Catalyzes the transfer of sialic acid from the substrate CMP-N-acetylneuraminate to the terminal galactose residue of the N-acetyllactosamine moiety of surface lipooligosaccharide (LOS). Thus, functions in the sialylation of LOS, which plays a role in the evasion of the host immune response. 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. Disruption of this gene results in persistence of sialylated glycoforms of lipooligosaccharide but a reduction in sialyl-N-acetyllactosamine-containing glycoforms. Belongs to the glycosyltransferase 52 family.