The story
On 15 July 1846, the UZB opened the lines from Pest to Waitzen (now Vac), Pest to Szolnok and Marchegg to Pressburg (now Bratislava).
The UZB was nationalised on 7 March 1850 and became the Imperial Royal Southeastern State Railway.
The lines from Pressburg to Waitzen and Cegléd via Félegyháza to Szeged begun by the HZB were completed by the SöStB in 1854.
On 1 January, 1855 the SöStB was privatised and became part of the StEG.
From Wikipedia’s article on Austrian Southeastern Railway, shared under CC BY-SA 4.0.3