[Detection of intracellular multiplication of Legionella pneumophila in protozoa by antigen quantification using ELISA].

Legionellae and Acanthamoeba castellanii were co-cultivated (37 degrees C, 2 days) to study the intracellular multiplication of Legionella pneumophila strains (n = 37) derived from different sources. The quantification of intracellular growth was observed by both traditional counting of colony forming units and antigen detection by ELISA using polyclonal and monoclonal antibodies. There was a good correlation between the two methods. Depending on detection antibodies chosen, the correlation coefficient ranged from 0.86 to 0.91. Clinical and water isolates associated with legionellosis exhibited significant higher multiplication rates than water isolates without association with legionelloses. Utilization of antigen estimation by ELISA proved to have the following advantages: (1) Availability of results within a few hours after lysis of cells, and (2) simple handling of co-cultivation owing to omission of killing non-ingested bacteria and elutriate the antibiotic. Therefore, the procedure described is recommended for virulence screening, particularly for large number of colonies of Legionella-positive water samples or genetically manipulated legionellae.