Abstract
The present study assesses the in vitro antibiofilm potential activity of extracts of wild Allium ursinum and Allium oschaninii. The active ingredients of the extracts were obtained with a technique named Naviglio (rapid solid–liquid dynamic extraction, RSLDE) which is based on an innovative and green solid–liquid extraction methodology. The extracts were tested against models of mono- and polymicrobial biofilm structures of clinically antibiotic-resistant pathogens, Klebsiella pneumoniae ATCC 10031 and Candida albicans ATCC 90028. Biofilms were studied using a static and a dynamic model (microtiter plates and a CDC reactor) on three different surfaces reproducing what happens on implantable medical devices. Antimicrobic activities were determined through minimum inhibitory concentration (MIC), while antibiofilm activity was assessed by minimum biofilm eradication concentration (MBEC) using a crystal violet (CV) biofilm assay and colony forming unit (CFU) counts. Results showed that both Allium extracts eradicated biofilms of the tested microorganisms well; biofilms on Teflon were more susceptible to extracts than those on polypropylene and polycarbonate, suggesting that when grown on a complex substrate, biofilms may be more tolerant to antibiotics. Our data provide significant advances on antibiotic susceptibility testing of biofilms grown on biologically relevant materials for future in vitro and in vivo applications.
Highlights
Biofilms formed by multidrug-resistant bacteria represent a major public health problem because high antibiotic doses are needed to eliminate them
This study aims to evaluate for the first time the antimicrobial and antibiofilm activities of crude extracts of two Allium species obtained with a green method, using a special device the Naviglio extractor that is able to reduce extraction times with a very good yield, and at the same time allows the extraction of the active ingredients avoiding their degradation
The active process due to the high pressure inside and the low pressure outside permitted the extraction of substances from the solid matrix in a short period of time and at low temperature with a good reproducibility of the extraction and above all the production of high-quality extracts that are phyto-complex with a synergic action [28]. Both compounds were extracted from the leaves of two fresh species of Allium, and the action of their sulfur compounds [37] toward microorganisms was tested because it is known that the antimicrobial action of sulfur compounds depends on their hydrophilic or lipophilic character [38]
Summary
Biofilms formed by multidrug-resistant bacteria represent a major public health problem because high antibiotic doses are needed to eliminate them. The spread of antibiotic resistance in the hospital environment and in communities where biofilms are involved has stimulated the development of innovative strategies that can solve this problem. Due to the slow spread of antibiotics through the biofilm matrix, the presence of biofilms represents a challenging eradication issue compared to planktonic bacteria [3]. Klebsiella pneumoniae is considered an important opportunistic pathogen in hospitalized patients and can cause extra-intestinal infections, such as urinary tract infections [4], bacteremia [5], device-related infections [6], ventilator-associated pneumonia [7], and community-acquired pneumonia [8].
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