Submitted to: American Society for Microbiology
Publication Type: Abstract Only
Publication Acceptance Date: 2/17/2006
Publication Date: 5/23/2006
Citation: Stanton, T.B., Sharma, V.K., Humphrey, S.B., Zuerner, R.L. 2006. Antimicrobial collateral effects: Induction of the prophage-like, gene transfer agent VSH-1 in cultures of the swine pathogen Brachypsira hyodysenteriae [abstract]. American Society for Microbiology. May 20-26, 2006, Orlando, Florida. 2006 CDROM. Interpretive Summary:
Technical Abstract: Background: B. hyodysenteriae (B hyo) is an anaerobic spirochete and the etiologic agent of swine dysentery. B hyo cells contain a mitomycin C-inducible, prophage-like element, named VSH-1. VSH-1 particles are non-infectious (do not form plaques), package random 7.5 kb fragments of the B hyo genome, and transduce genes between B hyo cells. Except for mitomycin C, chemicals and environmental conditions inducing VSH-1 production are unknown. We hypothesized that antimicrobials and stresses known to induce prophages of other bacteria might induce VSH-1 and thereby stimulate lateral gene transfer between B hyo cells. Methods: Inducers of VSH-1 were presumptively identified by quantitative real time PCR (QRTPCR) to detect increased transcription of hvp38 (VSH-1 head protein gene). To confirm that increased hvp38 transcription correlated with VSH-1 virion production, DNA from B hyo cells was analyzed by gel electrophoresis to detect VSH-1 7.5 kb DNA. Cells were also examined by electron microscopy to detect virions. Carbadox-induced VSH-1 virions from B hyo strain A203 (TyrCmr) were tested for the ability to transduce tylosin and chloramphenicol resistance genes to B hyo strain B78 (TysCms). Results: Thirteen antimicrobials did not increase hvp38 transcription. By contrast, hvp38 transcription increased 16 to > 500-fold in B hyo cultures treated with ('g/ml, final conc): enrofloxacin (10), novobiocin (50), heat (50OC, 1h), coumermycin A1 (0.5), H2O2 (300 'M), mitomycin C (10), carbadox (0.5), and metronidazole (1.0). VSH-1 virions were detected in cultures exhibiting the highest levels of hvp38 transcription. Metronidazole and carbadox were potent VSH-1 inducers. Carbadox-induced virions transduced both tylosin and chloramphenicol resistance genes. Conclusions: In the US, carbadox is a common feed additive for preventing swine dysentery. Our in vitro results suggest a need to evaluate VSH-1 induction and lateral gene transfer as possible collateral effects of carbadox therapy. Additionally, a potentially broader impact of carbadox and metronidazole, as prophage inducers, on intestinal microbial ecology deserves investigation.