Sentence:  Note that "L.[Listeria] monocytogenes" is one of the few <WSD>Gram-positive</WSD> bacteria against which vancomycin is not effective — hence the need for ampicillin. 
Meaning of the word marked with <WSD> tags:  That stains dark blue or violet after Gram staining, due to large quantities of peptidoglycan in the cell wall.