Isolation, identification and ecology of Ewingella americana (the causal agent of internal stipe necrosis) from cultivated mushrooms in New Zealand

Internal stipe necrosis of cultivated mushrooms ( Agaricus bisporus) is caused by the bacterium Ewingella americana, a member of the Enterobacteriaceae. Recently, E. americana was isolated from healthy cultivated button mushrooms grown in New Zealand and from mushrooms showing mild stipe browning. E. americana forms a part of the endogenous bacterial population present in mushroom sporocarp tissues. This is the first time that E. americana has been isolated from a non-human host in New Zealand. Previously, the bacterium has been found associated with human blood and sputum samples. Presented here are the details of the identification methods used in providing evidence that this strain of E. americana has the capacity to induce typical symptoms of internal stipe necrosis. Ecological studies give a possible explanation as to why E. americana has previously been unnoticed in New Zealand.