Dissociated resistance among cephalosporins

Area of Science:

• Microbiology
• Bacteriology
• Antimicrobial Resistance

Background:

• Enterobacter species can develop resistance to antibiotics.
• Cephalosporins and penicillins are important classes of antibiotics.
• Understanding mechanisms of antibiotic resistance is crucial for effective treatment.

Purpose of the Study:

• To investigate the effect of cefoxitin (FOX) on the susceptibility of Enterobacter to cefuroxime (CXM) and HR 756.
• To identify potential mechanisms of induced resistance.
• To determine the reversibility of FOX-induced resistance.

Main Methods:

• Disk diffusion assays on agar plates.
• Checkerboard titration in broth cultures.
• Retesting of resistant colonies for susceptibility.
• Culturing and characterization of resistant mutants.

Main Results:

• Cefoxitin (FOX) disks adjacent to cefuroxime (CXM) or HR 756 disks showed reduced zones of inhibition against FOX-resistant Enterobacter.
• Organisms growing in broth with high concentrations of CXM or HR 756 plus FOX became resistant to these drugs.
• Enterobacter broth cultures contained mutants resistant to and inactivating CXM and HR 756.
• FOX induced resistance in Enterobacter to nine cephalosporins and four penicillins, which rapidly reverted upon FOX removal.

Conclusions:

• Cefoxitin (FOX) can induce a transient state of resistance in Enterobacter to multiple beta-lactam antibiotics, including cephalosporins and penicillins.
• This induced resistance is mediated by properties acquired by the bacteria, possibly through the action of FOX.
• The resistance is reversible, suggesting a regulatory mechanism rather than stable genetic mutation.