In vitro activities of nisin alone or in combination with vancomycin and ciprofloxacin against methicillin-resistant and methicillin-susceptible Staphylococcus aureus strains.
BACKGROUND
We investigated the in vitro activities of nisin alone or in combination with vancomycin and ciprofloxacin against methicillin-resistant (MRSA) and -susceptible Staphylococcus aureus (MSSA) strains.


METHODS
The minimum inhibitory concentrations were determined by microbroth dilution technique. Antibiotic combinations were assessed using the checkerboard technique. The time-kill curve method was used for determining the bactericidal activity of nisin alone and in combination.


RESULTS
For both MSSA and MRSA strains, the minimum inhibitory concentrations of nisin ranged between 4 and 16 mg/l. With a fractional inhibitory concentration of ≥0.5 as borderline, synergistic interactions were seen in three of five isolates with nisin-ciprofloxacin compared to two of five isolates with nisin-vancomycin combinations against both MSSA and MRSA. No antagonism was observed. The results of time-kill curve analysis demonstrated concentration-dependent rapid bactericidal activity of nisin and synergism almost in all strains when nisin was used in combination with ciprofloxacin, and early synergistic interactions in some of the strains when it was used in combination with vancomycin.


CONCLUSIONS
Nisin seems to be a good candidate for further investigations in the treatment of Gram-positive bacteria, alone or in combination with antibiotics.
Department of Pharmaceutical Microbiology, Faculty of Pharmacy, Istanbul University, Turkey. sibeldosler@hotmail.com
Sibel
S
Dosler
A Alev
AA
Gerceker
D002939:Ciprofloxacin / Q000008:administration & dosage*; D004357:Drug Synergism; D004359:Drug Therapy, Combination; D006801:Humans; D008712:Methicillin / Q000008:administration & dosage*; D016106:Methicillin Resistance / Q000187:drug effects* / Q000502:physiology; D008826:Microbial Sensitivity Tests / Q000379:methods; D009561:Nisin / Q000008:administration & dosage*; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000302:isolation & purification; D014640:Vancomycin / Q000008:administration & dosage*
D009561:Nisin; D002939:Ciprofloxacin; D014640:Vancomycin; D008712:Methicillin