由体虱传播,可引起人类战壕热(Trench fever)、心内膜炎和杆菌性血管瘤(Bacillary angiomatosis)等多种疾病。一战时,人们通过战壕热认识了这种病原体,曾被命名为五日热立克次体(Rickettsia quintana)和五日热罗莎利马体(Rochalimaea quintana)。这种疾病曾在百万士兵中流行,主要表现为每隔4-6 d反复发热、头疼、腰痛及一过性皮疹,尤以胫骨疼痛为甚,故又称之为五日热(five-day fever)和胫骨热(Shin-bone fever)[1]。二战时也有暴发,此后仅有极少散发病例,归于沉寂。20世纪80年代,这种病原开始出现在HIV感染者、无家可归者和酗酒人群中,引起杆菌性血管瘤、心内膜炎和慢性菌血症等疾病,被称之为“城市战壕热(Urban trench fever)”,再次进入人们的视野,引起关注[2]。作为传染病,人类一直被认为是五日热巴尔通体的唯一宿主,直到O'Rourke等[3]从食蟹猕猴(Macaca fascicularis)血液中分离到这种病原体,人们才开始注意到其他灵长类动物作为自然宿主的可能性。随后,黄儒婷等[4]和Li等[5]在中国的猕猴(Macaca mulatta)中陆续发现了五日热巴尔通体,Shingo等[6]在日本雪猴(Macaca fuscata)中也分离到了这种病原体。为了进一步了解中国猴群中五日热巴尔通体的分布情况,积累更多数据,我们在国内不同地区采集实验用灵长类动物血液样品,用以分离培养、检测特异核酸片段及血清抗体,初步探究猴源及人源五日热巴尔通体菌株的遗传差异。

1 材料和方法 1.1 样品采集

2012至2013年,分别在北京、广东、云南和四川一次性采集实验用灵长类动物的血液样品,抗凝全血及血清各550份(表 1)。除北京26只食蟹猴引自广西,其余均为本地自行繁殖。

表 1. 灵长类样品采集情况 Table 1. The information of the primate samples
Sampling site Species Gender
Macaca mulatta Macaca fascicularis Male Female
Beijing 50 50 86a 14b
Sichuan 250 0 67 183
Guangdong 0 100 45 55
Yunnan 0 100 66 34
Total 300 250 264 286
a: Comprising of 50 Macaca mulatta and 36 Macaca fascicularis;
b: 14 Macaca fascicularis.

1.2 分离培养

将被检猴血用灭菌胰酶大豆肉汤(Tryptic soy broth,BD)按1:4稀释,接种于含5%羊血的胰酶大豆琼脂培养基(Tryptic soy agar,BD)上,置于含5% CO2培养箱中,潮湿环境中35 ℃培养30 d,对疑似巴尔通体菌落进行2-4次纯分后,收集纯菌培养物于30%甘油-脑心浸液(Brain Heart Infusion,BD)中,保存于-80 ℃。液体培养应用含10%胎牛血清的昆虫细胞培养基(Schneider’s Insect Medium,Sigma)[7]

1.3 核酸提取及扩增

应用DNeasy® Tissue Kit (Qiagen)按照操作手册相应步骤分别提取菌株及全血DNA,应用核酸浓度测定仪NanoDrop-1000测定浓度后置于-20 ℃保存备用。应用引物BhCS.781p-BhCS.1137n[8]、Bfp1-Bfp2[9]、1400F-2300R[10]、HSPF1d-BbHS1630.n、BARTON-1-BARTON-2和fDl-fD2分别扩增柠檬酸合酶基因(Citrate synthase gene,gltA),细胞分裂蛋白基因(Cell division protein gene,ftsZ)、RNA聚合酶β亚基基因(RNA polymerase beta-subunit gene,rpoB)、热休克蛋白基因groEL、核黄素合成酶β亚基(riboflavin synthase beta chain,ribE)和16S rRNA基因的部分片段;应用Pfu DNA Polymerase (北京全式金生物技术)进行PCR扩增,程序为:94 ℃ 2 min;94 ℃ 30 s,53 ℃ 30 s,72 ℃ 2 min,循环30次;72 ℃ 5 min。扩增仪为Sensoquest Labcycler (德国)。

应用TaqMan探针Bq-yT (FAM-TCATCGATC ATCAAACCGTTGCCG-BHQ1)和引物Bq.yF-Bq.yR (5 -GTAAACCTCGGGGGAAGCA-3′,5′-TGCATT TCCATTCTCGAAGGAT-3′)检测猴血样DNA中五日热巴尔通体的yopP基因(BQ11580)片段。PCR反应体系(20 μL)为:10 μL GoTaq® qPCR Master Mix (Promega),0.4 μL荧光标记探针及引物(10 μmol/L),1μL DNA模板,去离子水补齐。扩增程序:95 ℃ 2 min;95 ℃ 3 s,60 ℃ 30 s,40个循环。扩增仪为CFX96 Real-Time PCR Detection System (Bio-Rad)。为控制结果质量,核酸提取、反应体系制备及PCR扩增在不同分区完成,每次PCR反应设空白对照。

1.4 RAPD (Random amplification polymorphic DNA)指纹图谱分析

应用随机引物3S[11] (S15:5′-GGAGGGTGTT-3′,S18:5′-CCACAGCAGT-3′,S103:5′-AGACGTCC AC-3′)对分离菌株和str. Fuller (五日热巴尔通体,ATCC VR-358)及str. Houston-1 (汉赛巴尔通体,ATCC 49882)进行扩增,比较RAPD指纹图谱差异。反应体系20 µL (QIAGEN Fast Cycling PCR Kit):引物10 pmol,DNA模板10-100 ng;扩增程序:94 ℃ 5 min;94 ℃ 40 s,40 ℃ 40 s,72 ℃ 1 min,35个循环;72 ℃ 5 min。扩增仪为Sensoquest Labcycler。电泳条件:扩增产物用GoldView™ (北京赛百盛生物工程公司)染色,1%琼脂糖电泳凝胶,0.5×TBE缓冲液,上样量8-10 µL,5 V/cm电压下电泳90 min,用Gel DOC XR System (Bio-Rad)拍照。

1.5 序列分析

应用BLASTn (美国国家生物技术信息中心,www.ncbi.nlm.nih.gov)进行核酸序列同源性搜索,下载全部巴尔通体同源基因序列(附件)。应用MEGA7[12]软件中MUSLE对各基因序列进行比对,最大似然法(Maximum likelihood,ML)建树。

将23种巴尔通体和分离菌株的gltA (313 bp)-ftsZ(788 bp)-groEL(1178 bp)-rpoB(770 bp)序列串联后,应用TOPALi2.5软件[13]中贝叶斯分析MCMC算法(HKY+I+G模型,8000000 generations,25% burn-in)构建系统发育树。选择与巴尔通体近缘的布氏杆菌(Brucella abortus)作为外群。

1.6 序列多态性分析

将本研究分离的菌株和其他来源菌株的16S rRNA基因和上述5个管家基因序列分别比对后,应用DnaSP v5.10软件[14]计算各基因的核酸多样性指数(Nucleotide diversity indices,π)和基因多样性指数(haplotype diversity,Hd),参比菌株为全基因组测序菌株Toulouse。应用NETWORK4.6.1.2软件经前处理(star contraction)[15]和后处理(Maximum parsimony calculation)[16]构建gltA基因序列的中介网络图(Median Joining network)[17],参数设置为默认值(epsilon and weight values=0,10)。从GenBank上下载巴尔通体菌株同源序列,信息和序列号见附件。

1.7 血清IgG抗体检测

应用抗五日热巴尔通体抗体IgG间接免疫荧光法检测试剂盒(No. FI 219d-1005 G,欧蒙医学实验诊断股份公司,德国)检测猴群血清抗体水平。血清稀释为1:100、1:320和1:1000,二抗改用荧光标记的anti-monkey IgG抗体(KPL,美国),试剂盒内提供阴性和阳性对照血清,按照操作手册进行检测,以推荐稀释度1:320为阳性作为判断标准。

1.8 提交序列

本研究的序列已提交至GenBank,16S rRNA基因、gltAftsZrpoBgroELribE其序列号依次为:KY436638-KY436645、KY436598-KY436605、KY436614-KY436621、KY436606-KY436613、KY436630-KY436637和KY436622-KY436629。

2 结果和分析 2.1 菌株分离与鉴定

共计接种培养550只猴血样,8只四川普通猕猴为阳性,其他地区猴血样培养均为阴性,总感染率为1.5%,普通猕猴感染率为2.7%,四川地区感染率为3.2% (8/250)。这8只宿主猴5只为雌性,3只为雄性,年龄为3-4岁,健康状况良好,未发现体表寄生虫。

这些分离菌株的16S rRNA基因、gltAftsZgroELrpoBribE基因片段与五日热巴尔通体的相似性为99%-100%,单基因及MLSA (gltA-ftsZ-groEL-rpoB)序列构建系统树均显示与五日热巴尔通体聚在同一分支(图 1),菌株鉴定为五日热巴尔通体。

图 1 五日热巴尔通体分离菌株及已知巴尔通体基于gltA(313 bp)-ftsZ(788 bp)-groEL(1178 bp)-rpoB(770 bp)串联序列用贝叶斯法构建的系统发育树 Figure 1 Phylogenetic tree highlighting the position of the Bartonella strains of monkeys relative to other type strains within Bartonella species. The concatenated gltA, ftsZ, groEL and rpoB gene sequences were aligned using MUSCLE and phylogenetic inferences obtained using Bayesian phylogenetic analysis with the TOPALi 2.5 software with the integrated MrBayes application with the following substitution models: HKY+I+G. Numbers at the nodes are posterior probability values. There are a total of 3049 positions in the final dataset. The scale bar indicates a 7% nucleotide sequence divergence.

2.2 RAPD指纹图谱

从3S引物扩增出来的指纹图谱(图 2)可以看出全部猕猴菌株带型完全相同,有8条可辨识扩增带;五日热巴尔通体人源菌株str. Fuller的带型与猴源分离菌株基本一致,但在400 bp和500 bp处各缺失一条带;全部五日热巴尔通体菌株与汉赛巴尔通体带型完全不同。

图 2 应用3S引物(S15,10-mer;S18,10-mer;S103,10-mer)扩增巴尔通体的RAPD指纹图谱 Figure 2 RAPD profiles of the strains of Bartonella spp. using the primer 3S (S15, 10-mer; S18, 10-mer; S103, 10-mer). The electrophoresis was performed at 90 V for 90 min. M: 100-bp ladder molecular weight marker; lane 1 to 8 indicate the isolates from the monkeys in the study; lane 9 and 10 indicate B. quintana (ATCC VR-358) and B. henselae (ATCC 49882), respectively.

2.3 序列多态性分析

2.3.1 各基因的多态位点分析: 选取16S rRNA基因和5个常用的管家基因分别比较本研究分离的菌株和其他来源菌株的单核苷酸多态性差异。结果显示,6个基因均有变异位点,gltAribE单态突变位点(singleton variable sites)主要来自食蟹猕猴菌株,一株人源菌株OK90-268的groEL有较多突变;在简约信息位点(Parsimony informative sites)突变中,各基因猴株与人株有明显差别;各基因的基因型多样性值(Haplotype diversity,Hd)在(0.275±0.148) (16S rRNA基因)-(0.758±0.084) (rpoB)之间,核苷酸多样性值(Nucleotide diversity,π)在(0.00063±0.00034) (16S rRNA基因)-(0.00445±0.00144) (gltA)之间。

2.3.2 基因型分析: 按所测基因的多态性将不同来源的菌株分为3-5个基因型不等(表 2),其中gltAftsZrpoBribE的人源菌株单倍型一致;人源菌株的groEL基因中变异位点较多,3株被分出3个基因型,其他猴源菌株为同一个基因型;2株来自中国(无菌株名)和美国(str. CM-01-01)的食蟹猕猴菌株在gltA(Hap_2)和ribE(Hap_3)基因中形成了单独的基因型;1株日本雪猴菌株(str. MF1-1) ribErpoBgltA的序列分别与大部分中国猕猴菌株形成相同基因型;中国猕猴菌株的gltAgroEL分型一致,在其他基因中被分成2-4基因型。

表 2. 五日热巴尔通体菌株6个管家基因的序列多态性分析 Table 2. Polymorphism and nucleotide diversity of six housekeeping genes among Bartonella quintana strains
Locus Sequence length/bp Singleton variable sitesa Parsimony informative sitesa Haplotype diversity (Hd) Nucleotide diversity (π) Haplotype numbers
16S rRNA gene 1057 T565A (AJ250247) A524G*, G525A*, 0.275±0.148 0.00063±0.00034 3
gltA 338 A1068G# T846C*, A975G*, C1038T, T1040C* 0.425±0.133 0.00445±0.00144 3
ftsZ 788 0 C126T*, T288C*, C327G*, T/C582C$, C837T* 0.560±0.125 0.00218±0.00065 3
rpoB 797 G2016A (H16SC), T2265C (H52SC) A2079G, A2106G*, C2124T*, G2274A* 0.758±0.084 0.00201±0.00050 5
ribE 438 G158A (KC108707)#, G225A (KC108707)#, C314A (KC108707)# C/A230A, T321C 0.647±0.095 0.00227±0.00068 4
groEL 1178 C289A & , C293G & , C346T & , T354C (G & ), C419A & , C425G & , C434G & , C446A & , C464G & , C467G & , C486T & , C510G & , C519G & , T522C & , C525T & , C527T & , C737T & A1179G, C1203T*, A1227G*, A1279G* 0.467±0.148 0.00347±0.00175 4
a: the sites of the isolates in this study on left; #: representing the mutation only from Macaca fascicularis; $: the mutation of the strains H6SC and M22 are T; & : representing the stain OK90-268 (GenBank accession No. AF014830); *: representing the mutation only from human strains.

2.3.3 亲缘关系分析: 将5个基因应用ML建树,除gltA的基因分型与系统树分支基本一致,其他基因显示各菌株没有完全按照其基因型在系统树中成簇分布;拓扑结构相同之处是人源和猴源菌株明显处于不同分支(图 3)。

图 3 五日热巴尔通体菌株5个管家基因序列的ML系统发育树 Figure 3 Phylogenetic trees based on five housekeeping genes using ML (Maximum Likelihood) method for the strains of B. quintana. The subfigures A, B, C, D and E are based on the genes of gltA (338 bp), ftsZ (788 bp), ribE (438 bp), rpoB (797 bp) and groEL (1178 bp), respectively. The hosts of unmarked strains are Macaca mulatta in the figure. The scale bar indicates the nucleotide sequence divergences. The numbers at the nodes indicate ML bootstrap values.

gltA基因型的网络图中,以汉赛巴尔通体作为外群,不同宿主来源五日热菌株分别聚集成簇,日本雪猴菌株与猕猴菌株同属一个基因型而聚在一起,与系统树结构一致(图 4)。

图 4 五日热巴尔通体菌株基于gltA基因片段(338 bp)中介网络图 Figure 4 Median-joining haplotype network of B. quintana stains based on gltA (338 bp). The number in the figure representing quantity of the strains and B. henselae (Bh) as outgroup.

2.4 荧光定量PCR检测结果

本研究所设计探针引物检测限为5拷贝/μL,R2=1.000,扩增效率E=97.3%。共计检测猴血样品550份,总感染率为8.2%,普通猕猴感染率(13.0%)明显高于食蟹猕猴(2.4%)(χ2=20.40,P<0.01),不同性别的猕猴感染率没有差别(χ2=0.96,P>0.05);四川猴感染水平明显高于其他地区(表 3)。

表 3. 不同地区猕猴五热日巴尔通体荧光定量PCR检测结果 Table 3. The results of fluorescence quantitative PCR of Bartonella quintana from macaques in the different areas
Areas Positive number Sample number Positive rate/%b
Guangdong 1 100 1.0
Beijinga 2 100 2.0
Sichuan 38 250 15.2
Yunnan 4 100 4.0
Total 45 550 8.2
a: Tested 1 positive sample in Macaca mulatta and Macaca fascicularis, respectively; b: χ2=30.67, P<0.01.

2.5 血清检测结果

检测北京、四川、广东和云南猕猴血清样品共计550份,71份样品IgG抗体阳性,总阳性率为12.9%,普通猕猴(19.0%,57/300)的感染水平明显高于食蟹猕猴(5.6%,14/250) (χ2=21.78,P<0.01);普通猕猴雌性和雄性的阳性率分别为16.7%和26.9%,食蟹猕猴雌性和雄性的阳性率分别为6.1%和4.9%,不同性别的猕猴感染水平无差异(χ2=0.08,P>0.05) (表 4)。北京与四川的普通猕猴阳性率分别为28.0%和17.2%;北京、广东和云南的食蟹猕猴阳性率分别为10.0%、6.0%和3.0%,不同地区猕猴的感染水平无显著差异(表 5)。

表 4. 中国实验用猕猴五热日巴尔通体血清阳性率结果 Table 4. Seropositivity rates of anti-Bartonella quintana IgG antibody of the experimental macaques in China
Animal species Positive number Testing number Positive ratea/%
Male Female Total Male Female Total
Macaca mulatta 39 18 57 233 67 300 19.0
Macaca fascicularis 9 5 14 147 103 250 5.6
Total 48 23 71 380 170 550 12.9
a: Comparison of seropositivity rates for the two species of macaques. χ2=21.78, P<0.01.

表 5. 不同地区猕猴五热日巴尔通体血清阳性率结果 Table 5. The seroprevalences of anti-Bartonella quintana antibody of the macaques in different areas
Areas Macaca mulattaa Macaca fascicularisb
Positive number Testing number Positive rate/% Positive number Testing number Positive rate/%
Beijing 14 50 28.0 5 50 10.0
Sichuan 43 250 17.2 0 0 0
Guangdong 0 0 0 6 100 6.0
Yunnan 0 0 0 3 100 3.0
Total 57 300 19.0 14 250 5.6
a: χ2=3.16, P>0.05; b: χ2=3.14, P>0.05.

3 讨论

从普通猕猴血液中分离五日热巴尔通体,生长非常缓慢,从样品接种后10-12 d才开始出现灰白色、直径1 mm的小菌落。这些原代培养的小菌落向琼脂平板内部生长,形成凹坑,且形态粗糙。在连续传代后,世代时间缩短,3-5 d即可出现菌落。这些猴源菌株可在添加胎牛血清的昆虫液体培养基中生长,对环丙沙星、阿奇霉素和强力霉素等抗生素均敏感[18],它们与人源菌株表型一致[19]。由于巴尔通体表型特征不明显,生化反应不活泼,无法用于鉴定,目前核酸分子分类鉴定是唯一的方法。

通过RAPD指纹图谱分析发现,8株分离菌株相同,与人源菌株有部分差异,说明应用随机引物扩增不同宿主来源五日热巴尔通体核酸时有不同退火位点,核酸序列有差异,可以初步确定五日热巴尔通体种群在基因组水平上具有多态性;而与汉赛巴尔通体的图谱差异较大,提示RAPD指纹图谱能够初步鉴别这2种巴尔通体的种间差异。这种方法鲜见用于鉴定巴尔通体,因此如果作为分类方法,仍需做更多巴尔通体菌株之间的比较。虽然应用PFGE鉴别菌株和追溯来源在传染病病原菌中应用较多,但在五日热巴尔通体中传代会造成菌株核酸结构重排,因此PFGE不适用于此菌[20],本研究未采用这种常规方法。本研究中应用的多位点序列分析是目前巴尔通体分类分型标准方法,一般用5-8个管家基因进行核酸序列变异位点和系统发育关系分析[21]

对管家基因核酸序列多态性和基因型的分析进一步显示出分离菌株核酸水平的多态性特征,不同基因多态位点不同,核基因的变异水平较低,gltA等5个常用的管家基因较高,符合巴尔通体属菌株的整体特征[22];三种宿主来源的菌株均有各自特异的变异位点,且人源与猴源菌株差异明显。依据这些变异位点分出的基因型在各基因间没有一一对应,但是总体上表现出人源菌株、食蟹猕猴菌株和普通猕猴菌株(包括日本雪猴菌株)分别处在不同的基因型中。系统进化分析的结果同样展示出人源与猴源菌株明显分离,食蟹猕猴菌株也出现了分化(图 3图 4)。应用数个基因来评估菌株间差异和遗传关系,局限性显而易见,不能够反应菌株整体情况,显现出的差异有偏倚。另外,由于目前公布在GenBank中的五日热巴尔通体菌株信息较少,特别是猴源菌株更少,使得我们的分析受限于样本数量,很多种群特征信息不能获取完全。虽然本研究存在上述2个问题,但是,从目前的研究结果来看,猴源与人源菌株确有遗传差异,研究结果与Li等研究结果一致。他们的研究发现,不同宿主来源菌株对应于不同STs型分组,如STs 8-14、STs 15-21和STs 1-7分别来源于食蟹猕猴、普通猕猴和人类,并认为五日热巴尔通体与宿主间存在协同进化的关系。我们的结果也提示这一线索,但证实这一关系仍需要更多的宿主和菌株之间关联的证据。

在本研究中,不同检测方法所得感染率不同,血清抗体水平阳性率(12.9%)高于核酸检测(8.2%)和分离培养(1.5%),且在各地和不同猴种中均有阳性个体,表明猴群既往感染水平较高,且有些个体已产生抗体并清除菌血症。本研究所用荧光定量核酸检测技术可以检测出核酸样品中数个拷贝的特异基因,在减少检测用时的同时提高了敏感性,与培养方法相比高效快速,对于巴尔通体这种难培养细菌更为适宜,且提高了对样品流行病学调查的准确性,提高检测效率。在本研究中的猴群总核酸阳性率明显大于细菌分离率,在食蟹猕猴群中查到了带菌个体,较培养方法敏感。因此,虽然仅从四川地区的猕猴中分离到五日热巴尔通体菌株,并不能排除其他地区动物携带的可能性,调查结果与样本自身情况有关,同检测方法的靶标和敏感性也密切相关。事实上,各种检查方法有各自的优缺点,运用综合的方法补充各自短板对于难培养细菌的检测和流行病学调查是目的所需。培养方法用时较长、阳性率低,但是可以直接获得病原菌株,并进一步分析其表型、遗传和耐药特征等,为后续研究奠定基础。因此,多种检测方法组合使用,是从不同水平观察样品,可以较为全面地评估所测宿主群体的病原携带和流行状况。

在发现非人灵长类可携带五日热巴尔通体之前,人类一直被认为是唯一宿主,虽然早已有人在动物实验中观察到猕猴是研究五日热的理想动物模型[23-24],但也从未考虑过这种病原体是否有自然动物宿主,直到有人从食蟹猕猴(美国)和普通猕猴(中国)中发现了五日热巴尔通体,才引起对这一问题的关注。近年国外同类研究显示,普通猕猴和日本雪猴(13.3%,6/45)[6]、食蟹猕猴(1.9%,1/52)[25]均可携带五日热巴尔通体,甚至大猩猩(Gorilla gorilla)也有较高核酸检出率(38.1%),只是该研究没有获得相应菌株,难以比较不同宿主来源菌株间的差异[26]。国内Li等对四川等5个地区研究发现,猴群总带菌率为8.3%,普通猕猴带菌率高于食蟹猕猴,分别为11.3% (37/328)和5.2% (16/308),核酸检出率高于分离培养,分别为18.0% (59/328)和12.0% (37/308),与本研究结果基本一致。综合对五日热巴尔通体的血清抗体、核酸检测和培养结果来看,国内实验用普通猕猴和食蟹猕猴种群都存在较高的感染率,所携带菌株与人源菌株有遗传差异。这些非人灵长类来源的五日热巴尔通体在野外种群中流行状况如何,会否引起动物和人类疾病,潜在威胁有多大,都是需要进一步探索的问题。除此,非洲黑猩猩可携带五日热巴尔通体的核酸证据提示我们更多的非人灵长类动物可能是这种病原的潜在宿主,对其他众多类别的调查将有助于完善非人灵长类作为五日热巴尔通体自然宿主的证据,并促进对不同宿主来源菌株间演化关系的研究。本研究所获得的四川猕猴菌株已无法追溯其来源,为什么在实验室种群中会有这类病原菌存在,是从野外种群引入的吗,或许通过对产地野生猕猴的调查能够给出答案。

到目前为止,在我国境内还没有战壕热病例明确的报道,只有1952年一篇论文报道人体虱携带一种类立克次体病原引起人群斑疹伤寒样发热,病原疑似是五日热巴尔通体[27],还有一些外文综述性文献中提及中国曾存在此病[28-29]。近年,云南的一些调查发现不明原因发热人群中有五日热巴尔通体抗体阳性个体[30-31],说明我国存在这类疾病潜在流行,确有必要摸清其相关宿主、人群感染状况和传播风险。

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