Table 2.

MICs of antimicrobials for wild-type L. monocytogenes grown in the absence of nisin and Nisr L. monocytogenes grown in the presence of nisin

AntimicrobialSite of actionMIC, μg/mla
Wild typeNisin resistant
BenzylpenicillinCell wall synthesis0.26 ± 0.04A0.03 ± 0.00B
AmpicillinCell wall synthesis0.33 ± 0.08A0.05 ± 0.00B
CycloserineCell wall synthesis26.18 ± 4.01A14.81 ± 2.47B
VancomycinCell wall synthesis0.63 ± 0.11A0.59 ± 0.11A
Gramicidin SCytoplasmic membrane2.07 ± 0.25A3.27 ± 0.64B
NigericinCytoplasmic membrane0.09 ± 0.02A0.09 ± 0.01A
GentamicinProtein synthesis (30S)2.79 ± 0.30A6.38 ± 1.26B
TetracyclineProtein synthesis (30S)1.31 ± 0.57A0.98 ± 0.30A
StreptomycinProtein synthesis (30S)10.89 ± 1.33A13.58 ± 2.68A
ErythromycinProtein synthesis (50S)0.39 ± 0.07A0.39 ± 0.10A
ChloramphenicolProtein synthesis (50S)3.57 ± 0.77A3.27 ± 0.98A
  • a Values are means ± standard deviations. Different letters for the wild-type and Nisrstrains for a given antimicrobial indicate statistically significant differences (P < 0.001).