We inoculated an in vitro pharmacodynamic model simultaneously with clinical isolates of methicillin-resistant Staphylococcus aureus and an
enterocin-producing enterococcus (
vancomycin-resistant Enterococcus faecalis,
ampicillin susceptible) at 7 log10 CFU/ml to examine
enterocin effects and antimicrobial activity on staphylococci. The investigated antimicrobial regimens were 100 mg
arbekacin every 12 h (q12h), 6 mg
daptomycin per kg of
body weight/day, 600 mg
linezolid q12h, and 100 mg
tigecycline q24h alone and in combination (
daptomycin,
linezolid, and
tigecycline) with
arbekacin. Simulations were performed in triplicate; bacterial quantification occurred over 48 h, and development of resistance was evaluated throughout. When we evaluated the impact of antimicrobial activity against S. aureus alone,
daptomycin demonstrated bactericidal activity (>or=3 log10 CFU/ml kill), whereas
arbekacin,
linezolid, and
tigecycline displayed bacteriostatic activities (<3 log10 CFU/ml kill). In the mixed-pathogen model, early and distinctive
stunting of S. aureus growth was noted (1.5 log CFU/ml difference) in the presence of
enterocin-producing E. faecalis compared to growth controls run individually (P=0.02). Most noteworthy was that in the presence of
enterocin-producing E. faecalis, bactericidal activity was observed with
arbekacin and
tigecycline and with the addition of
arbekacin to
linezolid. Antagonism was noted for the combination of
tigecycline and
arbekacin against S. aureus in the presence of
enterocin-producing E. faecalis. Our research demonstrates that the inhibitory effect of E. faecalis contributed significantly to its overall antimicrobial impact on S. aureus. This contribution was enhanced or improved compared to the activity of each antimicrobial alone. Further research is warranted to determine the impact of
polymicrobial infections on antimicrobial activity.