Gram-positive

Generally, ionophore antibiotics are highly effective against Gram-positive bacteria but exhibit little or no activity against Gram-negative bacteria (Chen and Wolin, 1979; Watanabe et al., 1981).

Note that L.^([Listeria]) monocytogenes is one of the few Gram-positive bacteria against which vancomycin is not effective — hence the need for ampicillin.

The majority of Gram-positive (82%) and Gram-negative (64%) genera carry either ribosomal protection genes alone or in combination with efflux/enzymatic genes as illustrated in Table 7.2.