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Scope and Predictive Genetic/Phenotypic Signatures of Bicarbonate (NaHCO3) Responsiveness and β-Lactam Sensitization in Methicillin-Resistant Staphylococcus aureus.

  • Author(s): Ersoy, Selvi C
  • Otmishi, Mariam
  • Milan, Vanessa T
  • Li, Liang
  • Pak, Youngju
  • Mediavilla, Jose
  • Chen, Liang
  • Kreiswirth, Barry
  • Chambers, Henry F
  • Proctor, Richard A
  • Xiong, Yan Q
  • Fowler, Vance G
  • Bayer, Arnold S
  • et al.

Addition of sodium bicarbonate (NaHCO3) to standard antimicrobial susceptibility testing medium reveals certain methicillin-resistant Staphylococcus aureus (MRSA) strains to be highly susceptible to β-lactams. We investigated the prevalence of this phenotype (NaHCO3 responsiveness) to two β-lactams among 58 clinical MRSA bloodstream isolates. Of note, ∼75% and ∼36% of isolates displayed the NaHCO3 responsiveness phenotype to cefazolin (CFZ) and oxacillin (OXA), respectively. Neither intrinsic β-lactam MICs in standard Mueller-Hinton broth (MHB) nor population analysis profiles were predictive of this phenotype. Several genotypic markers (clonal complex 8 [CC8]; agr I and spa t008) were associated with NaHCO3 responsiveness for OXA.

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