Effet du pesticide savahaler sur quelques protéobactéries en microcosme aquatique : impact de la température d’incubation

Abstract

The study was carried out in an aquatic microcosm, at the Hydrobiology and Environment Laboratory of the Faculty of Sciences, University of Yaoundé 1 during the period from January to June 2021, with the aim of evaluating the effect of the pesticide SAVAHALER on some aquatic bacteria of health importance and to determine the impact of temperature. The bacterial solutions of each species considered were brought into contact with 5 pesticide solutions of increasing concentrations (C1=0.94 g/L, C2=1.87 g/L, C3=3.75 g/L, C4=7.5 g /L and C5= 15g/L) and incubated at 7°C, room temperature and 44°C, for 3h, 6h, 9h and 24h.In the presence of the pesticide, the densities of Escherichia coli, Salmonella typhi and Vibrio cholerae gradually decreased as the duration of contact increased. At room temperature and according to the different concentrations, the densities of E. coli, S. typhi and V. cholerae respectively varied between 8.285 and 5.549 log (CFU/100 mL), between 8.301 and 4.959 log (CFU/100 mL) and between 8.300 and 2.221 log (CFU/100 mL). At 7°C and according to the different concentrations, the densities of E. coli varied between 8.287 and 5.23 log (CFU/100 mL) while those of S. typhi varied between 8.301 and 4.560. As for the cell densities of V. cholerae, they decreased ranging from 8,300 to 2,074 log (UFC/100 mL). At 44ºC and according to the different concentrations, the densities of E. coli, S. typhi and V. cholerae respectively varied between 8.287 and 5.028 log (UFC/100 mL), between 8.301 and 2.151 log (UFC/100 mL) and between 8.300 and 8.221 log (CFU/100 mL). The regression rates of bacterial densities varied according to the incubation temperature, the concentration of the pesticide of the bacterial species and the duration of incubation. The greatest regression rate (-0.2526 CFU/100 mL/h) was obtained in V. cholerae and the smallest regression rate (-1.442 CFU/100 mL/h) was noted in S. typhi.The incubation temperature would influence the abundances of E. coli and S. typhi in the presence of the pesticide. On the other hand, the variation in the concentrations of pesticides would influence only the abundances of V. cholerae.