Ceftolozane Susceptibility Testing 

Ceftolozane-tazobactam is a combination of a novel cephalosporin (ceftolozane) with a beta-lactamase inhibitor (tazobactam). This combination is designed to treat Gram-negative infections, including multidrug-resistant (MDR) strains of Pseudomonas aeruginosa and Enterobacterales. It is particularly effective against strains producing extended-spectrum beta-lactamases (ESBLs) and AmpC beta-lactamases. Susceptibility testing is critical for guiding therapy, especially in patients with infections caused by resistant pathogens.

Content:

• Testing Methods:
  • Disk Diffusion (Kirby-Bauer Method):
    • Disks containing ceftolozane-tazobactam (30/10 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 ceftolozane-tazobactam that inhibits visible bacterial growth.

Application:

• Clinical Use:
  • Ceftolozane-tazobactam 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 susceptible Gram-negative organisms.
    • Bloodstream infections (BSIs) caused by multidrug-resistant Pseudomonas aeruginosa and ESBL-producing Enterobacterales.
  • Susceptibility testing ensures its efficacy, particularly for multidrug-resistant infections.
• Antimicrobial Stewardship:
  • Promotes the appropriate use of ceftolozane-tazobactam in resistant infections to reduce reliance on colistin or tigecycline.
  • Supports de-escalation of therapy based on susceptibility results, avoiding unnecessary exposure to broader-spectrum agents.
  • Encourages its use as an alternative to carbapenems for infections caused by ESBL-producing Enterobacterales.

Ceftolozane-tazobactam susceptibility testing is essential for managing infections caused by multidrug-resistant Gram-negative bacteria, particularly Pseudomonas aeruginosa and ESBL-producing Enterobacterales. Standardized methods, such as MIC testing and disk diffusion, ensure reliable results.