Leaf age as a risk factor in contamination of lettuce with Escherichia coli O157:H7 and Salmonella enterica
Leaf age as a risk factor in contamination of lettuce with Escherichia coli O157:H7 and Salmonella enterica
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DOI：
10.1128/aem.02459-07
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发表时间：
2008-04-01
影响因子：
4.4
通讯作者：
Amundson, R.
中科院分区：
文献类型：
--
作者：
Brandl, M. T.;Amundson, R.
大肠杆菌O 157：H7感染的爆发越来越多地与绿叶蔬菜，特别是生菜有关。我们在这里提出的第一个证据表明，这种肠道病原体可以繁殖的生菜植物的叶子。种群数量的增加与E.大肠杆菌O 157：H7在年轻的莴苣植物叶际的范围从16- 100倍的条件下温暖的温度和自由水的存在下，叶龄变化显着。人口规模一直保持不变。10-在幼叶（内叶）上比在中间叶上高一倍。肠道沙门氏菌和天然细菌微生物区系的生长速率同样依赖于叶龄。这两种肠道病原体也实现了较高的人口规模的幼叶比从成熟的莴苣头收获的中间叶，这表明叶龄影响收获前以及采后殖民。从不同年龄的叶片表面收集的分泌物的元素分析表明，三叶分泌物中的总氮和碳，分别是2.9和1.5倍，比中间叶分泌物。这种趋势反映了叶片组织中的氮和碳含量。中部叶施硝酸铵促进了E. coliO 157：H7的生长，表明低氮限制了其在这些叶片上的生长。我们的研究结果表明，叶龄和氮含量有助于形成收获前和收获后生菜的细菌群落，年轻的生菜叶可能与E. coli O157：H7。
Outbreaks of Escherichia coli O157:H7 infections have been linked increasingly to leafy greens, particularly to lettuce. We present here the first evidence that this enteric pathogen can multiply on the leaves of romaine lettuce plants. The increases in population size of E. coli O157:H7 in the phyllosphere of young lettuce plants ranged from 16- to 100-fold under conditions of warm temperature and the presence of free water on the leaves and varied significantly with leaf age. The population size was consistently ca. 10-fold higher on the young (inner) leaves than on the middle leaves. The growth rates of Salmonella enterica and of the natural bacterial microflora were similarly leaf age dependent. Both enteric pathogens also achieved higher population sizes on young leaves than on middle leaves harvested from mature lettuce heads, suggesting that leaf age affects preharvest as well as postharvest colonization. Elemental analysis of the exudates collected from the surfaces of leaves of different ages revealed that young-leaf exudates were 2.9 and 1.5 times richer in total nitrogen and carbon, respectively, than middle-leaf exudates. This trend mirrored the nitrogen and carbon content of the leaf tissue. Application of ammonium nitrate, but not glucose, to middle leaves enhanced the growth of E. coli O157:H7 significantly, suggesting that low nitrogen limits its growth on these leaves. Our results indicate that leaf age and nitrogen content contribute to shaping the bacterial communities of preharvest and postharvest lettuce and that young lettuce leaves may be associated with a greater risk of contamination with E. coli O157:H7.