Staphylococcus epidermidis is an important opportunistic pathogen associated with a range of chronic healthcare-associated infections often involving biofilm. As part of efforts to understand the regulation of biofilm in clinical isolates of S. epidermidis, we identified an cerebrospinal fluid isolate (CSF41498) from Beaumont Hospital Dublin that exhibited a growth defect in low-phosphate culture media. Phosphate utilisation is important for pathogen resistance to nitric oxide stress and growth at alkaline pH suggesting that it may represent a novel antimicrobial drug target. To investigate this possibility, we isolated suppressor mutants of CSF41498 that exhibited normal patterns of growth in low-phosphate media. Whole genome sequence analysis identified an intriguing single amino acid substitution in a nucleotide (uracil) permease in all of the suppressor mutants examined. This project will begin to characterise the role of this permease in growth under low phosphate conditions, as well as its role in resistance to nucleoside analogue drugs such as 5-fluorouracil (5FU) and thioguanine (TG). A permease mutant will be constructed by allele replacement and the impact of this mutation on growth in low-phosphate medium and resistance to 5FU and TG characterised. Phage transduction will be employed to transfer this mutation to device-related and diabetic foot disease isolates of S. epidermidis. These experiments will provide novel insights on a potential new drug target in S. epidermidis and the relationship between phosphate utilisation and purine/pyrimidine analogue drug resistance.
