Vancomycin-intermediate S. aureus (VISA)

Definition

Vancomycin-intermediate S. aureus (VISA) is a strain of Staphylococcus aureus with intermediate resistance to vancomycin. This reduced susceptibility complicates treatment options for infections.

5 Must Know Facts For Your Next Test

1. VISA strains have a vancomycin MIC (minimum inhibitory concentration) of 4-8 μg/mL.
2. The mechanism of resistance in VISA involves thickening of the bacterial cell wall.
3. VISA was first identified in Japan in 1996.
4. Treatment options for VISA infections often include alternative antibiotics like linezolid or daptomycin.
5. Detection of VISA requires specialized laboratory testing to differentiate from vancomycin-susceptible and vancomycin-resistant strains.

Review Questions

• What is the minimum inhibitory concentration (MIC) range for VISA?
• Describe one mechanism that contributes to the intermediate resistance in VISA strains.
• Name two alternative antibiotics commonly used to treat VISA infections.

Related terms

MRSA: Methicillin-resistant Staphylococcus aureus, a type of staph bacteria resistant to methicillin and other common antibiotics.

VRSA: Vancomycin-resistant Staphylococcus aureus, a strain of Staphylococcus aureus that shows complete resistance to vancomycin.

MIC: Minimum inhibitory concentration, the lowest concentration of an antimicrobial agent that inhibits the visible growth of a microorganism after overnight incubation.