BioVector® 蜡样芽胞杆菌（产呕吐毒素/携带 cesB 基因标准株）

BioVector® Bacillus cereus (Emetic Toxin/Cereulide-Producing, cesB+ Reference Strain)

第一部分 中文说明

一 产品基本信息与遗传学背景

• 细菌名称：Bacillus cereus (产呕吐毒素型标准参考株)

• 分类学地位：厚壁菌门 (Bacillota/Firmicutes)、芽胞杆菌纲 (Bacilli)、芽胞杆菌目 (Bacillales)、芽胞杆菌科 (Bacillaceae)、芽胞杆菌属 (Bacillus)。

• 主要病理生理学背景：

  • 蜡样芽胞杆菌是一种广泛存在于自然界（土壤、农产品、谷物及熟米饭）中的革兰氏阳性、兼性厌氧、能形成抗逆性极强内生芽胞的兼性致病菌。

  • 呕吐型（Emetic type）食物中毒核心菌株：该特定菌株在遗传学上携带完整的呕吐毒素合成酶基因簇，能够在食品（尤其是富含淀粉的米饭、面条）基质中或体外培养期间，大量分泌高致病性的呕吐毒素（Cereulide）。

• 核心遗传学标志（cesB 基因阳性）：

  • 非核糖体肽合成酶系统（NRPS）：呕吐毒素（Cereulide）并非由常规核糖体直接翻译生成，而是由位于大质粒（如 pBCE9801 或 pCERE01）上的 ces 操纵子 所编码的非核糖体肽合成酶（Non-ribosomal peptide synthetase, NRPS）复合体催化组装。

  • cesB 基因靶点：cesB 基因编码该酶学复合体中的核心关键亚基。本菌株经聚合酶链式反应（PCR）及基因组测序验证，cesB 基因呈现绝对阳性。该位点是国际上进行食品卫生微生物学检验、鉴别产呕吐毒素株与普通肠毒素（腹泻型）株最权威的特异性分子诊断靶标。

• 生物安全级别：2级（BSL-2）。本菌株具有产生强效胃肠道毒素的能力，涉及活菌及内生芽胞的所有实验操作、培养和分装，必须在二级生物安全实验室（BSL-2/P2）的生物安全柜内进行，并严格预防气溶胶吸入或意外摄入。

二 毒素理化特性与临床危害

1. 呕吐毒素（Cereulide）的极端理化抗性：

   • 超强耐热性：Cereulide 是一种环状十二去肽（Cyclic dodecadepsipeptide）。由于其特殊的环状疏水性骨架，该毒素能承受 121 摄氏度高压灭菌（Autoclaving）30 分钟而不被破坏。常规的烹饪、煮沸、加热食品无法使其失活。

   • 耐酸与耐蛋白酶性：该毒素在 pH 2.0 至 pH 9.0 范围内保持完全稳定，且能抵抗胃蛋白酶（Pepsin）和胰蛋白酶（Trypsin）的降解。在被人类误食后，能以完整的活性分子结构顺利通过胃酸屏障。

2. 临床毒理学机制：Cereulide 是一种强效的离子载体（Ionophore），对钾离子（$K^+$）具有高度选择性亲和力。进入肠道后，它能特异性识别并结合迷走神经（Vagus nerve）上的 5-HT3（五羟色胺）受体，向呕吐中枢发送化学信号，从而在摄入后数小时内（通常 1-5 小时内）引发剧烈的急性呕吐症状。此外，它能破坏宿主细胞线粒体跨膜电位，引发微泡样脂肪变性并展现严重的肝毒性（Hepatotoxicity）。

三 形态学与培养环境

• 形态学特征：

  • 显微形态：革兰氏阳性大杆菌（通常长 3-5 $\mu$m，宽 1-1.2 $\mu$m），两端相对平齐，常呈短链或长链状排列。在培养后期、营养匮乏或暴露于空气中时，会在细胞中央或亚端自发形成椭圆形的内生芽胞（Endospore），芽胞不使菌体膨大。

  • 菌落形态：在标准营养琼脂平板上，菌落较大（直径 2-5 mm），呈现微白或灰白色、表面粗糙不平如毛玻璃状（Ground-glass appearance）、边缘常有不规则的伪足状扩散。在 MYP 选择性琼脂平板上，因不发酵甘露醇而使菌落呈现粉红色，且其外围环绕着由卵磷脂酶（Lecithinase）分解卵磷脂产生的强烈白色沉淀环。在羊血琼脂上展现强烈的 $\beta$-溶血（$\beta$-hemolysis）。

• 生长模式与增殖动力学：兼性厌氧，但在有氧条件下生长更为迅速。群体倍增时间在对数生长期约为 20 约 30 分钟。

• 标准完全培养基配方：

  • BioVector® 标准营养肉汤（Nutrient Broth）/ 营养琼脂。

  • 脑心浸液培养基（BHI 液体/固体）。

  • 鉴定/筛选专用：MYP（甘露醇-卵磷脂-多粘菌素）琼脂培养基。

• 物理培养参数：30摄氏度至37摄氏度恒温、空气有氧环境或兼性厌氧环境。注：为了诱导最高产量的 Cereulide 毒素表达，国际标准方案通常推荐在 30 摄氏度下进行震荡培养。

四 菌株复苏、常规传代与保存标准操作

1. 冻存管复苏与划线（Revival Protocol）：

   • 在 BSL-2 级安全柜内，快速将冻存管从超低温环境中移出，置于 37 摄氏度水浴中摇晃解冻。

   • 吸取 100 $\mu$l 菌液，接种至预热的 BHI 肉汤或直接在营养琼脂/血平板上进行三区或四区划线以获得单菌落。30°C-37°C 培养 18-24 小时即可长出丰满菌落。

2. 芽胞与毒素产生的监控传代：

   • 本菌株在液体培养中进入平台期（Stationary phase）后，NRPS 系统开始高负荷工作合成 Cereulide。若需提取毒素，建议培养 24 到 48 小时。

   • 传代时按 1比100 的比例转接新肉汤。为防止菌株在频繁常规传代中发生大质粒（携带 ces 基因簇）的自发丢失或突变沉默，严禁连续无限制液体传代。通常建议在复苏后 3-5 代内即进行冷冻保藏。

3. 长期菌种保藏：

   • 甘油冻存：取对数晚期的液体培养物，与无菌甘油混合，使甘油终浓度达到 20% 至 25%，分装后于 -80 摄氏度保存。

   • 芽胞保藏法：由于其能形成极耐干燥的内生芽胞，可将其在无菌蒸馏水中诱导完全形成芽胞后，以芽胞悬液的形式置于 4 摄氏度常规冰箱中保存，或进行真空冷冻干燥（Lyophilization）长期锁定保藏。

五 核心科研应用方向

1. 食品安全与微生物学检验技术验证（Diagnostic Validation）：作为法定的产呕吐毒素蜡样芽胞杆菌标准阳性对照菌株。用于验证各种食品、乳制品、快餐米饭基质中蜡样芽胞杆菌分子检测标准（如针对 cesB、cesA 基因的 Real-time PCR、LAMP 环介导 isothermal 扩增技术及全自动全基因组质检体系）的特异性与灵敏度。

2. 非核糖体肽合成酶（NRPS）与新型抗生素药理学研究：Cereulide 的环状肽链组装结构对生物化学界具有极高的研究价值。本菌株是深入解析 NRPS 多酶复合体空间构象、底物识别机制及定向化学修饰的天然生物学催化反应活体模型。

3. 线粒体毒性与靶向细胞毒理学屏障评估：利用该菌株产生的内源性 Cereulide 毒素，提取后用于建立各种哺乳动物体外细胞模型（如 HepG2 肝癌细胞、Caco-2 肠上皮细胞）的线粒体损伤、跨膜电位崩溃及急性肝衰竭毒理学信号通路筛查。

PART 2 ENGLISH SECTION

I General Information and Genetic Background

• Strain Name:Bacillus cereus (Emetic Toxin-Producing Reference Strain)

• Taxonomy: Phylum Bacillota/Firmicutes, Class Bacilli, Order Bacillales, Family Bacillaceae, Genus Bacillus.

• Pathophysiological Background:

  • Bacillus cereus is a ubiquitous, Gram-positive, facultatively anaerobic, endospore-forming rod frequently isolated from soil, agricultural produce, crops, and carbohydrate-rich cooked foods (e.g., fried rice, pasta).

  • Emetic Type Food Poisoning Reference Organism: This specialized strain genetically harbors the complete cereulide synthetase operon, enabling it to actively synthesize and release the high-potency emetic toxin (Cereulide) into food matrices or in vitro culture media.

• Core Genetic Framework (cesB Gene Positive):

  • Non-Ribosomal Peptide Synthetase (NRPS) Biosynthesis: Cereulide is not synthesized via standard ribosomal translation. Instead, it is assembled by a massive non-ribosomal peptide synthetase complex encoded by the ces operon located on a large endogenous virulence plasmid (e.g., pBCE9801 or pCERE01).

  • cesB Gene Target: The cesB locus encodes a crucial enzymatic subunit within this NRPS machinery. Verified via polymerase chain reaction (PCR) and whole-genome profiling, this strain is strictly positive for the cesB gene. This sequence serves as the international definitive diagnostic biomarker for distinguishing highly toxic emetic strains from common enterotoxigenic (diarrheal type) B. cereus isolates in food safety screenings.

• Biosafety Level: Biosafety Level 2 (BSL-2). Due to its capacity to produce a robust, highly stable gastrointestinal and mitochondrial toxin, all procedures involving viable vegetative cells or resilient endospores must be strictly executed within a certified BSL-2/P2 containment facility utilizing certified biosafety enclosures, under rigorous adherence to personal protective parameters to prevent accidental ingestion or aerosol inhalation.

II Physiochemical Resistance of Toxin & Clinical Toxicology

1. Extreme Resilience Profiles of Emetic Toxin (Cereulide):

   • Exceptional Thermal Stability: Cereulide is structurally arranged as a highly hydrophobic cyclic dodecadepsipeptide. This cyclic architecture allows the toxin to withstand autoclaving temperatures of 121°C for up to 30 minutes without losing active structural integrity. Standard household cooking, boiling, or microwaving profiles are entirely insufficient to inactivate it.

   • Acid and Protease Resistance: It remains functional across a wide pH spectrum (pH 2.0 to 9.0) and demonstrates complete immunity against degradation by major digestive proteases, including pepsin and trypsin. Upon ingestion, it transits the gastric acid barrier fully intact.

2. Clinical Toxicological Mode of Action: Cereulide acts as a highly potent ionophore with a strong selective affinity for potassium ions ($K^+$). Upon reaching the intestinal tract, it binds specifically to 5-HT3 (serotonin) receptors on the vagus nerve, sending direct emetic signals to the central nervous system to prompt violent, acute vomiting episodes within 1 to 5 hours post-ingestion. Furthermore, it causes severe mitochondrial swelling, membrane potential collapse, and microvesicular steatosis, posing a risk of acute fulminant liver failure.

III Morphological Attributes and Cultivation Conditions

• Morphology:

  • Microscopic Appearance: Large, Gram-positive rectangular rods (measuring 3–5 $\mu$m in length by 1–1.2 $\mu$m in width) with square ends, arranging predominantly in short or long chain configurations. Under conditions of nutrient depletion or aging, cells form an elliptical, highly resistant endospore positioned centrally or sub-terminally, which does not cause the sporangium to swell.

  • Macroscopic Colonial Traits: On standard Nutrient Agar plates, colonies appear large (2–5 mm in diameter), dull grayish-white, exhibiting a characteristic rough "ground-glass" topography with irregular, fimbriate, or arborescent extensions. On selective MYP (Mannitol-Egg Yolk-Polymyxin) agar arrays, it presents as pink-to-purple colonies due to its inability to ferment mannitol, encircled by a dense white precipitation zone triggered by intensive lecithinase activity. It exhibits strong $\beta$-hemolysis zones on sheep blood agar.

• Growth Mode and Kinetics: Facultative anaerobe, growing with optimal velocity under aerobic parameters. The generation doubling interval spans approximately 20 to 30 minutes during peak log-phase acceleration.

• Standard Complete Media Specifications:

  • BioVector® Standard Nutrient Broth / Nutrient Agar matrices.

  • Brain Heart Infusion (BHI) broth or agar.

  • Identification/Screening Matrix:MYP Agar Formulations.

• Physical Incubation Parameters: Regulated strictly within a thermal window of 30°C to 37°C under aerobic or facultatively anaerobic parameters.Note: To stimulate peak expression and optimization of the Cereulide toxin, international analytical protocols highly recommend running liquid cultures under robust agitation at 30°C.

IV Thawing, Subculturing, and Long-Term Preservation Protocols

1. Cryovial Revival and Seeding Routine:

   • Inside a BSL-2 cabinet, rapidly transfer the cryovial from ultra-low storage parameters into a 37°C water bath with gentle agitation until thawed.

   • Siphon a 100 $\mu$l aliquot of the suspension and streak directly onto fresh BHI agar or sheep blood agar plates using standard quadrant streaking patterns to isolate single colonies. Incubate at 30°C–37°C for 18–24 hours to obtain fully developed colonies.

2. Monitoring Spore and Toxin Production Intervals:

   • The NRPS expression machinery starts heavy transcription as cells transition into the stationary phase. For emetic toxin harvesting protocols, cultivate the broth continuously for 24 to 48 hours.

   • For routine passaging, introduce a 1:100 split ratio into fresh BHI broth. To prevent spontaneous curing of the large virulence plasmid hosting the ces operon,avoid continuous, long-term liquid subculturing. It is highly recommended to cryopreserve the lineage within 3 to 5 passages post-revival.

3. Long-Term Cryopreservation Methods:

   • Glycerol Stocks: Combine late log-phase broth cultures with sterile preservation glycerol to lock in a final concentration matrix of 20% to 25% $\text{v/v}$, before storing aliquots at -80°C.

   • Spore Suspension Preparation: Capitalizing on the long-term resilience of its endospores, the strain can be induced to complete sporulation, harvested in sterile distilled water, and stored as a spore suspension at 4°C, or processed via vacuum lyophilization for secure multi-decade preservation.

V Strategic Research Applications

1. Validation of Food Safety Diagnostics and Metrology Systems: Deployed as the definitive global standard positive reference control strain for food hygiene compliance validation. It is leveraged to assess the specific sensitivity, specificity, and detection limits of real-time PCR assays, Loop-Mediated Isothermal Amplification (LAMP) kits, and automated Whole-Genome Sequencing (WGS) pipeline matrices targeting the cesB or cesA virulence genes in dairy products and cooked rice commodities.

2. Deciphering Non-Ribosomal Peptide Synthetase (NRPS) Biosynthesis Pathways: The molecular architecture of the multi-modular enzyme complex responsible for synthesizing the cyclic configuration of cereulide represents a major target in structural biology. This strain serves as a live model for mapping enzymatic domain structures, substrate recognition profiles, and rational bio-engineering of novel macrocyclic peptide templates.

3. Mitochondrial Toxicity and In Vitro Toxicological Prototyping: Purified native emetic toxin derived from this positive reference strain is widely utilized to establish in vitro toxicity screening platforms across human cell lines (e.g., HepG2 hepatocyte lines, Caco-2 enterocyte networks), tracking specific signaling loops involved in transmembrane potential breakdown and cellular apoptosis.