In vitro response of Enterobacter to ampicillin.

Area of Science:

• Microbiology
• Bacterial resistance mechanisms

Background:

• Enterobacter species are known to develop antibiotic resistance.
• Ampicillin resistance in bacteria can be influenced by environmental factors and genetic mutations.

Purpose of the Study:

• To investigate the mechanisms of ampicillin resistance in three Enterobacter strains.
• To characterize the antibiotic inactivation capabilities of resistant mutants.
• To explain observed discrepancies in antibiotic susceptibility testing.

Main Methods:

• Studying Enterobacter strains' response to ampicillin across different media.
• Selecting and analyzing ampicillin-resistant mutants.
• Utilizing biological assays to measure antibiotic inactivation.
• Comparing results with traditional broth dilution and automated procedures.

Main Results:

• A baseline ampicillin resistance was observed, dependent on the growth medium.
• High-level mutational resistance occurred at a frequency of 10(-5) to 10(-7).
• Two distinct mutant classes emerged: one with significantly enhanced antibiotic inactivation, the other similar to the wild type.
• Both mutant classes exhibited cross-resistance to other beta-lactam antibiotics.

Conclusions:

• Mutations in Enterobacter can lead to significant ampicillin inactivation and broad beta-lactam cross-resistance.
• The characterized resistance mechanisms help reconcile differences between standard and automated antibiotic testing methods.
• Understanding these resistance patterns is crucial for effective antimicrobial therapy and diagnostics.