Multiple low-level antibiotic resistance in Aeromonas salmonicida

Area of Science:

• Microbiology
• Bacterial Genetics
• Drug Resistance

Background:

• Aeromonas salmonicida is a significant fish pathogen.
• Antibiotic resistance is a growing concern in aquaculture.
• Understanding resistance mechanisms is crucial for effective treatment.

Purpose of the Study:

• To investigate the mechanisms of multiple low-level antibiotic resistance in Aeromonas salmonicida.
• To identify genetic and protein alterations associated with this resistance.
• To explore the link between antibiotic resistance and virulence.

Main Methods:

• Isolation of antibiotic-resistant mutants from wild-type Aeromonas salmonicida strains.
• Phenotypic characterization of antibiotic susceptibility profiles.
• Analysis of outer membrane protein expression using SDS-PAGE.
• Assessment of exoprotease activity.

Main Results:

• Mutants displayed low-level resistance to beta-lactams, quinolones, tetracyclines, chloramphenicol, and novobiocin.
• Resistance was not observed for higher-molecular-mass antibiotics.
• Mutants showed altered outer membrane protein profiles, lacking a 38.5 kDa protein and gaining a 37 kDa protein.
• Exoprotease activity was absent in resistant mutants.
• Loss of exoprotease activity correlated with multiple antibiotic resistance.

Conclusions:

• Multiple low-level antibiotic resistance in Aeromonas salmonicida is associated with specific outer membrane protein changes and loss of exoprotease activity.
• These alterations may be driven by point mutations.
• The findings suggest a potential link between antibiotic resistance and reduced virulence.