TZW: DVGW-Technologiezentrum Wasser (German Water Center), Karlsruhe, Germany.
Appl Environ Microbiol. 2022 Jul 26;88(14):e0047122. doi: 10.1128/aem.00471-22. Epub 2022 Jul 11.
Surface waters are one of the main sources for drinking water production, and thus microbial contamination should be as minimal as possible. However, high concentrations of coliform bacteria were detected in reservoirs and lakes used for drinking water production during summer months due to autochthonous proliferation processes. Here, we present the genomic analyses of 17 strains of Enterobacter asburiae and spp. proliferating in reservoirs and lakes with special focus on the hygienic relevance, antibiotic resistance, and adaptations to the oligotrophic environments. The genomes contain neither genes for the type III secretion system nor cytotoxins or hemolysins, which are considered typical virulence factors. Examination of antibiotic resistance genes revealed mainly efflux pumps and β-lactamase class C () genes. Phenotypically, single isolates of Enterobacter asburiae showed resistance to fosfomycin and ceftazidime. The genome analyses further suggest adaptations to oligotrophic and changing environmental conditions in reservoirs and lakes, e.g., genes to cope with low nitrate and phosphate levels and the ability to utilize substances released by algae, like amino acids, chitin, alginate, rhamnose, and fucose. This leads to the hypothesis that the proliferation of the coliform bacteria could occur at the end of summer due to algae die-off. Certain strains of coliform bacteria have been shown to proliferate in the oligotrophic water of drinking water reservoirs and lakes, reaching values above 10 per 100 mL. Such high concentrations challenge drinking water treatment, and occasionally the respective coliform bacteria have been detected in the treated drinking water. Thus, the question of their hygienic relevance is of high importance for water suppliers and authorities. Our genomic analyses suggest that the strains are not hygienically relevant, as typical virulence factors are absent and antibiotic resistance genes in the genomes most likely are of natural origin. Furthermore, their presence in the water is not related to fecal contamination. The proliferation in reservoirs and lakes during stable summer stratification is an autochthonic process of certain E. asburiae and strains that are well adapted to the surrounding oligotrophic environment.
地表水体是饮用水生产的主要来源之一，因此微生物污染应尽可能低。然而，由于自生源增殖过程，夏季用于饮用水生产的水库和湖泊中的大肠菌群浓度很高。在这里，我们介绍了在水库和湖泊中增殖的 17 株阴沟肠杆菌和泛菌的基因组分析，特别关注其卫生相关性、抗生素耐药性和对贫营养环境的适应。这些基因组既不包含 III 型分泌系统基因，也不包含细胞毒素或溶血素基因，这些基因被认为是典型的毒力因子。抗生素耐药基因的检测主要发现了外排泵和β-内酰胺酶 C 类（）基因。表型上，阴沟肠杆菌的单个分离株对磷霉素和头孢他啶表现出耐药性。基因组分析还进一步表明，这些细菌适应水库和湖泊中贫营养和不断变化的环境条件，例如，适应低硝酸盐和磷酸盐水平的基因，以及利用藻类释放的物质（如氨基酸、壳聚糖、藻酸盐、鼠李糖和岩藻糖）的能力。这导致了这样的假设，即由于藻类死亡，大肠菌群的增殖可能在夏末发生。某些大肠菌群已被证明在贫营养饮用水水库和湖泊的水中增殖，达到每 100 毫升超过 10 个的水平。如此高的浓度给饮用水处理带来了挑战，偶尔在处理后的饮用水中也能检测到相应的大肠菌群。因此，它们的卫生相关性问题对供水商和当局来说非常重要。我们的基因组分析表明，这些菌株在卫生上并不相关，因为缺乏典型的毒力因子，并且基因组中的抗生素耐药基因很可能是自然起源的。此外，它们在水中的存在与粪便污染无关。在稳定的夏季分层期间，在水库和湖泊中的增殖是某些阴沟肠杆菌和泛菌的自生源过程，它们很好地适应了周围的贫营养环境。
