Killing of Escherichia coli strains from clinical specimens in human serum and polymorphonuclear leucocytes.

Hundred Escherichia coli strains were collected from extra-intestinal and intestinal disease for the present study. Of the strains isolated 49 (49%) were serum sensitive and 47 (47%) serum resistant. The remaining 4 (4%) strains showed intermediate sensitivity to the pooled normal human serum (PNHS). Strains isolated from faeces were significantly more sensitive than strains of extra-intestinal origin (P<0.01). Response of Escherichia coli strains to killing by polymorphonuclear leucocytes was seen in 50 isolates (50%). Faecal strains showed significantly more intracellular killing as compared to extra-intestinal strains (P<0.01). Thus, clinical significance of Escherichia coli strains from different sources can be determined by the resistance to the bactericidal effect of human serum and killing in polymorphonuclear leucocytes.