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

A total of 46 α-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%) α-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 a-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 α-hemolysin was more frequent in serogrops O2, O6, O8, O18 and O75. Thus, the resistance to human serum can determine clinical significance of Escherichia colifrom different sources and α-hemolysin contributes to the virulence of Escherichia coli in initiation and perpetuation of clinical infection.