Cefotaxime Susceptibility Testing 

Cefotaxime is a third-generation cephalosporin antibiotic with broad-spectrum activity against Gram-positive and Gram-negative bacteria, including members of the Enterobacterales family. It is widely used to treat serious bacterial infections, including meningitis, pneumonia, urinary tract infections (UTIs), and septicemia. Susceptibility testing for cefotaxime is essential, particularly in light of increasing resistance due to extended-spectrum beta-lactamases (ESBLs) and other resistance mechanisms.

Content:

• Testing Methods:
  • Disk Diffusion (Kirby-Bauer Method):
    • Disks containing cefotaxime (30 µg) are placed on Mueller-Hinton agar plates inoculated with the bacterial isolate.
    • After incubation, the zone of inhibition 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 cefotaxime that inhibits visible bacterial growth.
  • E-test (Gradient Diffusion):
    • A strip with a gradient of cefotaxime concentrations is placed on an inoculated agar plate.
    • The MIC is determined at the point where the elliptical growth inhibition zone intersects the strip.

Application:

• Clinical Use:
  • Cefotaxime is used for treating:
    • Meningitis caused by susceptible Streptococcus pneumoniae and Haemophilus influenzae.
    • Community-acquired pneumonia (CAP).
    • Urinary tract infections (UTIs) caused by E. coli and other susceptible organisms.
    • Intra-abdominal infections (often in combination with metronidazole for anaerobic coverage).
    • Sepsis and bloodstream infections caused by Enterobacterales.
  • Susceptibility testing ensures its efficacy in treating infections caused by resistant organisms.
• Antimicrobial Stewardship:
  • Encourages targeted use of cefotaxime when susceptibility is confirmed, avoiding overuse of broader-spectrum antibiotics.
• Epidemiological Surveillance:
  • Tracks resistance trends in Enterobacterales, particularly the prevalence of ESBL-producing strains.

Cefotaxime susceptibility testing is critical for managing infections caused by Gram-positive and Gram-negative bacteria, particularly in the context of rising resistance due to ESBLs and AmpC beta-lactamases. Standardized methods like MIC testing and disk diffusion ensure reliable results.