Abstract Title

Comparison of Ancestral and Evolved KPC-2-Bearing Plasmids in Serratia marcescens

Additional Funding Sources

The project described was supported by the Research Experience for Undergraduates Program Site: Molecular and organismal evolution at the University of Idaho under Award No. 1757826.

Abstract

Millions of people in the United States become infected with antibiotic resistant strains of bacteria each year, which are more difficult to treat and can persist longer than nonresistant strains. Many bacteria are able to transfer their antibiotic resistance genes to nearby bacteria through conjugation of circular pieces of DNA called plasmids. Serratia marcescens (CAV1492) contains a plasmid that encodes a resistance gene for a class of antibiotics known as carbapenems. This gene, known as KPC-2, is found on the 10kb Tn4401b transposon, which is able to move between plasmids and chromosomes. After growth for 30 days with meropenem, a carbapenem, the KPC-2 gene transferred from its original 70-kb plasmid to a smaller 6-kb plasmid within CAV1492, creating a novel 16-kb plasmid. The goal of this research project is to better understand the difference in persistence, fitness cost, and transferability between the ancestral 70-kb plasmid and the evolved 16-kb plasmid in CAV1492. To do this, the growth rate, plasmid persistence, and plasmid transferability of strains containing either the evolved or ancestral plasmid will be compared. In comparison to the ancestral 70-kb KPC-2-bearing plasmid, the data suggests that the evolved KPC-2-bearing plasmid is not able to mobilize itself during conjugation. The evolved plasmid also appears to be less persistent in an environment without antibiotic selection than the ancestral plasmid. The growth rates of the evolved and ancestral plasmid-containing strains are comparable. For the three factors that were analyzed — conjugation ability, persistence, and growth rate — the evolved KPC-2-bearing plasmid does not appear to have any noticeable advantage over the larger ancestral plasmid.

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Comparison of Ancestral and Evolved KPC-2-Bearing Plasmids in Serratia marcescens

Millions of people in the United States become infected with antibiotic resistant strains of bacteria each year, which are more difficult to treat and can persist longer than nonresistant strains. Many bacteria are able to transfer their antibiotic resistance genes to nearby bacteria through conjugation of circular pieces of DNA called plasmids. Serratia marcescens (CAV1492) contains a plasmid that encodes a resistance gene for a class of antibiotics known as carbapenems. This gene, known as KPC-2, is found on the 10kb Tn4401b transposon, which is able to move between plasmids and chromosomes. After growth for 30 days with meropenem, a carbapenem, the KPC-2 gene transferred from its original 70-kb plasmid to a smaller 6-kb plasmid within CAV1492, creating a novel 16-kb plasmid. The goal of this research project is to better understand the difference in persistence, fitness cost, and transferability between the ancestral 70-kb plasmid and the evolved 16-kb plasmid in CAV1492. To do this, the growth rate, plasmid persistence, and plasmid transferability of strains containing either the evolved or ancestral plasmid will be compared. In comparison to the ancestral 70-kb KPC-2-bearing plasmid, the data suggests that the evolved KPC-2-bearing plasmid is not able to mobilize itself during conjugation. The evolved plasmid also appears to be less persistent in an environment without antibiotic selection than the ancestral plasmid. The growth rates of the evolved and ancestral plasmid-containing strains are comparable. For the three factors that were analyzed — conjugation ability, persistence, and growth rate — the evolved KPC-2-bearing plasmid does not appear to have any noticeable advantage over the larger ancestral plasmid.