Note - if using morelikethis, and your query is on a numeric ID, then you will not be able to access the moreLikeThis object in the results...
when q=id:3493 searching with mlt, result is:
SolrObject Object
(
...
[moreLikeThis] => SolrObject Object
(
[3493] => SolrObject Object
(
[numFound] => 6286
[start] => 0
[docs] => Array
(
....etc
the numeric object name (3493 above) is impossible to access
not by $response->moreLikeThis->{3493} nor $response->moreLikeThis->{'3493'}, nothing...
only way is to convert the moreLikeThis object into an array with:
$response_array = (array) $response->moreLikeThis;
then iterate the array as the array key is known.