Why wouldnt Mysql use index on the Primary query in a nested query

I have two tables: search_criteria and pricing.

There is an index on search_id column in search_criteria table and on pricing_id column in pricing table.

But running this nested query does not use index on search_criteria table.

explain 
select *  
from  search_criteria USE INDEX (idx_search_id) 
where  search_id in 
    (select search_id 
    from pricing
     where pricing_id = '009330be-d041-444f-a624-ca652f3f61ed');


+----+--------------------+---------------------+------+------------------------------+----------------+---------+-------+----------+-------------+
| id | select_type        | table               | type | possible_keys                | key            | key_len | ref   | rows     | Extra       |
+----+--------------------+---------------------+------+------------------------------+----------------+---------+-------+----------+-------------+
|  1 | PRIMARY            | search_criteria | ALL  | NULL                         | NULL           | NULL    | NULL  | 19582252 | Using where |
|  2 | DEPENDENT SUBQUERY | pricing      | ref  | idx_pricing_id,idx_search_id | idx_pricing_id | 36      | const |        1 | Using where |
+----+--------------------+---------------------+------+------------------------------+----------------+---------+-------+----------+-------------+

If I use this table without the nested query it uses the index

explain extended select *  from  search_criteria where  search_id in ('36afabcc-e896-48b6-ad0f-c683845d4a4f')

+----+-------------+---------------------+------+---------------+---------------+---------+-------+------+----------+-------------+
| id | select_type | table               | type | possible_keys | key           | key_len | ref   | rows | filtered | Extra       |
+----+-------------+---------------------+------+---------------+---------------+---------+-------+------+----------+-------------+
|  1 | SIMPLE      | search_criteria | ref  | idx_search_id | idx_search_id | 103     | const |    1 |   100.00 | Using where |

Why is this happening ?

MYSQL VARIABLES

+-------------------------+------------------------------+
| Variable_name           | Value                        |
+-------------------------+------------------------------+
| innodb_version          | 1.1.8                        |
| protocol_version        | 10                           |
| slave_type_conversions  |                              |
| version                 | 5.5.16-log                   |
| version_comment         | MySQL Community Server (GPL) |
| version_compile_machine | x86_64                       |
| version_compile_os      | linux2.6                     |
+-------------------------+------------------------------+