We prepared composite ultrafiltration membranes by directly electrospinning a top layer of poly(acrylic acid) (PAA) and poly(vinyl alcohol) (PVA) onto polysulfone (PSU). The electrospun layer was cross-linked by heat curing, and the previous irradiation of the PSU support allowed creating stable composites that did not detach under cross-flow operation. The physicochemical properties of the composites were measured using FTIR spectroscopy, water contact angle, surface zeta-potential, and permeation measurements. We showed that PAA-PVA electrospun layers increased membrane hydrophilicity and reduced organic fouling without affecting permeability and protein rejection performance. The antibacterial performance of the top-layer composites was investigated using Escherichia coli and Staphylococcus aureus strains and tracked counting colony forming units, SEM images of colonized specimens, and cell viability using confocal microscopy. The results showed that PAA-PVA coating resulted in clear antimicrobial performance, particularly for the bacteriumS. aureus, which we attributed to the chelating of the cations stabilizing cell envelopes. Composite membranes were compared with neat PSU membranes in 48 h cross-flow experiments. The composites showed good mechanical integrity and antimicrobial behavior under flow conditions with average reduction of 1-log for electrospun composites exposed to S. aureus over PSU. This work demonstrates that top-layer nanofiber composites can lead to ultrafiltration membranes with enhanced functionalities.