THE PAPG TIP ADHESIN OF P-FIMBRIAE PROTECTS ESCHERICHIA-COLI FROM NEUTROPHIL BACTERICIDAL ACTIVITY

Compared with Escherichia cell ORN103, a nonfimbriated K-12 strain, P- fimbriated E. coli ORN103/pPAP5 was found to interact poorly with huma n neutrophils and resist their bactericidal activity in vitro. PapG, t he Gal alpha(1-->4)Gal binding moiety located at the distal end of the P fimbrial filament, appeared to be responsible for this effect becau se an isogenic PapG(-) mutant, E. coli ORN103/pPAP24, exhibited bindin g interactions with neutrophils that were similar to nonfimbriated E. coli ORN103. Although no direct evidence is available, the poor adhere nce mediated by PapG could be related to its electrostatic properties because the isolated PapG protein had a pi of 5.2, which indicated tha t in the physiological pH range it possessed a net negative charge. An tibodies against PapG overcame the protective effect of PapG and marke dly enhanced the interactions of P-fimbriated E. coli with neutrophils resulting in bacterial killing. When a P-fimbriated clinical E. call strain or its isogenic PapG(-) derivative was injected into the perito neal cavities of mice, a similar number of neutrophils was recruited t o the site of injection. After 2 h, the number of P-fimbriated E. coli organisms that survived the neutrophil influx in the mouse peritoneum was approximately four times more than the number of surviving PapG(- ) bacteria. This result demonstrates that the PapG protein, which is s trategically located at the distal region of the P-fibrillum structure , protects E. coli from the bactericidal action of neutrophils.