False identification ofNeisseria gonorrhoeae in lower respiratory tract secretions—Result of mixed culture

Abstract

A Gram-negative diplococcus obtained by transtracheal aspiration was initially identified asNeisseria gonorrhoeae by three different laboratories. Further examination indicated that the culture did not containN. gonorrhoeae, but did contain a mixture ofBranhamella catarrhalis andHaemophilus influenzae. B. catarrhalis had provided growth factors that permittedH. influenzae to grow in cystine tryptophan peptone agar with resultant production of acid from glucose and misidentification of the diplococcus. When all isolates from respiratory secretions are fully identified, erroneous conclusions because of bacterial interactions could be avoided if tests were performed from pure culture plates rather than from the primary inoculum plate.