The exposure you describe was very low, but not no risk.  Most commercial sex workers do not have STIs (it's bad for business).  This is particularly true to high end CSWs for whom the added expense is expected to bring additional  benefits such as lower risk.  Further, oral STIs are less common than genital infections and even in the unlikely circumstance that your partner had an oral STI, most single exposures do not lead to infection.  The only STI acquired with any regularity from receipt of oral sex is gonorrhea.  There are no proven cases of HIV acquired from receipt of oral sex and chlamydia is extraordinarily uncommon.  Syphilis required direct lesion contact so unless you saw a lesion, I would not be concerned.  French kissing is suggested by some to lead to the occasional transfer of gonorrhea to a partner's throat but this too is quite uncommon.

Personally, I would probably not be worried however, if you want to be 100% sure there are no STIs acquired, a urine test and throat swab for gonorrhea and chlamydia any time more than 3-5 days after your encounter will provide definitive results.  

I hope this helps