title: β-Lactam resistance in methicillin-resistant Staphylococcus aureus USA300 is increased by inactivation of the ClpXP protease.
abstract: Methicillin-resistant Staphylococcus aureus (MRSA) has acquired the mecA gene encoding a peptidoglycan transpeptidase, penicillin binding protein 2a (PBP2a), which has decreased affinity for β-lactams. Quickly spreading and highly virulent community-acquired (CA) MRSA strains recently emerged as a frequent cause of infection in individuals without exposure to the health care system. In this study, we found that the inactivation of the components of the ClpXP protease substantially increased the β-lactam resistance level of a CA-MRSA USA300 strain, suggesting that the proteolytic activity of ClpXP controls one or more pathways modulating β-lactam resistance. These pathways do not involve the control of mecA expression, as the cellular levels of PBP2a were unaltered in the clp mutants. An analysis of the cell envelope properties of the clpX and clpP mutants revealed a number of distinct phenotypes that may contribute to the enhanced β-lactam tolerance. Both mutants displayed significantly thicker cell walls, increased peptidoglycan cross-linking, and altered composition of monomeric muropeptide species compared to those of the wild types. Moreover, changes in Sle1-mediated peptidoglycan hydrolysis and altered processing of the major autolysin Atl were observed in the clp mutants. In conclusion, the results presented here point to an important role for the ClpXP protease in controlling cell wall metabolism and add novel insights into the molecular factors that determine strain-dependent β-lactam resistance.
authors.affiliation: Faculty of Health and Medical Sciences, Department of Veterinary Disease Biology, University of Copenhagen, Frederiksberg, Denmark.
authors.forename: Kristoffer T
authors.initials: KT
authors.lastname: Bæk
authors.affiliation: Section of Microbiology and MRC Centre for Molecular Bacteriology and Infection, Imperial College London, London, United Kingdom.
authors.forename: Angelika
authors.initials: A
authors.lastname: Gründling
authors.affiliation: Faculty of Health and Medical Sciences, Department of Veterinary Disease Biology, University of Copenhagen, Frederiksberg, Denmark.
authors.forename: René G
authors.initials: RG
authors.lastname: Mogensen
authors.affiliation: Faculty of Health and Medical Sciences, Department of Veterinary Disease Biology, University of Copenhagen, Frederiksberg, Denmark.
authors.forename: Louise
authors.initials: L
authors.lastname: Thøgersen
authors.affiliation: Statens Serum Institut, Copenhagen, Denmark.
authors.forename: Andreas
authors.initials: A
authors.lastname: Petersen
authors.affiliation: Faculty of Health and Medical Sciences, Department of Veterinary Disease Biology, University of Copenhagen, Frederiksberg, Denmark.
authors.forename: Wilhelm
authors.initials: W
authors.lastname: Paulander
authors.affiliation: Faculty of Health and Medical Sciences, Department of Veterinary Disease Biology, University of Copenhagen, Frederiksberg, Denmark df@sund.ku.dk.
authors.forename: Dorte
authors.initials: D
authors.lastname: Frees
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins; D002473:Cell Wall / Q000187:drug effects / Q000201:enzymology / Q000235:genetics*; D049071:Endopeptidase Clp / Q000172:deficiency / Q000235:genetics*; D015964:Gene Expression Regulation, Bacterial; D007527:Isoenzymes / Q000172:deficiency / Q000235:genetics; D053858:Metabolic Networks and Pathways / Q000235:genetics; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects / Q000201:enzymology / Q000235:genetics*; D009154:Mutation; D009238:N-Acetylmuramoyl-L-alanine Amidase / Q000235:genetics / Q000378:metabolism; D046915:Penicillin-Binding Proteins; D010457:Peptidoglycan / Q000378:metabolism; D018440:beta-Lactam Resistance / Q000235:genetics*; D047090:beta-Lactams / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D007527:Isoenzymes; D046915:Penicillin-Binding Proteins; D010457:Peptidoglycan; D047090:beta-Lactams; C487789:mecA protein, Staphylococcus aureus; D049071:Endopeptidase Clp; D009238:N-Acetylmuramoyl-L-alanine Amidase