Isolation of Tn916-like conjugal elements from swine lot effluent

Isolates of Enterococcus faecalis obtained from a swine farrowing house outflow were examined for genetic elements similar to Tn916. Of the enterococci isolated, 71% were resistant to tetracycline. Among the tetracycline-resistant enterococci isolated from the outflow samples, approximately 34% were able to transfer the tetracycline resistance phenotype to Bacillus thuringiensis in cross-genus matings. The frequencies of transfer for 10 random isolates were comparable to those for transfer of Tn916 from E. faecalis to B. thuringiensis. In addition, these elements were shown to mobilize plasmid pC194 between Bacillus species, as did Tn916. Southern blot and polymerase chain reaction (PCR) analysis showed these elements share extensive structural homology with Tn916. The selected conjugal elements were capable of transfer to a Bacillus recipient in a soil environment. When the swine waste was introduced into the soil, the tetracycline resistant fecal enterococci levels rose from essentially undetectable levels to approximately 4 × 104and remained at this level for 4 weeks. After six months, including one winter, levels had decreased to 5 × 103.Key words: Enterococcus faecalis, Tn916, swine waste, genetic exchange, Bacillus thuringiensis, PCR.

Acquisition of Chloramphenicol Resistance by the Linearization and Integration of the Entire Staphylococcal Plasmid pC194 into the Chromosome of Streptococcus pneumoniae

ABSTRACT Chloramphenicol resistance in Streptococcus pneumoniaewas associated with cat, which has 100% identity withcat pC194 from Staphylococcus aureus. Inverse PCR with primers specific for pC194 confirmed that in some isolates the entire staphylococcal plasmid was present in the S. pneumoniae chromosome, with linearization having occurred between cat pC194 and the origin of replication.