Amikacin Susceptibility Testing 

Ceftazidime-avibactam is a combination of a third-generation cephalosporin (ceftazidime) and a beta-lactamase inhibitor (avibactam). This combination is designed to overcome resistance caused by beta-lactamase-producing organisms, including extended-spectrum beta-lactamases (ESBLs), AmpC beta-lactamases, and certain carbapenemases (e.g., KPC and OXA-48). However, it is not effective against metallo-beta-lactamases (MBLs) such as NDM, VIM, or IMP. Susceptibility testing is essential to determine its efficacy against multidrug-resistant Gram-negative pathogens.

Content:

• Testing Methods:
  • Disk Diffusion (Kirby-Bauer Method):
    • Disks containing ceftazidime-avibactam (30/20 µg) are placed on Mueller-Hinton agar plates 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 testing is performed using broth microdilution, agar dilution, or automated systems.
    • The MIC is the lowest concentration of ceftazidime-avibactam that inhibits visible bacterial growth.
• • Automated Systems:
    • Platforms like Vitek, Phoenix, or MicroScan may include ceftazidime-avibactam in their susceptibility testing panels.

Application:

• Clinical Use:
  • Ceftazidime-avibactam is used for treating:
    • Complicated urinary tract infections (cUTIs), including pyelonephritis.
    • Complicated intra-abdominal infections (cIAIs), often in combination with metronidazole for anaerobic coverage.
    • Hospital-acquired and ventilator-associated pneumonia (HAP/VAP) caused by multidrug-resistant Gram-negative organisms.
    • Bloodstream infections (BSIs) caused by carbapenem-resistant Enterobacterales (CRE) or Pseudomonas aeruginosa.
    • Infections caused by carbapenemase-producing organisms (KPC, OXA-48-like).
• Antimicrobial Stewardship:
  • Encourages the targeted use of ceftazidime-avibactam in resistant infections to preserve the activity of other last-line agents like carbapenems.
  • Supports de-escalation of therapy based on susceptibility results to avoid unnecessary exposure to broader-spectrum agents.
  • Promotes its use as an alternative to colistin or tigecycline for carbapenem-resistant organisms.

Ceftazidime-avibactam susceptibility testing is essential for guiding therapy in infections caused by multidrug-resistant Gram-negative bacteria, including carbapenemase-producing organisms. Standardized methods such as disk diffusion and MIC testing provide reliable results.