In vitro activities of various antibiotics, alone and in combination with colistin methanesulfonate, against Pseudomonas aeruginosa strains isolated from cystic fibrosis patients

Background: The in vitro activities of various antibiotics, either alone or in combination with colistin methanesulfonate, were assessed using Pseudomonas aeruginosa strains isolated from cystic fibrosis patients. Methods: Except for colistin methanesulfonate, minimum inhibitory concentrations were determined by microbroth dilution technique as described by the Clinical and Laboratory Standards Institute ( CLSI); for colistin methanesulfonate, a modified method of the CLSI was used. Minimum bactericidal concentrations were determined as described by the CLSI. The in vitro activities of antibiotics in combination were determined by microbroth checkerboard technique, and results were interpreted by fractional inhibitory concentration index. Results: According to MIC values, 100, 98, 96 and 84% of the isolates were found susceptible to amikacin, colistin methanesulfonate, meropenem and ceftazidime, respectively. The minimum bactericidal concentrations were generally equal to or twice as high as those of the minimum inhibitory concentrations. With a fractional inhibitory concentration index of <= 0.5 as borderline, synergistic interactions were more frequent with combinations where amikacin was involved than with those with colistin methanesulfonate. No antagonism was observed. Conclusion: The findings of this study may play a useful role in selecting the appropriate combinations when a single agent is inadequate to treat cystic fibrosis patients with P. aeruginosa infections. Copyright (c) 2008 S. Karger AG, Basel

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. Conclusion: Nisin seems to be a good candidate for further investigations in the treatment of Gram-positive bacteria, alone or in combination with antibiotics. Copyright (C) 2012 S. Karger AG, Base

In vitro activities of antimicrobial cationic peptides; melittin and nisin, alone or in combination with antibiotics against Gram-positive bacteria

The in vitro activities of two antimicrobial cationic peptides, melittin and nisin alone and in combination with frequently used antibiotics (daptomycin, vancomycin, linezolid, ampicillin, and erythromycin), were assessed against clinical isolates of methicillin-susceptible Staphylococcus aureus, methicillin-resistant S. aureus and Enterococcus faecalis. Using the broth microdilution method, minimum inhibitory concentration (MIC) ranges of melittin and nisin against all strains were 2-8 mu g/ml and 2-32 mu g/ml respectively. In combination studies performed with the microdilution checkerboard method using a fractional inhibitory concentration index of <= 0.5 as borderline, synergistic interactions occurred more frequently with nisin-ampicillin combination against MSSA and nisin-daptomycin combination against E. faecalis strains. The results of the time-killing curve analysis demonstrated that the concentration dependent rapid bactericidal activity of nisin, and that synergism or early synergism was detected in most strains when nisin or melittin was used in combination with antibiotics even at concentrations of 0.5 x MIC

Antibacterial and anti-biofilm activities of melittin and colistin, alone and in combination with antibiotics against Gram-negative bacteria

In vitro antibacterial and anti-biofilm activities of antimicrobial cationic peptides (AMPs) melittin and colistin both alone and in combination with antibiotics were evaluated against clinical isolates of Gram-negative bacteria. Minimum inhibitory concentration (MIC) and fractional inhibitory concentration (FIG) index were determined by the microbroth dilution and chequerboard techniques, respectively. The time-kill curve (TKC) method was used for determining the bactericidal activities of AMPs alone and in combination. Measurements of anti-biofilm activities were performed spectrophotometrically for both inhibition of attachment and 24-hour biofilm formation at MIC or subMIC. According to MIC, values, the most active agents against Pseudomonas aeruginosa, Escherichia colt and Klebsiella pneumoniae were colistin, imipenem and ciprofloxacin, respectively. In combination studies, synergistic effects were mostly seen with colistin imipenem against E. coif and K. pneumoniae (50 and 54%, respectively), colistin ciprofloxacin against P. aeruginosa (77%). In TKC studies, synergism was observed with almost all expected combinations, even more frequently than chequerboard method. All of the antimicrobial agents were able to inhibit attachment and 24-hour biofilm formation between 0-57% at 1/10 x MIC and 7-73% at 1 x or 1/10 x MIC, respectively. AMPs seem to be a good candidate for antimicrobial chemotherapy with their antibacterial and anti-biofilm activities as a single agent or in combination with antibiotics

In vitro Activities of Nisin Alone or in Combination with Vancomycin and Ciprofloxacin against Methicillin-Resistant and Methicillin-Susceptible <i>Staphylococcus aureus</i> 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. Conclusion: Nisin seems to be a good candidate for further investigations in the treatment of Gram-positive bacteria, alone or in combination with antibiotics. Copyright (C) 2012 S. Karger AG, Base