Nisin is an antibacterial peptide.

Nisin is produced by the lactic acid bacterium L. lactis using uncommon amino acids, including lanthionine, and is a member of the class of antibiotics referred to as lantibiotics.

In vitro: Previous study showed that the sperm motility could be completely inhibited with nisin. The minimum effective concentration of nisin required to immobilize sperm in vitro within 20 s was found to be 50 μg in rat, 200 μg in rabbit and 300-400 μg in monkey and human. Such inhibitory effect on sperm motility was found to be dose- and time-dependent [1].

In vivo: Intravaginal administration of nisin before mating during proestrus-estrous transition phase caused complete arrest of sperm motility and blockage of conception. Subacute toxicity studies in rats showed that, repetitive intravaginal application of nisin at the dose of 200 microg for 14 days caused no abnormalities either in the length of estrous cycle or in the morphology of vaginal epithelial cells. Moreover, no histopathological abnormalities in vaginal tissue or any change in blood and serum biochemical profiles were seen. In addition, no adverse effects were found on subsequent reproductive performance, development of pups and neonate survival [1].

Clinical trial: Up to now, nisin is still in the preclinical development stage.

Reference:
[1] Aranha C, Gupta S, Reddy KV.  Contraceptive efficacy of antimicrobial peptide Nisin: in vitro and in vivo studies. Contraception. 2004 Apr;69(4):333-8.