title: Effect of subtherapeutic concentrations of tylosin on the inhibitory stringency of a mixed anaerobe continuous-flow culture of chicken microflora against Escherichia coli O157:H7.
abstract: OBJECTIVE
  The aim of this study was twofold: first to determine the effect of subtherapeutic concentrations of tylosin, a macrolide antibiotic used for growth promotion, on a mixed anaerobic continuous-flow fermentation culture of chicken gastrointestinal microorganisms (CCF) and secondly, to determine if these concentrations would allow persistence of Escherichia coli O157:H7 in CCF.
  
  
  RESULTS
  CCF was treated with tylosin at 10.0, 20.0 and 40.0 microg ml(-1). Tylosin treatment resulted in a significant (P < 0.0001) decrease in total volatile fatty acids (VFAs) from a mean concentration of 101 +/- 10.8 micromol ml(-1) in control cultures to 32.0 +/- 6.3 and 40.2 +/- 9.6 micromol ml(-1) in 10 and 40 microg ml(-1) treated cultures, respectively. Untreated CCF challenged with E. coli O157:H7 cleared the challenge microorganism in 7 days at a rate of 0.96 log10 CFU ml(-1) day(-1). In contrast, E. coli O157:H7 persisted in all tylosin treated cultures.
  
  
  CONCLUSIONS
  In the presence of tylosin, E. coli O157:H7 was able to persist in the CCF culture. The significant decrease in the production of VFAs may have been a contributing factor.
  
  
  CONCLUSIONS
  The use of low-level, growth-promoting antimicrobials may compromise the ability of normal microflora that serve as a natural host defence against infection.
authors.affiliation: United States Department of Agriculture, Agricultural Research Service, College Station Texas, USA. poole@ffsru.tamu.edu
authors.forename: T L
authors.initials: TL
authors.lastname: Poole
authors.forename: K J
authors.initials: KJ
authors.lastname: Genovese
authors.forename: K D
authors.initials: KD
authors.lastname: Knape
authors.forename: T R
authors.initials: TR
authors.lastname: Callaway
authors.forename: K M
authors.initials: KM
authors.lastname: Bischoff
authors.forename: D J
authors.initials: DJ
authors.lastname: Nisbet
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001439:Bacteroides / Q000187:drug effects; D002645:Chickens / Q000382:microbiology*; D003470:Culture Media; D024881:Drug Resistance, Bacterial; D016983:Enterococcus / Q000187:drug effects; D019453:Escherichia coli O157 / Q000187:drug effects* / Q000254:growth & development; D005232:Fatty Acids, Volatile / Q000096:biosynthesis; D006089:Gram-Negative Anaerobic Bacteria / Q000187:drug effects*; D006094:Gram-Positive Bacteria / Q000187:drug effects*; D007422:Intestines / Q000382:microbiology; D007778:Lactobacillus / Q000187:drug effects; D008826:Microbial Sensitivity Tests / Q000379:methods; D015645:Tylosin / Q000494:pharmacology*; D014678:Veillonella / Q000187:drug effects
chemical_list: D000900:Anti-Bacterial Agents; D003470:Culture Media; D005232:Fatty Acids, Volatile; D015645:Tylosin