Medium-dependent activity of gentamicin sulfate against enterococci

Area of Science:

• Clinical microbiology
• Antimicrobial susceptibility testing

Background:

• Enterococci are significant human pathogens.
• Accurate susceptibility testing is crucial for effective gentamicin therapy.
• Previous studies suggest variability in enterococcal gentamicin susceptibility.

Purpose of the Study:

• To investigate the medium-dependent activity of gentamicin against clinical enterococcal isolates.
• To compare gentamicin susceptibility results across different agar and broth media.
• To evaluate the correlation of in vitro results with potential in vivo conditions (serum/urine).

Main Methods:

• Disc diffusion (Bauer-Kirby technique) and agar dilution methods were employed.
• Testing utilized Mueller-Hinton agar with 5% sheep blood, and Brain Heart Infusion (BHI) and Trypticase soy (TS) broth/agar.
• Gentamicin sulfate discs (10-mug) were used for diffusion tests.

Main Results:

• Enterococcal isolates showed sensitivity to gentamicin on Mueller-Hinton agar with 5% sheep blood.
• Conversely, isolates demonstrated resistance when tested in BHI and TS broth or agar.
• Supplementation with 5% sheep blood enhanced gentamicin activity in BHI and TS agars.

Conclusions:

• Gentamicin exhibits significant medium-dependent activity against enterococci.
• Standard Mueller-Hinton agar with blood is more reliable for assessing gentamicin activity than BHI or TS media.
• Correlation with gentamicin activity in human serum or urine was not established due to suboptimal enterococcal growth.