Sublethal Kanamycin Induced Cross Resistance to Functionally and Structurally Unrelated Antibiotics

Previous studies have shown that pretreatment with sub-lethal kanamycin to E. coli B23 cells provided protection against subsequent exposure to lethal amounts of the same antibiotic. It has also been shown that exposure to sub-inhibitory levels of certain antibiotic can induce cross resistance by promoting the development of low-level resistance to other functional and structural unrelated antibiotics. In this study, the kanamycin protection experiment by Lu et al. was reproduced using Minimal Inhibitory Concentration (MIC) assays in microplates to assess antbiotic resistance. The potential for development of cross resistance against streptomycin, tetracycline and ampicilin elicited by sublethal kanamycin pretreatment was also investigated. Short term protection was assessed by monitoring the growth rate in the presence of antibiotic for 1.5 hours, whereas long term protection was determined by the shift in the MIC of each antibiotic after 24 hours incubation. Both short and long term protection against kanamycin were found to be induced in the sublethal kanamycin pretreated culture. It was also observed that kanamycin pretreated E. coli B23 cells developed short term antibiotic resistance against streptomycin, tetracycline and ampicillin, whereas long term resistance was only observed against kanamycin and streptomycin. Thus suggesting different mechanisms may be involved in the short and long term protection.