Multi-drug-resistant Staphylococcus aureus and future chemotherapy

Antimicrobial Peptides with Antibacterial Activity against Vancomycin-Resistant Staphylococcus aureus Strains: Classification, Structures, and Mechanisms of Action

The emergence of bacteria resistant to conventional antibiotics is of great concern in modern medicine because it renders ineffectiveness of the current empirical antibiotic therapies. Infections caused by vancomycin-resistant Staphylococcus aureus (VRSA) and vancomycin-intermediate S. aureus (VISA) strains represent a serious threat to global health due to their considerable morbidity and mortality rates. Therefore, there is an urgent need of research and development of new antimicrobial alternatives against these bacteria. In this context, the use of antimicrobial peptides (AMPs) is considered a promising alternative therapeutic strategy to control resistant strains. Therefore, a wide number of natural, artificial, and synthetic AMPs have been evaluated against VRSA and VISA strains, with great potential for clinical application. In this regard, we aimed to present a comprehensive and systematic review of research findings on AMPs that have shown antibacterial activity against vancomycin-resistant and vancomycin-intermediate resistant strains and clinical isolates of S. aureus, discussing their classification and origin, physicochemical and structural characteristics, and possible action mechanisms. This is the first review that includes all peptides that have shown antibacterial activity against VRSA and VISA strains exclusively.

Phenotypic homogeneity of emetic Bacillus cereus isolates in China

Emetic Bacillus cereus strains produce a potent cereulide cytotoxin, which can cause acute and fatal cases of food poisoning. We isolated 18 emetic B. cereus strains from a food poisoning event, and from clinical and non-random food surveillance in China and phenotypic characteristics of haemolysis, starch hydrolysis, salicin fermentation, gelatin liquefaction, cytotoxicity, and susceptibility to antibiotics were assessed. All isolates were positive for haemolysis and gelatin liquefaction, and negative for starch hydrolysis and salicin fermentation. Their haemolytic potentials were intermediate to Bacillus anthracis and B. cereus ATCC 14579 (a non-emetic strain). All isolates were cytotoxic to CHO, Hep-2, and Vero cells, and were sensitive to ampicillin. The homogeneous phenotypes of emetic isolates from China are similar to the corresponding traits of European and Japanese isolates that have been characterized, suggesting highly similar phenotypes of emetic B. cereus worldwide.

Zebrafish: An Attractive Model to Study Staphylococcus aureus Infection and Its Use as a Drug Discovery Tool

Non-mammalian in vivo disease models are particularly popular in early drug discovery. Zebrafish (Danio rerio) is an attractive vertebrate model, the success of which is driven by several advantages, such as the optical transparency of larvae, the small and completely sequenced genome, the small size of embryos and larvae enabling high-throughput screening, and low costs. In this review, we highlight zebrafish models of Staphyloccoccus aureus infection, which are used in drug discovery and for studying disease pathogenesis and virulence. Further, these infection models are discussed in the context of other relevant zebrafish models for pharmacological and toxicological studies as part of early drug profiling. In addition, we examine key differences to commonly applied models of S.aureus infection based on invertebrate organisms, and we compare their frequency of use in academic research covering the period of January 2011 to January 2021.

Antimicrobial, modulatory, and antibiofilm activity of tt-farnesol on bacterial and fungal strains of importance to human health

In this study, we analyzed the antimicrobial, antibiofilm, and modulatory activities of trans-trans-farnesol (tt-farnesol). The minimum inhibitory concentration (MIC) of this sesquiterpene was evaluated against 31 Gram-positive and Gram-negative bacterial strains and 4 species of the genus Candida. Furthermore, we examined its inhibitory action on biofilm production as well as antibiotic modulation. Only Gram-positive species presented susceptibility to tt-farnesol (MIC ranging from 8 µg/mL to 128 µg/mL). No synergistic or antagonistic effects were observed between tt-farnesol (1/4 and 1/8 of MIC) and first-choice antibiotics against multidrug resistant strains. However, the modulatory action of tt-farnesol (1/2 and 1/4 of the MIC) decreased 8 × MIC of non-inhibitory β-lactam antibiotic against a Methicillin-resistant strain. In the antibiofilm assay, tt-farnesol inhibited biofilm formation, especially in Methicillin-resistant Staphylococcus aureus (MRSA) strains, at concentrations ranging from 2 μg/mL to 128 μg/mL. Additionally, in the molecular docking study, the tt-farnesol molecule demonstrated a remarkable binding affinity with important proteins involved in the biofilm production, such as IcaA and Srt proteins. The antimicrobial action of tt-farnesol on Streptococcus pyogenes and Streptococcus agalactiae strains was evaluated for the first time, presenting an MIC of 16 µg/mL for both strains. Our findings reveal the antibacterial, antibiofilm, and modulatory potential of tt-farnesol to aid in the fight against infectious processes.

Enhanced efficacy of a Cu2+ complex of curcumin against Gram-positive and Gram-negative bacteria: Attributes of complex formation

Curcumin is a tantalizing molecule with multifaceted therapeutic potentials. However, its therapeutic applications are severely hampered because of poor bioavailability, attributed to its instability and aqueous insolubility. In an attempt to overcome this inherent limitation and develop curcumin-based antibacterials, we had earlier synthesized and characterized a metal complex of Cu(II) with curcumin, having the formula [Cu(Curcumin)(OCOCH₃)(H₂O)], hereafter referred to as Cu(Cur). In this study, the complex, i.e., Cu(Cur), was investigated for its stability and antibacterial activity along with its possible mechanism of action in comparison to the parent molecule, curcumin. Complex formation resulted in improved stability as Cu(Cur) was found to be highly stable under different physiological conditions. Such improved stability was verified with the help of UV-Vis spectroscopy and HPLC. With improved stability, Cu(Cur) exhibited potent and significantly enhanced activity over curcumin against both E. coli and S. aureus. Calcein leakage assay revealed that the complex triggered immediate membrane permeabilization in S. aureus. This membrane disruptive mode of action was further corroborated by microscopic visualization. The excellent potency of the complex was augmented by its safe toxicological profile as it was non-hemolytic and non-cytotoxic towards mammalian cells, making it a suitable candidate for in vivo investigations. Altogether, this investigation is a critical appraisal that advocates the antibacterial potential of this stable, membrane-targeting and non-toxic complex, thereby presenting new perspectives for its therapeutic application against bacterial infections.

UV-Assisted Deposition of Antibacterial Ag-Tannic Acid Nanocomposite Coating

The marked increase in bacterial colonization of medical devices and multiple drug resistance to traditional antibiotics underline the pressing need for developing novel antibacterial surface coatings. In the present investigation, natural polyphenol tannic acid (TA)-capped silver nanoparticles (TA-Ag NPs) were synthesized via an environmentally friendly and sustainable one-step redox reaction under UV irradiation with a simultaneous and uniform deposition on polydimethylsiloxane (PDMS) and other substrate surfaces. In the synthesis process, the dihydroxyphenyl and trihydroxyphenyl groups of TA actively participate in Ag⁺ reduction, forming co-ordination linkages with Ag NPs and bestowing the deposition on the PDMS surface. The physico-chemical features of TA-Ag NPs were characterized in detail. Microscopic examination, surface elemental analysis, and wettability measurements clearly reveal the decoration of TA-Ag NPs on the substrate surfaces. The modified PDMS surfaces can kill the adhered bacteria or resist the bacterial adhesion, and no live bacteria can be found on their surfaces. Most importantly, the modified PDMS surfaces exhibit predominant antibacterial effects both in vitro in the catheter bridge model and in vivo in a rat subcutaneous infection model. On the other hand, the functionalized surfaces exhibit only a negligible level of cytotoxicity against L929 mouse fibroblasts with no side effects on the major organs of Sprague-Dawley rats after implantation, indicating their biocompatibility for potential biomedical applications.

Biotechnological Potential of Streptomyces Siderophores as New Antibiotics

BACKGROUND

Siderophores are small-molecule iron-chelators produced by microorganisms and plants growing mostly under low iron conditions. Siderophores allow iron capture and transport through cell membranes into the cytoplasm, where iron is released for use in biological processes. These bacterial iron uptake systems can be used for antibiotic conjugation or as targets for killing pathogenic bacteria. Siderophores have been explored recently because of their potential applications in environmental and therapeutic research. They are present in Streptomyces, Grampositive bacteria that are an important source for discovering new siderophores.

OBJECTIVE

This review summarizes siderophore molecules produced by the genus Streptomyces emphasizing their potential as biotechnological producers and also illustrating genomic tools for discovering siderophores useful for treating bacterial infections.

METHODS

The literature search was performed using PUBMED and MEDLINE databases with keywords siderophore, secondary metabolites, Trojan horse strategy, sideromycin and Streptomyces. The literature research focused on bibliographic databases including all siderophores identified in the genus Streptomyces. In addition, reference genomes of Streptomyces from GenBank were used to identify siderophore biosynthetic gene clusters by using the antiSMASH platform.

RESULTS

This review has highlighted some of the many siderophore molecules produced by Streptomyces, illustrating the diversity of their chemical structures and a wide spectrum of bioactivities against pathogenic bacteria. Furthermore, the possibility of using siderophores conjugated with antibiotics could be an alternative to overcome bacterial resistance to drugs and could improve their therapeutic efficacy.

CONCLUSION

This review confirms the importance of Streptomyces as a rich source of siderophores, and underlines their potential as antibacterial agents.

Cranberry-Derived Proanthocyanidins Potentiate β-Lactam Antibiotics against Resistant Bacteria

The emergence and spread of extended-spectrum β-lactamases (ESBLs), metallo-β-lactamases (MBLs), or variant low-affinity penicillin-binding proteins (PBPs) pose a major threat to our ability to treat bacterial infection using β-lactam antibiotics. Although combinations of β-lactamase inhibitors with β-lactam agents have been clinically successful, there are no MBL inhibitors in current therapeutic use. Furthermore, recent clinical use of new-generation cephalosporins targeting PBP2a, an altered PBP, has led to the emergence of resistance to these antimicrobial agents. Previous work shows that natural polyphenols such as cranberry-extracted proanthocyanidins (cPAC) can potentiate non-β-lactam antibiotics against Gram-negative bacteria. This study extends beyond previous work by investigating the in vitro effect of cPAC in overcoming ESBL-, MBL-, and PBP2a-mediated β-lactam resistance. The results show that cPAC exhibit variable potentiation of different β-lactams against β-lactam-resistant Enterobacteriaceae clinical isolates as well as ESBL- and MBL-producing E. coli We also discovered that cPAC have broad-spectrum inhibitory properties in vitro on the activity of different classes of β-lactamases, including CTX-M3 ESBL and IMP-1 MBL. Furthermore, we observe that cPAC selectively potentiate oxacillin and carbenicillin against methicillin-resistant but not methicillin-sensitive staphylococci, suggesting that cPAC also interfere with PBP2a-mediated resistance. This study motivates the need for future work to identify the most bioactive compounds in cPAC and to evaluate their antibiotic-potentiating efficacy in vivoIMPORTANCE The emergence of β-lactam-resistant Enterobacteriaceae and staphylococci compromises the effectiveness of β-lactam-based therapy. By acquisition of ESBLs, MBLs, or PBPs, it is highly likely that bacteria may become completely resistant to the most effective β-lactam agents in the near future. In this study, we described a natural extract rich in proanthocyanidins which exerts adjuvant properties by interfering with two different resistance mechanisms. By their broad-spectrum inhibitory ability, cranberry-extracted proanthocyanidins could have the potential to enhance the effectiveness of existing β-lactam agents.

Antimicrobial Benzyltetrahydroisoquinoline-Derived Alkaloids from the Leaves of Doryphora aromatica

Four new alkaloids, (R)-nomimantharine trifluoroacetate (2), 12-demethylphaeantharine trifluoroacetate (3), nominanthranal trifluoroacetate (4), and the enolic form of 1-hydroxy-6,7-dimethoxy-2-methylisoquinoline trifluoroacetate (5), together with the known dimeric alkaloid phaeantharine trifluoroacetate (1), have been isolated from the extract of the leaves of the rainforest tree Doryphora aromatica (Monimiaceae). The structures of these compounds were elucidated by HRMS and 1D and 2D NMR data. (R)-Nomimantharine trifluoroacetate (2) contains an ether linkage connecting a benzylisoquinoline unit with a tetrahydroisoquinoline, a novel class of dimeric alkaloid. The absolute configuration of (R)-nomimantharine trifluoroacetate (2) was established via electronic circular dichroism data. The compounds isolated were subjected to in vitro antimicrobial assays against a panel of pathogenic microorganisms, including Mycobacterium smegmatis, M. tuberculosis, Escherichia coli, Staphylococcus aureus (SA), and five clinical isolates of oxacillin/methicillin-resistant S. aureus (MRSA). Phaeantharine trifluoroacetate (1) and (R)-nomimantharine trifluoroacetate (2) showed moderate inhibitory activities against Mycobacteria and MRSA strains.

Influence of nanoscale-modified apatite-type calcium phosphates on the biofilm formation by pathogenic microorganisms

Nanoparticles (25–50 nm) of chemically modified calcium phosphates Ca10−x−y M ii x Na y (PO4)6−z (CO3) z (OH)2 (M ii  – Cu2+, Zn2+) were synthesized via a wet precipitation method at room temperature. The Fourier-transform infrared spectroscopy data confirmed the partial substitution of PO 4 3 − {\text{PO}}_{4}^{3-} → CO 3 2 − {\text{CO}}_{3}^{2-} (B-type) in apatite-type structure. The influence of prepared phosphates on biofilm formation by pathogenic microorganisms was investigated. It was found that the samples Na+, CO 3 2 − {\text{CO}}_{3}^{2-} -hydroxyapatite (HAP) and Na+, Zn2+, CO 3 2 − {\text{CO}}_{3}^{2-} -HAP (5–20 mM) had the highest inhibitory effect on biofilm formation by Staphylococcus aureus strains. The sample Na+, CO 3 2 − {\text{CO}}_{3}^{2-} -HAP had the slight influence on the formation of the biofilm by Pseudomonas aeruginosa, while for the samples Na+, Cu2+, CO 3 2 − {\text{CO}}_{3}^{2-} -HAP and Na+, Zn2+, CO 3 2 − {\text{CO}}_{3}^{2-} -HAP such an effect was not detected. According to transmission electron microscopy data, a correlation between the activity of synthesized apatite-related modified calcium phosphates in the processes of biofilm formation and their ability to adhere to the surface of bacterial cells was established. The prepared samples can be used for the design of effective materials with antibacterial activity for medicine.

Promising Anti-MRSA Activity of Brevibacillus sp. Isolated from Soil and Strain Improvement by UV Mutagenesis

Antibiotic-resistant infection is a major health problem, and a limited number of drugs are currently approved as antibiotics. Soil bacteria are promising sources in the search for novel antibiotics. The aim of the present study is to isolate and assess soil bacteria with anti-MRSA activity and improve their capabilities by UV mutagenesis. Soil samples from the upper south of Thailand were screened for antibacterial activity using the cross-streak method. Agar well diffusion was used to examine the activity of isolates against a spectrum of human pathogens. The most active isolate was identified by 16S rRNA sequencing, and the production kinetics and stability were investigated. The most promising isolate was mutated by UV radiation, and the resulting activity and strain stability were studied. The results show that isolates from the cross-streak method could inhibit Staphylococcus aureus TISTR 517 (94 isolates) and Escherichia coli TISTR 887 (67 isolates). Nine isolates remained active against S. aureus TISTR 517 and MRSA, and eight isolates inhibited the growth of E. coli TISTR 887 as assessed using agar well diffusion. The most active strain was Brevibacillus sp. SPR-20, which had the highest activity at 24 h of incubation. The active substances in culture supernatants exhibited more than 90% activity when subjected to treatments involving various heat, enzymes, surfactants, and pH conditions. The mutant M201 showed significantly higher activity (109.88–120.22%) and strain stability compared to the wild-type strain. In conclusion, we demonstrate that soil Brevibacillus sp. is a potential resource that can be subjected to UV mutagenesis as a useful approach for improving the production of anti-MRSA in the era of antibiotic resistance.

Functional Identification of Serine Hydroxymethyltransferase as a Key Gene Involved in Lysostaphin Resistance and Virulence Potential of Staphylococcus aureus Strains

Gaining an insight into the mechanism underlying antimicrobial-resistance development in Staphylococcus aureus is crucial for identifying effective antimicrobials. We isolated S. aureus sequence type 72 from a patient in whom the S. aureus infection was highly resistant to various antibiotics and lysostaphin, but no known resistance mechanisms could explain the mechanism of lysostaphin resistance. Genome-sequencing followed by subtractive and functional genomics revealed that serine hydroxymethyltransferase (glyA or shmT gene) plays a key role in lysostaphin resistance. Serine hydroxymethyltransferase (SHMT) is indispensable for the one-carbon metabolism of serine/glycine interconversion and is linked to folate metabolism. Functional studies revealed the involvement of SHMT in lysostaphin resistance, as ΔshmT was susceptible to the lysostaphin, while complementation of the knockout expressing shmT restored resistance against lysostaphin. In addition, the ΔshmT showed reduced virulence under in vitro (mammalian cell lines infection) and in vivo (wax-worm infection) models. The SHMT inhibitor, serine hydroxymethyltransferase inhibitor 1 (SHIN1), protected the 50% of the wax-worm infected with wild type S. aureus. These results suggest SHMT is relevant to the extreme susceptibility to lysostaphin and the host immune system. Thus, the current study established that SHMT plays a key role in lysostaphin resistance development and in determining the virulence potential of multiple drug-resistant S. aureus.

Staphylococcus aureus grown in anaerobic conditions exhibits elevated glutamine biosynthesis and biofilm units

The enormous spread of Staphylococcus aureus infections through biofilms is a major concern in hospital-acquired infections. Biofilm formation by S. aureus on any surface is facilitated by adjusting its redox status. This organism is a facultative anaerobe shift more towards reductive conditions by enhancing nitrogen metabolism where glutamine synthesis plays a key role. Glutamine is synthesized by glutamine synthetase (GS) encoded by the glnA gene. The gene was amplified by PCR from the chromosomal DNA of S. aureus, sequenced (HQ329146.1), and cloned. The pure recombinant GS exhibited K_m of 11.06 ± 0.05 mmol·L^-1 for glutamate and 2.4 ± 0.03 mmol·L^-1 for ATP. The glnA gene sequence showed a high degree of variability with its human counterpart, while it was highly conserved in bacteria. Structural analysis revealed that the GS structure of S. aureus showed close homology with other Gram-positive bacteria and exhibited a high degree of variation with Escherichia coli GS. In the present study, we observed the increased presence of GS activity in multidrug-resistant strains of S. aureus with elevated biofilm units, grown in brain heart infusion broth; among them methicillin-resistant strains S. aureus LMV 3, 4, and 5 showed higher biofilm units. All these results explain the important role of glutamine biosynthesis with elevated biofilm units in the pathogenesis of S. aureus.

Multifunctional antibiotic- and zinc-containing mesoporous bioactive glass scaffolds to fight bone infection

Bone regeneration is a clinical challenge which requires multiple approaches. Sometimes, it also includes the development of osteogenic and antibacterial biomaterials to treat the emergence of possible infection processes arising from surgery. This study evaluates the antibacterial properties of gelatin-coated meso-macroporous scaffolds based on the bioactive glass 80%SiO₂-15%CaO-5%P₂O₅ (mol-%) before (BL-GE) and after being doped with 4% of ZnO (4ZN-GE) and loaded with both saturated and the minimal inhibitory concentrations of one of the antibiotics: levofloxacin (LEVO), vancomycin (VANCO), rifampicin (RIFAM) or gentamicin (GENTA). After physical-chemical characterization of materials, release studies of inorganic ions and antibiotics from the scaffolds were carried out. Moreover, molecular modelling allowed determining the electrostatic potential density maps and the hydrogen bonds of antibiotics and the glass matrix. Antibacterial in vitro studies (in planktonic, inhibition halos and biofilm destruction) with S. aureus and E. coli as bacteria models showed a synergistic effect of zinc ions and antibiotics. The effect was especially noticeable in planktonic cultures of S. aureus with 4ZN-GE scaffolds loaded with VANCO, LEVO or RIFAM and in E. coli cultures with LEVO or GENTA. Moreover, S. aureus biofilms were completely destroyed by 4ZN-GE scaffolds loaded with VANCO, LEVO or RIFAM and the E. coli biofilm total destruction was accomplished with 4ZN-GE scaffolds loaded with GENTA or LEVO. This approach could be an important step in the fight against microbial resistance and provide needed options for bone infection treatment. STATEMENT OF SIGNIFICANCE: Antibacterial capabilities of scaffolds based on mesoporous bioactive glasses before and after adding a 4% ZnO and loading with saturated and minimal inhibitory concentrations of levofloxacin, vancomycin, gentamicin or rifampicin were evaluated. Staphylococcus aureus and Escherichia coli were the infection model strains for the performed assays of inhibition zone, planktonic growth and biofilm. Good inhibition results and a synergistic effect of zinc ions released from scaffolds and antibiotics were observed. Thus, the amount of antibiotic required to inhibit the bacterial planktonic growth was substantially reduced with the ZnO inclusion in the scaffold. This study shows that the ZnO-MBG osteogenic scaffolds are multifunctional tools in bone tissue engineering because they are able to fight bacterial infections with lower antibiotic dosage.

Antibody-Enabled Antimicrobial Nanocapsules for Selective Elimination of Staphylococcus aureus

Targeted bactericide nanosystems hold significant promise to improve the efficacy of existing antimicrobials for treatment of severe bacterial infections, minimizing the side effects and lowering the risk of the development of antibiotic resistance. In this work, we developed antibody-functionalized nanocapsules (NCs) containing antibacterial essential oil (EO) for selective and effective eradication of Staphylococcus aureus. Antibacterial EO NCs were produced via self-assembly nanoencapsulation in the plant-derived protein zein. The obtained EO NCs were decorated with aminocellulose to provide more reactive surface groups for carboxyl-to-amine immobilization of a antibody that is specific against S. aureus. The antibody-enabled EO NCs (Ab@EO NCs) demonstrated 2-fold higher bactericidal efficacy against the targeted bacterium compared to the pristine EO NCs at the same concentrations. The improved antibacterial effect of the Ab@EO NCs toward S. aureus was also confirmed in a real-time assay by monitoring bacterial cells elimination using a quartz crystal microbalance. Furthermore, the Ab@EO NCs selectively decreased the load and changed the cell morphology of the targeted S. aureus in a mixed inoculum with nontargeted Pseudomonas aeruginosa. Applying the nanoformulated antibacterial actives to an in vitro coculture model of the bacteria and skin fibroblasts resulted in suppression of S. aureus growth while preserving the human cells viability. The novel antibody-enabled antibacterial NCs showed potential for improving the treatment efficacy of staphylococcal infections, minimally affecting the beneficial microbial and human cells.

A Systems-Wide Analysis of Proteolytic and Lipolytic Pathways Uncovers The Flavor-Forming Potential of The Gram-Positive Bacterium Macrococcus caseolyticus subsp. caseolyticus

Macrococcus caseolyticus subsp. caseolyticus is a Gram-positive, commensal organism documented to be present as a component of the secondary microflora in fermented foods such as Ragusano and Fontina cheeses and Cantonese sausage. In these products, the organism appears to play a role in ripening and the development of the final organoleptic qualities. However, the role of this organism in flavor generation is not well understood. Therefore, the objective of this study was to investigate the role of M. caseolyticus subsp. caseolyticus in flavor compound formation through an examination of enzymatic, metabolomic and genomic data. A bank of M. caseolyticus subsp. caseolyticus strains derived from a variety of niches were examined. Enzyme activities analyzed comprised those of the proteolytic and lipolytic cascades including cell-envelope proteinase (CEP), peptidases, esterases, lipases, aminotransferases and glutamate dehydrogenase (GDH). Strain to strain variation was observed, often associated with niche. All strains, except those isolated from non-dairy sources, demonstrated high CEP activity. Such high CEP activity associated with dairy strains implies the importance of this characteristic in the adaptation of these strains to a dairy-specific niche. However, limited downstream peptidolytic activity, in addition to a limited ability to generate free amino acids (FAA) was observed across all strains, indicating weak ability of this organism to generate amino-acid derived flavor compounds. Interestingly, the strains with high CEP activity also demonstrated high esterase activity and gas chromatography-mass spectrometry (GC-MS) analysis of the volatile compounds produced when these strains were grown in lactose-free milk demonstrated differences in the range and types of volatiles produced. In contrast to this metabolic versatility, comparative genome analysis revealed the distribution of components of the proteolytic and lipolytic system in these strains to be conserved. Overall, this study demonstrates the potential of M. caseolyticus subsp. caseolyticus to generate diverse volatile flavor compounds. Additionally, the identification of the highly active strain-specific cell wall bound caseolytic proteases deriving extensive casein hydrolysis, serves as a promising avenue which can be potentially harnessed in the future to produce greater and more diverse flavor compounds.

Potential combinations of endocannabinoid/endocannabinoid-like compounds and antibiotics against methicillin-resistant Staphylococcus aureus

Infections caused by antibiotic-resistant strains of Staphylococcus aureus have reached epidemic proportions globally. Our previous study showed antimicrobial effects of anandamide (AEA) and arachidonoyl serine (AraS) against methicillin (MET)-resistant S. aureus (MRSA) strains, proposing the therapeutic potential of these endocannabinoid/endocannabinoid-like (EC/EC-like) agents for the treatment of MRSA. Here, we investigated the potential synergism of combinations of AEA and AraS with different types of antibiotics against MRSA grown under planktonic growth or biofilm formation. The most effective combinations under planktonic conditions were mixtures of AEA and ampicillin (AMP), and of AraS and gentamicin (GEN). The combination with the highest synergy in the biofilm formation against all tested bacterial strains was AEA and MET. Moreover, the combination of AraS and MET synergistically caused default of biofilm formation. Slime production of MRSA was also dramatically impaired by AEA or AraS combined with MET. Our data suggest the novel potential activity of combinations of EC/EC-like agents and antibiotics in the prevention of MRSA biofilm formation.

Synthesis of novel monocarbonyl curcuminoids, evaluation of their efficacy against MRSA, including ex vivo infection model and their mechanistic studies

In continuation of our effort to improve the physiological stability and the antibacterial activity of curcuminoids against drug-resistant bacteria, a series of novel monocarbonyl curcuminoids were synthesized and screened for antibacterial activity against S. aureus and E. coli strains. These curcuminoids showed potent antibacterial activity against both methicillin-sensitive and methicillin-resistant strains of S. aureus with MIC values 2-8 and 4-16 μg/mL, respectively. They also exhibited moderate potency against E. coli strains. The four most active curcuminoids (7d, 7i, 7m, and 7p) were on further investigation found to be very stable under physiological conditions, non-hemolytic, and non-toxic toward mammalian cells up to 150 μg/mL concentration. Mechanistic studies revealed that these curcuminoids displayed potent bactericidal activity by targeting cell membranes. Further, in an ex vivo mammalian co-culture infection model study, remarkably, the curcuminoids 7i and 7p were able to clear the internalized bacteria in mammalian cells and the activity was found to be superior to conventional antibiotics such as vancomycin and linezolid. Therefore, the present study affords us water-soluble, stable, non-toxic curcuminoids that may serve as lead molecules for development as antibacterial agents against MRSA infections.

Multi-functionalized nanocarriers targeting bacterial reservoirs to overcome challenges of multi drug-resistance

INTRODUCTION

Infectious diseases associated with intracellular bacteria such as Staphylococcus aureus, Salmonella typhimurium and Mycobacterium tuberculosis are important public health concern. Emergence of multi and extensively drug-resistant bacterial strains have made it even more obstinate to offset such infections. Bacteria residing within intracellular compartments provide additional barriers to effective treatment.

METHOD

Information provided in this review has been collected by accessing various electronic databases including Google scholar, Web of science, Scopus, and Nature index. Search was performed using keywords nanoparticles, intracellular targeting, multidrug resistance, Staphylococcus aureus; Salmonella typhimurium; Mycobacterium tuberculosis. Information gathered was categorized into three major sections as 'Intracellular targeting of Staphylococcus aureus, Intracellular targeting of Salmonella typhimurium and Intracellular targeting of Mycobacterium tuberculosis' using variety of nanocarrier systems.

RESULTS

Conventional management for infectious diseases typically comprises of long-term treatment with a combination of antibiotics, which may lead to side effects and decreased patient compliance. A wide range of multi-functionalized nanocarrier systems have been studied for delivery of drugs within cellular compartments where bacteria including Staphylococcus aureus, Salmonella typhimurium and Mycobacterium tuberculosis reside. Such carrier systems along with targeted delivery have been utilized for sustained and controlled delivery of drugs. These strategies have been found useful in overcoming the drawbacks of conventional treatments including multi-drug resistance.

CONCLUSION

Development of multi-functional nanocargoes encapsulating antibiotics that are proficient in targeting and releasing drug into infected reservoirs seems to be a promising strategy to circumvent the challenge of multidrug resistance. Graphical abstract.

Well-Defined Gold Nanorod/Polymer Hybrid Coating with Inherent Antifouling and Photothermal Bactericidal Properties for Treating an Infected Hernia

Biomedical device-associated infection (BAI) is a great challenge in modern clinical medicine. Therefore, developing efficient antibacterial materials is significantly important and meaningful for the improvement of medical treatment and people's health. In the present work, we developed a strategy of surface functionalization for multifunctional antibacterial applications. A functionalized polyurethane (PU, a widely used biomedical material for hernia repairing) surface (PU-Au-PEG) with inherent antifouling and photothermal bactericidal properties was readily prepared based on a near-infrared (NIR)-responsive organic/inorganic hybrid coating which consists of gold nanorods (Au NRs) and polyethylene glycol (PEG). The PU-Au-PEG showed a high efficiency to resist adhesion of bacteria and exhibited effective photothermal bactericidal properties under 808 nm NIR irradiation, especially against multidrug-resistant bacteria. Furthermore, the PU-Au-PEG could inhibit biofilm formation long term. The biocompatibility of PU-Au-PEG was also proved by cytotoxicity and hemolysis tests. The in vivo photothermal antibacterial properties were first verified by a subcutaneous implantation animal model. Then, the anti-infection performance in a clinical scenario was studied with an infected hernia model. The results of animal experiment studies demonstrated excellent in vivo anti-infection performances of PU-Au-PEG. The present work provides a facile and promising approach to develop multifunctional biomedical devices.

Synergistic Inhibition by Bacteriocin and Bacteriophage against Staphylococcus aureus

Staphylococcus aureus is a representative pathogenic bacterium carefully controlled in the dairy industry because it causes bovine mastitis and thus, can enter the dairy chain. Furthermore, the emergence of multi-drug resistant S. aureus is a big problem. We previously isolated a Lactococcus lactis strain producing a bacteriocin that exhibited strong antimicrobial activity against S. aureus. In this study, we investigated the synergistic inhibition of S. aureus by the bacteriocin and a bacteriophage (SAP84) which is specific to the organism. The bacteriocin (12.5-100 AU/mL) inhibited the growth of S. aureus KCTC 3881 in a dose-dependent manner, as did the bacteriophage SAP84 (0.001-1 MOI; multiplicity of infection). Co-treatment with the bacteriocin (100 AU/mL) and the bacteriophage (0.1 MOI) significantly inhibited the growth of S. aureus compared to each treatment alone (bacteriocin or bacteriophage), indicating the two components showed synergistic inhibition of S. aureus. Therefore, the bacteriocin and bacteriophage combination can be used as a good strategy for controlling pathogenic bacteria.

Synthesis and Antimicrobial Activity of Thiohydantoins Obtained from L-Amino Acids

Background:

Thiohydantoins are an important class of heterocyclic compounds in drug discovery since they are related to a wide range of biological properties including antimicrobial activity.

Objective:

The objective of this study was to synthesize a series of thiohydantoins derived from Laminoacids and to evaluated their inhibitory effect on the growth of Gram-negative and Grampositive bacteria.

Methods:

All title compounds were synthetized by reaction of L-amino acids with thiourea or ammonium thiocyanate. Their antimicrobial activities were evaluated against bacterial strains by broth microdilution assays. The time-kill kinetics, the antibiofilm activity and the cytotoxicity to mammalian cells were determined for the compound that exhibited the best antimicrobial profile (1b).

Results:

Eleven thiohydantoins were readily obtained in good yields (52-95%). In general, thiohydantoins were more effective against Gram-positive bacteria. Compound 1b (derived from Lalanine) showed the best antibacterial activity against Staphylococcus epidermis ATCC 12228 and S. aureus BEC 9393 with MIC values of 940 and 1921 µM, respectively. The time-kill kinetics demonstrated time-dependent bactericidal effect in both strains for this derivative. Besides, 1b also exhibited antibacterial activity against biofilms of S. epidermidis ATCC 12228, leading to a 40% reduction in their metabolic activity compared to the untreated control. No cytotoxicity of 1b to mammalian cells was observed at MIC values.

Conclusion:

The data reported herein indicate relevant antimicrobial activity of thiohydantoins derived from L-aminoacid, mainly 1b, as potential pharmacophore to guide further chemical modification aiming at the search for new and improved antimicrobial agents.

The Environmental Exposures and Inner- and Intercity Traffic Flows of the Metro System May Contribute to the Skin Microbiome and Resistome

The skin functions as the primary interface between the human body and the external environment. To understand how the microbiome varies within urban mass transit and influences the skin microbiota, we profiled the human palm microbiome after contact with handrails within the Hong Kong Mass Transit Railway (MTR) system. Intraday sampling time was identified as the primary determinant of the variation and recurrence of the community composition, whereas human-associated species and clinically important antibiotic resistance genes (ARGs) were captured as p.m. signatures. Line-specific signatures were notably correlated with line-specific environmental exposures and city characteristics. The sole cross-border line appeared as an outlier in most analyses and showed high relative abundance and a significant intraday increment of clinically important ARGs (24.1%), suggesting potential cross-border ARG transmission, especially for tetracycline and vancomycin resistance. Our study provides an important reference for future public health strategies to mitigate intracity and cross-border pathogen and ARG transmission.

Epidemiology of efflux pumps genes mediating resistance among Staphylococcus aureus; A systematic review

BACKGROUND

Efflux of antibiotics is an effective resistance mechanism among antibiotic-resistant Staphylococcus aureus. This systematic review aims to evaluate the frequency and expression of efflux pump genes in S.aureus around the world.

METHOD

A comprehensive literature search of several databases (Medline Pub Med, ISI, Scopus, Google Scholar, ISC, Science direct and Persian Journals Online, and citation lists) was performed. We considered published studies from 2001 to 2018. Articles reporting the prevalence and expression of efflux pump genes were selected.

RESULT

Among 183 articles, 36 studies were selected. Of the 36, 23 articles were conducted in Asia.6 in Europe, 5 in America and 2 in African countries. In most of these studies norA, norB, qacA/B genes were commonly evaluated by molecular methods. The presence of efflux pump genes such as norA, norB, norC, mepA, mdeA, qacA/B was detected by PCR in 21 studies and over-expression of genes were reported in 13 studies. The most frequently reported genes in Asia were norA (75%), norB (60%), mepA (35%), mdeA (33%) and qacA/B (20.8%). In European studies, the prevalence of norB was mostly reported among S.aureus isolates and norA and qacA/B were commonly found in similar studies in America. The investigation of gene expression patterns showed that norA was most frequent single-pattern in Asia and America, norB or mdeA in Europe.

CONCLUSION

According to this study MDR efflux pumps not only cause high-level resistance but also it considerably associated with over-expression of these genes. Due to the selective pressure on MRSA isolate, the enormous diversity of plasmid-encoded genes had been recorded in different regions, owing to the various numbers and types of isolates in each study or types of disinfectants for general use.

Phenotypic and genotypic methods for identification of slime layer production, efflux pump activity, and antimicrobial resistance genes as potential causes of the antimicrobial resistance of some mastitis pathogens from farms in Menoufia, Egypt

Mastitis caused by multi- or pan-drug resistant bacteria is a growing health concern. A total of 110 milk samples were collected: Staphylococcus aureus, Streptococcus agalactiae, Streptococcus dysgalactiae, Enterococcus faecalis, and Escherichia coli were present in 54/110 (49.09%), 37/110 (33.63%), 25/110 (22.72%), 7/110 (6.36%), and 50/110 (45.45%) samples, respectively. A total of 20 methicillin-resistant S. aureus (MRSA) isolates, 19 Streptococcus sp. isolates, and 15 E. coli isolates were selected, and 100% were positive for (coagulase and hemolysins), streptokinase, and hemolytic activity, respectively. A number of 11 E. coli isolates were serotyped, and the serotypes were: O26, O55, O111, O119, O124, O125, O127, and O158. The antimicrobial resistance index ranges for MRSA, Streptococcus sp., and E. coli were 0.49-0.83, 0.39-0.83, and 0.56-1, respectively. The most effective antimicrobials on Gram-positive isolates were cephradine, ciprofloxacin, doxycycline, norfloxacin, and vancomycin, while doxycycline and norfloxacin were effective on E. coli serotypes. All of the selected isolates exhibited slime layer production. The efflux pumps of the 12 MRSA, 12 Streptococcus sp., and 11 E. coli isolates exhibited activity with ethidium bromide concentrations of 1, 1.5, and 0.5 µg/ml, respectively. There was a simultaneous antimicrobial activity of the efflux pump inhibitor chlorpromazine with amoxicillin/clavulanic acid, erythromycin, and oxacillin, to which the isolates were resistant. The 12 MRSA isolates harboured the methicillin resistance genes mec(A,A1, and A2), mecA1, and mecC at frequencies of 9/12 (75%), 9/12 (75%), and 8/12 (66.7%), respectively, and the penicillin resistance gene BlaZ was present at a frequency of 5/12 (41.7%). The distributions of erm(A), erm(B), erm(C), erm(F), erm(G), and erm(Q) were 8/12 (66.7%), 5/12 (41.7%), 12/12 (100%), 2/12 (16.7%), 0/12 (0.0%), and 8/12 (66.7%), respectively. The 12 Streptococcus sp. isolates harboured mec(A, A1, and A2), mecA1, mecC, and blaZ at rates of 4/12 (33.33%), 4/12 (33.33%), 5/12 (41.7%), and 4/12 (33.33%), respectively. The frequencies of erm(A) and erm(F) were 4/12 (33.33%), and 9/12 (75%), respectively. The 11 E. coli isolates harboured the extended-spectrum β-lactamases integrase1, integrase2, blaCTX-M, blaCTX-M-1, and blaTEM at frequencies of 10/11 (90.90%), 11/11 (100%), 9/11 (81.81%), 6/11 (54.54%), and 10/11 (90.90%), respectively. Moreover, the frequencies of erm(A), erm(B), erm(C), erm(F), erm(G), and erm(Q) were 7/11 (63.63%), 4/11 (36.36%), 4/11 (36.36%), 5/11 (45.45%), 10/11 (90.90%), and 10/11 (90.90%), respectively. Our results demonstrated the high antimicrobial resistance of the investigated isolates and confirmed the existence of multiple mechanisms underlying multidrug resistance.

Effects of gamma-irradiation on antibiotic resistance and diagnostic molecular markers of methicillin-resistant Staphylococcus aureus in Egyptian cancer patients

Purpose: This in-vitro study aimed to assess in 120 [40 community-acquired (CA-MRSA) & 80 hospital-acquired (HA-MRSA)] isolates from cancer patients whether the transmissible staphylococcal cassette chromosome mec (SCCmec) typing, and the Panton-Valentine leukocidin (PVL) virulence genes detection could be employed as tools for molecular diagnostic purposes to distinguish both methicillin-resistant Staphylococcus aureus (MRSA) categories in radiotherapy treated cancer patients.Materials and methods: SCCmec typing was determined by the combination of the type of the cassette chromosome recombinase genes (ccr) gene complex and the class of the methicillin resistance (mec) gene complex. Besides, a rapid slide latex agglutination test (LAT) and antibiotic resistance spectrum determination before and after irradiation were performed.Results: In the strict sense, with the effect of irradiation; the presence of SCCmec subtypes IVa (22.5% vs. 10.0%), b (47.5% vs. 25.0%), & d (7.5 vs. 2.5%) or type V (15.0% vs. 7.5%) genetic elements and PVL genes (p < .001) were not proved as a signature for CA-MRSA. While, the larger SCCmec types II, and III elements were not detected in 14, and 19 from the 38, and 36 typed HA-MRSA isolates (p < .001), respectively. Remarkable effects on class A & class B mec gene complex and type2, type 3 & type 5 ccr gene complex and an increase in agglutination reaction strength in response to gamma irradiation external stimulus were observed.Conclusions: Different heterogeneous genetic composition with upregulation mecA gene expression was detected after irradiation in the HA- MRSA studied population. CA-MRSA showed remarkable ability to acquire multi-antibiotic resistance after irradiation and propose a novel paradigm for future chemotherapy against the multi-resistant pathogens whose proliferation especially among immunocompromised cancer patients is on the increase.

Comparative Genomic Analysis of Staphylococcus haemolyticus Reveals Key to Hospital Adaptation and Pathogenicity

Staphylococcus haemolyticus is a skin commensal gaining increased attention as an emerging pathogen of nosocomial infections. However, knowledge about the transition from a commensal to an invasive lifestyle remains sparse and there is a paucity of studies comparing pathogenicity traits between commensal and clinical isolates. In this study, we used a pan-genomic approach to identify factors important for infection and hospital adaptation by exploring the genomic variability of 123 clinical isolates and 46 commensal S. haemolyticus isolates. Phylogenetic reconstruction grouped the 169 isolates into six clades with a distinct distribution of clinical and commensal isolates in the different clades. Phenotypically, multi-drug antibiotic resistance was detected in 108/123 (88%) of the clinical isolates and 5/46 (11%) of the commensal isolates (p < 0.05). In the clinical isolates, we commonly identified a homolog of the serine-rich repeat glycoproteins sraP. Additionally, three novel capsular polysaccharide operons were detected, with a potential role in S. haemolyticus virulence. Clinical S. haemolyticus isolates showed specific signatures associated with successful hospital adaption. Biofilm forming S. haemolyticus isolates that are resistant to oxacillin (mecA) and aminoglycosides (aacA-aphD) are most likely invasive isolates whereas absence of these traits strongly indicates a commensal isolate. We conclude that our data show a clear segregation of isolates of commensal origin, and specific genetic signatures distinguishing the clinical isolates from the commensal isolates. The widespread use of antimicrobial agents has probably promoted the development of successful hospital adapted clones of S. haemolyticus clones through acquisition of mobile genetic elements or beneficial point mutations and rearrangements in surface associated genes.

Bacteria's different ways to recycle their own cell wall

The ability to recover components of their own cell wall is a common feature of bacteria. This was initially recognized in the Gram-negative bacterium Escherichia coli, which recycles about half of the peptidoglycan of its cell wall during one cell doubling. Moreover, E. coli was shown to grow on peptidoglycan components provided as nutrients. A distinguished recycling enzyme of E. coli required for both, recovery of the cell wall sugar N-acetylmuramic acid (MurNAc) of the own cell wall and for growth on external MurNAc, is the MurNAc 6-phosphate (MurNAc 6P) lactyl ether hydrolase MurQ. We revealed however, that most Gram-negative bacteria lack a murQ ortholog and instead harbor a pathway, absent in E. coli, that channels MurNAc directly to peptidoglycan biosynthesis. This "anabolic recycling pathway" bypasses the initial steps of peptidoglycan de novo synthesis, including the target of the antibiotic fosfomycin, thus providing intrinsic resistance to the antibiotic. The Gram-negative oral pathogen Tannerella forsythia is auxotrophic for MurNAc and apparently depends on the anabolic recycling pathway to synthesize its own cell wall by scavenging cell wall debris of other bacteria. In contrast, Gram-positive bacteria lack the anabolic recycling genes, but mostly contain one or two murQ orthologs. Quantification of MurNAc 6P accumulation in murQ mutant cells by mass spectrometry allowed us to demonstrate for the first time that Gram-positive bacteria do recycle their own peptidoglycan. This had been questioned earlier, since peptidoglycan turnover products accumulate in the spent media of Gram-positives. We showed, that these fragments are recovered during nutrient limitation, which prolongs starvation survival of Bacillus subtilis and Staphylococcus aureus. Peptidoglycan recycling in these bacteria however differs, as the cell wall is either cleaved exhaustively and monosaccharide building blocks are taken up (B. subtilis) or disaccharides are released and recycled involving a novel phosphomuramidase (MupG; S.aureus). In B. subtilis also the teichoic acids, covalently bound to the peptidoglycan (wall teichoic acids; WTAs), are recycled. During phosphate limitation, the sn-glycerol-3-phosphate phosphodiesterase GlpQ specifically degrades WTAs of B. subtilis. In S. aureus, in contrast, GlpQ is used to scavenge external teichoic acid sources. Thus, although bacteria generally recover their own cell wall, they apparently apply distinct strategies for breakdown and reutilization of cell wall fragments. This review summarizes our work on this topic funded between 2011 and 2019 by the DFG within the collaborative research center SFB766.

Discovery of Furanoquinone Derivatives as a Novel Class of DNA Polymerase and Gyrase Inhibitors for MRSA Eradication in Cutaneous Infection

Methicillin-resistant Staphylococcus aureus (MRSA) is the primary microbe responsible for skin infections that are particularly difficult to eradicate. This study sought to inhibit planktonic and biofilm MRSA using furanoquinone-derived compounds containing imine moiety. A total of 19 furanoquinone analogs were designed, synthesized, and assessed for anti-MRSA potency. Among 19 compounds, (Z)-4-(hydroxyimino)naphtho[1,2-b]furan-5(4H)-one (HNF) and (Z)-4-(acetoxyimino)naphtho[1,2-b]furan-5(4H)-one (ANF) showed antibacterial activity superior to the others based on an agar diffusion assay. HNF and ANF exerted a bactericidal effect with a minimum inhibitory concentration (MIC) of 9.7 ∼ 19.5 and 2.4 ∼ 9.7 μg/ml, respectively. Both compounds were able to reduce the MRSA count by 1,000-fold in biofilm as compared to the control. In vivo efficacy was evaluated using a mouse model of skin infection. Topical application of lead compounds significantly suppressed abscess occurrence and the MRSA burden, and also ameliorated the skin-barrier function. The biochemical assay indicated the compounds’ inhibition of DNA polymerase and gyrase. In silico docking revealed a favorable interaction of the compounds with DNA polymerase and gyrase although the binding was not very strong. The total DNA analysis and proteomic data suggested a greater impairment of some proteins by HNF than ANF. In general, HNF and ANF were similarly potent in MRSA inhibition in vitro and in vivo. The findings demonstrated that there was room for structural modification of furanoquinone compounds that could be used to identify anti-MRSA agent candidates.

Draft Genome Sequences of the Type Strains of Six Macrococcus Species

We report here the draft genome sequences of Macrococcus bovicus ATCC 51825^T, Macrococcus carouselicus ATCC 51828^T, Macrococcus equipercicus ATCC 51831^T, Macrococcus brunensis CCM4811^T, Macrococcus hajekii CCM4809^T, and Macrococcus lamae CCM4815^T. The availability of the genome sequences of these species will enable cross-species comparison, which could lead to a more comprehensive understanding of organisms of the Macrococcus genus.

We report here the draft genome sequences of Macrococcus bovicus ATCC 51825^T, Macrococcus carouselicus ATCC 51828^T, Macrococcus equipercicus ATCC 51831^T, Macrococcus brunensis CCM4811^T, Macrococcus hajekii CCM4809^T, and Macrococcus lamae CCM4815^T. The availability of the genome sequences of these species will enable cross-species comparison, which could lead to a more comprehensive understanding of organisms of the Macrococcus genus.

Ultrasensitive and Rapid-Response Sensor for the Electrochemical Detection of Antibiotic Residues within Meat Samples

Antimicrobial use in livestock has emerged as a pressing global issue because of the rise of antimicrobial-resistant bacteria. Regulatory authorities across the globe have taken steps to discourage the misuse of these antibiotics by banning or limiting the use of medically important antibiotics in food animals. However, to ensure that food animals are not being administered antibiotics inappropriately, there is a need for a reliable, raid-response biosensor that can detect the presence of these antibiotic residuals in meat products. We have developed an affinity-based electrochemical biosensor for the label-free detection of ceftiofur residues in meat samples. The sensor uses a self-assembled immunoassay to target the ceftiofur biomarker by employing electrochemical impedance spectroscopy to probe the interfacial capacitive changes as ceftiofur binds to the sensor surface. We have demonstrated a platform that can detect ceftiofur within 15 min of introducing the sample at concentrations down to 0.01 ng/mL in 1× phosphate-buffered saline and 10 ng/mL in 220 mg ground turkey meat samples.

Alternative Enzyme Protection Assay To Overcome the Drawbacks of the Gentamicin Protection Assay for Measuring Entry and Intracellular Survival of Staphylococci

Precise enumeration of living intracellular bacteria is the key step to estimate the invasion potential of pathogens and host immune responses to understand the mechanism and kinetics of bacterial pathogenesis. Therefore, quantitative assessment of host-pathogen interactions is essential for development of novel antibacterial therapeutics for infectious disease. The gentamicin protection assay (GPA) is the most widely used method for these estimations by counting the CFU of intracellular living pathogens. Here, we assess the longstanding drawbacks of the GPA by employing an antistaphylococcal endopeptidase as a bactericidal agent to kill extracellular Staphylococcus aureus We found that the difference between the two methods for the recovery of intracellular CFU of S. aureus was about 5 times. We prove that the accurate number of intracellular CFU could not be precisely determined by the GPA due to the internalization of gentamicin into host cells during extracellular bacterial killing. We further demonstrate that lysostaphin-mediated extracellular bacterial clearance has advantages for measuring the kinetics of bacterial internalization on a minute time scale due to the fast and tunable activity and the inability of protein to permeate the host cell membrane. From these results, we propose that accurate quantification of intracellular bacteria and measurement of internalization kinetics can be achieved by employing enzyme-mediated killing of extracellular bacteria (enzyme protection assay [EPA]) rather than the host-permeative drug gentamicin, which is known to alter host physiology.

A staphylococcal cyclophilin carries a single domain and unfolds via the formation of an intermediate that preserves cyclosporin A binding activity

Cyclophilin (Cyp), a peptidyl-prolyl cis-trans isomerase (PPIase), acts as a virulence factor in many bacteria including Staphylococcus aureus. The enzymatic activity of Cyp is inhibited by cyclosporin A (CsA), an immunosuppressive drug. To precisely determine the unfolding mechanism and the domain structure of Cyp, we have investigated a chimeric S. aureus Cyp (rCyp) using various probes. Our limited proteolysis and the consequent analysis of the proteolytic fragments indicate that rCyp is composed of one domain with a short flexible tail at the C-terminal end. We also show that the urea-induced unfolding of both rCyp and rCyp-CsA is completely reversible and proceeds via the synthesis of at least one stable intermediate. Both the secondary structure and the tertiary structure of each intermediate appears very similar to those of the corresponding native protein. Conversely, the hydrophobic surface areas of the intermediates are comparatively less. Further analyses reveal no loss of CsA binding activity in rCyp intermediate. The thermodynamic stability of rCyp was also significantly increased in the presence of CsA, recommending that this protein could be employed to screen new CsA derivatives in the future.

Essential Oil, Extracts, and Sesquiterpenes Obtained From the Heartwood of Pilgerodendron uviferum Act as Potential Inhibitors of the Staphylococcus aureus NorA Multidrug Efflux Pump

Staphylococcus aureus is a serious human pathogen that is highly adaptive to environmental conditions and rapidly develops antibiotic resistance. The use of efflux pumps to reduce antibiotic concentrations at the intracellular level is one of the main mechanisms by which bacteria develop antibiotic resistance. The management of efflux pumps, specifically NorA, which is expressed by S. aureus strains, is a valuable strategy for restoring susceptibility in strains resistant to antibacterial agents. In recent years, many studies have focused on searching for natural substances that can reverse efflux pump-mediated resistance in S. aureus. Extracts and compounds obtained from plants can be efficient efflux pump inhibitors (EPIs) and represent a potentially patient-friendly strategy for controlling S. aureus. In the present study, we evaluated the ability of essential oils, petroleum ether extracts, dichloromethane extract (DCME) and six compounds isolated from the heartwood of Pilgerodendron uviferum (Cupressaceae) and two synthetic derivatives to inhibit efflux in NorA pumps in the following three S. aureus strains: K2378, which overexpressed the norA gene (norA++), K1902 (norA-deleted, ΔnorA) and the parental strain, NCTC 8325-4. Efflux activity was evaluated using a fluorometric method that measured the accumulation of the universal efflux pump substrate ethidium bromide (EtBr). Only DCME and the compounds 15-copaenol and epi-cubenol inhibited EtBr efflux by K2378. Even the lowest concentration of 15-copaenol exhibited a stronger inhibitory effect than carbonyl cyanide m-chlorophenyl hydrazone on EtBr efflux by K2378. 15-copaenal only showed inhibition of EtBr efflux in K2378 cells at 125 μg/mL, but not superior to the control inhibitor and 15-copaenyl acetate exerted no intrinsic EPI activity against K2378. Fractional inhibitory concentration index (FICI) values obtained in the checkerboard assays, indicated that all combinations between DCME, epi-cubenol and 15-copaenol, and tested antibiotics showed a synergistic effect in wild type, norA ++ and ΔnorA strains. Moreover, those were not toxic for the HeLa cell line at concentrations in which the synergistic effect and inhibitory activity of efflux pumps was determined. Other extracts and compounds obtained from P. uviferum did not display EtBr efflux-inhibiting activity against the evaluated S. aureus strains.

Genetic and Transcriptomic Analyses of Ciprofloxacin-Tolerant Staphylococcus aureus Isolated by the Replica Plating Tolerance Isolation System (REPTIS)

We developed a simple, efficient, and cost-effective method, named the replica plating tolerance isolation system (REPTIS), to detect the antibiotic tolerance potential of a bacterial strain. This method can also be used to quantify the antibiotic-tolerant subpopulation in a susceptible population. Using REPTIS, we isolated ciprofloxacin (CPFX)-tolerant mutants (mutants R2, R3, R5, and R6) carrying a total of 12 mutations in 12 different genes from methicillin-sensitive Staphylococcus aureus (MSSA) strain FDA209P. Each mutant carried multiple mutations, while few strains shared the same mutation. The R2 strain carried a nonsense mutation in the stress-mediating gene, relA Additionally, two strains carried the same point mutation in the leuS gene, encoding leucyl-tRNA synthetase. Furthermore, RNA sequencing of the R strains showed a common upregulation of relA Overall, transcriptome analysis showed downregulation of genes related to translation; carbohydrate, fat, and energy metabolism; nucleotide synthesis; and upregulation of amino acid biosynthesis and transportation genes in R2, R3, and R6, similar to the findings observed for the FDA209P strain treated with mupirocin (MUP0.03). However, R5 showed a unique transcription pattern that differed from that of MUP0.03. REPTIS is a unique and convenient method for quantifying the level of tolerance of a clinical isolate. Genomic and transcriptomic analyses of R strains demonstrated that CPFX tolerance in these S. aureus mutants occurs via at least two distinct mechanisms, one of which is similar to that which occurs with mupirocin treatment.

Anthropogenic influence shapes the distribution of antibiotic resistant bacteria (ARB) in the sediment of Sundarban estuary in India

The abundance and dissemination of antibiotic resistance genes as emerging environmental contaminants have become a significant and growing threat to human and environmental health. Traditionally, investigations of antibiotic resistance have been confined to a subset of clinically relevant antibiotic-resistant bacterial pathogens. During the last decade it became evident that the environmental microbiota possesses an enormous number and diversity of antibiotic resistance genes, some of which are very similar to the genes circulating in pathogenic microbiota. Recent studies demonstrate that aquatic ecosystems are potential reservoirs of antibiotic-resistant bacteria (ARBs) and antibiotic resistance genes (ARGs). Therefore, these aquatic ecosystems serve as potential sources for their transmission of ARGs to human pathogens. An assessment of such risks requires a better understanding of the level and variability of the natural resistance background and the extent of the anthropogenic impact. We have analyzed eight sediment samples from Sundarban mangrove ecosystem in India, collected at sampling stations with different histories of anthropogenic influences, and analyzed the relative abundance of the bla_TEM gene using quantitative real-time PCR. The bla_TEM gene abundance strongly correlated with the respective anthropogenic influences (polyaromatic hydrocarbon, heavy metals etc.) of the sampling stations. Besides, 18 multidrug-resistant (ampicillin, kanamycin, vancomycin, and tetracycline resistant) bacterial strains (ARBs) were isolated and characterized. Moreover, the effect of different antibiotics on the biofilm forming ability of the isolates was evaluated quantitatively under a variety of experimental regimes. This is the first report of preservation and possible dissemination of ARGs in the mangrove ecosystem.

Multifunctional Coatings and Nanotopographies: Toward Cell Instructive and Antibacterial Implants

In biomaterials science, it is nowadays well accepted that improving the biointegration of dental and orthopedic implants with surrounding tissues is a major goal. However, implant surfaces that support osteointegration may also favor colonization of bacterial cells. Infection of biomaterials and subsequent biofilm formation can have devastating effects and reduce patient quality of life, representing an emerging concern in healthcare. Conversely, efforts toward inhibiting bacterial colonization may impair biomaterial-tissue integration. Therefore, to improve the long-term success of medical implants, biomaterial surfaces should ideally discourage the attachment of bacteria without affecting eukaryotic cell functions. However, most current strategies seldom investigate a combined goal. This work reviews recent strategies of surface modification to simultaneously address implant biointegration while mitigating bacterial infections. To this end, two emerging solutions are considered, multifunctional chemical coatings and nanotopographical features.

In Vitro Inhibition of Staphylococcus aureus subsp. aureus (ATCC® 6538™) by Artemether-Lumefantrine Tablets: A Comparative Study of Three Dosage Strengths

Purpose:

Antibiotics are progressively failing in the fight against infections due to S. aureus because the bacterium has an outstanding ability to acquire multi-antibiotic resistance and become resistant to most antibiotics. Multi-drug resistant S. aureus poses a major threat to the foundation upon which standard antibacterial chemotherapy stands, hence the need to consider non-antibiotic solutions to manage invasive bacterial infections. This study investigated the inhibitory activities of three dosage strengths of artemether-lumefantrine tablets against Staphylococcus aureus subsp. aureus (ATCC® 6538™) and determined the minimum concentrations of the tablets that are able to completely inhibit growth of the bacterium in vitro.

Methods:

The agar dilution and broth macrodilution techniques were used to determine the susceptibility of the Staphylococcus aureus subsp. aureus (ATCC® 6538™) strain to artemether-lumefantrine 20/120mg, 40/240mg and 80/480mg tablets.

Results:

The most active inhibitor was artemether-lumefantrine 80/480mg tablet with a minimum inhibitory concentration value of 2.5mg/mL while artemether-lumefantrine 20/120mg and 40/240mg tablets exhibited moderate but equal activities against the test strain.

Conclusions:

The study has revealed that artemether-lumefantrine, an antimalarial drug, also has anti-staphylococcal properties and inhibits S. aureus in vitro. This study presents the first report on the in vitro activity of artemether-lumefantrine tablet against S. aureus and suggests the need to consider it as an alternative in the treatment of staphylococcus infections.

Inactivation of the Monofunctional Peptidoglycan Glycosyltransferase SgtB Allows Staphylococcus aureus To Survive in the Absence of Lipoteichoic Acid

The bacterial cell wall acts as a primary defense against environmental insults such as changes in osmolarity. It is also a vulnerable structure, as defects in its synthesis can lead to growth arrest or cell death. The important human pathogen Staphylococcus aureus has a typical Gram-positive cell wall, which consists of peptidoglycan and the anionic polymers LTA and wall teichoic acid. Several clinically relevant antibiotics inhibit the synthesis of peptidoglycan; therefore, it and teichoic acids are considered attractive targets for the development of new antimicrobials. We show that LTA is required for efficient peptidoglycan cross-linking in S. aureus and inactivation of a peptidoglycan glycosyltransferase can partially rescue this defect, together revealing an intimate link between peptidoglycan and LTA synthesis.

The cell wall of Staphylococcus aureus is composed of peptidoglycan and the anionic polymers lipoteichoic acid (LTA) and wall teichoic acid. LTA is required for growth and normal cell morphology in S. aureus. Strains lacking LTA are usually viable only when grown under osmotically stabilizing conditions or after the acquisition of compensatory mutations. LTA-negative suppressor strains with inactivating mutations in gdpP, which resulted in increased intracellular c-di-AMP levels, were described previously. Here, we sought to identify factors other than c-di-AMP that allow S. aureus to survive without LTA. LTA-negative strains able to grow in unsupplemented medium were obtained and found to contain mutations in sgtB, mazE, clpX, or vraT. The growth improvement through mutations in mazE and sgtB was confirmed by complementation analysis. We also showed that an S. aureussgtB transposon mutant, with the monofunctional peptidoglycan glycosyltransferase SgtB inactivated, displayed a 4-fold increase in the MIC of oxacillin, suggesting that alterations in the peptidoglycan structure could help bacteria compensate for the lack of LTA. Muropeptide analysis of peptidoglycans isolated from a wild-type strain and sgtB mutant strain did not reveal any sizable alterations in the peptidoglycan structure. In contrast, the peptidoglycan isolated from an LTA-negative ltaS mutant strain showed a significant reduction in the fraction of highly cross-linked peptidoglycan, which was partially rescued in the sgtB ltaS double mutant suppressor strain. Taken together, these data point toward an important function of LTA in cell wall integrity through its necessity for proper peptidoglycan assembly.

IMPORTANCE The bacterial cell wall acts as a primary defense against environmental insults such as changes in osmolarity. It is also a vulnerable structure, as defects in its synthesis can lead to growth arrest or cell death. The important human pathogen Staphylococcus aureus has a typical Gram-positive cell wall, which consists of peptidoglycan and the anionic polymers LTA and wall teichoic acid. Several clinically relevant antibiotics inhibit the synthesis of peptidoglycan; therefore, it and teichoic acids are considered attractive targets for the development of new antimicrobials. We show that LTA is required for efficient peptidoglycan cross-linking in S. aureus and inactivation of a peptidoglycan glycosyltransferase can partially rescue this defect, together revealing an intimate link between peptidoglycan and LTA synthesis.

Molecular Characterization and Antibiotic Resistance of Foodborne Pathogens in Street-Vended Ready-to-Eat Meat Sold in South Africa

ABSTRACT

The consumption of food contaminated with microbial populations remains a key route of foodborne infection in developing countries and creates a serious public health burden. This study aimed at identifying foodborne pathogens and their antibiotic resistance profiles in ready-to-eat meat sold in public eateries in the Johannesburg area. A total of 115 samples were examined for the incidence of bacteria pathogens and their antibiotic resistance profiles against commonly used antibiotics (ampicillin, tetracycline, chloramphenicol, erythromycin, ciprofloxacin, streptomycin, and sulphonamides) using the molecular and the disc diffusion methods. Fifteen bacteria species were detected in the samples. Staphylococcus aureus had the highest prevalence (25%), and 53.33% of the isolates exhibited multidrug resistance to the antibiotics tested. Among the isolated bacteria, S. aureus; was resistant to at least six antimicrobial agents, whereas 100% of S. aureus,Enterococcus faecalis, and Planomicrobium glaciei were resistant to streptomycin, ciprofloxacin, and chloramphenicol, respectively. This study revealed that a wide diversity of bacteria species contaminate meat sold on the street, which indicates that consumers of ready-to-eat meat sold in public eateries are at risk of food poisoning. Hence, strict intervention strategies should be put in place by government agencies to reduce the menace of food poisoning in the country.

HIGHLIGHTS

RTE meats were analyzed for microbial contamination. Foodborne pathogens were detected in the meat samples. Antibiotic resistance profiles were tested. RTE meats contain foodborne pathogens, and isolates exhibited antibiotic resistance. Consumers of RTE meat in the Johannesburg CBD are at risk of food poisoning.

Recovery of the Peptidoglycan Turnover Product Released by the Autolysin Atl in Staphylococcus aureus Involves the Phosphotransferase System Transporter MurP and the Novel 6-phospho-N-acetylmuramidase MupG

The peptidoglycan of the bacterial cell wall undergoes a permanent turnover during cell growth and differentiation. In the Gram-positive pathogen Staphylococcus aureus, the major peptidoglycan hydrolase Atl is required for accurate cell division, daughter cell separation and autolysis. Atl is a bifunctional N-acetylmuramoyl-L-alanine amidase/endo-β-N-acetylglucosaminidase that releases peptides and the disaccharide N-acetylmuramic acid-β-1,4-N-acetylglucosamine (MurNAc-GlcNAc) from the peptido-glycan. Here we revealed the recycling pathway of the cell wall turnover product MurNAc-GlcNAc in S. aureus. The latter disaccharide is internalized and concomitantly phosphorylated by the phosphotransferase system (PTS) transporter MurP, which had been implicated previously in the uptake and phosphorylation of MurNAc. Since MurP mutant cells accumulate MurNAc-GlcNAc and not MurNAc in the culture medium during growth, the disaccharide represents the physiological substrate of the PTS transporter. We further identified and characterized a novel 6-phospho-N-acetylmuramidase, named MupG, which intracellularly hydrolyses MurNAc 6-phosphate-GlcNAc, the product of MurP-uptake and phosphorylation, yielding MurNAc 6-phosphate and GlcNAc. MupG is the first characterized representative of a novel family of glycosidases containing domain of unknown function 871 (DUF871). The corresponding gene mupG (SAUSA300_0192) of S. aureus strain USA300 is the first gene within a putative operon that also includes genes encoding the MurNAc 6-phosphate etherase MurQ, MurP, and the putative transcriptional regulator MurR. Using mass spectrometry, we observed cytoplasmic accumulation of MurNAc 6-phosphate-GlcNAc in ΔmupG and ΔmupGmurQ markerless non-polar deletion mutants, but not in the wild type or in the complemented ΔmupG strain. MurNAc 6-phosphate-GlcNAc levels in the mutants increased during stationary phase, in accordance with previous observations regarding peptidoglycan recycling in S. aureus.