杭州地区临床和食品来源德尔卑沙门菌耐药特征与基因组分析

目的了解杭州地区临床和食品来源德尔卑沙门菌的耐药特征, 并进行溯源分析。方法对2015—2020年杭州地区分离的60株德尔卑沙门菌进行药敏分析、脉冲场凝胶电泳(PFGE)分型和全基因组测序, 并下载公共数据库基因组进行比较;利用测序数据对菌株进行多位点序列分型(MLST)、核心基因组多位点序列分型(cgMLST)和耐药基因扫描, 并构建基于单核苷酸多态性(SNP)位点的系统发育树。结果杭州地区德尔卑沙门菌临床株和食品株对28种药物的耐药率差异均无统计学意义, 多重耐药率为76.7%(46/60);所有菌株均检出氨基糖苷乙酰转移酶基因aac(6′)-Iaa和磷霉素耐药基因fosA7;60株德尔卑沙门菌共分为46种PFGE带型、53种cgMLST(HC2)型别, 除1株为ST3220型外, 其余均为ST40型;基于439株德尔卑沙门菌(包括60株杭州菌株和379株公共数据库菌株)SNP位点构建的系统发育树显示:部分杭州菌株与东南亚菌株进化距离较近, 提示可能存在跨境传播, 食品株主要来自猪肉和水产类;其他杭州菌株与北京、广州、湖北、重庆等省市的菌株距离较近, 提示可能存在跨省传播, 食品株...     

广东省腹泻病例非伤寒沙门菌耐药谱和PFGE分型研究

目的 了解广东省腹泻病例非伤寒沙门菌的耐药状况,并对多重耐药菌株进行脉冲场凝胶电泳(PFGE)分型研究.方法 利用血清学方法对2009-2011年广东省腹泻病例分离的非伤寒沙门菌进行分型,并用CLSI( Clinical and Laboratory Standards Institute)推荐的纸片法对分离的沙门菌株进行抗生素敏感性检测,采用PFGE进行分型研究.结果 91.76％ (256/279)的鼠伤寒沙门菌对3种及以上抗生素耐药,40株鼠伤寒沙门菌同时对9种及以上抗生素耐药,其中有3株对全部12种抗生素耐药.96.91％ (94/97)的I4,5,12:i:-沙门菌对3种及以上抗生素耐药,9株14,5,12:i:-沙门菌同时对9种及以上抗生素耐药,其中有1株对全部12种抗生素耐药.47％(47/100)的肠炎沙门菌对3种及以上抗生素耐药,其中1株对9种及以土抗生素耐药.环内沙星的耐药率为4.27％( 27/632),其中,17株为鼠伤寒沙门菌,6株为14,5,12:i:-沙门菌.31.96％( 202/632)的沙门菌对环丙沙星显示为中介敏感性.这些多重耐药的菌株和具有相同耐药谱的菌株PFGE指纹图谱不完全一致,PFGE型别存在明显的遗传多样性.结论 广东省非伤寒沙门菌多重耐药现象严重.多重耐药菌株的PFGE型别多样,存在明显的遗传多样性.继续加强耐药监测和控制抗生素的合理使用刻不容缓.     

伤寒沙门菌PFGE分子分型及耐药性研究

目的对深圳市2004—2011年伤寒沙门菌进行脉冲场凝胶电泳（PFGE）分子分型及耐药性分析,为临床用药和追踪传染源提供依据。方法采用K-B法对42株伤寒沙门菌进行20种抗菌药物敏感性测试,并用PFGE对其进行分子分型。结果42株伤寒沙门菌株对氨苄西林、阿莫西林／克拉维酸、氨苄西林／舒巴坦、头孢噻吩、头孢他啶、头孢曲松、头孢吡肟、头孢西丁、阿米卡星、庆大霉素、卡那霉素、环丙沙星、左旋氧氟沙星、复方新诺明、甲氧苄啶、氯霉素和四环素17种药物的敏感率均超过90％,对萘啶酸耐药率最高达61．5％。42株伤寒沙门菌株可分为SZ0001～SZ0028共28个PFGE型别,其中流行优势型为SZ0023型别。结论结合药物敏感试验结果和PFGE分子分型结果可以判断伤寒疫情的优势株型。     

沙门菌属外膜蛋白的抗原同源性分析

目的 分析沙门菌属外膜蛋白（outer membrane protein，OMP）的抗原同源性。方法 十二烷基肌氨酸钠法提取甲型副伤寒沙门菌、伤寒沙门菌、鼠伤寒沙门菌、大肠埃希菌、福氏志贺菌、肺炎克雷伯菌、阴沟肠杆菌和粘质沙雷菌的OMP。用甲型副伤寒沙门菌的OMP与完全佐剂制成乳油状，多次多部位免疫日本大耳兔，获得抗OMP抗体血清。35％饱和硫酸铵沉淀并纯化IgG，用HRP标记。SDS-PAGE法分离检测上述8种细菌的OMP。Western blot测定兔抗甲型副伤寒沙门菌OMP抗体与上述其他细菌OMP抗原的反应特异性。斑点印迹．酶联免疫吸附试验（Dot blot-ELISA）测定兔抗甲型副伤寒沙门菌OMP抗体与肠炎沙门菌、费氏枸橼酸杆菌、变形杆菌、铜绿假单胞菌、蜂房哈夫尼亚菌、棒状杆菌、嗜麦芽窄食假单胞菌、金黄色葡萄球菌、摩根摩根菌、屎链球菌、肺炎链球菌、新型隐球菌、热带念珠菌、光滑念珠菌和白色念珠菌提取物的反应性。结果 沙门菌属成员的OMP可与兔抗甲型副伤寒沙门菌OMP抗体血清发生特异性反应；其他革兰阴性菌OMP与之无反应；革兰阳性菌和真菌亦不发生反应。结论 沙门菌属OMP具有高度的抗原同源性，有别于其他细菌。     

萘啶酸抗性甲型副伤寒病原菌的克隆扩散和遗传多样性

目的 认识肠沙门菌甲型副伤寒血清型(SPA)的克隆扩散和遗传多样性,建立并确定病原菌流行克隆的分型方法.方法 采用有对照的K-B纸片扩散技术对分离的3980株SPA进行抗微生物药物敏感性试验;经PCR扩增和基因测序检测15个萘啶酸抗性菌株喹诺酮抗性决定区的gyrA、gyrB、syrC和syrE基因;采用Spe Ⅰ和Xba Ⅰ消化染色体DNA脉冲场凝胶电泳(PFGE)对来自7个县的121个分离株进行分型和聚类分析.结果 萘啶酸敏感菌株在1999年占有优势,但2000年以后被萘啶酸抗性菌株替代;15个萘啶酸抗性菌株的PCR扩增和基因测序显示抗性机制是由gyrA基因的单点突变引起;121个菌株spe Ⅰ和Xba Ⅰ消化产物分别得出以Spe Ⅰ 01、spe Ⅰ 02或Xba Ⅰ 01型占优势的5种和4种PFGE型,Spe Ⅰ 01和Spe Ⅰ 02分别占37.2%和57.9%,或Xhn Ⅰ 01占95.0%.结论 在研究期间SPA分离株萘啶酸抗性率上升;PFGE型的SpeⅠ01和SpeⅠ 02或XbaⅠ01是玉溪流行的主要克隆;采用Spe Ⅰ和Xba Ⅰ的PFGE是鉴别SPA的一项有用技术.     

MLVA和Spoligotyping用于西藏地区216株结核分枝杆菌临床分离株的基因分型研究

目的评价间隔区寡核苷酸分型（Spoligotyping）及多位点可变数量串联重复序列分析（MLVA）两种分型方法在西藏地区结核病分子流行病学中的应用。方法收集西藏地区结核分枝杆菌（Mycobacteriumtuberculosis）临床分离株，应用Spoligotyping及MLVA两种分型方法进行比较分析。结果共在西藏地区收集到216株结核分枝杆菌临床分离株，采用Spoligotyping分型方法，216株菌可分为3个基因群13种基因型，其中最大的1个基因群即北京家族（8eijingfamily）含有195株菌，占90．28％。北京家族菌株中，有BCG接种史者占45．64％（89／195），无BCG接种史者占54．36％（106／1195），两者间的差异无统计学意义（X^2=0．059，P〉0．05）。采用MLVA分型方法，216株菌可分成19个基因群108种基因型，其中80种基因型只有1株菌，占37．03％（80／216），另有136株菌表现出28种基因型，成簇数为28，占62．96％（136／216）。在20个VNTR位点的等位基因多态性发现Miru31位点的多态性最高，多态性指数（h）达到0．77，而Mtub29、Mtubl2位点的多态性较差，都低于0．05。其中Mtuh02位点可鉴别北京家族和非北京家族，它鉴别的北京家族与Spoligotyping鉴别的北京家族符合率达到100％。结论西藏地区结核分枝杆菌具有明显的接引多态性，其主要流行型为北京家族。北京家族菌株与BCG接种无相关性。应用Spoligotyping和MLVA两种分型方法进行结核病流行病学研究，将提高结核病的流行病学调查和病原学监测效果。     

甲型副伤寒沙门菌减毒株的构建与鉴定

目的构建甲型副伤寒沙门菌减毒株,测试其减毒效果,为制备减毒疫苗奠定基础。方法利用同源重组技术敲除甲型副伤寒沙门菌CMCC50093株的ync D基因和aro C基因,构建出ync D单基因敲除株和ync D-aro C双基因敲除菌株;通过测定和比较野生株、ync D单基因敲除株及ync D-aro C双基因敲除株的生长曲线,评估基因敲除对细菌生长的影响;以猪胃黏蛋白增毒小鼠为模型,测定野生株和双基因敲除株对模型动物的半数致死量LD50,评价双基因敲除株的减毒效果。结果成功构建并筛选到ync D单基因及ync D-aro C双基因敲除的甲型副伤寒沙门菌突变菌株。生长曲线测定显示ync D基因和aro C基因敲除后,敲除株生长明显缓慢。野生株和双基因敲除株针对模型小鼠的LD50分别为7.90×101和3.33×106CFU,结果表明ync D-aro C双敲除菌株的毒力较野生株下降约42 202倍,具有显著的减毒效果。结论本研究所构建的甲型副伤寒沙门菌ync D-aro C双基因敲除突变株毒力明显降低,安全性好,为研制甲型副伤寒减毒活疫苗奠定了坚实基础。     

广东省历年流行性脑脊髓膜炎病原体分子特征分析

目的 了解广东省历年流行性脑脊髓膜炎(流脑)病原体的外膜蛋白编码基因porA和porB基因特征,并确定病原体的优势克隆型.方法 对1967-2007年从流脑患者分离的18株脑膜炎奈瑟球菌(Neisseria meningitidis)进行复苏培养和生化鉴定;通过DNA序列测定分析外膜蛋白编码基因porA、porB特征;对菌株进行多位点序列分型(multilocus sequence typing, MLST),采用PHYLIP软件制作进化树,并与脑膜炎余瑟球菌MIST全球数据库(PubMLST)中的菌株比较,确定优势克隆型菌株,探讨广东省历年流脑疫情分离株的看家基因序列多态性.结果 porA可变区(VR)1的型别以20型为主,VR2的型别在2004年前主要为9型,以后呈现多态性;porB可变区Ⅰ、Ⅳ、Ⅴ、Ⅵ主要分别为4、7、11、10型,2004年后可变区Ⅴ、Ⅵ型别增多;除2007年分离的1株W135菌株外,其余菌株的porB基因均无Ⅶ、Ⅷ可变区.在7个看家基因中,abcZ等位基因多态性最低,pgm最高.广东省历年流行性脑脊髓膜炎分离株2004年前的优势克隆为ST-5克隆系,自2004年开始出现高致病性ST-4821克隆系,2007年首次出现高致病性ST-11克降系.结论 广东省历年脑膜炎奈瑟球菌分离株的外膜蛋白编码基冈呈现多态性特征,分离株为多克隆系并存,近期以高致病性克隆系为主.     

泛耐药肺炎克雷伯菌株的医院内流行特性的研究

目的 了解华山医院泛耐药肺炎克雷伯菌株及其流行的特点.方法 收集2006年8月-2009年12月对CLSI推荐常规检测药物均耐药的肺炎克雷们菌临床分离株,共57株.所有菌株都进行药物敏感试验、超广谱β-内酰胺酶(ESBLs)初筛及表型确证试验、改良Hodge试验、等电聚焦电泳,聚合酶链反应及其产物测序、接合试验、肠杆菌基因间重复共有序列PCR(ERIC-PCR)和多位点序列分型(MLST).结果 所有菌株都携带blaKPC-2、blaCTX-M-14、blaSHV12和blaTEM-1及qnrB和aac(6')-I b-cr基因.57株细菌中ST423型5株,MIST ST11型52株.ST423型散发,而ST11型呈医院内流行.57株细菌都对替加环素耐药,对多黏菌素、米诺环素和多西环素部分敏感.结论 本次泛耐药肺炎克雷们流行主要为ST11型菌株;不同的肺炎克雷伯菌株,播散能力不同;检出泛耐药肺炎克雷伯菌时应增加检测药物的种类.     

泛耐药肺炎克雷伯菌株的医院内流行特性的研究

目的 了解华山医院泛耐药肺炎克雷伯菌株及其流行的特点.方法 收集2006年8月-2009年12月对CLSI推荐常规检测药物均耐药的肺炎克雷们菌临床分离株,共57株.所有菌株都进行药物敏感试验、超广谱β-内酰胺酶(ESBLs)初筛及表型确证试验、改良Hodge试验、等电聚焦电泳,聚合酶链反应及其产物测序、接合试验、肠杆菌基因间重复共有序列PCR(ERIC-PCR)和多位点序列分型(MLST).结果 所有菌株都携带blaKPC-2、blaCTX-M-14、blaSHV12和blaTEM-1及qnrB和aac(6')-I b-cr基因.57株细菌中ST423型5株,MIST ST11型52株.ST423型散发,而ST11型呈医院内流行.57株细菌都对替加环素耐药,对多黏菌素、米诺环素和多西环素部分敏感.结论 本次泛耐药肺炎克雷们流行主要为ST11型菌株;不同的肺炎克雷伯菌株,播散能力不同;检出泛耐药肺炎克雷伯菌时应增加检测药物的种类.     

DNA疫苗的运送载体——减毒霍乱沙门氏菌

霍乱沙门氏菌是人兽共患病原菌,遗传背景清楚,利用它作为载体表达外源抗原基因已得到较广泛的研究并取得了一定的效果。本文从沙门氏菌的侵入途径、减毒重组菌对基因疫苗的呈递及诱发免疫应答的机制、作为载体的优势以及免疫存在的问题等方面就减毒霍乱沙门氏菌作为运送DNA疫苗的载体作简要概述。     

The rectal biopsy appearances in Salmonella colitis

Rectal biopsies were examined from 22 patients with Salmonella infection of food-poisoning type and from seven patients with inflammatory bowel disease and coincidental Salmonella infection. In the former group the changes observed were mucosal oedema with acute inflammation of varying severity but with preservation of the crypt architecture. Crypt abscesses were present in a few cases but were usually localized in the crypt and mucus depletion only occurred with severe inflammation. These features are not specific and are similar to those seen in other types of infective colitis such as Shigella dysentery, gonococcal proctitis and amoebic colitis. In the majority of cases of infective colitis the appearances are usually sufficiently distinctive, however, to distinguish them from those seen in ulcerative colitis and Crohn's disease. The changes in the biopsies from the seven patients with coincidental Salmonella infection were in general those of the underlying idiopathic inflammatory bowel disease.     

Characteristics of non-typhoidal Salmonella isolates from human and broiler-chickens in southwestern Seoul, Korea

Non-typhoidal Salmonella (NTS) is an important commensal microorganism. The purpose of this study was to determine the epidemiological relation between NTS isolates from livestock and NTS isolates from human by analyzing antimicrobial susceptibilities and performing molecular typing. We determined the serotypes of 36 human clinical isolates and 64 livestock isolates, performed antimicrobial susceptibility testing against 8 antibiotics, and determined the molecular types of isolated NTS spp. by pulsed field gel electrophoresis (PFGE). In human isolates, S. enteritidis was the most common serotype (17 isolates; 47.2%) and S. typhimurium the second most (8 isolates; 22.2%). In livestock isolates, S. typhimurium was the most common serotype (15 isolates; 23.44%), and S. enteritidis was the second most (14 isolates; 21.88%). Ampicillin and tetracycline resistance were 50% (32/64 isolates) each among broiler-chicken NTS isolates. No human or livestock NTS isolates showed resistance to ciprofloxacin, TMP-SMX, or ceftriaxone. However, 19.4% (7/36) and 46.8% (30/64) of the human and livestock NTS isolates were resistant to nalidixic acid (MIC > or = 16 mg/mL), respectively. The presence of the three identical PFGE molecular types from human and broiler-chicken NTS isolates suggests the possibility of transmission from livestock to humans.     

实时荧光PCR同时检测丙型副伤寒沙门菌和猪霍乱沙门菌方法的建立和应用

目的建立丙型副伤寒沙门菌和猪霍乱沙门菌的实时荧光PCR快速检测方法,用于沙门菌属内的分型鉴定。方法根据GenBank公布的丙型副伤寒沙门菌和猪霍乱沙门菌的保守序列,设计引物和改良分子信标探针,建立实时PCR检测方法。结果检测体系灵敏度高,纯DNA和菌液的最低检出限分别可达10fg和20CFU/反应体系;特异性好,对71株细菌的检测符合率达100%。20株沙门菌采取盲号模拟血培养标本进行血培养检测及鉴定,检出5株丙型副伤寒沙门菌和4株猪霍乱沙门菌,与试验的菌株相符。70份食品中用实时荧光PCR同时检测丙型副伤寒沙门菌和猪霍乱沙门菌均为阴性,而用传统方法分离培养未检出。结论建立的实时PCR检测方法可以快速、特异、灵敏地检测出丙型副伤寒沙门菌和猪霍乱沙门菌。     

Sequence analysis and distribution in Salmonella enterica serovars of IS3-like elements

The genome of Salmonella enterica serovar Enteritidis was shown to possess three IS3-like insertion elements, designated IS1230A, B and C, and each was cloned and their respective deoxynucleotide sequences determined. Mutations in elements IS1230A and B resulted in frameshifts in the open reading frames that encoded a putative transposase to be inactive. IS1230C was truncated at nucleotide 774 relative to IS1230B and therefore did not possess the 3' terminal inverted repeat. The three IS1230 derivatives were closely related to each other based on nucleotide sequence similarity. IS1230A was located adjacent to the sef operon encoding SEF14 fimbriae located at minute 97 of the genome of S. Enteritidis. IS1230B was located adjacent to the umuDC operon at minute 42.5 on the genome, itself located near to one terminus of an 815-kb genome inversion of S. Enteritidis relative to S. Typhimurium. IS1230C was located next to attB, the bacteriophage P22 attachment site, and proB, encoding gamma-glutamyl phosphate reductase. A truncated 3' remnant of IS1230, designated IS1230T, was identified in a clinical isolate of S. Typhimurium DT193 strain 2391. This element was located next to attB adjacent to which were bacteriophage P22-like sequences. Southern hybridisation of total genomic DNA from eighteen phage types of S. Enteritidis and eighteen definitive types of S. Typhimurium showed similar, if not identical, restriction fragment profiles in the respective serovars when probed with IS1230A.     

Salmonella prosthetic joint septic arthritis

We describe a case of Salmonella enteritidis infection of a prosthetic knee joint that was cured with ceftriaxone therapy for 6 weeks and replacement of the tibial component of the prosthesis. Eleven other cases of salmonella prosthetic joint infection have been reported in the English-language literature. Five infections occurred within 20 days of prosthesis placement, and seven occurred several months to years later; ten of 12 infections involved hip prostheses. Nine of 12 patients who had prosthesis removal were cured of the infection. Two of the three patients with retention of the prosthesis required long-term suppressive antibiotic therapy.     

Phage types, antibiotic susceptibilities and plasmid profiles of Salmonella typhimurium and Salmonella enteritidis strains isolated in Istanbul, Turkey

Objective   To examine 13 Salmonella typhimurium and 22 S. enteritidis strains isolated from individual cases of gastroenteritis for their phage types, antibiotic susceptibilities and plasmid profiles.
Methods   The phage typing of S. typhimurium strains was done according to the method of Anderson et al, and the phage typing scheme of Ward et al was used for phage typing of S. enteritidis strains. Antibiotic susceptibility testing was performed by the Kirby–Bauer disk diffusion method. Extended-spectrum β-lactamase production of the strains was determined by the three-dimensional method. Plasmid profiles of the strains were examined using the method described by Kado and Liu with some modification by Graeber et al.
Results   Two S. typhimurium strains were DT 193 and one was DT 22, whereas 10 strains were untypable. PT 4 was the predominant phage type among S. enteritidis strains. Four S. enteritidis strains were DT 6a, three strains were PT 1 and one strain was PT 8, whereas only one strain was untypable. Eleven of 13 S. typhimurium and three of 22 S. enteritidis strains were found to be multiresistant. Ten different resistance patterns among S. typhimurium and four different resistance patterns among S. enteritidis strains were detected. Extended-spectrum β-lactamase production was detected in 10 of 13 S. typhimurium and in three of 22 S. enteritidis strains. All S. typhimurium strains but one were found to contain at least one plasmid, with molecular masses varying between 4 and 107 MDa, and 11 different plasmid patterns were determined. Plasmid pattern analysis permitted further differentiation of the S. enteritidis strains into nine groups. A serovar-specific virulence plasmid of 36 MDa was detected in 13 of 22 S. enteritidis strains.
Conclusions   The results suggest that the majority of S. typhimurium strains were closely related.     

抗甲型副伤寒沙门氏菌鞭毛抗原单克隆抗体的研制及初步应用

本文采用杂交瘤技术,制备了７ 株抗甲型副伤寒沙门氏菌鞭毛抗原单克隆抗体（ｍ Ａｂ） 的杂交瘤细胞株。对３ 株ｍＡｂ（２Ｃ８、２Ｅ６ 和５Ｄ７） 进行了鉴定,ｍＡｂ ２Ｃ８ 和５Ｄ７ 为ＩｇＭ,２Ｅ６ 为ＩｇＧ１（κ）亚类,可分别识别不同的抗原表位,均具有很强的特异性,即只与甲型副伤寒沙门氏菌及其鞭毛抗原起反应,而与相关肠道细菌：尼亚里木沙门氏菌、达卡沙门氏菌及伤寒沙门氏菌、乙型和丙型副伤寒杆菌、猪霍乱沙门氏菌、纽波特沙门氏菌等均无交叉反应。免疫印迹显示,３ 株ｍＡｂ 只能与甲型副伤寒沙门氏菌鞭毛抗原Ｍｒ 为５２ ０００ 的蛋白结合。用ｍＡｂ ２Ｅ６ 和５Ｄ７ 建立的双ｍＡｂ 夹心ＥＬＩＳＡ 法,检测了１３ 例血培养阳性的副伤寒患者血清中的甲型副伤寒沙门氏菌鞭毛抗原,１２ 例呈阳性,阳性符合率为９２－３％ 。     

Assessment of antimutagenic activity with Salmonella typhimurium strain TM677

A method is described for the detection of antimutagenic agents in a forward mutation assay with Salmonella typhimurium strain TM677. Bacterial cells are treated with test compounds in the presence of a known mutagen. Antimutagenic activity is indicated by a reduction in the induced mutant fraction. This assay has been used to detect and/or confirm the antimutagenic activity of a number of known compounds. This method is currently being used in our laboratory for the bioassay-directed fractionation of potential cancer chemoprevention agents from plant extracts.     

Antigenically stable 35 kDa outer membrane protein of Salmonella

Outer membrane protein (OMP) extracts from Salmonella species representing seven serogroups were examined by SDS‐PAGE followed by immunoblotting. Two major proteins with apparent molecular weight of 24 and 35 kDa were identified. The latter protein was present only in Salmonella. Immunoblotting with a monoclonal antibody (MAb) 1D6 (IgA) demonstrated the 35 kDa OMP contains an antigen common for all tested Salmonella species with the exception of atypical species such as S. arizona. The type of growth media had no effect on the antigenicity of 35 kDa protein. However, the electrophoretic appearance of the 35 kDa protein was influenced by heat‐treatment. Analysis of OMP extracts by SDS‐PAGE and immunoblotting without heat‐treatment revealed that MAb 1D6 bound several isoforms of this protein, a major form at 28 kDa and about eight minor forms in the range between 34 and 40 kDa. None of these forms contained carbohydrate moieties that may be responsible for the polymorphic appearance of the protein. These forms were converted to a single form by heat‐treatment at 100°C indicating that the 35 kDa OMP is most likely a heat‐modifiable protein. Furthermore, extended heat‐treatment (121°C, 15 min) did not affect the antigenicity of the 35 kDa OMP. Electron microscopy studies revealed that the 35 kDa OMP is exposed on a surface of the bacterial cells, although the frequency of epitopes recognized by the Mab 1D6 was low as can be inferred from the low number of gold particles attached to the cells.