Katarzyna Markowska

Modulation of antibiotic resistance and induction of a stress response in Pseudomonas aeruginosa by silver nanoparticles

The objective of this study was to characterize the effects of silver nanoparticles on Pseudomonas aeruginosa. Their interactions with several conventional antibiotics and ability to induce a stress response were examined. Interactions between silver nanoparticles (AgNPs) and antibiotics against free-living cells and biofilm of P. aeruginosa were studied using the chequerboard method and time-kill assays. The ability of AgNPs to induce a stress response was determined by evaluation of cellular levels of the DnaK and HtpG chaperones using SDS-PAGE and Western blot analysis. Synergistic activity against free-living P. aeruginosa between AgNPs and ampicillin, streptomycin, rifampicin and tetracycline, but not oxacillin, ciprofloxacin, meropenem or ceftazidime, was demonstrated by the chequerboard method. No such interactions were observed against P. aeruginosa biofilm. The results of time-kill assays confirmed synergy only for the AgNPs-streptomycin combination. AgNPs induced the expression of chaperone DnaK. No induction of the HtpG chaperone was detected. In conclusion, AgNPs not only display potent bactericidal activity against P. aeruginosa, but also act synergistically with several conventional antibiotics to enhance their effect against free-living bacteria as determined by the chequerboard method. The time-kill assay proved synergy between AgNPs and streptomycin only. The ability of AgNPs to induce the major chaperone protein DnaK may influence bacterial resistance to antimicrobials.

Genetic control of bacterial biofilms

Nearly all bacterial species, including pathogens, have the ability to form biofilms. Biofilms are defined as structured ecosystems in which microbes are attached to surfaces and embedded in a matrix composed of polysaccharides, eDNA, and proteins, and their development is a multistep process. Bacterial biofilms constitute a large medical problem due to their extremely high resistance to various types of therapeutics, including conventional antibiotics. Several environmental and genetic signals control every step of biofilm development and dispersal. From among the latter, quorum sensing, cyclic diguanosine-5’-monophosphate, and small RNAs are considered as the main regulators. The present review describes the control role of these three regulators in the life cycles of biofilms built by Pseudomonas aeruginosa, Staphylococcus aureus, Salmonella enterica serovar Typhimurium, and Vibrio cholerae. The interconnections between their activities are shown. Compounds and strategies which target the activity of these regulators, mainly quorum sensing inhibitors, and their potential role in therapy are also assessed.

Nitroxide-coated silver nanoparticles: synthesis, surface physicochemistry and antibacterial activity

In this paper, we describe the facile synthesis and physicochemical characteristics of nitroxide-coated silver nanoparticles. The proposed procedure allows us to obtain isolatable, devoid of Ag+ impurities, long-term stable, spherical nanoparticles with an average diameter ca. 7 nm, which exhibit high antibacterial activity towards both Gram-negative and Gram-positive strains. The determined Minimum Bactericidal Concentrations (MBCs) are significantly lower than the values reported for other thiolate-capped silver nanoparticles and range from 4 μg ml−1 (against Pseudomonas aeruginosa) to 12 μg ml−1 (against Staphylococcus aureus). Our studies proved that the nitroxide coverage favours the antibacterial activity of silver nanoparticles, probably due to the ability of nitroxides to be oxidized by reactive oxygen species (ROS) to positively charged oxoammonium ions which can interact strongly with the bacterial membrane. Furthermore, the mechanism of chemisorption of disulphide bisnitroxide on a silver surface has been discussed on the basis of XPS, FTIR and ESR results.

The Potential of Metal Nanoparticles for Inhibition of Bacterial Biofilms

The majority of bacterial species are capable of forming biofilms. These structures are responsible for many diseases of bacterial origin. The increased biofilm resistance to chemical disinfection, human immune responses, and conventional antibiotic therapy creates a great medical problem. Therefore, the number of laboratories performing studies aimed to develop novel therapeutics and strategies efficient against biofilms constantly increases. Metal nanoparticles (NP) are a promising antibiofilm agent. They are already used as additives, mainly to medical devices. Among metal NPs, nanosilver is the most active and commonly used in medicine and hygiene. The cellular targets and the mechanisms of NPs activity have been intensively studied.

The Effect of Silver Nanoparticles on Listeria monocytogenes PCM2191 Peptidoglycan Metabolism and Cell Permeability

Abstract Listeria monocytogenes is Gram-positive bacterial pathogen, a causative agent of food poisoning and systemic disease – listeriosis. This species is still susceptible to several conventionally used antibiotics but an increase in its resistance has been reported. For this reason the search for new, alternative therapies is an urgent task. Silver nanoparticles seem to be the promising antibacterial agent. Minimal inhibitory concentration of silver nanoparticles was determined. Sublethal concentrations were used in study of nanosilver effect on cells lysis by estimation of the number of cells surviving the treatment with 0.25 or 0.5 of minimal inhibitory concentrations of silver nanoparticles. Autolysis of isolated peptidoglycan was studied by measuring the absorbance of preparation subjected to nanosilver treatment. Silver nanoparticles effect on L. monocytogenes envelopes permeability was determined by measuring the efflux of cF, DNA and proteins. It was demonstrated that nanosilver enhanced the lysis of L. monocytogenes cells and, to the lesser extent, autolysis of isolated peptidoglycan. The increase in the efflux of carboxyfluoresceine, DNA and proteins was also noted. The obtained results allow to postulate that L. monocytogenes peptidoglycan, constituting the main component of cell wall, is the target of silver nanoparticles activity against this pathogen.

Inhibition of Bacterial Quorum Sensing Systems by Metal Nanoparticles

Quorum sensing (QS) is a commonly used way for intercellular communication utilizing small, self-generated signal molecules called autoinducers. QS-controlled genes can constitute as much as 10% of bacterial genome. This system controls a variety of bacterial physiological traits, including biofilm formation and pathogenesis. QS signaling pathways are well described in several species including Pseudomonas aeruginosa and Staphylococcus aureus . The inhibition of QS, called quorum quenching (QQ), can be a potential and promising strategy to combat bacterial infections. Nanoparticles (NPs) are considered to be potential QS inhibitors which was proved mainly by in vitro experiments. The QQ potential was proved for silver nanoparticles (AgNPs) which was demonstrated by their ability to inhibit bacterial biofilms. Antibiofilm activity of gold nanoparticles (AuNPs), zinc oxide nanoparticles (ZnONPs), copper nanoparticles (CuNPs), and platinum nanoparticles (PtNPs) was also shown. As an antibacterial potential of metal NPs is well documented, the ability to inhibit QS additionally argues toward their future usage as an alternative of antibiotics. Moreover, the development of bacterial resistance to NPs was not yet well documented.