DERIVATION OF DNA PROBES FOR ENUMERATION OF A SPECIFIC STRAIN OF LACTOBACILLUS-ACIDOPHILUS IN PIGLET DIGESTIVE-TRACT SAMPLES

Four DNA probes were derived that hybridized specifically to DNA from Lactobacillus acidophilus O. The probes were constructed by randomly c loning lactobacillus DNA in plasmid vector pBR322. Two of the probes ( pSR1 and pSR2) were composed of vector and plasmid DNA inserts (3.6 an d 1.6 kb, respectively); the others (pSR3 and pSR4) were composed of v ector and chromosomally derived inserts (6.9 and 1.4 kb, respectively) . The probes were used to enumerate, by colony hybridization, strain O in digestive tract samples collected from piglets inoculated 24 hours previously with a culture of the strain. The probes did not hybridize to DNA from lactobacilli inhabiting the digestive tract of uninoculat ed piglets. Strain O made up about 10% of the total lactobacillus popu lation of the pars esophagea and about 20% of the population in other digestive tract samples.