GENETIC MARKING OF LACTOCOCCUS-LACTIS SHOWS ITS SURVIVAL IN THE HUMANGASTROINTESTINAL-TRACT

A human feeding study was performed with Lactococcus lactis TC165.5, w hich is genetically marked by insertion of the sucrose-nisin conjugati ve transposon Tn5276 and chromosomal resistance to rifampin and strept omycin. The fate of strain TC165.5 and its nucleic acids was monitored by conventional plating methods and by molecular detection techniques based on specific PCR amplification of the nisin (nisA) gene from DNA extracted from human feces. A method was developed for the efficient extraction of microbial DNA from human feces. The results show that a fraction of viable cells of L. lactis TC165.5 survived passage through the human gastrointestinal tract. Only cells that passed within 3 day s of ingestion could be recovered from the feces of the volunteers, an d they accounted for approximately 1% of the total number of cells con sumed. The presence of nisA in DNA extracted from feces could be detec ted up to 4 days, when viable cells were no longer present.