Completely agree to Jacque-Lucca, without further information no way to lend a helping hand. What kind of sample was streaked? However, I would put into consideration yeasts as an alternative.
Having performed quite a lot of field work, (i might be wrong but...) this resembles very much insect trails on agar. Is there a possibility that you would have invited a few ants or other very small insects in your lab or plates.