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Silver as an Antimicrobial Agent: The Resistance Issue
Published in Huiliang Cao, Silver Nanoparticles for Antibacterial Devices, 2017
Kristel Mijnendonckx, Rob Van Houdt
The silCFBA(orf105)PRSE gene products mediate silver resistance via active efflux and silver sequestration in the periplasm. SilF, a periplasmic chaperone protein, probably transports Ag+ to the SilCBA complex (Figure 7.2). This complex forms a three-polypeptide membrane potential-dependent cation/proton antiporter system that spans the entire cell membrane and belongs to the Heavy Metal Efflux-Resistance Nodulation cell Division (HME-RND) family of efflux. The complex consists of an efflux pump (SilA), an outer membrane factor (SilC) and a membrane fusion protein (SilB) and pumps Ag+ from the periplasm to the exterior of the cell (Franke 2007; Silver 2003). The orf105 gene, coding for a hypothetical protein of 105 aa, was recently reanalysed and was predicted to code for a periplasmic metal chaperone of 146 aa that contains the conserved metal-binding site CxxC and shares 45% protein identity with CopG from Cupriavidus metallidurans CH34 (Randall et al. 2015). SilP is a putative P-type ATPase efflux pump that transports silver ions from the cell cytoplasm to the periplasm (Franke 2007; Silver 2003). However, neither silP nor orf105 is essential for silver resistance as deletion mutants of silP or orf105 or both did not show an increased silver sensitivity (Randall et al. 2015). The transcription of the silCFBA(ORF105aa)P genes is controlled by the two-component regulatory system SilRS, consisting of a transmembrane histidine kinase SilS and a response regulator SilR. This regulatory system is homologous to other two-component regulatory systems involved in the regulation of metal resistance (Franke 2007; Silver 2003). Finally, the silE gene located downstream of silRS, is not controlled by SilRS; nevertheless, transcription is strongly induced in the presence of Ag+ (Silver et al. 1999). SilE codes for a periplasmic protein that shares 48% identity with PcoE, which acts as a ‘metal sponge’ because of its ability to bind multiple Cu+ and Ag+ ions and is encoded by the pcoABCDRSE copper resistance from E. coli plasmid pRJ1004 (Zimmermann et al. 2012). SilE could provide a first line of defense by binding Ag+ before it enters the cytoplasm, as one SilE molecule can bind up to 38 Ag+ ions depending on the experimental conditions (Silver et al. 1999). Additionally, it could act as a chaperone, transporting Ag+ ions to the SilCBA complex either directly or via SilF (Franke 2007; Randall et al. 2015; Silver 2003).
A mechanistic perspective on targeting bacterial drug resistance with nanoparticles
Published in Journal of Drug Targeting, 2021
Khatereh Khorsandi, Saeedeh Keyvani-Ghamsari, Fedora Khatibi Shahidi, Reza Hosseinzadeh, Simab Kanwal
However, there are possibilities for NP resistance in bacteria which remains a clinical problem [163]. One of the examples of NP resistance is seen in Cu++ and Cu-doped TiO2 NPs treatment in Shewanella oneidensis, where a decline in the antimicrobial effect of TiO2 NPs has been found. This impact is related to reduced absorption or enhanced efflux of Cu+ and Cu-doped TiO2 NPs [53,164]. Also, low uptake and enhanced efflux of TiO2 and Al2O3 NPs in Cupriavidus metallidurans have been shown that leads to low toxic effects of both NPs [16].
Growth and biofilm formation of Cupriavidus metallidurans CH34 on different metallic and polymeric materials used in spaceflight applications
Published in Biofouling, 2022
Nissem Abdeljelil, Najla Ben Miloud Yahia, Ahmed Landoulsi, Abdelwaheb Chatti, Ruddy Wattiez, Rob Van Houdt, David Gillan
Squire et al. (2014) indicate that due to technical limitations, the routine antimicrobial procedure (gamma irradiation or extended heat treatment at 87.7 °C) cannot be applied to all ORUs elements before launch. In fact, 5 from 16 items that are launched wet or containing water are not subjected to disinfection. This could create favorable conditions for inflight microbial growth and potential biofilm formation that could spread inside the wet system. Also microbial monitoring campaigns onboard the ISS showed recurrent microbial contamination events (Van Houdt and Leys 2020; Zea et al. 2020). Although biofilms in water systems are interacting multispecies communities (Thompson et al. 2020; Yang et al. 2021), one species that attracted attention is Cupriavidus metallidurans. A Gram-negative bacterium belonging to the Burkholderiaceae family that has been detected from 2009 to 2019 in almost all samples coming from the wastewater tank, the potable waterbus or the condensate (Mijnendonckx et al. 2013; Zea et al. 2020). This facultative chemolithotrophic motile microbe shows resistance to a broad range of metals, including silver used as disinfectant onboard ISS, and is able to adapt to various harsh conditions, including low nutrients environments (Mijnendonckx et al. 2013; Zhang et al. 2018; Mijnendonckx et al. 2019; Maertens et al. 2020; Van Houdt et al. 2021). In addition, bacteria are exposed to specific conditions (e.g. microgravity and cosmic radiation) during spaceflight (Horneck et al. 2010; Huang et al. 2018; Acres et al. 2021; Bijlani et al. 2021), which have also been studied for C. metallidurans type strain CH34 (Leys et al. 2009; Byloos et al. 2017) (De Gelder et al. 2009; Leroy et al. 2010). Furthermore, it is used to explore future spaceflight applications such as testing antimicrobial surfaces (Siems et al. 2022) as well as biomining and bioremediation (Byloos et al. 2017; Cockell et al. 2020; Santomartino et al. 2020). It is therefore a representative of the contaminant species found in humid spacecraft systems as well as a microbe with potential extra-terrestrial applications.