Growth of facultative anaerobic population of human intestinal bacteria with the carbamate pesticide aminocarb

Abstract

The effect of different concentrations of the carbamate pesticide, aminocarb (Matacil), on the growth and selection of facultative anaerobic bacteria and degradation of the pesticide by human endoflora of the intestinal tract was examined in vitro. Microorganisms were cultured under aerobic or anaerobic conditions, in nutrient broth and mineral media. The intestinal population was more sensitive to 10–1000 μg/ml aminocarb under anaerobic conditions than in aerobic culture; however, spontaneous degradation of aminocarb in media markedly affected the degree of bacterial growth inhibition in prolonged cultures. In addition, the type of culture medium appeared to influence the degree of aminocarb-induced bacterial growth inhibition. A dose of aminocarb inducing 50% growth inhibition was established for different culture conditions: for mineral medium, aminocarb inhibited bacterial growth by 50% at 600 μg/ml under anaerobic and aerobic conditions, whereas less than 50% inhibition was observed even at 1000 μg/ml aminocarb when bacteria were grown in nutrient broth. A selection of bacterial strains occurred in the presence of increasing aminocarb concentrations, which was determined quantitatively and qualitatively by the identification of codominants. A shift in several Escherichia coli biotypes was also observed in cultures with aminocarb, in comparison to control cultures. Bacterial degradation of aminocarb, under anaerobic and aerobic conditions, was determined in a mixed population of the intestinal microflora by high-performance liquid chromatography analysis of culture media. Data showed that aminocarb can be quickly degraded by human intestinal bacteria at relatively high pesticide concentrations. Moreover, other HPLC data suggest rapid spontaneous degradation of aminocarb in neutral and slightly alkaline pH conditions characteristic of the human intestinal tract, which can effectively eliminate the pesticide. Therefore, aminocarb, at the concentrations used, does not seriously affect the bacterial microflora of the human gut.