title: Comparison of spontaneous antibiotic resistance frequency of Salmonella Typhimurium growth in glucose amended continuous culture at slow and fast dilution rates.
abstract: The objective of the study was to determine the frequency of spontaneous acquisition of resistance to select antibiotics by Salmonella Typhimurium (ST) when grown in glucose amended continuous flow culture at slow (D = 0.025 h(-1)) or fast (D = 0.27 h(-1)) dilution rates. The bacterium was grown in LB minimal medium (pH 6.25) containing no antibiotics. Upon achieving steady state, samples were plated to tryptic soy agar (TSA) alone or supplemented (per ml) with 2 and 16 microg oxytetracycline, 4 and 16 microg tetracycline, 2 and 64 microg kanamycin, and 0.25 and 2 microg enrofloxacin. Regardless of growth rate, CFU of resistant ST from the TSA containing antibiotics was less than 2 x 10(1) except for 2 microg kanamycin and 0.25 microg enrofloxacin treatments (higher than 1 x 10(9) and 4 x 10(7) CFU of resistant ST for trials 1 and 2, respectively). Frequency of recovering resistant ST from the TSA containing the higher antibiotic concentrations was less than 1 in 10(9) for all antibiotics, but was higher on the media containing 2 microg kanamycin and 0.25 microg enrofloxacin at both slow and fast growth rates. In general, minimal susceptibility differences were detected for isolates from slow and fast dilution rates.
authors.affiliation: Department of Poultry Science, Texas A&M University College Station, Texas 77843-2472, USA.
authors.forename: W K
authors.initials: WK
authors.lastname: Kim
authors.forename: N
authors.initials: N
authors.lastname: Karabasil
authors.forename: S
authors.initials: S
authors.lastname: Bulajic
authors.forename: K D
authors.initials: KD
authors.lastname: Dunkley
authors.forename: T R
authors.initials: TR
authors.lastname: Callaway
authors.forename: T L
authors.initials: TL
authors.lastname: Poole
authors.forename: S C
authors.initials: SC
authors.lastname: Ricke
authors.forename: R C
authors.initials: RC
authors.lastname: Anderson
authors.forename: D J
authors.initials: DJ
authors.lastname: Nisbet
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D015169:Colony Count, Microbial; D003470:Culture Media; D004305:Dose-Response Relationship, Drug; D024881:Drug Resistance, Bacterial; D000077422:Enrofloxacin; D024841:Fluoroquinolones / Q000494:pharmacology; D005947:Glucose / Q000378:metabolism*; D007612:Kanamycin / Q000494:pharmacology; D008826:Microbial Sensitivity Tests; D010118:Oxytetracycline / Q000494:pharmacology; D012486:Salmonella typhimurium / Q000187:drug effects* / Q000254:growth & development*; D013754:Tetracyclines / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D003470:Culture Media; D024841:Fluoroquinolones; D013754:Tetracyclines; D000077422:Enrofloxacin; D007612:Kanamycin; D005947:Glucose; D010118:Oxytetracycline