Serum resistance of Escherichia coli strains causing urinary tract infection and diarrhoea in relation to alpha haemolysin production and O type.

A total of 46 alpha-hemolytic and 40 non-hemolytic clinical isolates of Escherichia coli were collected from pediatric patients with urinary tract infection and diarrhoea. Of 39 (84.7%) alpha-hemolytic strains and 27 (67.5%) non-hemolytic strains were resistant to 10% serum and there was no significant difference between urinary and stool isolates. On the contrary when 100% serum was used, 22 (47.8%) of the alpha-hemolytic and 7 (17.5%) of the non-hemolytic strains were resistant (p<0.01). and significantly greater resistance was found in urinary tract infection than from the stool samples (47% versus 24%, p<0.01). Serum resistance was higher in serogroups O6, O18 and O75. Production of alpha-hemolysin was more frequent in serogrops O2, O6, O8, O18 and O75. Thus, the resistance to human serum can determine clinical significance of Escherichia coli from different sources and alpha-hemolysin contributes to the virulence of Escherichia coli in initiation and perpetuation of clinical infection.