Department of Veterinary Microbiology and Pathology, 402 Bustad Hall, Washington State University Pullman, Pullman, WA 99164-7040, USA.
Appl Environ Microbiol. 2011 Apr;77(7):2345-51. doi: 10.1128/AEM.03150-09. Epub 2011 Feb 4.
We describe a novel proximity-dependent inhibition phenotype of Escherichia coli that is expressed when strains are cocultured in defined minimal media. When cocultures of "inhibitor" and "target" strains approached a transition between logarithmic and stationary growth, target strain populations rapidly declined >4 log CFU per ml over a 2-h period. Inhibited strains were not affected by exposure to conditioned media from inhibitor and target strain cocultures or when the inhibitor and target strains were incubated in shared media but physically separated by a 0.4-μm-pore-size membrane. There was no evidence of lytic phage or extracellular bacteriocin involvement, unless the latter was only present at effective concentrations within immediate proximity of the inhibited cells. The inhibitory activity observed in this study was effective against a diversity of E. coli strains, including enterohemorrhagic E. coli serotype O157:H7, enterotoxigenic E. coli expressing F5 (K99) and F4 (K88) fimbriae, multidrug-resistant E. coli, and commensal E. coli. The decline in counts of target strains in coculture averaged 4.8 log CFU/ml (95% confidence interval, 4.0 to 5.5) compared to their monoculture counts. Coculture of two inhibitor strains showed mutual immunity to inhibition. These results suggest that proximity-dependent inhibition can be used by bacteria to gain a numerical advantage when populations are entering stationary phase, thus setting the stage for a competitive advantage when growth conditions improve.
我们描述了一种新型的大肠杆菌邻近依赖性抑制表型，这种表型在菌株在定义明确的最小培养基中共培养时表达。当“抑制剂”和“靶标”菌株的共培养物接近对数生长期和静止期生长的过渡时，靶标菌株的种群在 2 小时内迅速下降了>4 个对数 CFU/ml。受抑制的菌株不会受到来自抑制剂和靶标菌株共培养物的条件培养基的影响，也不会受到抑制剂和靶标菌株在共享培养基中孵育但通过 0.4-μm 孔径大小的膜物理分离的影响。没有证据表明溶菌噬菌体或细胞外细菌素参与其中，除非后者仅以有效浓度存在于受抑制细胞的邻近区域。本研究中观察到的抑制活性对多种大肠杆菌菌株有效，包括肠出血性大肠杆菌血清型 O157:H7、表达 F5（K99）和 F4（K88）菌毛的肠毒性大肠杆菌、多药耐药大肠杆菌和共生大肠杆菌。与单培养物相比，共培养物中靶标菌株的数量平均下降了 4.8 个对数 CFU/ml（95%置信区间为 4.0 到 5.5）。两种抑制剂菌株的共培养显示出相互免疫抑制。这些结果表明，当种群进入静止期时，邻近依赖性抑制可以被细菌用来获得数量上的优势，从而为生长条件改善时的竞争优势奠定基础。
