Prevalence of Ewingella americana in retail fresh cultivated mushrooms (Agaricus bisporus, Lentinula edodes and Pleurotus ostreatus) in Zaragoza (Spain).

The prevalence and mycopathogenic potential of Enterobacteriaceae (especially Ewingella americana) in cultivated mushrooms were studied. A total of 95 samples of Agaricus bisporus, Lentinula edodes and Pleurotus ostreatus were analyzed to quantify the Enterobacteriaceae and to identify the species isolated. The host pathogenicity test was used to verify their mycopathogenic potential. The genus Pseudomonas was also quantified, since it is the predominant bacterial group in cultivated mushrooms. The counts of Enterobacteriaceae ranged from 2.88 to 3.66 log(10) CFU g(-1), which was significantly lower than the counts of Pseudomonas spp. (4.52-7.80 log(10) CFU g(-1)). Among the 151 strains of Enterobacteriaceae isolated, 112 strains (74.2%) were classified as Ewingella americana by the API 20 E system. Other species identified were Enterobacter amnigenus bgp. 1, Enterobacter cloacae, Klebsiella terrigena, Pantoea spp. bgp. 2 and Serratia rubidaea. Only E. americana showed mycopathogenic effect, causing a browning lesion and necrosis in the center of the A. bisporus stipe. This is the first report of the isolation of E. americana from healthy cultivated button mushroom as well as from other species of cultivated mushrooms different from A. bisporus.