Aminoglycoside modification by gentamicin-resistant isolates of Staphylococcus aureus

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Clinical isolates of Staphylococcus aureus harbor plasmids conferring aminoglycoside resistance.
• Aminoglycoside-modifying enzymes are a common mechanism of antibiotic resistance.

Purpose of the Study:

• To investigate the specific modifying enzymes responsible for aminoglycoside resistance in three clinical Staphylococcus aureus isolates.
• To confirm the plasmid-borne nature of these resistance mechanisms.

Main Methods:

• Screening of wild-type and heat-cured Staphylococcus aureus isolates for acetyl-, adenylyl-, and phosphotransferase activities.
• Testing enzyme activity against aminoglycoside substrates: gentamicin, amikacin, and netilmicin.

Main Results:

• All three types of modifying enzyme activities (acetyl-, adenylyl-, phosphotransferase) were detected in the wild-type isolates.
• Phosphotransferase activity was identified as the predominant enzyme conferring resistance to gentamicin, amikacin, and netilmicin.
• Heat-cured derivatives, lacking the plasmid, showed the absence of these modifying activities.

Conclusions:

• The study confirms that aminoglycoside resistance in these Staphylococcus aureus strains is plasmid-mediated.
• Phosphotransferase activity is the principal mechanism of resistance to the tested aminoglycosides.
• Plasmid loss eliminates the expression of aminoglycoside-modifying enzymes.