The Occurrence of Aeromonads in Activated Sludge: Isolation of Aeromonas sobria and its Possible Confusion with Escherichia coli

Strains of Aeromonas have been isolated in high numbers from several activated sludge samples. Immediately after isolation, some displayed only weak or negative oxidase activity, produced both acid and gas from lactose, formed 'metallic'colonies on Endo agar, and had IMViC reactions which were identical with those of Escherichia coli . Although such strains could have been readily confused with E. coli , further biochemical characterization showed that these belonged to the recently-described A. sobria . Nitrogenase activity was absent in all strains of both A. hydrophila and A. sobria . Almost all strains of both taxa were resistant to ampicillin and penicillin V and 67% of both were bete -hemolytic.