Actually anti-Jewish sentiment was probably invented by the Greeks around 2300 years ago. The most likely cause was competition. Both were colonizing traders with a tight knit ethnic community and belief in their own cultural superiority.

The Romans were originally somewhat positive on Jews (particularly since they were fighting the Greeks on many fronts), but the Jewish revolt in the first century (and the complete subjugation of the Greeks around a century before this), made Jews very unpopular in the Roman era. This Greco-Roman tradition was passed onto the Church and through the Church most of Europe.

Usury is often used as an explanation, but the feeling was there before the usury, and probably usury was used as an excuse.

Being traders though did not help. There has always been a long standing apathy towards traders.