Prevalence of Listeria in soil.

One hundred thirty soil samples from agricultural fields and animal-inhabited areas were examined for the presence of Listeria. The microorganism was identified in 23 (17.7%) samples. L. monocytogenes was detected in 7 samples (5.4%), L. ivanovii in 2 (1.5%), L. innocua in 10 (7.7%) and L. welshimeri in 4 samples (3.1%). Prevalence of Listeria in soil from agricultural fields (17.5%) did not differ considerably from that in the soil and animal-inhabited area (18.0%), but L. ivanovii was isolated only from the latter source. Frequency of occurrence of different species of Listeria differed from place to place.

Detection and characterization of enterocins from Enterococcus sp.

Examination of 90 isolates of Enterococcus sp. revealed production of enterocin by two isolates of E. faecalis which was inhibitory to Listeria monocytogenes. Two isolates of E. gallinarum produced enterocin active against Staphylococcus aureus. None of the isolates antagonized Salmonella enteritidis. The enterocins of E. faecalis isolates were inactivated by alpha-chymotrypsin but not by trypsin and papain, while those of E. gallinarum were resistant to all the three enzymes. Enterocins produced by all 4 strains were resistant to heating at 60 degrees C for 30 min and 80 degrees C for 10 min, but sensitive to 121 degrees C for 15 min. At 100 degrees C for 10 min, two enterocins, one each of E. faecalis and E. gallinarum were inactivated, while the remaining two retained the bactericidal activity.