Persistence of Antibiotic Resistance and Capsule in E. coli B23 after Removal from Sublethal Kanamycin Treatment

Kanamycin belongs to the aminoglycoside class of bacteriostatic antibiotics that inhibits protein synthesis. Previous studies have shown that treatment with sublethal levels of kanamycin causes the extracellular polysaccharide capsule in E. coli B23 to increase in size, and potentially confers the bacterium with kanamycin resistance. This study attempted to confirm this by establishing that increased capsule size is the cause of kanamycin resistance by looking at the correlation between the increase in capsule size and the kanamycin resistance. This correlation was investigated by monitoring the change in capsule size and the kanamycin resistance of pretreated E. coli B23 after it was transferred back to antibiotic-free M9 minimal medium. The degree of kanamycin resistance was found to be directly related to the capsule content of the cell. Immediately after removal from pre-lethal levels of kanamycin, the cells were resistant and had high levels of capsule. After 2.5 h, pretreated cells began to lose capsule and kanamycin resistance simultaneously.