Zinc effects on bacteria: insights from Escherichia coli by multi-omics approach

IMPORTANCE

A long-term exposure of bacteria to zinc oxide and zinc oxide nanoparticles leads to major alterations in bacterial morphology and physiology. These included biochemical and physiological processes promoting the emergence of strains with multi-drug resistance and virulence traits. After the removal of zinc pressure, bacterial phenotype reversed back to the original state; however, certain changes at the genomic, transcriptomic, and proteomic level remained. Why is this important? The extensive and intensive use of supplements in animal feed effects the intestinal microbiota of livestock and this may negatively impact the health of animals and people. Therefore, it is crucial to understand and monitor the impact of feed supplements on intestinal microorganisms in order to adequately assess and prevent potential health risks.

Escherichia coli from Human Wounds: Analysis of Resistance to β-Lactams and Expression of RND Efflux Pumps

Purpose

Resistance of pathogenic strains of Escherichia coli to β-lactams, particularly to ampicillin, is on the rise and it is attributed to intrinsic and acquired mechanisms. One important factor contributing to resistance, together with primarily resistance mechanisms, is a mutation and/or an over-expression of the intrinsic efflux pumps in the resistance-nodulation-division (RND) superfamily. Among these efflux pumps, AcrA, AcrB, TolC, and AcrD play an important role in antimicrobial co-resistance, including resistance to β-lactams.

Materials and Methods

Twelve E. coli isolates obtained from patients' wounds and the control strain of E. coli ATCC 25922 were analyzed. The phenotypic resistance of these isolates to selected β-lactams was assessed by determination of the minimal inhibitory concentration. Additionally, the prevalence of β-lactamase genes (blaTEM, blaCTX-M, blaSHV, and blaAmpC) was screened by PCR. Real-time qPCR was used to determine the expression of the selected efflux pumps acrA, acrB, tolC, and acrD and the repressor acrR after the exposure of E. coli to ampicillin.

Results

Phenotypic resistance to β-lactams was detected in seven isolates, mainly to ampicillin and piperacillin. This was corroborated by the presence of at least one acquired bla gene in each of these isolates. Although E. coli strains varied in the expression of RND-family efflux pumps after the ampicillin exposure, their gene expression indicated that these pumps did not play a major role in the phenotypic resistance to ampicillin.

Conclusion

Each E. coli isolate displayed unique characteristics, differing in minimum inhibitory concentration (MIC) values, prevalence of acquired blaTEM and blaCTX-M genes, and expression of the RND-family pumps. This together demonstrates that these clinical isolates employed distinct intrinsic or acquired resistance pathways for their defense against ampicillin. The prevalence and spread of ampicillin resistant E. coli has to be monitored and the search for ampicillin alternatives is needed.

Development of New Silver Nanoparticles Suitable for Materials with Antimicrobial Properties

Silver nanoparticles are the most important nanoparticles in connection with the antimicrobial effect. Nowadays, the green synthesis of various types of nanoparticles is rapid, effective and produce less toxic nanoparticles often with specific properties. In our experiment we have developed and described in details various types of silver nanoparticles synthesized chemically or by the green synthesis. Nine different silver nanoparticles were synthesized, three by citrate method at different pHs (8; 9; 10), four using gallic acid at alkaline pHs (10; 11), and two by green synthesis using green tea and coffee extracts, both at pH 9. Characterisation of silver nanoparticles was performed using dynamic light scattering, scanning electron microscopy, and ultraviolet-visible absorption spectroscopy. Silver nanoparticles prepared by green synthesis showed the highest antioxidant activity and also ability for quenching of free radicals. Antibacterial activity of silver nanoparticles was determined on bacterial cultures such as Staphylococcus aureus and Escherichia coli. Silver nanoparticles synthesized using green tea and coffee extracts showed the highest antibacterial activity for both bacterial strains. Minimal inhibition concentration for both strains was found to be 65 μM at each silver nanoparticle synthesized using green synthesis.

Effect of arsenic (III and V) on oxidative stress parameters in resistant and susceptible Staphylococcus aureus

The presented study deals with the observation of properties of methicillin-susceptible Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus (MRSA) in the toxic arsenic environment and influence of arsenic on antioxidant capacity. Two forms of arsenic (As(III), As(V)) with different concentrations were used for induction of the oxidative stress in tested strains. Microbiological methods showed that the growth inhibition of MSSA was higher than that of MRSA in presence of both arsenic ions. As(III) showed 24% and 33% higher anti-microbial effects than As(V) against MSSA and MRSA respectively. A similar result was found also in the experiment of reduction of biofilm-formation. By using spectrophotometry, it was revealed that As(III) induced higher antioxidant production in both bacterial cultures. Methicillin-susceptible S. aureus produced an app. 50 mg equivalent of gallic acid (GAE/1 mg of protein) and MRSA produced an app. 15 mg of GAE/1 mg of protein. The productions of metallothionein in MSSA and MRSA were decreased up to 62.41% and 55.84% respectively in presence of As ions. Reduction of As(III) and As(V) concentrations leads to a decrease in antioxidant production and increased the formation of metallothionein. All of these changes in the results were found to be significant statistically. Taken together, these experiments proved that in comparison with MSSA, MRSA is less susceptible not only to the antimicrobial effects of antibiotics but also against effects caused by metalloids, as arsenic. Thus, it can be stated that MRSA abounds with complex defensive mechanisms, which may in the future constitute significant problem in the efficiency of antibiotics alternatives as metal ions or nanoparticles.

Platinum nanoparticles induce damage to DNA and inhibit DNA replication

Sparsely tested group of platinum nanoparticles (PtNPs) may have a comparable effect as complex platinum compounds. The aim of this study was to observe the effect of PtNPs in in vitro amplification of DNA fragment of phage λ, on the bacterial cultures (Staphylococcus aureus), human foreskin fibroblasts and erythrocytes. In vitro synthesized PtNPs were characterized by dynamic light scattering (PtNPs size range 4.8-11.7 nm), zeta potential measurements (-15 mV at pH 7.4), X-ray fluorescence, UV/vis spectrophotometry and atomic absorption spectrometry. The PtNPs inhibited the DNA replication and affected the secondary structure of DNA at higher concentrations, which was confirmed by polymerase chain reaction, DNA sequencing and DNA denaturation experiments. Further, cisplatin (CisPt), as traditional chemotherapy agent, was used in all parallel experiments. Moreover, the encapsulation of PtNPs in liposomes (LipoPtNPs) caused an approximately 2.4x higher of DNA damage in comparison with CisPt, LipoCisPt and PtNPs. The encapsulation of PtNPs in liposomes also increased their antibacterial, cytostatic and cytotoxic effect, which was determined by the method of growth curves on S. aureus and HFF cells. In addition, both the bare and encapsulated PtNPs caused lower oxidative stress (determined by GSH/GSSG ratio) in the human erythrocytes compared to the bare and encapsulated CisPt. CisPt was used in all parallel experiments as traditional chemotherapy agent.

Comparative study on toxicity of extracellularly biosynthesized and laboratory synthesized CdTe quantum dots

Nanobiosynthesis belongs to the most recent methods for synthesis of nanoparticles. This type of synthesis provides many advantages including the uniformity in particle shape and size. The biosynthesis has also a significant advantage regarding chemical properties of the obtained particles. In this study, we characterized the basic properties and composition of quantum dots (QDs), obtained by the extracellular biosynthesis by Escherichia coli. Furthermore, the toxicity of the biosynthesized QDs was compared to QDs prepared by microwave synthesis. The obtained results revealed the presence of cyan CdTe QDs after removal of substantial amounts of organic compounds, which stabilized the nanoparticle surface. QDs toxicity was evaluated using three cell lines Human Foreskin Fibroblast (HFF), Human Prostate Cancer cells (PC-3) and Breast Cancer cells (MCF-7) and the MTT assay. The test revealed differences in the toxicity between variants of QDs, varying about 10% in the HFF and 30% in the MCF-7 cell lines. The toxicity of the biosynthesized QDs to the PC-3 cell lines was about 35% lower in comparison with the QDs prepared by microwave synthesis.

Staphylococcus aureus and MRSA Growth and Biofilm Formation after Treatment with Antibiotics and SeNPs

Methicillin-resistant Staphylococcus aureus (MRSA) is a dangerous pathogen resistant to β-lactam antibiotics. Due to its resistance, it is difficult to manage the infections caused by this strain. We examined this issue in terms of observation of the growth properties and ability to form biofilms in sensitive S. aureus and MRSA after the application of antibiotics (ATBs)-ampicillin, oxacillin and penicillin-and complexes of selenium nanoparticles (SeNPs) with these ATBs. The results suggest the strong inhibition effect of SeNPs in complexes with conventional ATBs. Using the impedance method, a higher disruption of biofilms was observed after the application of ATB complexes with SeNPs compared to the group exposed to ATBs without SeNPs. The biofilm formation was intensely inhibited (up to 99%±7% for S. aureus and up to 94%±4% for MRSA) after application of SeNPs in comparison with bacteria without antibacterial compounds whereas ATBs without SeNPs inhibited S. aureus up to 79%±5% and MRSA up to 16%±2% only. The obtained results provide a basis for the use of SeNPs as a tool for the treatment of bacterial infections, which can be complicated because of increasing resistance of bacteria to conventional ATB drugs.

The Composites of Graphene Oxide with Metal or Semimetal Nanoparticles and Their Effect on Pathogenic Microorganisms

The present experiment describes a synthesis process of composites based on graphene oxide, which was tested as a carrier for composites of metal- or metalloid-based nanoparticles (Cu, Zn, Mn, Ag, AgP, Se) and subsequently examined as an antimicrobial agent for some bacterial strains (Staphylococcus aureus (S. aureus), methicillin-resistant Staphylococcus aureus (MRSA) and Escherichia coli (E. coli). The composites were first applied at a concentration of 300 µM on all types of model organisms and their effect was observed by spectrophotometric analysis, which showed a decrease in absorbance values in comparison with the control, untreated strain. The most pronounced inhibition (87.4%) of S. aureus growth was observed after the application of graphene oxide composite with selenium nanoparticles compared to control. Moreover, the application of the composite with silver and silver phosphate nanoparticles showed the decrease of 68.8% and 56.8%, respectively. For all the tested composites, the observed antimicrobial effect was found in the range of 26% to 87.4%. Interestingly, the effects of the composites with selenium nanoparticles significantly differed in Gram-positive (G⁺) and Gram-negative (G⁻) bacteria. The effects of composites on bacterial cultures of S. aureus and MRSA, the representatives of G⁺ bacteria, increased with increasing concentrations. On the other hand, the effects of the same composites on G⁻ bacteria E. coli was observed only in the highest applied concentration.

3D-printed chip for detection of methicillin-resistant Staphylococcus aureus labeled with gold nanoparticles

Methicillin-resistant Staphylococcus aureus (MRSA) is a dangerous pathogen occurring not only in hospitals but also in foodstuff. Currently, discussions on the issue of the increasing resistance, and timely and rapid diagnostic of resistance strains have become more frequent and sought. Therefore, the aim of this study was to design an effective platform for DNA isolation from different species of microorganisms as well as the amplification of mecA gene that encodes the resistance to β-lactam antibiotic formation and is contained in MRSA. For this purpose, we fabricated 3D-printed chip that was suitable for bacterial cultivation, DNA isolation, PCR, and detection of amplified gene using gold nanoparticle (AuNP) probes as an indicator of MRSA. Confirmation of the MRSA presence in the samples was based on a specific interaction between mecA gene with the AuNP probes and a colorimetric detection, which utilized the noncross-linking aggregation phenomenon of DNA-functionalized AuNPs. To test the whole system, we analyzed several real refractive indexes, in which two of them were positively scanned to find the presence of mecA gene. The aggregation of AuNP probes were reflected by 75% decrease of absorbance (λ = 530 nm) and change in AuNPs size from 3 ± 0.05 to 4 ± 0.05 nm (n = 5). We provide the one-step identification of mecA gene using the unique platform that employs the rapid, low-cost, and easy-to-use colorimetric method for MRSA detection in various samples.

Comparison of the effects of silver phosphate and selenium nanoparticles on Staphylococcus aureus growth reveals potential for selenium particles to prevent infection

Interactions of silver phosphate nanoparticles (SPNPs) and selenium nanoparticles (SeNPs) with Staphylococcus aureus cultures have been studied at the cellular, molecular and protein level. Significant antibacterial effects of both SPNPs and SeNPs on S. aureus were observed. At a concentration of 300 μM, SPNPs caused 37.5% inhibition of bacterial growth and SeNPs totally inhibited bacterial growth. As these effects might have been performed due to the interactions of nanoparticles with DNA and proteins, the interaction of SPNPs or SeNPs with the amplified zntR gene was studied. The presence of nanoparticles decreased the melting temperatures of the nanoparticle complexes with the zntR gene by 23% for SeNPs and by 12% for SPNPs in comparison with the control value. The concentration of bacterial metallothionein was 87% lower in bacteria after application of SPNPs (6.3 μg mg(-1) protein) but was increased by 29% after addition of SeNPs (63 μg mg(-1) protein) compared with the S. aureus control (49 μg mg(-1) protein). Significant antimicrobial effects of the nanoparticles on bacterial growth and DNA integrity provide a promising approach to reducing the risk of bacterial infections that cannot be controlled by the usual antibiotic treatments.