Abstract
Staphylococcus aureus can develop resistance by mutation, transfection or biofilm formation. Resistance was induced in S. aureus by growth in sub-inhibitory concentrations of ciprofloxacin for 30 days. The ability of the antimicrobials to disrupt biofilms was determined using crystal violet and live/dead staining. Effects on the cell membranes of biofilm cells were evaluated by measuring release of dyes and ATP, and nucleic acids. None of the strains developed resistance to AMPs while only S. aureus ATCC 25923 developed resistance (128 times) to ciprofloxacin after 30 passages. Only peptides reduced biofilms of ciprofloxacin-resistant cells. The antibiofilm effect of melimine with ciprofloxacin was more (27%) than with melimine alone at 1X MIC (p < 0.001). Similarly, at 1X MIC the combination of Mel4 and ciprofloxacin produced more (48%) biofilm disruption than Mel4 alone (p < 0.001). Combinations of either of the peptides with ciprofloxacin at 2X MIC released ≥ 66 nM ATP, more than either peptide alone (p ≤ 0.005). At 2X MIC, only melimine in combination with ciprofloxacin released DNA/RNA which was three times more than that released by melimine alone (p = 0.043). These results suggest the potential use of melimine and Mel4 with conventional antibiotics for the treatment of S. aureus biofilms.
Highlights
Staphylococcus aureus is a major human pathogen that can cause several recalcitrant infections due to the acquisition of antibiotic resistance and formation of biofilm on living tissues and medical devices [1,2]
The current study investigates the interaction of antimicrobial peptides (AMPs) melimine or Me4 alone or in combination with ciprofloxacin against S. aureus biofilm in conjunction with their mode of activity
Melimine and Mel4 had the lowest minimum inhibitory concentration (MIC) of 62.5 μg/mL and 125 μg/mL, respectively, against S. aureus ATCC 6538
Summary
Staphylococcus aureus is a major human pathogen that can cause several recalcitrant infections (deep-seated abscess, osteomyelitis, and endocarditis) due to the acquisition of antibiotic resistance and formation of biofilm on living tissues and medical devices [1,2]. Methicillin-resistant S. aureus (MRSA) has been named as a “serious threat” by the Center for Disease Control and Prevention [3,4]. There are limited reports on antimicrobial compounds that are able to control biofilm-associated infections caused by S. aureus [7]. Various strategies such as physical removal of materials colonized with bacteria or delivery of high doses of antibiotics at the site of infections have been used to treat biofilmassociated infection [8]. High doses of antibiotics may cause cytotoxicity to human cells. Combinations of different antimicrobials may be required [10]
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