Cefazolin Susceptibility Testing 

Cefazolin is a first-generation cephalosporin antibiotic with activity primarily against Gram-positive bacteria and limited activity against certain Gram-negative bacteria. It is widely used in the treatment of skin and soft tissue infections, surgical prophylaxis, and uncomplicated urinary tract infections. Susceptibility testing for cefazolin is essential to determine its efficacy against specific bacterial pathogens and guide clinical therapy, especially in light of beta-lactamase-mediated resistance in some bacteria.

Content:

• Testing Methods:
  • Disk Diffusion (Kirby-Bauer Method):
    • Disks containing cefazolin (30 µg) are placed on an agar plate inoculated with the bacterial isolate.
    • After incubation, the diameter of the inhibition zone is measured and interpreted using CLSI or EUCAST guidelines.
  • Minimum Inhibitory Concentration (MIC) Testing:
    • MIC is determined using broth microdilution or agar dilution methods.
    • The MIC is the lowest concentration of cefazolin that inhibits visible bacterial growth.
• • Automated Testing Systems:
    • Automated systems such as Vitek, Phoenix, or MicroScan may provide MIC values for cefazolin.

Application:

• Clinical Use:
  • Cefazolin is widely used for:
    • Surgical prophylaxis.
    • Skin and soft tissue infections caused by susceptible Gram-positive bacteria.
    • Urinary tract infections caused by E. coli or Proteus mirabilis.
    • Bone and joint infections caused by susceptible Staphylococcus aureus.
• Antimicrobial Stewardship:
  • Promotes cefazolin use for infections caused by susceptible organisms to reduce reliance on broader-spectrum cephalosporins.
  • Encourages switching to cefazolin when susceptibility results confirm its activity, minimizing resistance development.
• Epidemiological Surveillance:
  • Monitors resistance trends in Staphylococcus aureus, E. coli, and Klebsiella pneumoniae.
  • Tracks the prevalence of ESBL-producing Enterobacterales, which are resistant to cefazolin.

Cefazolin susceptibility testing is critical to determine its efficacy against Gram-positive and certain Gram-negative bacteria. Standardized methods, such as disk diffusion and MIC testing, provide reliable results for guiding therapy.