Most efficient Dictionary.ToString() with formatting?

What's the most efficient way to convert a Dictionary to a formatted string.

e.g.:

My method:

public string DictToString(Dictionary<string, string> items, string format){

    format = String.IsNullOrEmpty(format) ? "{0}='{1}' " : format;

    string itemString = "";
    foreach(var item in items){
        itemString = itemString + String.Format(format,item.Key,item.Value);
    }

    return itemString;
}

Is there a better/more concise/more efficient way?

Note: the Dictionary will have at most 10 items and I'm not committed to using it if another similar "key-value pair" object type exists

Also, since I'm returning strings anyhow, what would a generic version look like?