The antisera has been reported to cross-react with other organisms, including Bordetella pertussis , which will grow on media for isolation of Legionella . The laboratory workup for Legionella should always include a culture. Both respiratory specimens and blood cultures have been successful in the diagnosis of legionellosis. The organism has been isolated from liver, spleen, pericardial fluid, kidney, and a variety of wound specimens for diseases that are extrapulmonary in nature. Because at least one of the three most common isolates of Legionella, L. micdadei , is inhibited by cephalosporins, a medium without these antibiotics should be included in any culture.
Acid treatment works well and is used routinely in our laboratory.
A sheep blood agar plate is also inoculated with the acid treated mixture and dots of staphylococci are placed on the blood plate. The staphylococcal dots allow growth of Haemophilus . Care must be taken to avoid drying of plates or use of old media, which will inhibit the growth of the organism. If a slender gram-negative rod grows on the CYE and not on the blood plate, the colony should be immediately stained with Legionella species antisera to determine a presumptive diagnosis of Legionella . Because some cross-reactions occur, it is necessary to confirm that the organism does not grow on blood agar on subculture.