There are some news articles about existing backdoors on CAs for use by Security Agencies, but the trustworthiness of these news must be checked,
New NSA Leak Shows MITM Attacks Against Major Internet Services
There is no evidence that shows the trusted CAs use their certificates for MITM attacks, because sooner or later will be identified or disclosed and that company will be convicted quickly. So, it seems unlikely that a trusted CA does it.
There are several ways users can detect MITM attacks, even when the certificate seems to be signed by a trusted CA. There are, for example, Firefox plugins available from Certificate Patrol as well as Perspectives that can help users by alerting on “new” certificates that have not been seen before.
Network Forensic Analysis of SSL MITM Attacks