Virulence factors in Escherichia coli isolated from the blood of bacteremic neonatal calves

Twenty-five Escherichia coli isolates from the blood of critically ill bact eremic calves sampled in two separate studies on a calf-rearing farm housin g over 15,000 calves, in the San Joaquin Valley, California were studied. Isolates were characterized for O serogroups and fur pathotypes as determin ed by the presence of specific virulence factors including heat-labile ente rotoxin (LT), heat-stable enterotoxins a and b (STa, STb), verotoxins 1 and 2 (VT1, VT2), cytotoxic necrotizing factor (CNF), aerobactin. intimin Ear and P, F17 and CS31A fimbrial adhesins, and resistance to bactericidal effe cts of serum. These isolates constituted a heterogeneous group. However. isolates were mo stly aerobactin positive and often resistant to the bactericidal effects of serum. isolates of pathotypes O78 (n = 6). O119:CS31a (n = 3), and P posit ive but O non-typeable in = 3) were associated with a high mortality rate. The remaining isolates belonged to diverse pathotypes, often possessing the adhesins P, F17. CS31A and Eae but belonging to O serogroups other than O7 8 and O119. and were less frequently associated with mortality. Although no virulence factor common to all isolates was identified, the cap acity to use iron by the pretence of aerobactin which is important to the c apture of iron was a predominant factor. Moreover, certain pathotypes appea r to be associated with primary colisepticemia whereas other pathotypes may cause a bacteremia without necessarily leading to septicemia. (C) 2001 Els evier Science B.V. All rights reserved.