Mongodb plugins to be included in a java app

Hey guys,
I have a transformation using Pentaho 5.1 (CE) and the job executed via spoon works. The transformation takes data from CSV like format and sends it to Mongodb.
Now I have webapp, via which I wanna run this job. I have included kettle-core (5.1.preview.506), kettle-engine(5.1.preview.506) for sure. That did not work. I then incuded all the jars under plugins/pentaho-mongodb-plugin. I am still getting this error

Missing plugins found while loading a transformation
Step : MongoDbOutput

Any ideas as to what plugin am I missing