title: Characterization of methicillin-resistant Staphylococcus aureus displaying increased MICs of ceftaroline.
abstract: OBJECTIVE
  To characterize the mechanisms responsible for elevated MICs of ceftaroline for methicillin-resistant Staphylococcus aureus (MRSA).
  
  
  METHODS
  During the 2008 Assessing Worldwide Antimicrobial Resistance Evaluation ('AWARE') surveillance programme, four S. aureus collected from separate patients in Athens, Greece, demonstrated ceftaroline MICs of 4 mg/L. These isolates were clonally related and one strain (13101) was selected for further characterization. Two strains (4981 and 4977) displaying ceftaroline MICs of 1 and 2 mg/L, respectively, were included for comparison. All strains originated from the same hospital. Penicillin-binding protein (PBP) affinities for ceftaroline and comparators were determined. Strains were typed by single-locus typing (i.e. spa typing), multilocus sequence typing ('MLST') and by multiple-locus variable-number tandem repeat fingerprinting (MLVF). The presence of Pantone-Valentine leucocidin and the staphylococcal cassette chromosome mec types was assessed. We also performed nucleotide sequencing of the mecA (encoding PBP2a) promoter and ribosomal binding site (rbs) regions and mecR1.
  
  
  RESULTS
  Ceftaroline demonstrated the highest PBP2a affinity with strain 4981 (ST5-MRSA-II) (IC(50) 0.06 mg/L; MIC 1 mg/L). Strains 4977 and 13101 (both ST239-MRSA-III) showed indistinguishable MLVF profiles. Ceftaroline PBP2a binding affinity in strains 4977 (IC(50) 0.25 mg/L; MIC 2 mg/L) and 13101 (IC(50) 1 mg/L; MIC 4 mg/L) was 4- and 16-fold lower than 4981, respectively. Strain 4981 contains a wild-type PBP2a, while strains 4977 and 13101 have N(146)K and E(150)K alterations in the non-penicillin-binding domain. Additionally, 13101 has one substitution (H(351)N) in the transpeptidase domain. Alterations in the mecR1, mecA promoter or rbs regions were not observed.
  
  
  CONCLUSIONS
  Increased ceftaroline MICs were associated with decreased PBP2a binding affinity and reflected alterations in PBP2a.
authors.affiliation: JMI Laboratories, North Liberty, IA 52317,  USA.
authors.forename: Rodrigo E
authors.initials: RE
authors.lastname: Mendes
authors.forename: Athanassios
authors.initials: A
authors.lastname: Tsakris
authors.forename: Helio S
authors.initials: HS
authors.lastname: Sader
authors.forename: Ronald N
authors.initials: RN
authors.lastname: Jones
authors.forename: Donald
authors.initials: D
authors.lastname: Biek
authors.forename: Pamela
authors.initials: P
authors.lastname: McGhee
authors.forename: Peter C
authors.initials: PC
authors.lastname: Appelbaum
authors.forename: Klaudia
authors.initials: K
authors.lastname: Kosowska-Shick
mesh_terms: D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics; D001427:Bacterial Toxins / Q000235:genetics; D002511:Cephalosporins / Q000494:pharmacology*; D016172:DNA Fingerprinting; D005098:Exotoxins / Q000235:genetics; D005838:Genotype; D006115:Greece; D006801:Humans; D007956:Leukocidins / Q000235:genetics; D055624:Methicillin-Resistant Staphylococcus aureus / Q000145:classification / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D058889:Molecular Typing; D046915:Penicillin-Binding Proteins / Q000378:metabolism; D011485:Protein Binding; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D013203:Staphylococcal Infections / Q000382:microbiology*; D037521:Virulence Factors / Q000235:genetics; D000097583:Ceftaroline
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D002511:Cephalosporins; D005098:Exotoxins; D007956:Leukocidins; D046915:Penicillin-Binding Proteins; D037521:Virulence Factors; D000097583:Ceftaroline; C078284:Panton-Valentine leukocidin; C487789:mecA protein, Staphylococcus aureus; C101641:mecR1 protein, Staphylococcus aureus