Combined Effect of Sucrose and Heat Treatment Temperature on the Thermal Resistance of Staphylococcus aureus MF-31

The combined effect of sucrose and heat treatment temperature on the thermal resistance of Staphylococcus aureus MF-31 was examined by determining the relationships between the D value, temperature and each of three parameters (water activity, osmotic pressure and water binding energy) related to sucrose-water binding. The results showed that sucrose and temperature had a significant interactive effect on thermal resistance. More specifically, sucrose increased the heat resistance, and this effect was greater at lower temperatures than at higher temperatures. The effect of sucrose on the Z value was slight compared to its effect on the D value.     

Factors Affecting Catalase Activity in Staphylococcus aureus MF-31

Selected conditions were examined for their possible roles in the regulation of catalase activity in Staphylococcus aureus MF-31. The addition of the heme precursor 5-aminolevulinic acid resulted in increased catalase activity whereas the addition of exogenous hydrogen peroxide did not. Catalase activity decreased when S. aureus MF-31 cells were grown in media containing glucose. Cells grown in media with succinate or citrate substituted for glucose exhibited increased catalase activity. Cells grown in tryptic soy broth (0.5% NaCl) supplemented with NaCl showed increased catalase activity at salt concentrations up to 3%.     

Combined Effect of Water Activity, pH and Sub-optimal Temperature on Growth and Enterotoxin Production of Staphylococcus aureus

Staphylococcus aureus growth and enterotoxin production in relation to a, (0.99–0.87), pH (4.0–7.0) and temperature (8–30°C) was determined in Brain-heart-infusion broth with respectively NaCl and sucrose as humectants. Growth of S. aureus was not observed at a_w 0.85, at pH 4.3 or at 8°C. At 12°C no growth occurred at a, 0.90 or at a, 0.93 in combination with pH < 5.5. At a_w 0.96 no growth occurred at pH ≤ 4.9. Production of staphylococcal enterotoxin type A (SEA) occurred under nearly all conditions allowing growth. Production of SEB appears to be determined by a_w; at a_w 0.96 SEB was produced at all temperatures allowing growth, while at a, 0.93 SEB was hardly produced. Production of SEC and SEF was affected both by a_w and temperaure. Production of these toxins was rarely observed at a, 0.93. No SEC and SEF were produced at 12°C. Extrapolation of these findings to food is discussed.     

微波杀菌动力学及其影响因素的研究

本实验研究了不同温度条件下微波杀菌动力学D值;并且就食品体系中相应的pH和盐浓度对微波杀菌效果的影响作了探讨;同时对微波杀菌的机理进行了初步的研究。结果表明,相同温度下,微波功率越大,细菌的致死率越高;相同功率下,设定微波温度越高,其D值越小;当pH低于最适生长温度时,细菌对微波的敏感性增加,致死率提高;金黄色葡萄球菌(60℃)在20g/L的NaCl溶液中的致死率最大,而大肠杆菌(55℃)致死率随NaCl浓度增加而降低。微波处理后的金黄色葡萄球菌,经Flou-3/AM作用,其荧光值随温度的升高而增加,说明微波致金黄色葡萄球菌死亡的原因主要是改变了细胞膜的通透性。     

温度和接种量对搅打奶油中金黄色葡萄球菌生长及产肠毒素的影响

目的：研究金黄色葡萄球菌在搅打奶油中的生长以及产毒特性。方法：将不同浓度的初始接种量的产A型肠毒素金黄色葡萄球菌菌液接种到奶油中并搅打成型,低接种量控制在2～3（lg（CFU/g））,高接种量控制在4（lg（CFU/g））以上。定时测量不同贮存温度条件下奶油中的金黄色葡萄球菌的菌落总数以及产毒状况。结果：36 ℃条件下生长速率最快,其他温度条件下依次降低;低初接种量水平下,只有36 ℃条件下于27 h检测到产生毒素,其他温度条件下未检测到毒素产生;高初接种量水平条件下,在36 ℃于12 h、25 ℃于24 h、15 ℃于66 h检测到产生毒素,5 ℃条件下金黄色葡萄球菌既不生长,又不产毒。结论：随着温度的升高,金黄色葡萄球菌的生长速率随之升高,产肠毒素的时间也随之缩短,高初始接种量水平肠毒素产生的时间短于低初始接种量水平,肠毒素的产生时间为一般在对数期的中后期,此时金黄色葡萄球菌菌落总数≥6（lg（CFU/g））。     

Effects of Salts and Preheating Temperature of Brine on the Texture of Pickled Cucumbers

The effects of salt type and preheating temperature on the texture and quality of pickled cucumber were studied. Four types of salt were used: bay salt, purified salt, and 2 prepared salts, 1 containing the same amount of Ca²⁺ and Mg²⁺ as those of bay salt, and the other containing a 3‐fold higher concentration of Ca²⁺ and Mg²⁺ than bay salt. Two different temperatures were used for the salt solutions: 98 °C and 65 °C. All samples were fermented for 30 d at 25 °C. To evaluate the quality of the pickled cucumber with fermentation, the pH level, total acidity, alcohol insoluble solids, and mineral contents were analyzed. Texture and sensory evaluation as well as a microscopic observation were performed to observe the textural change of the pickled cucumber during fermentation. Pickled cucumbers with 98 °C of preheated brine showed better texture than the ones with 65 °C. The pickled cucumbers brined with prepared salt, 1 which had the same amount of Ca²⁺ and Mg²⁺ to bay salt, displayed the best result among the samples tested, in terms of sensory, textural, and physical properties.     

含肉桂醛猪肉糜中金黄色葡萄球菌热失活模型的建立

研究了添加不同质量分数的肉桂醛(0,0.1%,0.5%和1.0%)后猪肉糜中金黄色葡萄球菌的热失活规律。在肉糜中添加不同浓度的肉桂醛后进行热处理(60～75℃),用选择性培养基进行活细胞计数。结果表明,不同温度条件下,肉桂醛对金黄色葡萄球菌的热失活有明显的促进作用,随着温度和肉桂醛浓度的升高,金黄色葡萄球菌的耐热性逐渐降低。在75℃条件下,肉桂醛使肉糜中金黄色葡萄球菌完全热失活所需的时间从5 min减少到3 min。将试验结果进行动力学模型拟合,多项式拟合作为初级模型,能准确地描述添加肉桂醛后肉糜中金黄色葡萄球菌的热失活规律。在二级模型的拟合中,线性模型具有更高的拟合系数值。通过扫描电镜观察肉桂醛处理条件下金黄色葡萄球菌细胞的形态变化,表明肉桂醛可破坏金黄色葡萄球菌的细胞膜,从而导致胞质泄露而死亡。     

食用防腐剂对金黄色葡萄球菌生长参数的影响

为了明确食用防腐剂对金黄色葡萄球菌生长的影响,以乳酸链球菌素、亚硝酸钠、苯甲酸钠、山梨酸钾、焦亚硫酸钠、丙酸钙为实验对象,确定临界生长质量浓度后,分别研究各防腐剂作用下金黄色葡萄球菌的生长规律,并比较部分防腐剂作用于对数期和稳定期菌体时最大比生长速率(μmax)和迟滞期(Lag)的差异。结果表明:乳酸链球菌素具有较强的杀菌作用,培养前6h内菌数持续降低,由6.09(lg(CFU/mL))降至3.68(lg(CFU/mL)),15h左右才恢复到初始值。其余5种防腐剂均表现为抑菌作用,Baranyi方程分析各生长参数,结果显示μmax值均比无防腐剂的对照值低,其中焦亚硫酸钠作用后的μmax值最低为0.45h-1;Lag值则有升有降,其中山梨酸钾作用后的λ值最大为2.87h。将山梨酸钾和焦亚硫酸钠分别作用于对数期和稳定期菌体,发现作用于对数期菌体的μmax值均较稳定期菌体的低,尤其是焦亚硫酸钠作用时,对数期菌体的μmax值(0.45h-1)约为稳定期的(0.88h-1)一半,差异极显著(P<0.01);而两种防腐剂作用于对数期和稳定期菌体时λ值的差异均不显著。     

Model for Combined Effects of Temperature, pH and Water Activity on Thermal Inactivation of Bacillus cereus Spores

Initially, the effect of water activity (a_w) on heat resistance of Bacillus cereus spores (decimal reduction time) was investigated. A linear relationship was found between log D and 1-a_w. The combined effects of temperature (85-105°C), pH (4.5-6.5) and water activity (0.80-1) were then studied. A four parameter model was fitted to the data. This model appeared to be parsimonious with each parameter having a biological significance. Interactions between factors were observed but they accounted for <2.4% of the total variation and they were not taken into account by the model.     

食品添加剂对食源性金黄色葡萄球菌生物被膜的影响

从腐败食品分离筛选金黄色葡萄球菌,研究食品添加剂对金黄色葡萄球菌生物被膜的影响。按国标方法鉴定金黄色葡萄球菌。在不同质量浓度的防腐剂和乳化剂作用的情况下,用96孔板法检测金黄色葡萄球菌生物被膜形成情况。结果表明:在添加低质量浓度防腐剂山梨酸钾和苯甲酸钠后,金黄色葡萄球菌成膜能力受抑制,当两者质量浓度均≥0.4g/L时无成膜作用,且山梨酸钾抑制成膜趋势比苯甲酸钠明显;添加单甘酯后,质量浓度3g/L成膜率最低,而双甘酯质量浓度4g/L成膜率最低,两者比较,在质量浓度2～4g/L范围内单甘酯抑制成膜比双甘酯好;对于蔗糖酯类乳化剂,在质量浓度0.3～4g/L范围SE7和SE13都显现抑制成膜作用,而SE11整体出现成膜率下降趋势;非离子型表面活性剂吐温-80、Span-60对金黄色葡萄球菌成膜影响不同,与两者自身亲水亲油性相关。因此,这几类食品添加剂对金黄色葡萄球菌生物被膜具有一定抑制作用。     

非生物性因素对乳酸链球菌素抗菌活性的影响

为了研究乳酸链球菌素(nisin)的抗菌活性,采用金黄色葡萄球菌为实验培养菌种,分别研究了不同的酸溶液(乙酸、硝酸、盐酸、柠檬酸)、不同的金属离子(Zn2+、K+、Fe3+、Cu2+)、不同的离子强度(以Na+的离子强度:0、0.2、0.4、0.6、0.8mol/L)和不同的pH值(4.0、4.5、5.0、5.5、6.0)等非生物性因素对Nisin抗菌活性的影响。实验结果表明,乙酸对Nisin的抗菌活性的提高效果最佳;加入金属离子会提高Nisin的抗菌活性,其中K+的促进作用最强;离子强度的增加对Nisin的抗菌活性有很大的提高;Nisin在pH4.0的酸性环境中抗菌活性最好。     

Effects of growth at low water activity on the thermal tolerance of Staphylococcus aureus

Staphylococcus aureus is the most osmotolerant foodborne pathogen, and outbreaks of staphylococcal food poisoning are often linked to foods of reduced water activity (a(w)) values. While it is generally known that the thermal tolerance of microorganisms increases as the a(w) of the heating menstruum is decreased, surprisingly little research has examined the influence of growth medium a(w) on microbial thermal tolerance. In the present study, we show that growth of S. aureus at an a(w) value of 0.94 leads to the development of dramatically enhanced thermal tolerance (i.e., less than 1 log reduction after heating for 20 min at 60 degrees C). We further show that the identity of the accumulated compatible solute within cells grown at low a(w) can also influence the overall level of thermal tolerance of S. aureus. Finally, we provide evidence that the synthesis of general stress and/or osmotic stress proteins is required for the development of enhanced thermal tolerance of S. aureus at low a(w).     

金黄色葡萄球菌鉴定方法研究

目的 为了筛选出能够快速准确鉴定金黄色葡萄球菌的方法。方法 利用国标法、VITEK 2 Compact生化鉴定、16s rDNA序列分析和PCR鉴定等4种方法对酱卤肉制品中分离出的典型菌落进行鉴定。结果 国标法检测结果显示菌株为革兰氏阳性菌,血平板上有明显的透明溶血圈且血浆凝固酶试验结果为阳性,符合金黄色葡萄球菌判定标准。VITEK 2 Compact生化鉴定结果中不吻合的典型生化谱仅有1项（dMAL）,判定菌株为金黄色葡萄球菌（98%概率）,为极好的鉴定。16s rDNA序列比对分析及以邻接法构建的进化树均显示典型菌落为金黄色葡萄球菌。以耐热核酸酶基因（nuc）设计的引物能扩增出单一的清晰条带,能快速准确的识别出金黄色葡萄球菌。结论 4种方法均能准确鉴定出金黄色葡萄球菌,但耗时都比较长,通过改进实验方法,缩短DNA提取时间,PCR鉴定将表现出较大优势。     

培养条件对细脚拟青霉抑制金黄色葡萄球菌的影响

目的:研究不同培养条件对细脚拟青霉抑制金黄色葡萄球菌的影响,确立最佳摇瓶培养条件。方法:以抑菌圈直径大小为指标,采用单因素实验和L9(34)正交实验,对碳源、氮源、无机盐、培养时间、起始pH、摇瓶装液量以及接种量等培养条件进行研究。结果:细脚拟青霉产抑菌活性物质的最佳培养基为:4%蔗糖、2%酵母浸出粉、0.15%MgSO4.7H2O和0.025%KH2PO4;最佳摇瓶培养条件为:起始pH5.5～6.5,装液量30mL/100mL,接种量5%～7.5%,培养时间6d。结论:在此优化条件下,细脚拟青霉发酵液对金黄色葡萄球的抑菌圈直径可达23.5mm。      

高静压与温度协同加工对食品微生物的影响

高静压协同温度处理的方法已成为高压食品加工研究的重要方向。本研究着重讨论高静压协同温度处理对微生物生命活动的影响、致死微生物的机理及其动力学等，由此建议该技术研究应在充分利用其它有利因素的前提下，力求降低工作压力；高静压协同中温与高静压协同低温加工的对象也应有所不同。     

Effects of teat dipping on intramammary infections by staphylococci other than Staphylococcus aureus

Effects of intramammary infections in herds 1) either not teat dipping or postmilking teat dipping with either 2) linear dodecyl benzene sulfonic acid, 3) chlorhexidine, or 4) iodophor containing products were determined. Duplicate quarter foremilk samples were collected once from all lactating cows in 16 herds, four for each practice. Mean percentage of quarters infected with Staphylococcus species other than Staph. aureus was 11.0 in herds not teat dipping and 7.2 in herds teat dipping. Prevalence of Staphylococcus species intramammary infections in herds teat dipping with linear dodecyl benzene sulfonic acid was comparable to herds not teat dipping and greater than in herds using chlorhexidine and iodophor. The predominant Staphylococcus species in herds not teat dipping was Staph. epidermidis (37.1%). Staphylococcus hyicus constituted 48.5% of total Staphylococcus species intramammary infections in herds teat dipping and 12.4% in herds not teat dipping. Differences were not observed among SCC for quarters infected with different Staphylococcus species. Application of germicidal teat dips appeared to have selectively altered both prevalence and distribution of Staphylococcus species intramammary infections.     

培养条件对金黄色葡萄球菌-大肠杆菌混合生物被膜的影响

以常见食源性致病菌金黄色葡萄球菌和大肠杆菌为研究对象,采用微孔板法对混合生物被膜形成过程中的不同影响因素进行了研究。结果表明：在25 ℃或30 ℃条件下,采用质量分数0.8%的胰酶大豆肉汤（TSB）或0.8%的脑心浸出液（BHI）培养基培养时,生物被膜形成量较高;添加适量的葡萄糖、乳糖、麦芽糖和蔗糖可提高混合生物被膜形成能力;培养基中NaCl质量分数＞8%时,混合生物被膜的生长明显受到抑制。     

餐饮具表面的大肠杆菌和金黄色葡萄球菌活性研究

目的研究温度、湿度及餐饮具材质对餐饮具表面大肠杆菌和金黄色葡萄球菌活性的影响。方法分别在同一湿度50%、不同温度(25℃、37℃和60℃)下及同一温度25℃、不同湿度(20%、50%)条件下接种大肠杆菌和金黄色葡萄球菌到陶瓷餐饮具表面,在10、30、60和120 min后检测两种细菌的存活数量;在25℃、湿度50%的条件下分别接种两种细菌到陶瓷、木质、不锈钢和铜合金的餐饮具上,在10、30 min后检测两种细菌的存活数量。结果在同一湿度(50%),25℃时,两种细菌活性均较好;37℃时,存活的大肠杆菌数量比金黄色葡萄球菌低10~2 CFU/m L;60℃时,大肠杆菌10 min后失活,金黄色葡萄球菌60 min后失活。在25℃,湿度20%时,存活的大肠杆菌数量10 min后下降103 CFU/m L,120 min后失活;湿度50%时,存活的大肠杆菌数量120 min后仅下降10~2 CFU/m L。而金黄色葡萄球菌在两种湿度条件下,存活的细菌数量120 min后仅下降10 CFU/m L。在25℃、湿度50%的条件下接种10 min后,铜合金餐饮具上的两种细菌比其他材质的低10~2CFU/m L,30 min后,铜合金餐饮具上的两种细菌均失活。结论大肠杆菌对高温和干燥的耐受性比金黄色葡萄球菌弱。陶瓷、木质和不锈钢餐饮具对大肠杆菌和金黄色葡萄球菌均无抑菌性,而铜合金餐饮具对两种细菌均有抑菌性。     

Effects of milk on activity of antimicrobics against Staphylococcus aureus isolated from bovine udders

Addition of milk to Mueller-Hinton susceptibility test medium permitted measurement of milk effect on agar disc diffusion zone diameters obtained from Staphylococcus aureus herd isolates and stock strains. Milk reduced zone diameters for all antimicrobics tested when compared with zones obtained by standard methods. Antimicrobics most affected included novobiocin, streptomycin, gentamycin, tetracycline, and vancomycin. Growth curves of a reference strain of Staphylococcus aureus in Mueller-Hinton broth with and without milk indicated no effect on growth rate of the organism, suggesting the observed effect was due to the action of milk on the antimicrobics being tested. The described method offers a simple in vitro test for milk effects on antimicrobic activity.