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

Antimicrob Agents Chemother. 2020 Apr 21;64(5):e02445-19. doi: 10.1128/AAC.02445-19. Print 2020 Apr 21.

Abstract

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.

Keywords: antimicrobial susceptibility testing; beta-lactams; methicillin-resistant Staphylococcus aureus; sodium bicarbonate.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Anti-Bacterial Agents / pharmacology*
  • Bacteremia / microbiology
  • Cefazolin / pharmacology
  • Humans
  • Methicillin-Resistant Staphylococcus aureus / drug effects*
  • Methicillin-Resistant Staphylococcus aureus / enzymology
  • Methicillin-Resistant Staphylococcus aureus / genetics*
  • Microbial Sensitivity Tests
  • Oxacillin / pharmacology
  • Phenotype
  • Predictive Value of Tests
  • Prevalence
  • Sodium Bicarbonate / pharmacology*
  • Staphylococcal Infections / microbiology
  • beta-Lactams / pharmacology*

Substances

  • Anti-Bacterial Agents
  • beta-Lactams
  • Sodium Bicarbonate
  • Cefazolin
  • Oxacillin