DEPENDENCE OF GROWTH, METABOLIC EXPRESSION, AND PATHOGENICITY OF NAEGLERIA-FOWLERI ON EXOGENOUS PORPHYRINS

The pathogenicity of the free-living amoeba Naegleria fowleri is modul ated by the composition of the medium used for cultivation. The consti tuents that determine the level of pathogenicity of N, fowleri, howeve r, have not been definitively established. The present study examined the effects of selected porphyrins on N. fowleri amoebae. The iron-con taining porphyrins, hemin or hematin, or the iron-free porphyrin, prot oporphyrin IX, were effective in supporting growth of N. fowleri in Cl ine medium lacking serum. Iron-binding proteins, including hemoglobin, could not satisfy the growth requirement of the amoebae for exogenous porphyrin. Expression of biological functions including azocaseinase activity, agglutination, mobility, complement susceptibility, and viru lence were altered by the composition of the growth medium. Amoebae gr own in Cline medium supplemented with either hemin or protoporphyrin I X displayed greater mobility and were more resistant to lysis by compl ement than those grown in Nelson medium. Similarly, amoebae grown in C line medium supplemented with either hemin or protoporphyrin IX were m ore pathogenic for B6C3F1 mice than those grown in Nelson medium. The addition of protoporphyrin IX to Nelson medium resulted in a modest in crease in mobility, resistance to complement lysis and virulence when compared to N. fowleri amoebae grown in Nelson medium without added po rphyrin.