An injection port assembly for coupling to and uncoupling from a first fluid pathway of a first connector and for coupling to a device provided with a second connector so as to provide fluid connection between the first and second connectors, the injection port assembly comprising: a body having a first mating structure configured to mate with the first connector, and a second mating structure coupled to the first mating structure and configured to mate with the second connector; a hollow cannula integrally formed with the first mating structure having an upper portion along which are lateral fluid pathway holes or slots, and a full-radius bullet nose on a distal end of the hollow cannula; a resilient barrier substantially contained within the body having a flat septum surface with a razor slit formed therein, the resilient barrier being compressible from a less compressed first position in which fluid flow between the first connector and the second connector is blocked to a more compressed second position in which fluid flow between the first connector and the second connector is permitted; the second mating structure includes a distal body end portion having a distal end flange extending laterally inward, the distal end flange having defined therein a first inner tapered body surface and a second inner tapered body sealing surface positioned below the first inner tapered body surface; the resilient barrier includes a resilient barrier distal end portion with a first sealing surface and a second sealing surface, the first and second sealing surfaces (28,29) both extending around an entire circumference of the resilient barrier; the first inner tapered body surface and the second inner tapered body sealing surface of the second mating structure are configured to apply a compression force against the first sealing surface and the second sealing surface of the resilient barrier respectively when the resilient barrier is in the less compressed first position; the resilient barrier includes a lower sealing flange configured to be compressed between the first and second mating structures (12,42) when the second mating structure is coupled to the first mating structure; and the first mating structure comprises a tapered well designed to couple with a tapered well ring of the resilient microbial barrier to form an additional fluid seal after assembly. a body having a first mating structure configured to mate with the first connector, and a second mating structure coupled to the first mating structure and configured to mate with the second connector; a hollow cannula integrally formed with the first mating structure having an upper portion along which are lateral fluid pathway holes or slots, and a full-radius bullet nose on a distal end of the hollow cannula; a resilient barrier substantially contained within the body having a flat septum surface with a razor slit formed therein, the resilient barrier being compressible from a less compressed first position in which fluid flow between the first connector and the second connector is blocked to a more compressed second position in which fluid flow between the first connector and the second connector is permitted; the second mating structure includes a distal body end portion having a distal end flange extending laterally inward, the distal end flange having defined therein a first inner tapered body surface and a second inner tapered body sealing surface positioned below the first inner tapered body surface; the resilient barrier includes a resilient barrier distal end portion with a first sealing surface and a second sealing surface, the first and second sealing surfaces (28,29) both extending around an entire circumference of the resilient barrier; the first inner tapered body surface and the second inner tapered body sealing surface of the second mating structure are configured to apply a compression force against the first sealing surface and the second sealing surface of the resilient barrier respectively when the resilient barrier is in the less compressed first position; the resilient barrier includes a lower sealing flange configured to be compressed between the first and second mating structures (12,42) when the second mating structure is coupled to the first mating structure; and the first mating structure comprises a tapered well designed to couple with a tapered well ring of the resilient microbial barrier to form an additional fluid seal after assembly.