Ceftizoxime Susceptibility Testing 

Ceftizoxime is a third-generation cephalosporin with broad-spectrum activity against Gram-positive and Gram-negative bacteria. It is particularly effective against many Enterobacterales and is commonly used for treating respiratory tract infections, urinary tract infections, intra-abdominal infections, and sepsis. Due to the increasing prevalence of resistance mechanisms such as extended-spectrum beta-lactamases (ESBLs) and AmpC beta-lactamases, susceptibility testing for ceftizoxime is essential to ensure appropriate therapy.

Content:

• Testing Methods:
  • Disk Diffusion (Kirby-Bauer Method):
    • Disks containing ceftizoxime (30 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 is determined using broth microdilution, agar dilution, or automated systems.
    • The MIC is the lowest concentration of ceftizoxime that inhibits visible bacterial growth.
  • E-test (Gradient Diffusion):
    • A strip with a gradient of ceftizoxime concentrations is placed on an agar plate inoculated with the bacterial isolate.

Application:

• Clinical Use:
  • Ceftizoxime is used for treating:
    • Respiratory tract infections, including community-acquired pneumonia (CAP).
    • Complicated urinary tract infections (cUTIs) caused by susceptible organisms.
    • Intra-abdominal infections, often in combination with anaerobic coverage (e.g., metronidazole).
    • Sepsis and bloodstream infections caused by susceptible Gram-negative bacteria.
    • Skin and soft tissue infections.
• Antimicrobial Stewardship:
  • Encourages targeted therapy with ceftizoxime to reduce the unnecessary use of carbapenems or broader-spectrum antibiotics.
  • Promotes de-escalation of therapy based on susceptibility results.
• Epidemiological Surveillance:
  • Tracks resistance trends in Enterobacterales and Haemophilus influenzae.
  • Monitors the prevalence of ESBL- and AmpC-producing organisms.

Ceftizoxime susceptibility testing is critical for guiding therapy in infections caused by Gram-negative bacteria, particularly in the presence of beta-lactamase-mediated resistance. Standardized methods, such as MIC testing and disk diffusion, provide reliable results.