A-041. Identifying Escherichia coli Multidrug Resistance Genes by Transposon Mutagenesis

M. Duo, S. Hou, D. Ren;
Syracuse Univ., Syracuse, NY.

Background: Bacterial multidrug resistance (MDR) is a major cause of clinical failures in treating infections. According to NIH, about 70% of nosocomial infections in the U.S. are caused by strains that are resistant to at least one antibiotic. Totally, 4.5% of such infections result in death, presenting a devastating threat to public health and economy. Increasing evidence suggests that bacteria can resist multiple antibiotics through intrinsic mechanisms that rely on gene products such efflux pumps that expel antibiotics and special membrane proteins that block the penetration of drug molecules. In this study, E. coli was used as a model system to explore the genetic basis of MDR. Methods: A random mutant library was constructed in E. coli EC100 using transposon mutagenesis. The library was screened by growth measurement to identify the mutants with enhance/reduced susceptibility to chloramphenicol (Cm). Out of the 4000 mutants screened, 6 mutants were found to be more sensitive to Cm and 7 were more tolerant compared to the wild-type EC100. Mutation sites for 12 out of the 13 mutants were identified by inverse PCR. Results: While 2 of the 12 genes have been reported previously as MDR genes, 10 genes were found to be related to MDR for the first time. Mutants of the genes rob, garP, bipA, insK, and yhhX were more sensitive to Cm compared to the wild-type EC100, while the mutants of the genes rhaB, yejM, dsdX, nagA, yccE, atpF, and htrB exhibited higher tolerance. The tolerance of the mutants to other antibiotics was also studied, including amplicillin, spectinomycin, cinoxacin, and tobramycin. Conclusion: A number of new genes were found to be related to MDR in E. coli. Further study of these genes and screening of more mutants are expected to improve our understanding of MDR and to develop better therapeutic methods.