Mutations in the β subunit of RNA polymerase alter intrinsic cephalosporin resistance in Enterococci.

As major causes of hospital-acquired infections, antibiotic-resistant enterococci are a serious public health concern. Enterococci are intrinsically resistant to many cephalosporin antibiotics, a trait that enables proliferation in patients undergoing cephalosporin therapy. Although a few genetic determinants of cephalosporin resistance in enterococci have been described, overall, many questions remain about the underlying genetic and biochemical basis for cephalosporin resistance. Here we describe an unexpected effect of specific mutations in the β subunit of RNA polymerase (RNAP) on intrinsic cephalosporin resistance in enterococci. We found that RNAP mutants, selected initially on the basis of their ability to provide resistance to rifampin, resulted in allele-specific alterations of the intrinsic resistance of enterococci toward expanded- and broad-spectrum cephalosporins. These mutations did not affect resistance toward a diverse collection of other antibiotics that target a range of alternative cellular processes. We propose that the RNAP mutations identified here lead to alterations in transcription of as-yet-unknown genes that are critical for cellular adaption to cephalosporin stress.