Caro Irma, García-Armesto María R
Research Centre for Food Science and Technology, Hidalgo State Autonomus University, Tulancingo Hgo. 43600, Mexico.
Int J Food Microbiol. 2007 May 30;116(3):410-3. doi: 10.1016/j.ijfoodmicro.2007.02.015. Epub 2007 Mar 6.
The aim of the present study was to investigate the occurrence of Escherichia coli O157:H7 and other Shiga toxin-producing E. coli (STEC) in 'Castellano' cheese, a non-cooked and hard or semi-hard Spanish cheese made from ewe's milk. A total of 83 raw milk cheese samples with different ripening times (2.5, 6 and 12 months) were taken at 30 cheese factories. Samples were examined for the presence of STEC using in the first stage the Association of Official Analytical Chemists (AOAC) official method number 997.11, and then, in the second stage, isolates were tested for virulence genes using genotypic (PCR) methods. Three STEC strains were detected in two samples (2.4%) of 'Castellano' cheese, one with 2.5 and the other one with 12 month-ripening period. From those STEC isolates, two were identified as E. coli O14 and the third presented an O-specific polysaccharide not-groupable serologically (ONG). PCR showed that all isolates were characterized by harbouring the Shiga toxin (stx) stx1 gene and by the absence of the genes for stx2, eaeA, and ehxA virulence factors. This study revealed the potential of STEC to survive in long-ripened-hard cheeses.
本研究的目的是调查“Castellano”奶酪中大肠杆菌O157:H7及其他产志贺毒素大肠杆菌（STEC）的存在情况，“Castellano”奶酪是一种未经烹饪的、用羊奶制成的硬质或半硬质西班牙奶酪。在30家奶酪工厂共采集了83份不同成熟时间（2.5个月、6个月和12个月）的生牛奶奶酪样本。首先使用美国官方分析化学师协会（AOAC）官方方法997.11检测样本中STEC的存在情况，然后在第二阶段，使用基因分型（PCR）方法检测分离株的毒力基因。在两份“Castellano”奶酪样本（2.4%）中检测到三株STEC菌株，一份成熟时间为2.5个月，另一份为12个月。从这些STEC分离株中，两株被鉴定为大肠杆菌O14，第三株呈现出一种血清学上不可分组的O特异性多糖（ONG）。PCR结果显示，所有分离株的特征是携带志贺毒素（stx）stx1基因，且不存在stx2、eaeA和ehxA毒力因子的基因。本研究揭示了STEC在长时间成熟的硬质奶酪中存活的可能性。
