LPS-targeting galectins-3 and -4 on blood group B positive E. coli O86: new aspects on its microbicidal action and association with antibiotics

Gal-3 and Gal-4 are mammalian lectins that recognize glycans containing β-galactosides. Both galectins recognize LPS-blood group B on Escherichia coli O86 (B+ E. coli), but only Gal-4 rapidly kills this microorganism. Our aim was to contribute to better understanding the Gal-4 killing mechanism on B+ E. coli. After 20 minutes of Gal-4 (5 µM and 1 µM) treatment, B+ E. coli viability was reduced to ~5% and ~40%, respectively. Anti-B (40 µM) inhibited the effect of Gal-4 (1 µM). Atomic force microscopy evaluation showed loss of membrane integrity and blebs induction for Gal-4 (5 µM) but not for Gal-3 (5 µM) treatments. Surprisingly, a high concentration of Gal-3 (40 µM) reduced B+ E. coli viability to ~50% and Gal-3 (5, 10 and 20 µM) concomitant addition with a non-lethal concentration of Gal-4 (0.2 µM) potentiated its bactericidal effects. Additionally, Gal-4 and Gal-3 potentiated Polymyxin-B bactericidal activity in B+ E. coli.