Davies C M, Evison L M
Department of Civil Engineering, University of Newcastle upon Tyne, UK.
J Appl Bacteriol. 1991 Mar;70(3):265-74. doi: 10.1111/j.1365-2672.1991.tb02935.x.
Escherichia coli and some salmonellas were exposed in seawater and freshwater to natural sunlight, visible light of comparable intensity, and light containing a similar proportion of u.v. as natural sunlight but of a much lower intensity. Direct viable bacterial counts and culturable counts on selective and non-selective media were made at intervals. The rate of decrease in numbers of culturable bacteria was significantly faster in seawater than in freshwater when exposed to natural sunlight. No significant difference was found between the rates of decrease in numbers of culturable bacteria in seawater and those in freshwater when bacteria were exposed to light with a small u.v. component of similar intensity. The effect of salinity no loss of culturability is, therefore, more significant in the presence of u.v. radiation. Direct counts by the acridine orange direct viable count method decreased much more slowly than the culturable counts in seawater but comparably with culturable counts in freshwater in natural sunlight. Direct viable counts and culturable counts decreased at a similar rate in seawater and in freshwater in visible light. This may signify the evolution of enteric bacteria towards a viable but non-culturable form in seawater when exposed to natural sunlight. The presence of humic acids significantly reduced loss of culturability but only in low salinity conditions. Salinity appears to be an important factor influencing culturability in bacteria exposed to sunlight.
将大肠杆菌和一些沙门氏菌置于海水和淡水中，分别暴露于自然阳光、强度相当的可见光以及紫外线比例与自然阳光相似但强度低得多的光线下。每隔一段时间对选择性和非选择性培养基上的细菌直接活菌计数和可培养计数。当暴露于自然阳光时，海水中可培养细菌数量的减少速率明显快于淡水中。当细菌暴露于紫外线含量少但强度相似的光线下时，海水中和淡水中可培养细菌数量的减少速率没有显著差异。因此，在紫外线辐射存在的情况下，盐度对可培养性丧失的影响更为显著。在自然阳光照射下，通过吖啶橙直接活菌计数法进行的直接计数在海水中下降得比可培养计数慢得多，但在淡水中与可培养计数相当。在可见光下，海水中和淡水中的直接活菌计数和可培养计数以相似的速率下降。这可能表明肠道细菌在暴露于自然阳光时在海水中向活的但不可培养的形式演变。腐殖酸的存在显著减少了可培养性的丧失，但仅在低盐度条件下。盐度似乎是影响暴露于阳光下细菌可培养性的一个重要因素。
