Submitted to: Journal of Environmental Science and Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/16/2004
Publication Date: 7/1/2005
Citation: Kim, W.K., Karabasil, N., Bulajic, S., Dunkley, K.D., Callaway, T.R., Poole, T.L., Ricke, S.C., Anderson, R.C., Nisbet, D.J. 2005. Comparison of spontaneous antibiotic frequency of Salmonella typhimurium growth in glucose amended continuous culture at slow and fast dilution rates. Journal of Environmental Science and Health Part B. 40:475-484.
Interpretive Summary: Salmonella typhimurium was grown in a test tube at different dilution rates. The frequency of mutation to become resistant to certain antibiotics (oxytetracycline, tetracycline, kanamycin and enrofloxacin) was not affected by growth at different rates. This result indicates that mutation rates are dependent on bacterial physiological factors other than doubling time and growth rate.
Technical Abstract: The objective of this study was to determine the frequency of spontaneous acquisition of resistance to select antibiotics by Salmonella typhimurium (ST) when grown in glucose limited 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 TSA alone or TSA supplemented with (per ml) 2 and 16 ug oxytetracycline, 4 and 16 ug tetracycline, 2 and 64 ug kanamycin and 0.25 and 2 ug enrofloxacin. Regardless of growth rate, CFU of resistant ST from the TSA containing antibiotics was less than 2 x 10**1 except for 2 ug kanamycin and 0.25 ug enrofloxacin treatments. 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 ug kanamycin and 0.25 ug enrofloxacin at both slow and fast growth rates. In general, minimal susceptibility differences were detected for isolates from slow and fast dilution rates.