Byappanahalli Muruleedhara N, Whitman Richard L, Shively Dawn A, Ting W T Evert, Tseng Charles C, Nevers Meredith B
United States Geological Survey, Great Lakes Science Center, Lake Michigan Ecological Research Station, 1100 North Mineral Springs Road, Porter, Indiana 46304, USA.
J Water Health. 2006 Sep;4(3):313-20. doi: 10.2166/wh.2006.518.
We studied the shoreward and seasonal distribution of E. coil and enterococci in sand (at the water table) at two southern Lake Michigan beaches-Dunbar and West Beach (in Indiana). Deep, backshore sand (approximately 20 m inland) was regularly sampled for 15 months during 2002-2003. E. coli counts were not significantly different in samples taken at 5-m intervals from 0-40 m inland (P = 0.25). Neither E. coli nor enterococci mean counts showed any correlation or differences between the two beaches studied. In laboratory experiments, E. coli readily grew in sand supplemented with lake plankton, suggesting that in situ E. coil growth may occur when temperature and natural organic sources are adequate. Of the 114 sand enterococci isolates tested, positive species identification was obtained for only 52 (46%), with E. faecium representing the most dominant species (92%). Genetic characterization by ribotyping revealed no distinct genotypic pattern (s) for E. coli, suggesting that the sand population was rather a mixture of numerous strains (genotypes). These findings indicate that E. coli and enterococci can occur and persist for extended periods in backshore sand at the groundwater table. Although this study was limited to two beaches of southern Lake Michigan, similar findings can be expected at other temperate freshwater beaches. The long-term persistence of these bacteria, perhaps independent of pollution events, complicates their use as indicator organisms. Further, backshore sand at the water table may act as a reservoir for these bacteria and potentially for human pathogens.
我们研究了密歇根湖南岸两个海滩——邓巴海滩和西海滩（位于印第安纳州）沙层（地下水位处）中大肠杆菌和肠球菌的向岸分布及季节性分布。在2002年至2003年期间，对距内陆约20米处的后滨深层沙地进行了为期15个月的定期采样。在内陆0至40米范围内，每隔5米采集的样本中大肠杆菌数量没有显著差异（P = 0.25）。在所研究的两个海滩中，大肠杆菌和肠球菌的平均数量均未显示出任何相关性或差异。在实验室实验中，大肠杆菌在添加了湖泊浮游生物的沙子中易于生长，这表明当温度和天然有机来源充足时，原位大肠杆菌可能会生长。在所测试的114株沙层肠球菌分离株中，仅52株（46%）获得了阳性菌种鉴定，其中粪肠球菌是最主要的菌种（92%）。通过核糖体分型进行的基因特征分析显示，大肠杆菌没有明显的基因型模式，这表明沙层中的菌群是多种菌株（基因型）的混合物。这些发现表明，大肠杆菌和肠球菌能够在地下水位处的后滨沙地中出现并长期存在。尽管这项研究仅限于密歇根湖南岸的两个海滩，但在其他温带淡水海滩可能会有类似的发现。这些细菌的长期存在，可能独立于污染事件，这使得它们作为指示生物的用途变得复杂。此外，地下水位处的后滨沙地可能是这些细菌以及潜在人类病原体的储存库。
