The present study evaluates the antibacterial activities of 18 conventional antibiotics in combination with nisin against three E. faecalis strains grown under routine culture conditions, as well as biofilms, thus exploring the feasibility of combinations of nisin and antibiotics against drugresistant pathogens. E. faecalis is among the most antibiotic-resistant bacteria known at present. E. faecalis has the ability to quickly acquire and disseminate antibiotic resistance genes by pheromone signals produced within the genus and species as well as by other bacterial genera. E. faecalis ATCC 29212 and OG1RF are generally used for survival and biofilm studies because they have been extensively used as a representative control strains for clinical and laboratory experiments. As E. faecalis has caused multiple antibiotic resistant infections, methods of effectively killing this drug-resistant pathogen have become key goals of microbiologists and drug development researchers. At present, vancomycin is considered a drug of last resort, and linezolid has also been introduced to treat severe infections with antibiotic-resistance Gram-positive bacteria. However, in the in vitro test for E. faecalis, not even these two potent antibiotics could effectively kill the three E. faecalis strains in this study. In contrast, the two conventional antibiotics penicillin and SCH772984 ampicillin exhibited better antibacterial activity and lower MIC and MBC values for penicillin and ampicillin than for vancomycin and linezolid. Similar results were found in a study by Weinstein et al. Therefore, the results of the in vitro evaluation showed that penicillin and ampicillin may have better antibacterial effects on E. faecalis than vancomycin and linezolid. The MBC has generally been defined as the lowest concentration of an antibiotic that kills.99.9% of the total bacteria. The MBC of penicillin against ATCC 29212 was 16 mg/L, and viable cells showed more than a 3-log10 reduction. However, in our determination, bacterial survival did not decrease, and even may have increased as the concentration of penicillin increased. Bacterial survival showed less than a 3-log10 reduction at.16 mg/L, so was 16 mg/L still considered the MBC? In an evaluation of the MBC of 18 test drugs, we found that no antibiotic completely killed E. faecalis, even at the high concentration of 1024 mg/L. These in vitro results indicated that E. faecalis is an antibiotic-resistant pathogen that is difficult to kill. The phenomenon that pathogens are relatively resistant to higher concentrations of some antibiotics while remaining susceptible to lower concentrations of antibiotics was first discovered by Eagle and Musselman in 1948. Nowadays, the phenomenon is often referred to as the “Eagle effect” and has been supported by additional studies.