Catalyzes the transfer of sialic acid from the substrate CMP-N-acetylneuraminate to the terminal galactose residue of the lacto-N-neotetraose branch of surface lipooligosaccharide (LOS), forming an alpha-2,3-sialyl linkage. Thus, functions in the sialylation of LOS, which plays a role in the evasion of the host immune response by protecting N.gonorrhoeae from complement-mediated serum killing and from phagocytic killing by neutrophils, and which is critical for establishing infection. a beta-D-galactosyl-(1->4)-N-acetyl-beta-D-glucosaminyl derivative + CMP-N-acetyl-beta-neuraminate = an N-acetyl-alpha-neuraminyl-(2->3)-beta-D-galactosyl-(1->4)-N-acetyl-beta-D-glucosaminyl derivative + CMP + H(+) Bacterial outer membrane biogenesis; lipooligosaccharide biosynthesis. Homodimer. Is exclusively found in outer membrane preparations of the pathogen and is surface exposed. Inner membrane, periplasmic, cytoplasmic, and culture supernatant fractions are devoid of Lst. Cells lacking this gene do not express sialyltransferase activity onto LOS. Belongs to the glycosyltransferase 52 family.