Dear aspirant,

 Various institutes that offer research opportunities are ICMR(Indian Council for Medical Research), CIMAP, CCMB(Centre for Cellular and Molecular Biology), St. John's Research institute. One can also join WHO. Many institutes like AIIMS, PGI, NIMHANS, Tata Institute of Fundamental Research, Mumbai (TIFR) offer a Ph.D. degree.

There are two ways to switch over to research  leading to Ph.D. for meritorious MBBS graduates.

The main option is to get admission to a three-year medical postgraduate programme (MD or MS). Thereafter one can go for medical research leading to Ph.D.

Besides this, a few research institutions admit meritorious medical graduates directly for research programmes.

Hope this helps.

Good luck