Amikacin Susceptibility Testing 

Aztreonam is a monobactam antibiotic primarily active against Gram-negative bacteria, including Enterobacteriaceae and Pseudomonas aeruginosa. It works by inhibiting bacterial cell wall synthesis through binding to penicillin-binding protein 3 (PBP3). Aztreonam is resistant to many beta-lactamases but remains susceptible to extended-spectrum beta-lactamases (ESBLs) and metallo-beta-lactamases (MBLs). Susceptibility testing for aztreonam is performed to determine its efficacy against specific pathogens and to guide antimicrobial therapy.

Content:

• Testing Methods:
  • Disk Diffusion (Kirby-Bauer Method):
    • Disks containing aztreonam (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 breakpoints.
  • Minimum Inhibitory Concentration (MIC) Testing:
    • MIC is determined using broth microdilution or agar dilution methods.
    • The MIC is the lowest concentration of aztreonam that inhibits visible bacterial growth.
  • E-test (Gradient Diffusion):
    • A strip with a gradient of aztreonam concentrations is placed on an inoculated agar plate.
    • The MIC is determined at the point where bacterial growth intersects the strip.

Application:

• Clinical Use:
  • Aztreonam is used to treat infections caused by susceptible Gram-negative bacteria, including:
    • Urinary tract infections (UTIs).
    • Respiratory tract infections, including hospital-acquired pneumonia.
    • Intra-abdominal infections.
    • Bacteremia and sepsis caused by Gram-negative pathogens.
    • Pseudomonas infections, particularly in patients with beta-lactam allergies.
• Antimicrobial Stewardship:
  • Promotes the appropriate use of aztreonam in infections caused by susceptible bacteria.
  • Helps prevent the overuse of broad-spectrum antibiotics when aztreonam is effective.
• Epidemiological Surveillance:
  • Tracks resistance patterns in key pathogens, such as Pseudomonas aeruginosa and Enterobacteriaceae.

Aztreonam susceptibility testing is crucial for determining its efficacy against Gram-negative pathogens, especially in patients with beta-lactam allergies. Standardized testing methods, including disk diffusion, MIC determination, and automated systems, provide reliable results.