FIG. 3.

Effect of fluid dilution on microbicidal activity. Six strains of bacteria were subjected to a CFU microassay of undiluted, 1:1-diluted, and 1:2-diluted minimally manipulated nasal fluid from donor 4. The CFU counts of S. aureus (clinical isolate) (A), E. coli (B), and S. typhimurium (C) were little affected. The antimicrobial effects of nasal secretions on S. aureus (isolate from nasal carrier donor 24) (D), P. aeruginosa CF (E), and P. aeruginosa H103 (F) were decreased with increasing dilution. The effects of undiluted, 1:1-diluted, and 1:2-diluted secretions are represented by closed circles, open triangles, and closed squares, respectively. The input inoculum (closed triangles) is shown for each graph.