Doctor of Philosophy

dissertationCarbapenem resistance is a growing public health threat, leaving few treatment options for Gram-negative bacterial infections. The rise in community-acquired carbapenem-resistant infections is particularly alarming, and recent evidence indicates that drinking water may serve as a source of these organisms. Furthermore, there is concern that drinking water distribution systems may also amplify resistant organisms as a result of horizontal gene transfer of resistance genes within water distribution system biofilms. Current methods for testing and monitoring drinking water for the presence of carbapenem-resistant organisms can be expensive, cumbersome, or require special expertise, and are not ideal for low-resource countries. This work sought to develop and validate a simple, cost-effective method for screening for carbapenem-resistant organisms in drinking water. A fluorogenic substrate was combined with various concentrations of meropenem and vancomycin antibiotics using known carbapenem-resistant and susceptible strains of bacteria. The bacterial strains were used to generate artificially contaminated tap water samples in the laboratory to determine if the combination and concentrations were ideal in selecting for the target organisms. The method was able to select for low numbers of resistant organisms while suppressing non-target tap water organisms. The method was then used to screen 19 samples from New Delhi, India. The method successfully identified eleven organisms clinically resistant to carbapenem antibiotics in seven samples. This work also explored whether or not carbapenem resistance factors can transfer within biofilms similar to those that exist in water distribution systems. Clinical donor strains carrying the blaNDM carbapenem resistance gene were used to transfer the gene to an E. coli intermediate by conjugation. The E. coli was then used to donate the blaNDM gene in both broth and biofilm environments to Pseudomonas aeruginosa, a common biofilm-forming bacteria found in water systems. Transfer of the blaNDM gene to P. aeruginosa was not seen in broth, but was observed in biofilm after a 72-hour incubation of the donor and recipient organism. This indicates that the blaNDM carbapenem resistance gene may be able to transfer within drinking water distribution system biofilms, and biofilms may serve as a source of blaNDM amplification and increased exposure via tap water