ABSTRACT Lactococcin A is a bacteriocin from Lactococcus lactis that permeabilizes the membrane of sensitive lactococcal cells and requires the presence of the membrane-bound components IIC and IID of the mannose phosphotransferase system (man-PTS). Recently, it was reported through cryo-electron microscopy analyses of man-PTS and several bacteriocins fused to a maltose-binding protein, including lactococcin A, that these bacteriocins create pores by inserting themselves between the Core and Vmotif domains of man-PTS. In our study, we obtained a dozen spontaneous mutants of L. lactis IL1403 resistant to lactococcin A. All but one of the mutants of IL1403 have mutations located in the genes encoding the IIC or IID proteins. These mutations also resulted in resistance to garvicin Q, a bacteriocin from Lactococcus garvieae with a broad inhibition spectrum and very little sequence homology to lactococcin A. Missense mutations were found in the sugar transport domain of man-PTS of bacteriocin-resistant IL1403 mutants, which also impeded the uptake of mannose. When lactococcin A, garvicin Q, or pediocin PA-1, an anti-listerial bacteriocin, were fused to a maltose-binding protein, we observed reduced or no antibacterial activity. Taken together, the precise mechanism of action of bacteriocins using the man-PTS remains to be fully understood. IMPORTANCE Many bacteriocins target the sugar transporter mannose phosphotransferase system (man-PTS) to exert their antibacterial activity. The elucidation in recent years of the structure of man-PTS has facilitated our understanding of how bacteriocins might interact with the receptor and which domains of the transporter are involved in bacteriocin resistance. Here, we show that missense mutations in the sugar-binding domain of the man-PTS not only impede the uptake of sugars but also prevent the antibacterial activity of the bacteriocins lactococcin A and garvicin Q.