Abstract

A Gram-negative bacillus isolated from the blood of a leukaemic patient with septicaemia was identified on the basis of common tests as Escherichia coli. However, the organism's antibiogram was atypical of E. coli and led to its re-examination and correct identification as Aeromonas hydrophila. A. hydrophila is sensitive to chloramphenicol and tetracycline, characteristics useful in differentiation from E. coli. A simple test differentiating this organism from the Enterobacteriaceae is the oxidase test. A. hydrophila is oxidase positive.