• E. faecalis-conditioned media from oxaliplatin treatment significantly promotes CRC cell growth and chemoresistance in vitro and in vivo.
• MOB3B down-regulation is a key mediator of E. faecalis-induced chemoresistance; overexpression enhances chemosensitivity.
• Lactate is elevated in E. faecalis-oxaliplatin CM and is responsible for MOB3B down-regulation and chemoresistance.
• Targeting lactate or restoring MOB3B expression may overcome CRC chemoresistance.