BioVector? 蠟樣芽胞桿菌（產(chǎn)嘔吐毒素/攜帶 cesB 基因標(biāo)準(zhǔn)株）

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

第一部分 中文說明

一 產(chǎn)品基本信息與遺傳學(xué)背景

• 細(xì)菌名稱：Bacillus cereus (產(chǎn)嘔吐毒素型標(biāo)準(zhǔn)參考株)

• 分類學(xué)地位：厚壁菌門 (Bacillota/Firmicutes)、芽胞桿菌綱 (Bacilli)、芽胞桿菌目 (Bacillales)、芽胞桿菌科 (Bacillaceae)、芽胞桿菌屬 (Bacillus)。

• 主要病理生理學(xué)背景：

  • 蠟樣芽胞桿菌是一種廣泛存在于自然界（土壤、農(nóng)產(chǎn)品、谷物及熟米飯）中的革蘭氏陽性、兼性厭氧、能形成抗逆性極強(qiáng)內(nèi)生芽胞的兼性致病菌。

  • 嘔吐型（Emetic type）食物中毒核心菌株：該特定菌株在遺傳學(xué)上攜帶完整的嘔吐毒素合成酶基因簇，能夠在食品（尤其是富含淀粉的米飯、面條）基質(zhì)中或體外培養(yǎng)期間，大量分泌高致病性的嘔吐毒素（Cereulide）。

• 核心遺傳學(xué)標(biāo)志（cesB 基因陽性）：

  • 非核糖體肽合成酶系統(tǒng)（NRPS）：嘔吐毒素（Cereulide）并非由常規(guī)核糖體直接翻譯生成，而是由位于大質(zhì)粒（如 pBCE9801 或 pCERE01）上的 ces 操縱子 所編碼的非核糖體肽合成酶（Non-ribosomal peptide synthetase, NRPS）復(fù)合體催化組裝。

  • cesB 基因靶點(diǎn)：cesB 基因編碼該酶學(xué)復(fù)合體中的核心關(guān)鍵亞基。本菌株經(jīng)聚合酶鏈?zhǔn)椒磻?yīng)（PCR）及基因組測序驗(yàn)證，cesB 基因呈現(xiàn)絕對陽性。該位點(diǎn)是國際上進(jìn)行食品衛(wèi)生微生物學(xué)檢驗(yàn)、鑒別產(chǎn)嘔吐毒素株與普通腸毒素（腹瀉型）株最權(quán)威的特異性分子診斷靶標(biāo)。

• 生物安全級別：2級（BSL-2）。本菌株具有產(chǎn)生強(qiáng)效胃腸道毒素的能力，涉及活菌及內(nèi)生芽胞的所有實(shí)驗(yàn)操作、培養(yǎng)和分裝，必須在二級生物安全實(shí)驗(yàn)室（BSL-2/P2）的生物安全柜內(nèi)進(jìn)行，并嚴(yán)格預(yù)防氣溶膠吸入或意外攝入。

二 毒素理化特性與臨床危害

1. 嘔吐毒素（Cereulide）的極端理化抗性：

   • 超強(qiáng)耐熱性：Cereulide 是一種環(huán)狀十二去肽（Cyclic dodecadepsipeptide）。由于其特殊的環(huán)狀疏水性骨架，該毒素能承受 121 攝氏度高壓滅菌（Autoclaving）30 分鐘而不被破壞。常規(guī)的烹飪、煮沸、加熱食品無法使其失活。

   • 耐酸與耐蛋白酶性：該毒素在 pH 2.0 至 pH 9.0 范圍內(nèi)保持完全穩(wěn)定，且能抵抗胃蛋白酶（Pepsin）和胰蛋白酶（Trypsin）的降解。在被人類誤食后，能以完整的活性分子結(jié)構(gòu)順利通過胃酸屏障。

2. 臨床毒理學(xué)機(jī)制：Cereulide 是一種強(qiáng)效的離子載體（Ionophore），對鉀離子（$K^+$）具有高度選擇性親和力。進(jìn)入腸道后，它能特異性識別并結(jié)合迷走神經(jīng)（Vagus nerve）上的 5-HT3（五羥色胺）受體，向嘔吐中樞發(fā)送化學(xué)信號，從而在攝入后數(shù)小時(shí)內(nèi)（通常 1-5 小時(shí)內(nèi)）引發(fā)劇烈的急性嘔吐癥狀。此外，它能破壞宿主細(xì)胞線粒體跨膜電位，引發(fā)微泡樣脂肪變性并展現(xiàn)嚴(yán)重的肝毒性（Hepatotoxicity）。

三 形態(tài)學(xué)與培養(yǎng)環(huán)境

• 形態(tài)學(xué)特征：

  • 顯微形態(tài)：革蘭氏陽性大桿菌（通常長 3-5 $\mu$m，寬 1-1.2 $\mu$m），兩端相對平齊，常呈短鏈或長鏈狀排列。在培養(yǎng)后期、營養(yǎng)匱乏或暴露于空氣中時(shí)，會(huì)在細(xì)胞中央或亞端自發(fā)形成橢圓形的內(nèi)生芽胞（Endospore），芽胞不使菌體膨大。

  • 菌落形態(tài)：在標(biāo)準(zhǔn)營養(yǎng)瓊脂平板上，菌落較大（直徑 2-5 mm），呈現(xiàn)微白或灰白色、表面粗糙不平如毛玻璃狀（Ground-glass appearance）、邊緣常有不規(guī)則的偽足狀擴(kuò)散。在 MYP 選擇性瓊脂平板上，因不發(fā)酵甘露醇而使菌落呈現(xiàn)粉紅色，且其外圍環(huán)繞著由卵磷脂酶（Lecithinase）分解卵磷脂產(chǎn)生的強(qiáng)烈白色沉淀環(huán)。在羊血瓊脂上展現(xiàn)強(qiáng)烈的 $\beta$-溶血（$\beta$-hemolysis）。

• 生長模式與增殖動(dòng)力學(xué)：兼性厭氧，但在有氧條件下生長更為迅速。群體倍增時(shí)間在對數(shù)生長期約為 20 約 30 分鐘。

• 標(biāo)準(zhǔn)完全培養(yǎng)基配方：

  • BioVector? 標(biāo)準(zhǔn)營養(yǎng)肉湯（Nutrient Broth）/ 營養(yǎng)瓊脂。

  • 腦心浸液培養(yǎng)基（BHI 液體/固體）。

  • 鑒定/篩選專用：MYP（甘露醇-卵磷脂-多粘菌素）瓊脂培養(yǎng)基。

• 物理培養(yǎng)參數(shù)：30攝氏度至37攝氏度恒溫、空氣有氧環(huán)境或兼性厭氧環(huán)境。注：為了誘導(dǎo)最高產(chǎn)量的 Cereulide 毒素表達(dá)，國際標(biāo)準(zhǔn)方案通常推薦在 30 攝氏度下進(jìn)行震蕩培養(yǎng)。

四 菌株復(fù)蘇、常規(guī)傳代與保存標(biāo)準(zhǔn)操作

1. 凍存管復(fù)蘇與劃線（Revival Protocol）：

   • 在 BSL-2 級安全柜內(nèi)，快速將凍存管從超低溫環(huán)境中移出，置于 37 攝氏度水浴中搖晃解凍。

   • 吸取 100 $\mu$l 菌液，接種至預(yù)熱的 BHI 肉湯或直接在營養(yǎng)瓊脂/血平板上進(jìn)行三區(qū)或四區(qū)劃線以獲得單菌落。30°C-37°C 培養(yǎng) 18-24 小時(shí)即可長出豐滿菌落。

2. 芽胞與毒素產(chǎn)生的監(jiān)控傳代：

   • 本菌株在液體培養(yǎng)中進(jìn)入平臺期（Stationary phase）后，NRPS 系統(tǒng)開始高負(fù)荷工作合成 Cereulide。若需提取毒素，建議培養(yǎng) 24 到 48 小時(shí)。

   • 傳代時(shí)按 1比100 的比例轉(zhuǎn)接新肉湯。為防止菌株在頻繁常規(guī)傳代中發(fā)生大質(zhì)粒（攜帶 ces 基因簇）的自發(fā)丟失或突變沉默，嚴(yán)禁連續(xù)無限制液體傳代。通常建議在復(fù)蘇后 3-5 代內(nèi)即進(jìn)行冷凍保藏。

3. 長期菌種保藏：

   • 甘油凍存：取對數(shù)晚期的液體培養(yǎng)物，與無菌甘油混合，使甘油終濃度達(dá)到 20% 至 25%，分裝后于 -80 攝氏度保存。

   • 芽胞保藏法：由于其能形成極耐干燥的內(nèi)生芽胞，可將其在無菌蒸餾水中誘導(dǎo)完全形成芽胞后，以芽胞懸液的形式置于 4 攝氏度常規(guī)冰箱中保存，或進(jìn)行真空冷凍干燥（Lyophilization）長期鎖定保藏。

五 核心科研應(yīng)用方向

1. 食品安全與微生物學(xué)檢驗(yàn)技術(shù)驗(yàn)證（Diagnostic Validation）：作為法定的產(chǎn)嘔吐毒素蠟樣芽胞桿菌標(biāo)準(zhǔn)陽性對照菌株。用于驗(yàn)證各種食品、乳制品、快餐米飯基質(zhì)中蠟樣芽胞桿菌分子檢測標(biāo)準(zhǔn)（如針對 cesB、cesA 基因的 Real-time PCR、LAMP 環(huán)介導(dǎo) isothermal 擴(kuò)增技術(shù)及全自動(dòng)全基因組質(zhì)檢體系）的特異性與靈敏度。

2. 非核糖體肽合成酶（NRPS）與新型抗生素藥理學(xué)研究：Cereulide 的環(huán)狀肽鏈組裝結(jié)構(gòu)對生物化學(xué)界具有極高的研究價(jià)值。本菌株是深入解析 NRPS 多酶復(fù)合體空間構(gòu)象、底物識別機(jī)制及定向化學(xué)修飾的天然生物學(xué)催化反應(yīng)活體模型。

3. 線粒體毒性與靶向細(xì)胞毒理學(xué)屏障評估：利用該菌株產(chǎn)生的內(nèi)源性 Cereulide 毒素，提取后用于建立各種哺乳動(dòng)物體外細(xì)胞模型（如 HepG2 肝癌細(xì)胞、Caco-2 腸上皮細(xì)胞）的線粒體損傷、跨膜電位崩潰及急性肝衰竭毒理學(xué)信號通路篩查。

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.