Antimicrobial susceptibility testing for Gram positive cocci towards vancomycin using scanning electron microscopy.

Area of Science:

• Microbiology
• Microscopy
• Infectious Diseases

Background:

• Rapid detection of antibiotic-resistant bacteria is crucial for effective treatment and antibiotic stewardship.
• Nosocomial infections caused by resistant pathogens necessitate advanced antimicrobial susceptibility testing (AST).

Purpose of the Study:

• To establish a proof-of-concept for a novel phenotypic AST strategy using scanning electron microscopy (SEM).
• To evaluate SEM for rapid detection of vancomycin resistance in Gram-positive cocci.

Main Methods:

• Phenotypic AST was performed on *Enterococcus faecalis*, *Enterococcus faecium*, and *Staphylococcus aureus* isolates.
• Scanning electron microscopy (SEM) was optimized for analyzing ultrastructural modifications after short vancomycin exposure.
• Two analytical strategies involving high and low magnification micrographs were employed to assess bacterial morphology and quantify changes.

Main Results:

• Susceptible strains showed reduced septation and increased cell size compared to controls.
• Resistant strains exhibited multiple septa formation at later timepoints.
• SEM analysis successfully discriminated between vancomycin-susceptible and resistant cocci within one hour.

Conclusions:

• SEM offers a promising new phenotypic AST strategy for rapid vancomycin resistance detection in Gram-positive cocci.
• The developed analytical strategies can potentially be integrated with AI for automated SEM-AST assays.
• This approach can significantly improve antibiotic stewardship and patient outcomes by enabling faster treatment decisions.