Submitted to: American Society for Microbiology
Publication Type: Abstract Only
Publication Acceptance Date: February 22, 2002
Publication Date: May 1, 2002
Citation: Stanton, T.B., Humphrey, S.B. 2002. Unusual tetracycline resistance in megasphaera elsdenii strains from swine cecal contents [abstract]. American Society for Microbiology. p. 515. Technical Abstract: In the U.S., tetracyclines have been commonly added to feed to promote growth and control diseases of swine. Grower phase (70-120 lbs) swine were obtained from farms with or without a history of in-feed chlortetracycline (CTC) use. Under anaerobic conditions, cecal contents were diluted and plated onto CCA agar containing CTC (0-256 ug/ml). CCA is a rumen fluid-based, nutritionally complex medium. Eight strains of Gram (-), obligately anaerobic, large cocci were isolated from CCA plates containing 64-256 ug CTC/ml. The sequences of a 16S rDNA variable (V3) region of the eight isolates were > 99% identical to that of M. elsdenii strain B159, establishing their identity as M. elsdenii strains. Based on PCR assays for specific tet genes, each strain contained a tet(O) gene. Control (Tc**s) M. elsdenii strains contained no detectable tet genes. PCR primers for tet(O) genes were used to amplify 1955 bp of DNA from Tc**r strain 7-11. A 1386 bp central region of the amplicon had > 98% sequence identity with the Butyrivibrio fibrisolvens tet(W) gene and was flanked by 324 bp and 245 bp regions sharing > 99.5% identity with Streptococcus tet(O) genes. PCR assays for different sections of this tet(O)/tet(W) hybrid detected the same tet gene in all eight Tc**r strains. To our knowledge this is the first report of Tc**r strains of M. elsdenii, a common inhabitant of the intestinal tracts of ruminants and non-ruminants. Although its activity remains to be demonstrated, the M. elsdenii tet gene appears to be a product of a recombination event between tet(O) and tet(W) genes. Such tet gene hybrids may be undetected in PCR assays targeting known tet genes.