title: Whole-Genome Sequencing of Methicillin-Resistant Staphylococcus aureus Resistant to Fifth-Generation Cephalosporins Reveals Potential Non-mecA Mechanisms of Resistance.
abstract: Fifth-generation cephalosporins, ceftobiprole and ceftaroline, are promising drugs for treatment of bacterial infections from methicillin-resistant Staphylococcus aureus (MRSA). These antibiotics are able to bind native PBP2a, the penicillin-binding protein encoded by the mecA resistance determinant that mediates broad class resistance to nearly all other beta-lactam antibiotics, at clinically achievable concentrations. Mechanisms of resistance to ceftaroline based on mecA mutations have been previously described. Here we compare the genomes of 11 total parent-daughter strains of Staphylococcus aureus for which specific selection by serial passaging with ceftaroline or ceftobiprole was used to identify novel non-mecA mechanisms of resistance. All 5 ceftaroline-resistant strains, derived from 5 different parental strains, contained mutations directly upstream of the pbp4 gene (coding for the PBP4 protein), including four with the same thymidine insertion located 377 nucleotides upstream of the promoter site. In 4 of 5 independent ceftaroline-driven selections, we also isolated mutations to the same residue (Asn138) in PBP4. In addition, mutations in additional candidate genes such as ClpX endopeptidase, PP2C protein phosphatase and transcription terminator Rho, previously undescribed in the context of resistance to ceftaroline or ceftobiprole, were detected in multiple selections. These genomic findings suggest that non-mecA mechanisms, while yet to be encountered in the clinical setting, may also be important in mediating resistance to 5th-generation cephalosporins.
authors.affiliation: Department of Laboratory Medicine, University of California San Francisco, San Francisco, California, United States of America.|UCSF-Abbott Viral Diagnostics and Discovery Center, San Francisco, California, United States of America.
authors.forename: Alexander L
authors.initials: AL
authors.lastname: Greninger
authors.affiliation: Division of Infectious Diseases, Department of Medicine, San Francisco General Hospital, San Francisco, California, United States of America.
authors.forename: Som S
authors.initials: SS
authors.lastname: Chatterjee
authors.affiliation: Division of Infectious Diseases, Department of Medicine, San Francisco General Hospital, San Francisco, California, United States of America.
authors.forename: Liana C
authors.initials: LC
authors.lastname: Chan
authors.affiliation: Division of Infectious Diseases, Department of Medicine, San Francisco General Hospital, San Francisco, California, United States of America.
authors.forename: Stephanie M
authors.initials: SM
authors.lastname: Hamilton
authors.affiliation: Division of Infectious Diseases, Department of Medicine, San Francisco General Hospital, San Francisco, California, United States of America.
authors.forename: Henry F
authors.initials: HF
authors.lastname: Chambers
authors.affiliation: Department of Laboratory Medicine, University of California San Francisco, San Francisco, California, United States of America.|UCSF-Abbott Viral Diagnostics and Discovery Center, San Francisco, California, United States of America.
authors.forename: Charles Y
authors.initials: CY
authors.lastname: Chiu
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002511:Cephalosporins / Q000494:pharmacology*; D016680:Genome, Bacterial; D016106:Methicillin Resistance / Q000187:drug effects / Q000235:genetics*; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects / Q000235:genetics*; D008958:Models, Molecular; D009154:Mutation / Q000235:genetics; D016366:Open Reading Frames / Q000235:genetics; D046915:Penicillin-Binding Proteins / Q000737:chemistry / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000235:genetics; D017422:Sequence Analysis, DNA; D047090:beta-Lactams / Q000494:pharmacology; D000097583:Ceftaroline
chemical_list: D001426:Bacterial Proteins; D002511:Cephalosporins; D046915:Penicillin-Binding Proteins; D047090:beta-Lactams; D000097583:Ceftaroline