METABOLIC VARIABLES AFFECTING THE EFFICACY, SAFETY, AND FATE OF AGRICULTURAL CHEMICALS
Location: Animal Metabolism-Agricultural Chemicals Research
Title: Effect of chlorate, molybdate, and shikimic acid on Salmonella Typhimurium in aerobic and anaerobic cultures
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: July 9, 2006
Publication Date: September 10, 2006
Citation: Oliver, C.E., Smith, D.J., Casey, T., Horrocks, S.M., Anderson, R.C., Nisbet, D.J. 2006. Effect of chlorate, molybdate, and shikimic acid on Salmonella Typhimurium in aerobic and anaerobic cultures. American Society of Microbiology National Meetings Victoria, British Columbia, Sept. 10-12, 2006. Abstract No. 85.
Two studies were conducted to examine the effects of shikimic acid (60 µg/mL) and(or) molybdate (1 mM) on the sensitivity of Salmonella enterica serovar Typhimurium to sodium chlorate (5 mM) during anaerobic (90% N2:5% CO2:5% H2) or aerobic growth in brain heart infusion broth supplemented with 5 mM NaNO3. In the first study, aerobic control cultures without additions reached their maximum absorbance (A600) of 1.99 by 4 h whereas the A600 of aerobic cultures incubated with added chlorate peaked at 0.62 at 5 h. Anaerobic controls incubated without additions reached maximum A600 of 1.60 by 8 h. Growth of anaerobic cultures incubated with added chlorate was practically nil (A600 < 0.12) until 10 h, whereupon cultures grew rapidly, attaining an A600 of 1.46 at 24 h, which was comparable to that measured in controls incubated without chlorate. In the second study, chlorate markedly affected growth of Salmonella, with growth of all cultures containing added chlorate by itself peaking at A600 of 0.43 compared to 1.14 measured in non-chlorate containing counterparts. In both studies, cultures incubated without chlorate did not develop chlorate resistance, as assessed by an agar overlay method, at concentrations above 103 CFU ml-1, which was our lower limit of detection. In the first study, two of the triplicate anaerobic cultures incubated with chlorate had detectible chlorate resistance by h 6 and had acquired or propagated to 100% resistance (>109 CFU ml-1) in all three by 24 h. In the aerobic chlorate-containing cultures, two of the triplicates had detectible chlorate resistance by 6 h, but only one retained detectible resistance at 24 h. In the second study, chlorate resistance in chlorate-containing anaerobic cultures ranged from 86 to 95% of total viable colonies at 8 h and 72 to 96% at 24 h. Anaerobic incubation of chlorate containing cultures with molybdate and shikimic acid had no effect on the quantitative development of chlorate resistance. In aerobic cultures, only one of the chlorate-containing triplicates had resistance at 8 or 24 h (72 and 83% of total viable colonies, respectively). When aerobic cultures were incubated with chlorate and either shikimic acid or molybdate, chlorate resistance was observed at 8 h (62 to 78% of total viable colonies in two of three and three of three cultures, respectively) but sensitivity was fully recovered in all tubes by 24 h. When shikimic acid and molybdate were included together in the presence of chlorate, they did not mitigate the effects of chlorate as chlorate resistance was observed in all triplicates at 8 h (64 to 72%) and 24 h (67 to 80%). Results illustrate the differential effects of chlorate against anaerobic- or aerobically grown Salmonella Typhimurium and demonstrate that shikimic acid or molybdate added individually, but not in combination, were able to reverse chlorate resistance in aerobically, but not anaerobically grown cultures.