Antimicrobial activity of Satureja montana L. essential oil against Clostridium perfringens type A inoculated in mortadella-type sausages formulated with different levels of sodium nitrite

This research evaluated the antimicrobial effect of the winter savory (Satureja montana L.) essential oil (EO) against Clostridium perfringens type A (ATCC 3624) inoculated in mortadella-type sausages formulated with different levels of sodium nitrite (NaNO₂: 0 ppm, 100 ppm and 200 ppm) in addition to EO at concentrations of 0.0%, 0.78%, 1.56% and 3.125% stored at 25 °C for 30 days. The EO extracted by hydrodistillation and analyzed by gas chromatography-mass spectrometry (CG-MS) was tested in vitro using an agar well diffusion method for determination of minimum inhibitory concentration (MIC) on C. perfringens. According to compositional analysis of the winter savory EO, 26 chemical compounds were identified, and the major constituents were thymol (28.99%), p-cymene (12.00%), linalool (11.00%) and carvacrol (10.71%). The results obtained showed that EO applied at a concentration of 1.56%, which was defined as the MIC, exhibited antimicrobial activity against C. perfringens in the in vitro assays, and the transmission electron microscopy (TEM) revealed structural damage and cell lysis of C. perfringens caused by EO treatment. A synergistic effect between NaNO₂ and EO was observed. In mortadella-type sausages formulated with 100 ppm of NaNO₂ and EO at all concentrations tested, the population of target microorganisms was reduced (p ≤ 0.05) compared to control samples during all storage period. This data suggests the potential combined use of savory EO and minimal amounts of the synthetic additive, NaNO₂ to control C. perfringens in mortadella, which goes according to current market trends, where consumers are requesting natural products.     

渗透压诱导表达重组Clostridium thermosulfurogenes β-淀粉酶基因

以热硫梭菌Clostridium thermosulfurogenes基因组为模板,PCR扩增出β-淀粉酶基因;将该基因克隆到pET-22b(+)载体上,转入大肠杆菌BL21-SI,采用NaCl形成的高渗透压诱导表达。研究了不同诱导条件对重组菌产β-淀粉酶的影响,结果以菌体密度达到OD600为0.6,诱导剂NaCl浓度为0.6 mol/L,诱导温度为35℃最佳。重组菌以LBON为培养基分批发酵时,由于营养限制,菌体密度OD600仅为4.60,β-淀粉酶活力为118U/mL。采用pH-Stat分批补料发酵时,在菌体密度仅是分批发酵的2.35倍的条件下,得到6.12倍的产酶量,酶活力达722U/mL。重组β-淀粉酶70℃水解可溶性淀粉3h的麦芽糖转化率为62.2%,高于大麦β-淀粉酶的转化率。     

一起疑似产气荚膜梭菌腹泻暴发事件实验室检测分析

目的 分析一起疑似由产气荚膜梭菌导致腹泻暴发事件的实验室检测结果，为产气荚膜梭菌食物中毒实验室检测策略的改进奠定基础。方法 采集暴发事件中4例病例肛拭子样本，应用荧光PCR方法检测肛拭子及其增菌液中cpa基因与cpe基因。对肛拭子样本进行产气荚膜梭菌分离培养，对部分分离单菌落进行产气荚膜梭菌毒力基因检测和脉冲场凝胶电泳（PFGE）分子分型。结果 4例病例样本中均检测到cpa基因和cpe基因。从病例1样本中挑取并鉴定为产气荚膜梭菌的18个单菌落中获得1个cpe+菌落，构成比为5.56%（1/18）；从病例2样本中挑取并鉴定为产气荚膜梭菌的6个单菌落中获得1个cpe+菌落，构成比为16.7%（1/6）；病例3未分离到cpe+菌落，病例4未分离到产气荚膜梭菌。11株产气荚膜梭菌菌株包括A型和C型两种，包含5种PFGE带型，分离自病例1和病例2的cpe+阳性菌株PFGE带型一致。结论 本次暴发事件可能由产气荚膜梭菌导致，综合使用各种实验室检测方法可在产气荚膜梭菌诊断标准滞后的情况下协助暴发事件分析。     

Microbiological aspects and challenges of whey powders – I thermoduric,thermophilic and spore-forming bacteria

For dairy processors, spoilage and pathogenic spore-forming bacteria are key sources of concern, not only due to their ability to remain dormant in a desiccated state in powders and to survive heat treatments, but also their ability to form biofilms in the vegetative state that lead to contamination of foods. These include members of the genera Bacillus, Geobacillus, Anoxybacillus, Brevibacillus, Paenibacillus and Clostridium, many of which are associated with food poisoning and spoilage. Here, we review the common bacterial species that form spores in whey powders and their sources and provide insights into their risks and strategies to control them.     

北京市顺义区87名健康人中产气荚膜梭菌携带特征研究

目的调查北京市顺义区健康人群携带产气荚膜梭菌(Clostridium perfringens, Cp)的生物特征,研究分离菌株携带产气荚膜梭菌肠毒素(Clostridium perfringens enterotoxin,Cpe)、β2毒力基因情况以及Cp在人群中的分布特征,为Cp导致食源性疾病的判定提供健康对照组数据。方法对采集的87份健康体检者粪便开展Cp分离培养、平板计数和菌株cpe、β2毒力基因的聚合酶链式反应(PCR)检测,对检测结果进行统计分析。结果 87名健康人粪便中血平板分离培养后Cp检出率为64.37%(56/87);Cp的月份、性别、年龄分布差异无统计学意义(P0.05)。共有57份粪便标本平板计数结果大于最低检出限(10 CFU/g),最高定量值为4.12×10~6 CFU/g,均值为1.70×10~5 CFU/g,中位数为5.30×10~3 CFU/g,95%分位数为7.00×10~5 CFU/g。分离的56株Cp中,cpe毒力基因检出率为0.00%(0/56),β2毒力基因检出率为73.21%(41/56)。结论 87名健康人粪便中Cp检出率较高,且β2毒力基因携带率较高,Cp引起食源性疾病的原因需要更深度生物标志识别或定量数据分析进行研究。     

Synthesis of Muramyl-δ-Lactam in Spore Peptidoglycan of Clostridioides difficile

Clostridioides difficile is a spore-forming human pathogen responsible for significant morbidity and mortality. Infections by this pathogen ensue dysbiosis of the intestinal tract, which leads to germination of the spores. The process of spore formation requires a transition for the cell-wall peptidoglycan of the vegetative C. difficile to that of spores, which entails the formation of muramyl-δ-lactam. We describe a set of reactions for three recombinant C. difficile proteins, GerS, CwlD, and PdaA1, with the use of four synthetic peptidoglycan analogs. CwlD and PdaA1 excise the peptidoglycan stem peptide and the acetyl moiety of N-acetyl muramate, respectively. The reaction of CwlD is accelerated in the presence of GerS. With the use of a suitable substrate, we document that PdaA1 catalyzes a novel zinc-dependent transamidation/transpeptidation reaction, an unusual reaction that requires excision of the stem peptide as a pre-requisite.