Studies of heterologous expression of a mycobacterial glutathione s-transferase gene

Abstract

Resistance to antibiotics still poses a major challenge to human and animal health as a result of wide spread dissemination of resistance genes. Study of the evolutionary origin of these determinants is of importance in order to understand how the mechanisms involved arose in the first place. Two approaches were used to study antibiotic resistance from the evolutionary point of view; a model system of heterologous expression of Gram positive DNAs in a Gram negative background giving rise to macrolide resistance, and expression of the Gram positive glutathione- S-transferase (gst) gene from Mycobacterium in both Gram positive and Gram negative backgrounds. Expression of the gst gene in Escherichia coli conferred a 3× increase in MIC in kanamycin and streptomycin and a ~ 2 fold increase for chloramphenicol. In the Gram positive Rhodococcus erythropolis ATCC 4277 it gave a ~ 5× increase in MIC for spectinomycin, streptomycin and nalidixic acid, while kasugamycin and chloramphenicol showed a 4× increase. Inactivation assay experiments also revealed the possibility of a novel chloramphenicol inactivation. Attempts made to create mutants with increased resistance by spontaneous selection, chemical mutagenesis or by use of an E. coli mutator strain were unsuccessful.