Emergence of cephalosporin resitance in cephalosporin-sensitive class A penicillin binding protein mutants in Enterococcus faecium

E. faecium is inherantly resistant to cephalosporins. Resistance is lost in Class A penicillin binding protein PbfF PonA mutants, but is reversible by pencillin exposure. E. faecium Affymetrix GeneChips were used to compare E. faecium expression properties of pbfF ponA mutant cells in the absence or presence of penicillin exposure. Significant differences were observed between the expression properties of mock and penicillin treated E. faecium CV571 (pbfF ponA double mutant) cells. E. faecium strain CV571 (pbfF ponA) were grown in laboratory medium to exponential under aerobic growth conditions. Cells were either mock treated or treated with penicillin for 30 min, total bacterial RNA was isolated, labeled and applied to Affymetrix GeneChips. We sought to determine whether the transcriptional profiles of E. faecium pbfF ponA mutant cells of penicillin challenged cells differed from that of mock treated CV571 cells.