Abstract
BackgroundMethicillin-resistant Staphylococcus aureus (MRSA) and coagulase-negative staphylococcus infections are a worldwide concern. Currently, these isolates have also shown resistance to vancomycin, the last therapy used in these cases. It has been observed that quinones and other related compounds exhibit antibacterial activity. This study evaluated the antibacterial activity, toxicity and in vivo dermal irritability of lapachol extracted from Tabebuia avellanedae and derivatives against methicillin-resistant staphylococcal isolates. In addition, its mechanism of action was also analyzed.MethodsThe compounds β-lapachone, 3-hydroxy β N lapachone and α-lapachone were tested to determine the MIC values against methicillin-resistant S. aureus, S. epidermidis and S. haemolyticus strains, being the two last ones hetero-resistant to vancomycin. Experiments of protein synthesis analysis to investigate the naphthoquinones action were assessed. In vitro toxicity to eukaryotic BSC-40 African Green Monkey Kidney cell cultures and in vivo primary dermal irritability in healthy rabbits were also performed.ResultsThe compounds tested showed antibacterial activity (MICs of 8, 4/8 and 64/128 μg/mL to β-lapachone, 3-hydroxy β N lapachone and α-lapachone, respectively), but no bactericidal activity was observed (MBC > 512 μg/mL for all compounds). Although it has been observed toxic effect in eukaryotic cells, the compounds were shown to be atoxic when applied as topic preparations in healthy rabbits. No inhibition of proteins synthesis was observed.ConclusionOur results suggest that quinones could be used in topic preparations against wound infections caused by staphylococci, after major investigation of the pharmacological properties of the compounds. Studies about the use of these compounds on tumoral cells could be carried on, due to their effect in eukaryotic cells metabolism.
Highlights
Methicillin-resistant Staphylococcus aureus (MRSA) and coagulase-negative staphylococcus infections are a worldwide concern
Several naphthoquinones are found in the nature showing activity against aerobic and anaerobic bacterial species
Minimal Inhibitory Concentration (MIC) and Minimal Bactericidal Concentration (MBC) determination The MIC and MBC determination was performed to compare the antimicrobial effect of the naphthoquinones in MSSA and MRSA strains (S. aureus) and evaluate this effect in resistant coagulase-negative staphylococci (S. epidermidis and S. haemolyticus)
Summary
Methicillin-resistant Staphylococcus aureus (MRSA) and coagulase-negative staphylococcus infections are a worldwide concern. Preparations made with this plant were used in South and North America as antineoplasic, antifungal, antiviral, antimicrobial, antiparasitical and anti-inflammatory treatment [1,2,3,4,5] Pharmacological activities of this species are related to saponins, flavonoids, coumarins, and natural antibiotics [3,6], while the chemical profile presented by most of the studies has shown the quinones as the main active substances [1,2,3,4,6]. Methicillin-resistant staphylococci infectionsmainly caused by Staphylococcus aureus (MRSA strains) and by coagulase-negative staphylococci (CNS), as S. epidermidis (MRSE) and S. haemolyticus (MRSH) isolates have increased in the last two decades [7] They are the pathogens most frequently isolated from nosocomial bacteraemias [8], with an attributable mortality rate ranging from 13% for CNS [9] to 42% for MRSA [11].
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