Typescript module importing cases classes to be undefined

I have two files

app.js

///<reference path='mongodb.d.ts'/>
///<reference path='MyDatabase.ts'/>
module MyModule {
  import mongodb = module("mongodb");
  new mongodb.Server();
  var db = new MyDatabase(); // this will not work with first import line in Database.js, but work with second
}

MyDatabase.js

///<reference path='mongodb.d.ts'/>

import mongodb = module("mongodb"); // adding this line here, will cause that app.js will not see MyDatabase class

module MyModule {
   import mongodb = module("mongodb"); // adding this line this will cause that classes in this module cant use mongodb

   export class MyData {
      _id: mongodb.Id; // second import line will cause this to be compilation error, with first line it works
   }

   export class MyDatabase {
       public test(): void {
          //with second line i can access mongodb here
       }
   }
}

So question is, what am I missing? How should i go about importing mongodb?