Evaluation of Phenotypic Variations in the Antibiotics Sensitivity of Escherichia Coli by Repeated Exposure

Enterobacteriaceae, in particular Escherichia coli, are habitual residents of the gastrointestinal tract, capable of causing a large number of infections. The MIC varies according to the bacterial strains and the antibiotics used, hence the need to carry out antibiotic sensitivity tests. The objective of this study is to evaluate the behavior of Escherichia coli after repeated exposure to the same antibiotic to demonstrate a possible correlation between excessive intake of antibiotics and bacterial resistance. A prospective and descriptive study was carried out in the Laboratory of Microbiology of Fundamental and Applied Biochemistry (Faculty of Sciences Antananarivo) during the month of November 2019. The strains studied were the reference strain Escherichia coli ATCC 25922 provided by the Laboratory and two clinical strains from the Microbiology Laboratory of the Joseph Ravoahangy Andrianavalona University Hospital Center (CHU JRA) Antananarivo. Repeated exposure to Tobramycin and Ofloxacin of these strains were performed. The results of our study showed that most E. coli is exposed to the antibiotic, the more it develops resistance. The evolution of E. coli's sensitivity is different in the presence of Tobramycin with MICs up to 4 times the starting value while in the presence of Ofloxacin, the MIC increases to 125 times the initial value. This difference may be due to the different target of the antibiotic which causes the bacteria to develop variable mechanisms to escape it. Key words: E. coli - MIC - antibiotics - repeated exposure