Cómo recuperar SAMAccountName de Active Directory

Implementé un método que devuelve una lista de usuarios de Active Directory, me gustaría recuperar SAMAccountName como esteDomain\Administrator.

Este es el método que utilizo:

<code>public Collection<software_user> GetUsersFromAD(String adConnectionString)
{
    var users = new Collection<software_user>();

    using (var directoryEntry = new DirectoryEntry(adConnectionString))
    {
        var directorySearcher = new DirectorySearcher(directoryEntry);
        directorySearcher.Filter = "(&(objectClass=user))";
        var propertiesToLoad = new[] 
        { 
           "SAMAccountName", 
           "displayName", 
           "givenName", 
           "sn", 
           "mail", 
           "userAccountControl", 
           "objectSid" 
        };
        directorySearcher.PropertiesToLoad.AddRange(propertiesToLoad);

        foreach (SearchResult searchEntry in directorySearcher.FindAll())
        {
            var userEntry = searchEntry.GetDirectoryEntry();
            var ldapUser = new software_user();
            ldapUser.User_name = NullHandler.GetString(userEntry.Properties["displayName"].Value);

            if (string.IsNullOrEmpty(ldapUser.User_name))
               continue;
            ldapUser.User_name = NullHandler.GetString(userEntry.Properties["SAMAccountName"].Value);
            ldapUser.email = NullHandler.GetString(userEntry.Properties["mail"].Value);
            ldapUser.user_shortname = NullHandler.GetString(userEntry.Properties["givenName"].Value);
            var userAccountControl = (int)userEntry.Properties["userAccountControl"].Value;
            //ldapUser.IsActive = (userAccountControl & UF_ACCOUNTDISABLE) != UF_ACCOUNTDISABLE;
            var sid = new SecurityIdentifier((byte[])userEntry.Properties["objectSid"][0], 0).Value;
            //ldapUser.SId = sid;
            users.Add(ldapUser);
         }
    }
    return users;
}
</code>

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