Production of enterotoxin A and thermonuclease by Staphylococcus aureus in legumes

Growth, enterotoxin A (SEA) and thermonuclease (TNase) production of S. aureus (Strains CP 7 and FRI 722) was determined in media produced from the following heat or irradiation sterilized legumes: peas, black beans, mung beans, adzuki beans and soybeans. Media containing the five legumes alone or in combination with Brain Heart Infusion Broth (BHI) were tested. With the exception of heat-sterilized black beans and adzuki beans, S. aureus growth was excellent in all media with cell counts after 48 h (25 °C) exceeding 10⁸ cfu/ml. In black beans and adzuki beans cell counts were 1–2 log-cycles lower. Enterotoxin A was produced in amounts of 33 to 72 ng/ml in BHI after 48 h. Almost no toxin was produced in the four different beans following heat or irradiation treatment; in peas the toxin concentration reached 14 to 15 ng/ml. In the medium prepared from irradiated soybeans and BHI the final toxin concentration was about the same as in BHI alone. In all the other media consisting of a combination of legumes with BHI toxin concentrations were there to four times higher than in BHI alone. Production of thermonuclease showed variation and did not always correlate with enterotoxin production.     

Growth of Staphylococcus aureus and synthesis of enterotoxins in home-made yoghurt

Staphylococcus aureus strains FRI-100, S6, FRI-137 and FRI 472 were inoculated into milk to study growth and enterotoxin production in home-made yogurts. The yogurt used as starter was progressively weakened by successive inoculations (up to four) in milk to prepare other yogurts in order to study the ability of yogurt microflora to inhibit staphylococci. After elaboration, yogurts were stored at 4 degrees C, 22 degrees C, and 37 degrees C for a maximum of 21 days. Periodically, staphylococcal counts, pH and the production of enterotoxins A, B, C, and D were determined. Enterotoxins were only detected in the last batch. It was concluded that the inhibitory effect of the starter culture is not only due to the decrease of pH, but also to other factors.     

乳源性金黄色葡萄球菌肠毒素的检测与基因分型

通过检验各类乳制品收集了大量乳源性金葡菌菌株,应用酶联荧光免疫分析法对菌株的肠毒素进行检测分析,并进一步使用荧光定量PCR法对肠毒素基因进行分型.结果表明,乳源性金葡菌肠毒素的检出率与基因型分布均呈现一定显著特征,应用酶联荧光免疫分析法与荧光定量PCR法对肠毒素的检测结果总体无显著性差异.     

Effect of growth of a commercial starter culture on growth of Staphylococcus aureus and thermonuclease and enterotoxins (C1 and C2) production in broth cultures

Staphylococcus aureus strains FRI 137 (enterotoxin C1 producer) and FRI 361 and L 2 (enterotoxin C2 producers) were grown alone and in the presence of a mixed commercial starter culture (Streptococcus lactis, Streptococcus cremoris and Streptococcus lactis subsp. diacetylactis). Lactic acid bacteria had a slight inhibitory effect on S. aureus population and only during the late stages of growth. In contrast, enterotoxin synthesis was strongly inhibited, inhibition at 18 h being 89% (FRI 137), 80% (FRI 361) and 69% (L 2). Enterotoxin C1 was produced and accumulated during all phases of growth in pure and mixed culture, but associative growth resulted in reduction of enterotoxin C2 after 24-36 h. In mixed culture, high producers of thermonuclease (FRI 137 and L 2) showed an early decrease in enzyme activity followed by an increase, but it never reached levels attained in pure culture. Thermonuclease was detected whenever enterotoxin was detected, but production curves did not parallel each other.     

植物多酚对金黄色葡萄球菌耐热核酸酶抑制作用的研究

利 用 甲 苯 胺 蓝 法 观 察 了 不 同 植 物 多 酚 提 取 物 对 金 黄 色 葡 萄 球 菌 耐 热 核 酸 酶 活 性 的 抑 制 作 用 。结 果 表 明 ,在 一 定 的 浓 度 范 围 内 (0～2m g/m L),多 酚 提 取 物 均 对 金 黄 色 葡 萄 球 菌 耐 热 核 酸 酶 的 活 性 存 在 抑 制 作 用 , 其 中 苹 果 多 酚 和 茶 多 酚 的 抑 制 效 果 最 佳 , 而 温 度 、pH 变 化 对 多 酚 提 取 物 抑 制 耐 热 核 酸 酶 的 活 性 无 明 显 影 响 。     

The detection of enterotoxins and toxic shock syndrome toxin genes in Staphylococcus aureus by polymerase chain reaction

A simple polymerase chain reaction (PCR)-based procedure was developed for the detection of fragments of staphylococcal enterotoxins (SEs) SEA, SEB, SEC, SED, SEE, SEG, SEH, and SEI together with the toxic shock syndrome toxin (TSST-1) genes of Staphylococcus aureus. One hundred and twenty-nine cultures of S. aureus were selected, 39 of which were recovered from 38 suspected staphylococcal food-poisoning incidents. The method was reproducible, and 32 different toxin genotypes were recognized. The presence of SE genes was associated with S. aureus strains reacting with phages in group III, and the TSST-1 gene with phages in group I. There was a 96% agreement between the PCR results for detection of SEA-D and TSST-1 as compared with a commercial reverse passive latex agglutination assay for the detection of SEs from cultures grown in vitro. Enterotoxin gene fragments were detected in S. aureus cultures recovered from 32 of the 38 suspected staphylococcal food poisoning incidents, and of these, 17 were associated with SEE, SEG, SEH, and SEI in the absence of SEA-D. Simple PCR procedures were also developed for the detection of SE directly in spiked food samples, and this was most successfully achieved in mushroom soup and ham. Detection was less successful in three types of cheese and in cream. SEA or SEB were detected by enzyme-linked immunosorbent assay in three food samples (two of which were associated with food poisoning incidents) naturally heavily contaminated with S. aureus: the appropriate SEA or SEB gene fragments were detected directly in these three foods by PCR.     

Staphylococcus aureus Growth and Enterotoxin Production in Mushrooms

An enterotoxin A (SEA) producing strain of Staphylococcus aureus was inoculated onto mushrooms and incubated under simulated pre-and post-canning conditions. S. aureus grew and produced SEA in mushrooms incubated at 25°C in 10% to 20% NaCl. Growth and SEA production occurred when mushrooms were stored in plastic bags at 37°C, but not at 25°C. Mushrooms heat-processed at 121.1°C supported S. aureus growth and SEA production. No SEA was recovered from mushrooms inoculated with 1 or 10 ng SEA/g and heated at 121.1°C for 4.5 min. At higher inoculated SEA levels (100 and 1,000 ng/g), SEA was detectable after 10 min of heating. Staphylococcal enterotoxin could be present in canned mushrooms as a result of pre-, but more likely post-processing contamination.     

东莞市区肉菜市场熟肉制品中金黄色葡萄球菌污染溯源分析

目的优化熟肉制品中金黄色葡萄球菌的快速污染溯源分析方法。方法对熟肉制品及其加工环境进行采样,应用3MPerifilmTM金黄色葡萄球菌快速测试片对样品定量检测,对分离出的阳性菌株运用全自动微生物基因指纹鉴定系统RiboPrinter,结合EcoRI酶,对其进行分子溯源。结果 168个样品中分离出的7株菌共分为2种核糖体基因型,其中6株为同一核糖体条带类型,显示来源于相同克隆株。结论该方法全程只需3 d时间,快速稳定,可满足监管快速检测鉴定、分型溯源的要求。RiboPrinter的优势在于快速溯源,进行种的鉴定时应结合其他手段来进行确认。     

Assessment of mathematical models for predicting Staphylococcus aureus growth in cooked meat products

The growth of Staphylococcus aureus in commercially available vacuum-packaged cooked ham, turkey breast meat, and chicken breast meat stored at 2.3, 6.5, 10, 13.5, and 17.7 degrees C was studied. Growth rates observed in these food products were compared with those predicted on the basis of various growth models found in the literature and with those generated by the Pathogen Modeling Program and the Food MicroModel software using graphical and mathematical analysis for performance evaluation. In general, the models studied overestimated the growth of S. aureus. The Dengremont and Membré model most closely matched the observed behavior of S. aureus in ham and chicken breast meat, with bias factors of 1.56 and 1.09, respectively. The Eifert et al. model accurately described the growth of S. aureus in turkey breast meat, with a bias factor of 1.51. The remaining models provided safe predictions of the growth rate of S. aureus, but with poor accuracy. Predictive microbiology models have an immediate practical application in improving microbial food safety and quality and are very useful decision support tools, but they should not be used as the sole determinant of product safety.     

Staphylococcus aureus Growth and Toxin Production in Imitation Cheeses

The ability of eleven imitation (or substitute) cheeses to support the growth and toxin production of Staphylococcus aureus at 26°C was evaluated. All established enterotoxin serotypes were tested by inoculating suspensions of the requisite strains into 100-g samples of cheese (about 30 staphylococci/g). Water activity (a_w) of the cheese samples ranged from 0.942–0.973; pH values ranged from 5.33–6.14. Seven cheeses supported extensive growth of S. aureus; one or more serotypes of enterotoxin were produced in six cheeses. Enterotoxin in the cheese was detected in 4 days at 3 × 10⁶ staphylococci/g. However, the ability of some cheeses to support growth and toxin production of S. aureus could not be correlated with pH, a_w, or product formulation.     

2009—2020年北京市朝阳区113株食源性金黄色葡萄球菌耐甲氧西林和肠毒素/类肠毒素基因携带与分子分型分析

目的 了解北京市朝阳区2009—2020年113株食源性金黄色葡萄球菌甲氧西林耐药、肠毒素/类肠毒素基因携带和分子分型情况.方法 采用纸片扩散法进行头孢西丁药物敏感性实验,结合mecA基因扩增鉴定耐甲氧西林金黄色葡萄球菌(methicillin-resistant Staphylococcus aureus,MRSA)...     

Effect of pre-incubation conditions on growth and survival of Staphylococcus aureus in sliced cooked chicken breast

In this work, the effect of pre-incubation conditions (temperature: 10, 15, 37 °C; pH 5.5, 6.5 and water activity, a_w: 0.997, 0.960) was evaluated on the subsequent growth, survival and enterotoxin production (SE) of Staphylococcus aureus in cooked chicken breast incubated at 10 and 20 °C. Results showed the ability of S. aureus to survive at 10 °C when pre-incubated at low a_w (0.960) what could constitute a food risk if osmotic stressed cells of S. aureus which form biofilms survive on dried surfaces, and they are transferred to cooked meat products by cross-contamination. Regarding growth at 20 °C, cells pre-incubated at pH 5.5 and a_w 0.960 had a longer lag phase and a slower maximum growth rate. On the contrary, it was highlighted that pre-incubation at optimal conditions (37 °C/pH 6.5/a_w 0.997) produced a better adaptation and a faster growth in meat products what would lead to a higher SE production. These findings can support the adoption of management strategies and preventive measures in food industries leading to avoid growth and SE production in meat products.     

Effect of pre-incubation conditions on growth and survival of Staphylococcus aureus in sliced cooked chicken breast

In this work, the effect of pre-incubation conditions (temperature: 10, 15, 37°C; pH 5.5, 6.5 and water activity, a(w): 0.997, 0.960) was evaluated on the subsequent growth, survival and enterotoxin production (SE) of Staphylococcus aureus in cooked chicken breast incubated at 10 and 20°C. Results showed the ability of S. aureus to survive at 10°C when pre-incubated at low a(w) (0.960) what could constitute a food risk if osmotic stressed cells of S. aureus which form biofilms survive on dried surfaces, and they are transferred to cooked meat products by cross-contamination. Regarding growth at 20°C, cells pre-incubated at pH 5.5 and a(w) 0.960 had a longer lag phase and a slower maximum growth rate. On the contrary, it was highlighted that pre-incubation at optimal conditions (37°C/pH 6.5/a(w) 0.997) produced a better adaptation and a faster growth in meat products what would lead to a higher SE production. These findings can support the adoption of management strategies and preventive measures in food industries leading to avoid growth and SE production in meat products.     

Analysis of specific IgE antibodies to staphylococcal enterotoxins,total serum IgE and hemogramme in carriers of Staphylococcus aureus

In order to evaluate the relationship between nasal carriers of S. aureus and their history of allergic diseases, the total serum IgE titer, the hemogramme pattern, and the titers of specific IgE antibody to Staphylococcal enterotoxins A and B (SEA and SEB) and of specific IgG antibody to SEB were investigated in 98 trade school students. Fifteen (15.3%) of the 98 students were sensitized to SEA and/or SEB (40.0% to SEA and 93.3% to SEB). In this group, 11 subjects were S. aureus carriers (73.0%) and 12 had a history of allergic diseases (80.0%). Low levels of specific IgG antibody to SEB were identified from both S. aureus carriers and non-carriers. The S. aureus carriers had significantly higher levels of total IgE titer than the non-carriers and the individuals with a history of allergic diseases had significantly higher total IgE titer levels than those having no history of allergic diseases (p < 0.01). In the hemogramme patterns of S. aureus carriers, a significant positive correlation was observed between the total IgE antibodies and the eosinophil rate (p < 0.05), and a negative correlation (p < 0.001) was recognized between the neutrophil and the lymphocyte rates.     

多重PCR检测金黄色葡萄球菌六型肠毒素基因的研究

目的:为了建立一种简单、快速检测金黄色葡萄球菌六型肠毒素基因的多重PCR方法。方法:根据相关文献和Genebank报道的编码金黄色葡萄球菌肠毒素A、B、C、D、E、H的基因序列,选择合成了6对特异性引物,建立多重PCR体系,并对反应条件进行了优化。结果:6对引物能同时特异地扩增出120、478、257、319、170、375bp的目的片段,表明6对引物具有良好的特异性。结论:成功地建立了一种同时检测金黄色葡萄球菌六型肠毒素基因的多重PCR方法,在金黄色葡萄球菌肠毒素快速筛查方面具有良好的应用前景。     

Growth and Enterotoxin A Production by Staphylococcus aureus in Precooked Bacon in the Intermediate Moisture Range

Different water activities were obtained in precooked bacon by varying the frying time. Water activity (a_w) correlated best to the moisture, salt and protein content. When stored aerobically at 37°C, S. aureus A100 was capable of rapid growth in precooked bacon at a a_w of 0.84 or above, whereas at 20°C a a_w of 0.88 or higher was required. Under anaerobic storage at 37°C, growth was observed at a a_w of 0.90, and at 20°C slight growth was noted at a a_w of 0.91. The increase in the minimal a_w required for aerobic growth at the lower temperature was reflected in the differences between the isotherms obtained at 37°C and 20°C. The maximum populations achieved were higher for samples stored aerobically. Enterotoxin A (19–821 ng/g) was found in all aerobically stored samples where growth occurred. Enterotoxin A (38–109 ng/g) was also found in all anaerobically incubated samples where the population of S. aureus increased more than one logarithmic cycle.