The effect of sub-lethal concentration of ciprofloxacin on the transfer of multidrug resistance plasmids, fitness costs on the host and the stability of the newly acquired plasmids

Abstract

The increase in reported cases of antimicrobial resistance has raised a lot of concerns in the public health community. This has prompted efforts aimed at finding out factors that have been contributing to this situation. In Gram-negative bacteria plasmids have been singled out as the most important vehicles behind the spread of antimicrobial resistance. Some plasmids can harbour several resistance genes resulting into host bacteria with multiple resistance profiles. These plasmids are spread horizontally from one bacterium to another. Of major concern is the increased dissemination of the carbapenemases among Gram-negative bacteria particularly New Delhi metallo-β-lactamase (NDM-1) and oxacillinase-48 (OXA-48). In this study the aim was to study the effects sub-lethal concentrations of ciprofloxacin (0.02µg/ml) have on the transfer frequency of plasmids carrying blaNDM-1 and blaOXA-48 genes. Further studies were carried out to analyse the stability of the newly acquired plasmids in the host in the absence of antimicrobial selection. In addition, studies were carried out to analyse the fitness costs the plasmids imposes on the host. In vitro conjugations experiments using two clinical strains of Escherichia coli containing plasmid borne blaNDM-1 and blaOXA-48 genes respectively were used as donors. Clinical plasmid-free E. coli strains with different genetic backgrounds were used as recipients. Our study showed a marked increase in plasmids transfer frequency in the presence of 0.02 µg/ml ciprofloxacin. In order to determine the fitness cost the plasmids imposes on the host, competition experiments that were done between the transconjugants, G2-06 (NDM-1) and G2-07 (OXA-48) respectively and the recipient (K56-75-1). G2-06 was found to have a fitness cost of 17 %, while G2-07 was found to have a fitness cost of 8 %. The plasmid stability tests that were done over a period of 10 days found that the plasmids in G2-06 and G2-07 were 100% stable.