Under a very high magnification of 20,000x, this scanning electron micrograph (SEM) shows a strain of Staphylococcus aureus bacteria taken from a vancomycin intermediate resistant culture (VISA).
Under SEM, one can not tell the difference between bacteria that are susceptible, or multidrug resistant, but with transmission electron microscopy (TEM), at least with VISA isolates one can see a thickening in the cell wall that may attribute to their reduced susceptibility to vancomycin . See PHIL 11157 for a colorized version of this image. VISA and VRSA are specific types of antimicrobial-resistant staph bacteria. While most staph bacteria are susceptible to the antimicrobial agent vancomycin some have developed resistance. VISA and VRSA cannot be successfully treated with vancomycin because these organisms are no longer susceptibile to vancomycin. However, to date, all VISA and VRSA isolates have been susceptible to other Food and Drug Administration (FDA) approved drugs.