Single Deletion of Escherichia coli K30 Group I Capsule Biosynthesis System Component, wzb, Is Not Sufficient to Confer Capsule-Independent Resistance to Erythromycin

09/01/2016

Gurneet Rana, Yuree Jang, Paul Ahn, Jeremy Nan​

Volume 20
Fall 2015 / Winter 2016

Escherichia coli overcomes different environmental stresses to survive, one of which is cellular death by antibiotics. The capsule is a high molecular weight bacterial surface polysaccharide layer, which is thought to confer resistance against antibiotics, perhaps by acting as a steric or charged barrier to entry. The Wzy system is responsible for the synthesis of group I capsule in E. coli K30. The wzy gene cassette is formed by three different genes: wza, wzb and wzc. Each protein expressed from the components of the wzy cassette serves its own specific function in bacterial capsule synthesis, which is capsule assembly and its secretion to the cell surface. It has been shown from previous studies that a complete knockout of the wzy gene cassette, as well as the knockout of the wza gene alone, is sufficient to confer a resistance phenotype against the macrolide antibiotic, erythromycin, in a capsule-independent manner. However, the mechanism behind this contradictory phenotype is not well known. We hypothesised that wzb may play a role in erythromycin resistance as it functions in the cytoplasm as a non-specific phosphatase, potentially inactivating macrolides by dephosphorylation. We examined resistance to erythromycin using five different strains, which were various mutants of the wzy cassette. Antibiotic resistance of the strains was tested using a disc diffusion assay and results were further supported by determining the minimum inhibitory concentrations. Our observations showed that the double knockout of wzb and wza, in addition to the single wza knockout, had the same resistance phenotype to erythromycin as the complete wzy knockout, while a single knockout of wzb did not. From these results, we conclude that the single deletion of the capsule biosynthesis gene wzb alone is not sufficient to confer the resistance phenotype to erythromycin.