Induction of Viable but Nonculturable Escherichia coli O157:H7 in the Phyllosphere of Lettuce: a Food Safety Risk Factor
Induction of Viable but Nonculturable Escherichia coli O157:H7 in the Phyllosphere of Lettuce: a Food Safety Risk Factor
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DOI：
10.1128/aem.05020-11
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发表时间：
2011-12-01
影响因子：
4.4
通讯作者：
Bach, Susan
中科院分区：
文献类型：
--
作者：
Dinu, Laura-Dorina;Bach, Susan
大肠杆菌O157：H7仍然是一种重要的人类病原体，并越来越多地与新鲜农产品，特别是绿叶蔬菜有关的食源性疾病有关。本工作的目的是研究低温条件下O157：H7大肠杆菌在生菜叶圈中的去向，并评估在这种胁迫条件下诱导的可存活但不可培养(VBNC)细胞的潜在危害。首先，我们研究了6株细菌在低温(4℃)水中长期储存后的存活情况，并选择了两株非培养反应不同的菌株构建了大肠杆菌O157：H7 Tn7gfp转化株，以定量评估植物表面是否存在人类病原体。在次适生长温度(16℃)下，两株大肠杆菌O157：H7在生菜叶片上都保持了可培养能力，但在更高的胁迫条件下(8℃)，细菌种群向VBNC状态进化。在不同接种量(10(9)和10(6)个大肠杆菌O157：H7细菌/g叶)的实验中，菌株BRMSID188在15d后失去可培养能力，ATCC 43895在7d内失去可培养能力时，无论接种量是多少，菌株依赖的非培养反应都更加明显。然而，高细胞密度接种组进入VBNC状态的细胞数量(约55%)低于低细胞密度接种组(约70%)。我们记录了3天内在含有4到5个对数(10)细胞的VBNC群体中存在Vero毒素，但没有检测到可培养细胞。这些发现表明，在生菜上诱导出了大肠杆菌O157：H7 VBNC细胞，这可能对食品安全有影响。
Escherichia coli O157:H7 continues to be an important human pathogen and has been increasingly linked to food-borne illness associated with fresh produce, particularly leafy greens. The aim of this work was to investigate the fate of E. coli O157:H7 on the phyllosphere of lettuce under low temperature and to evaluate the potential hazard of viable but nonculturable (VBNC) cells induced under such stressful conditions. First, we studied the survival of six bacterial strains following prolonged storage in water at low temperature (4 degrees C) and selected two strains with different nonculturable responses for the construction of E. coli O157:H7 Tn7gfp transformants in order to quantitatively assess the occurrence of human pathogens on the plant surface. Under a suboptimal growth temperature (16 degrees C), both E. coli O157:H7 strains maintained culturability on lettuce leaves, but under more stressful conditions (8 degrees C), the bacterial populations evolved toward the VBNC state. The strain-dependent nonculturable response was more evident in the experiments with different inoculum doses (10(9) and 10(6) E. coli O157:H7 bacteria per g of leaf) when strain BRMSID 188 lost culturability after 15 days and strain ATCC 43895 lost culturability within 7 days, regardless of the inoculum dose. However, the number of cells entering the VBNC state in high-cell-density inoculum (approximately 55%) was lower than in low-cell-density inoculum (approximately 70%). We recorded the presence of verotoxin for 3 days in samples that contained a VBNC population of 4 to 5 log(10) cells but did not detect culturable cells. These findings indicate that E. coli O157:H7 VBNC cells are induced on lettuce plants, and this may have implications regarding food safety.