Environmental and genetic factors affecting mutability to aminoglycoside antibiotics among Escherichia coli K12 strains

Abstract

Environmental and genetic factors affecting the in vitro spontaneous mutation frequencies to aminoglycoside resistance in Escherichia coli K12 were investigated. Spontaneous mutation frequencies to kanamycin resistance were at least 100 fold higher on modified Luria agar (L2) plates, when compared to results obtained in experiments carried out with Nutrient agar (NA) plates. In contrast to rifampincin, the increased mutability to kanamycin resistance could not be attributed to a mutator phenotype expressed by DNA repair defective strains. Kanamycin mutant selection windows and mutant preventive concentrations on L2 plates were at least fourfold higher than on NA plates, further demonstrating the role of growth medium composition on the mutability to aminoglycosides. Mutability to kanamycin resistance was increased following addition of sorbitol, suggesting that osmolarity is involved on the spontaneous mutability of E. coli K12 strains to aminoglycosides. The spontaneous mutation rates to kanamycin resistance on both L2 and NA plates were strictly associated with the selective antibiotic concentrations. Moreover, mutants selected at different antibiotic concentrations expressed heterogeneous resistance levels to kanamycin and most of them expressing multiple resistance to all tested aminoglycoside antibiotics (gentamicin, neomycin, amykacin and tobramycin). These results will contribute to a better understanding of the complex nature of aminoglycoside resistance and the emergence of spontaneous resistant mutants among E. coli K12 strains.

Intracellular polyamine pools, oligopeptide-binding protein A expression, and resistance to aminoglycosides in Escherichia coli

“…As previously reported by our group, plating of E. coli J53 strains on media containing kanamycin resulted in the high frequency selection of mutants expressing multiple resistance to aminoglycosides (Acosta et al 2000, Monteiro et al 2003. Some mutants had colonies smaller than those produced by the parental strain and did not grow in succinate minimal plates, indicating the expression of impaired respiratory chain component, whereas others with no detectable growth impairment were shown to express reduced OppA levels and/or defective activity of ornithine/arginine decarboxylases (Acosta et al 2000, Monteiro et al 2003.…”

“…The R26, R60, and R69 mutants were selected on L2 plates. All selected resistant mutants displayed growth rates similar to the parental strain and were able to grow on succinate as the sole carbon source, an indication of functional aerobic metabolism (Monteiro et al 2003). The polyamine synthesis inhibitors cyclohexilamine (CHA) and methylglyoxal bis(guanyl-hydrazone) (MGBG) were added to the MM medium before inoculation with the different strains at a final concentration of 100 mg/ml.…”

“…Some mutants had colonies smaller than those produced by the parental strain and did not grow in succinate minimal plates, indicating the expression of impaired respiratory chain component, whereas others with no detectable growth impairment were shown to express reduced OppA levels and/or defective activity of ornithine/arginine decarboxylases (Acosta et al 2000, Monteiro et al 2003.…”

Host strain influences on supercoiled plasmid DNA production in Escherichia coli: Implications for efficient design of large‐scale processes

“…Whilst each strain may exhibit different trends under optimised conditions, by keeping the growth conditions constant for each strain/ plasmid combination, we are only looking at one variable which is the host strain. Literature indicates that conditions similar to those used in this study have been previously applied to the culturing of some E. coli strains investigated (Cooke et al, 2004;Macphee et al, 1988;Monteiro et al, 2003;O'Mahoney et al, 2007;Shiloach et al, 1996).…”

The effect of environmental pollutants and food processing on the development of antibiotic resistance

“…Different stresses such as starvation, oxidation or UV irradiation can increase the mutation rates of bacteria 2 . All factors affecting the mutability of chromosomal genes confer resistance among different bacterial species 3 . As suggested by Martinez and Baquero 1 mutation frequencies are probably much higher in the course of infection than those determined in vitro, because bacteria growing in vivo are frequently under environmental stress and challenges.…”