Cefoxitin sensitivity as a marker for inducible beta-lactamases.

Area of Science:

• Microbiology
• Clinical Pharmacy
• Infectious Diseases

Background:

• Beta-lactamase enzymes confer resistance to beta-lactam antibiotics.
• Inducible beta-lactamase production can lead to treatment failures.
• Accurate prediction of beta-lactamase inducibility is essential for effective antimicrobial therapy.

Purpose of the Study:

• To investigate the inducibility of beta-lactamase activity by cefoxitin in resistant gram-negative clinical isolates.
• To determine if bacterial identification and cefoxitin susceptibility can predict beta-lactamase induction.
• To compare the inducibility of beta-lactamase activity against cefotaxime, cefoperazone, and latamoxef.

Main Methods:

• Examined beta-lactamase inducibility by cefoxitin in 626 gram-negative clinical isolates resistant to amoxycillin and cephalothin.
• Utilized precise bacterial identification and cefoxitin sensitivity/resistance testing.
• Compared beta-lactamase activities against cefotaxime, cefoperazone, and latamoxef.

Main Results:

• Beta-lactamase induction was observed in 68% of 326 inducible species and was predictable by identification and cefoxitin data.
• No induction occurred in other species.
• Induction rates against cefotaxime and cefoperazone were similar; minimal induction occurred against latamoxef.
• Many Enterobacteriaceae strains with inducible beta-lactamases would be misclassified as susceptible to third-generation cephalosporins using disk diffusion alone.
• Pseudomonas strains showed higher resistance to tested cephalosporins and produced inducible enzymes.

Conclusions:

• Precise identification and cefoxitin susceptibility testing are reliable predictors of beta-lactamase inducibility.
• Disk diffusion may underestimate resistance in strains with inducible beta-lactamases, particularly Enterobacteriaceae.
• Inducible beta-lactamase production poses a significant challenge for cephalosporin therapy in gram-negative infections.