single connection (or pool) with node.js to mongodb

I am a greenhorn in node.js. I need to get singleton DB object or connection pool in order to send multiple requests. Currently I'm using the following code:

var http = require('http'),
    io = require('/usr/local/lib/node_modules/socket.io'),

server = http.createServer(function(req, res) 
{
 res.writeHead(200, {'Content-Type': 'text/html'}); 
 res.end('<h1>Hello world</h1>'); 
});
server.listen(1337);


var socket = io.listen(server);


socket.on('connection', function(client)
{
    Init();
});

var dataBaseSource = 'mongodb://127.0.0.1:27017/GameDatabase';
var MongoClient = require('/usr/local/lib/node_modules/mongodb').MongoClient, format = require('util').format;
var dataBase;

function Init() 
{
    MongoClient.connect(dataBaseSource, function (error, db)
    {
        if (error) 
        {
            throw error;
        }
        else
        {
            dataBase = db;
        }
    });
}

After applicaton started console throws an error:

info  - socket.io started
   debug - client authorized
   info  - handshake authorized lhDeq1WSfXUpiIlb06fv
   debug - setting request GET /socket.io/1/websocket/lhDeq1WSfXUpiIlb06fv
   debug - set heartbeat interval for client lhDeq1WSfXUpiIlb06fv
   debug - client authorized for 
   debug - websocket writing 1::

/usr/local/lib/node_modules/mongodb/lib/mongodb/mongo_client.js:409
          throw err
                ^
Error: failed to connect to [127.0.0.1:27017]
    at null.<anonymous> (/usr/local/lib/node_modules/mongodb/lib/mongodb/connection/server.js:546:74)
    at emit (events.js:106:17)
    at null.<anonymous> (/usr/local/lib/node_modules/mongodb/lib/mongodb/connection/connection_pool.js:150:15)
    at emit (events.js:98:17)
    at Socket.<anonymous> (/usr/local/lib/node_modules/mongodb/lib/mongodb/connection/connection.js:533:10)
    at Socket.emit (events.js:95:17)
    at net.js:440:14
    at process._tickCallback (node.js:419:13)

Can you adjust my snapshot or provide an example.

Many thanks.