Submitted to: Poultry Science Association Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: April 2, 2004
Publication Date: July 25, 2004
Citation: Poole, T., McReynolds, J., Callaway, T., Nisbet, D. 2004. Acquisition and persistence of a high level macrolide resistant Veillonella sp. without selection pressure [abstract]. Journal of Animal Science. 82(Suppl. 1):166. Technical Abstract: High level resistance to macrolide antibiotics, but not lincosamide or streptogramin antibiotics, is characteristic of enzymatic drug inactivation by macrolide phosphotransferase (mph) or esterase (ere) gene families. A Veillonella sp (VL2) was found to have acquired high level resistance to tylosin (a macrolide antibiotic), but not lincomycin, in a closed population of chicken ceca bacteria cultured anaerobically in the absence of selection pressure. This suggests that a gene, or gene complex, conferring high-level macrolide resistance was acquired from a bacterial species present in the mixed anaerobic population. PCR amplication of VL2 genomic DNA with primers specific to known macrolide, lincosamide, and streptogramin resistance genes (erm, ere, vat, mef, and msr gene families) were negative. However, PCR amplification with mph A/B primers generated a DNA fragment of approximately 750 bp with tylosin resistant (TY^r) VL2, but not tylosin susceptible (TY^s) VL1 DNA. PCR amplification of genomic DNA from three E. coli isolates present in the same culture generated the expected (836bp) mph specific fragments. To date sequence alignments of the 750 bp fragment have shown 92% amino acid identity with a Salmonella tyrosine kinase, but very little homology to published sequences of macrolide phosphotransferases. Additional studies are underway to determine the protein responsible for high level macrolide resistance by VL2, as well as the source of gene acquisition. To determine the competitive fitness of VL2, 10**7 CFU/ml was inoculated simultaneously with 100ml of reconstituted PREEMPT (devoid of high-level tylosin resistant veillonella) to three continuous-flow fermentation devices. To date, two cultures have maintained VL2 for four months at 10**3 CFU/ml without selective pressure. These preliminary experiments suggest a low metabolic cost from the acquisition of high level macrolide resistance.