De Novo Acquisition of Resistance to Three Antibiotics by Escherichia coli

Abstract

General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. The acquisition of resistance to amoxicillin, tetracycline, and enrofloxacin by Escherichia coli MG 1655 was examined by exposing growing cells to constant or stepwise increasing concentrations of these compounds. The minimal inhibitory concentration (MIC) of E. coli for amoxicillin increased from 4-8 to 32 mg/ml after growth in the presence of 1.25 or 2.5 mg/ml. By stepwise increasing the exposure, an MIC of 512 mg/ml was reached. This high MIC was maintained after removal of the antibiotics, whereas the lesser increase after exposure to low levels was reversed, indicating that the high MIC was due to a genetic change, but the lower one to phenotypic adaptation only. The MIC for tetracycline increased from 2 mg/ml to maximally 32 mg/ml. The MIC decreased to control levels in the absence of tetracycline, so no genetic changes seem to have occurred. The MIC for enrofloxacin increased from 0.25 mg/ml to maximally 512 mg/ml depending on the concentration during growth. These data mostly support the ''radical-based'' theory that bactericidal antibiotics induce a common mechanism that contributes to cell killing. Our findings indicate that exposure to low levels of antibiotics causes an increase in MIC above the concentration that the cells were exposed to. The implication is that exposure to low levels of antibiotics should be prevented as much as possible, because this causes resistance far more than high concentrations that inhibit growth or kill the cell and thus prevent acquisition of resistance.

Effects of Therapeutical and Reduced Levels of Antibiotics on the Fraction of Antibiotic-Resistant Strains of Escherichia coli in the Chicken Gut

“…In the in vivo experiments reported here, resistance against enrofloxacin was easily reverted after short-term exposure. In contrast, when a higher level of resistance had been reached in longer term in vitro experiments, these remained at that level after the selection pressure was removed (van der Horst et al, 2011).…”

“…In vitro an increase of the minimal inhibitory concentration (MIC) of E. coli for enrofloxacin can be induced by a factor of up to 1000, from 0.3 to 512 lg/mL after approximately 100 generation times. Increasing doses of oxytetracycline and amoxicillin induced resistance to a lesser degree, but still enough for the cells to be effectively resistant (van der Horst et al, 2011). That the long-term exposure to antibiotics in vivo leads to resistance has amply been demonstrated.…”

Effects of Chlorophyll-Derived Efflux Pump Inhibitor Pheophorbideaand Pyropheophorbideaon Growth and Macrolide Antibiotic Resistance of Indicator and Anaerobic Swine Manure Bacteria

“…As with other macrolides, erythromycin is classically considered as bacteriostatic, but it has shown bactericidal activity against S. aureus at higher drug/cell ratios [84][85][86]. Bactericidal antimicrobials at sublethal concentrations induce mutational rather than adaptive resistance [10]. It is likely that the serial exposure of S. aureus to increasing concentrations of erythromycin ultimately resulted in the selection of cells bearing additive, high-level resistance-conferring mutations from naturally occurring subpopulations with, due to overexpression of the regular cellular machinery, low-level phenotypic adaptive resistance [10,29,87,88].…”

“…This results in exposures of the animals' gastrointestinal tract and waste microbiota to inconsistent, often sublethal or subinhibitory concentrations [1,6]. As even ultralow (≪MIC) antimicrobial concentrations can confer a selective pressure towards the persistence of resistance in microbial communities [7][8][9][10][11][12], induction of gut and waste microbial resistance is an inevitable collateral effect of oral antimicrobials in animal agriculture [13][14][15][16].…”

Antibiotic use and resistance in animals: Belgian initiatives

“…[18] The use of antibiotics, even in very low (sub-therapeutic) doses, may select for antibiotic-resistant bacteria. [29,30] These resistant strains can spread in the environment or survive in the food chain, where they pose a possible threat for human health. Resistant bacteria can pass resistance genes to commensals and pathogens via horizontal gene transfer.…”