Abstract
BackgroundAmpicillin-resistant S. aureus (ARSA) now poses a serious problem for hospitalized patients, and their care providers. Plant-derived antibacterial that can reverse the resistance to well-tried agents which have lost their original effectiveness are the research objectives of far reaching importance. To this aim, the present study investigated antibacterial and synergistic activities of Stephania suberosa extracts (SSE) against ARSA when used singly and in combination with ampicillin.ResultsThe majority chemical compounds of SSE were alkaloid (526.27 ± 47.27 mg/1 g of dried extract). The Minimum inhibitory concentration (MICs) for ampicillin and SSE against all ARSA strains were >512 μg/ml and 4 mg/ml, respectively. Checkerboard assay revealed synergistic activity in the combination of ampicillin (0.15 μg/ml) and SSE (2 mg/ml) at fractional inhibitory concentration index (FICI) <0.5. The killing curve assay had confirmed that the viability of ARSA was dramatically reduced from 5x105 cfu/ml to 103 cfu/ml within 6 h after exposure to SSE (2 mg/ml) plus ampicillin (0.15 μg/ml) combination. Electron microscopic study clearly revealed that these ARSA cells treated with this combination caused marked morphological damage, peptidoglycan and cytoplasmic membrane damage, and average cell areas significant smaller than control. Obviously, Immunofluorescence staining and confocal microscopic images confirmed that the peptidoglycan of these cells were undoubtedly disrupted by this combination. Furthermore, the CM permeability of ARSA was also increased by this combination. Enzyme assay demonstrated that SSE had an inhibitory activity against β-lactamase in concentrations manner.ConclusionsSo, these findings provide evidence that SSE has the high potential to reverse bacterial resistance to originate traditional drug susceptibility of it and may relate to three modes of actions of SSE: (1) inhibits peptidoglycan synthesis, resulting in morphological damage, (2) inhibits β-lactamases activity, and (3) increases CM permeability. It is widely recognized that many types of drugs are derived from alkaloids. So, this SSE offers the prominent potential to develop a novel adjunct phytopharmaceutical to ampicillin for the treatment of ARSA. Further active ingredients study, toxicity of it, and the synergistic effect on blood and tissue should be performed and confirmed in an animal test or in humans.
Highlights
Ampicillin-resistant S. aureus (ARSA) poses a serious problem for hospitalized patients, and their care providers
According to CLSI, these outcomes suggested that ARSA used in this study revealed high resistant to ampicillin and nisin, but susceptible to reference strain S. aureus American Type Culture Collection (ATCC) 29213
These results are in substantial correspondence with those of Eumkeb et al that galangin, quercetin or baicalein plus ampicillin exhibited synergistic activity against penicillins-resistant S. aureus strains at Fraction inhibitory concentration (FIC) indices < 0.03 [9]
Summary
Ampicillin-resistant S. aureus (ARSA) poses a serious problem for hospitalized patients, and their care providers. Plant-derived antibacterial that can reverse the resistance to well-tried agents which have lost their original effectiveness are the research objectives of far reaching importance. To this aim, the present study investigated antibacterial and synergistic activities of Stephania suberosa extracts (SSE) against ARSA when used singly and in combination with ampicillin. The production of blaZ encoded β-lactamase that can hydrolyze and inactivate β-lactam antibiotic activity, in particular penicillins This enzyme is one of the most important resistant mechanisms to β-lactam in this strain [10,11,12]. It should be considered to use in a different paradigm, including combination with conventional antibiotic that has been resisted by bacteria to achieve synergism in treatment of bacterial infections [14]
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