NEUTRALIZING ANTIBODIES AGAINST SHIGA-LIKE TOXINS FROM ESCHERICHIA-COLI IN COLOSTRA AND SERA OF CATTLE

Previous or present infection with Shiga-like toxin producing E. coli (SLTEC) was detected by an indirect neutralization assay of antibody t iter. Bovine colostra and sera blocked the cytotoxic effects of Shiga- like toxin on Vero cell monolayers. SLT neutralizing antibodies were p resent in 84.0% (189/225) of the colostrum samples from randomly chose n cows in Bavaria, Germany. While all of the colostra with neutralizin g activity reacted with SLT-I, only 14.7% neutralized both SLT-I and I I. Approximately 93.0% (37/40) of sera from heifers had SLT neutralizi ng activity. To quantify the neutralizing antibodies, colostra were te sted in the Vero cell assay for their capability to reduce the 50% cyt otoxic dose (CD50) of SLT standards, where the neutralizing units/ml ( nu/ml) equal the log(10) of CD50 reduction. Almost half of reactive co lostra (48.7%) reduced the CD50 of the SLT-I standard by 10(4) to 10(5 ) (4-5 nu/ml). Higher reactivity (5-7 nu/ml) was found in 46.5% of pos itive colostra. The remaining colostra samples had over 7 nu/ml. To de termine if the colostra were blocking receptors for SLT on Vero cells, cells were preincubated with colostra, and SLT was later added. No ne utralizing activity was detected, indicating the reactivity of colostr a was directed against SLT. When the colostra were subjected to ammoni um sulphate precipitation and DEAE anion exchange chromatography, high levels of neutralizing activity were found in the IgG(1) containing f ractions. Colostrum fractions were tested for SLT-I binding antibodies in a capture ELISA, based on the binding of SLT-I to the toxin recept or analogue P-1-glycoprotein. Only fractions from colostra with over 5 nu/ml were reactive in this assay, indicating the ELISA was less sens itive than the Vero cell assay. The results support the theory that SL TEC exposure of cows in Germany is more widespread than expected from epidemiological studies based on bacterial isolation. This possibly in dicates a higher risk of human SLTEC infection via beef and milk produ cts.