Bacterial infections rendered almost untreatable by resistance to last-line antibiotics such as carbapenems are now a common occurrence worldwide. Genes conferring carbapenem resistance are commonly associated with structures called integrons, but little is known about their regulation, particularly in species of clinical importance. Integron gene expression is regulated by two divergently orientated promoters (Pc and Pint) that co-ordinate the expression of the resistance gene cassettes and the integron integrase, respectively. This PhD aimed to use a rational high-throughput approach to identify novel regulators of clinical integrons in the pathogenic species Pseudomonas aeruginosa. We hypothesised that the opposing physiological roles of integrase and cassette expression would result in mutually exclusive expression from the two promoters.

To explore regulation of integron promoter activity, a carbapenemase-containing integron from a clinical source was identified, sourced, and modified to allow investigation of integron promoter activities in P. aeruginosa through transcriptional reporters of Pc and Pint activity. A functional analysis of carbapenem susceptibility was also performed through assessment of carbapenemase expression from Pc.

From these examinations, we report the first evidence of carbon source dependent regulation of mobile integrons, via the Pseudomonas catabolite regulatory control system, crc and cbrAB, demonstrating that there is a clear need for further study before the full nature of integron regulation in response to pressures from the ambient environment is understood.

Furthermore, we have validated the use of a compendium approach to simultaneously examine large numbers of potential regulatory targets, by identifying at least one further effector of regulatory control of integron promoters: PA14_31900, which encodes the MuxC component of the MuxABC-OpmB RND-type efflux pump. A PA14_31900 loss of function mutant exhibits decreased in vitro transcription from Pint, increased in vitro transcription from Pc, and increased resistance to carbapenems in vitro and in vivo, in a murine model of gastrointestinal colonisation.