Laboratory of Microbiology and Biotechnology of Foods, Department of Food Science and Technology, Agricultural University of Athens, Iera Odos 75, Athens GR-118 55, Greece.
Int J Food Microbiol. 2013 Feb 15;161(3):197-202. doi: 10.1016/j.ijfoodmicro.2012.12.017. Epub 2013 Jan 2.
The aim of this study was to evaluate the survival of Salmonella, Escherichia coli O157:H7, Listeria monocytogenes, and Staphylococcus aureus on natural black olives during aerobic storage without brine and to conclude about the safety of this fermented food. Fermented black olives (pH 3.95; NaCl 6.02%) were artificially inoculated with 4 strains of Salmonella enterica ser. Enteritidis, 4 strains of S. enterica ser. Typhimurium, 3 strains of E. coli O157:H7, 3 strains of L. monocytogenes, and 3 strains of S. aureus either in monoculture or in mixed culture by submerging the fruits in a solution containing ca. 7.0 log CFU/ml of each target pathogen. The olives were subsequently stored aerobically at 4 and 20 °C, and the pathogens were recovered on selective media for a time period of 15 days. Enrichment was employed to define the presence/absence of the target pathogens when their counts were below the detection limit of direct plating. Results showed that the population of all pathogens presented a rapid decline within the first 2 days of storage depending on storage temperature, type of inoculation (monoculture or cocktail) and strain. Storage at 4 °C seemed to prolong the survival of certain strains of pathogens as compared to 20 °C by ca. 1 day. Enrichment revealed the absence (<1CFU/25 g) of Salmonella and E. coli O157:H7 from olive samples with the exception of all strains of L. monocytogenes at 4 °C and one strain at 20 °C that were detected by selective enrichment until the end of storage. The results of this study indicate that natural black olives are not a favorable environment to support the growth of the investigated pathogens after post-processing contamination provided that the olives have been subjected to proper fermentation process.
本研究旨在评估未经盐水腌制的有氧贮藏条件下，天然黑橄榄中沙门氏菌、大肠杆菌 O157:H7、李斯特菌和金黄色葡萄球菌的存活情况，并以此推断这种发酵食品的安全性。发酵黑橄榄（pH3.95；NaCl6.02%）被人工接种 4 株肠炎沙门氏菌血清型肠炎亚种、4 株鼠伤寒沙门氏菌血清型鼠伤寒亚种、3 株大肠杆菌 O157:H7、3 株李斯特菌和 3 株金黄色葡萄球菌，分别采用单种或混合培养的方式，即将果实浸泡在含约 7.0 log CFU/ml 目标病原菌的溶液中。随后，将橄榄在 4 和 20°C 下进行有氧贮藏，并在选择性培养基上回收病原菌，时间为 15 天。当目标病原菌的计数低于直接平板计数的检测限时，采用富集法来确定其存在/不存在情况。结果表明，所有病原菌的数量在贮藏的最初 2 天内迅速下降，具体取决于贮藏温度、接种类型（单种或混合）和菌株。与 20°C 相比，4°C 似乎可以延长某些菌株的存活时间，延长时间约为 1 天。富集法显示，除了 4°C 下的所有李斯特菌菌株和 20°C 下的 1 株李斯特菌菌株外，黑橄榄样本中均未检出沙门氏菌和大肠杆菌 O157:H7（<1CFU/25 g），直至贮藏结束时，通过选择性富集法才检测到这些菌株。本研究结果表明，在经过适当发酵处理的情况下，天然黑橄榄不是支持这些病原菌在后加工污染后生长的有利环境。
