Miller Fátima A, Brandão Teresa R S, Teixeira Paula, Silva Cristina L M
Universidade Católica Portuguesa, Escola Superior de Biotecnologia, Rua Dr. António Bernardino de Almeida, 4200-072 Porto, Portugal.
Int J Food Microbiol. 2006 Dec 1;112(3):261-5. doi: 10.1016/j.ijfoodmicro.2006.04.013. Epub 2006 Jun 19.
Listeria innocua was subjected to thermal inactivation and the extent of heat-injured cells was quantified. Cultures were heated in liquid medium for different times, using temperatures in the range of 52.5 to 65.0 degrees C, and plated on Tryptic Soy Agar with 0.6% yeast extract (TSAYE) used as non-selective medium and on TSAYE plus 5% NaCl (TSAYE+NaCl) and Palcam agar with selective supplement (Palcam agar) as selective media. The difference observed in counts in non-selective and in selective media gave an indication of cell injury during the heat treatment. D- and z- values were calculated for all conditions considered. For each temperature, D-values obtained using non-selective recovery procedures were higher than the ones obtained using the two selective media. When comparing the selective media, it can be concluded that Palcam agar allowed recovery and growth of thermally injured cells and so it was less inhibitor than TSAYE+NaCl. Another important result was the influence of temperature on the degree of cellular injury. As temperature increases, the degree of heat-injured cells also increases, and consequently concern has to be taken with the temperature and the counting medium used in food processing studies. The results of this work clearly demonstrated that selective media used for Listeria monocytogenes enumeration/detection might not be suitable for the recovery of heat-injured cells, which can dangerously underestimate the presence of this foodborne pathogen.
无害李斯特菌接受了热灭活处理，并对热损伤细胞的程度进行了量化。将培养物在液体培养基中于52.5至65.0摄氏度的温度范围内加热不同时间，然后接种在添加0.6%酵母提取物的胰蛋白胨大豆琼脂（TSAYE）上作为非选择性培养基，以及接种在TSAYE加5%氯化钠（TSAYE+NaCl）和添加选择性补充剂的Palcam琼脂（Palcam琼脂）上作为选择性培养基。在非选择性培养基和选择性培养基上观察到的菌落计数差异表明了热处理过程中的细胞损伤情况。计算了所有考虑条件下的D值和z值。对于每个温度，使用非选择性复苏程序获得的D值高于使用两种选择性培养基获得的D值。比较选择性培养基时，可以得出结论，Palcam琼脂能够使热损伤细胞复苏和生长，因此其抑制作用比TSAYE+NaCl小。另一个重要结果是温度对细胞损伤程度的影响。随着温度升高，热损伤细胞的程度也增加，因此在食品加工研究中必须关注温度和所用的计数培养基。这项工作的结果清楚地表明，用于单核细胞增生李斯特菌计数/检测的选择性培养基可能不适用于热损伤细胞的复苏，这可能会危险地低估这种食源性病原体的存在。
