Human Pathogenic Strains Research Articles

Antibiotic resistance genes and antibiotic sensitivity in bacterial aerosols and their comparisons with known respiratory pathogens

Airborne transmission of antibiotic resistance genes (ARGs) has emerged as a global health threat, while their hosts’ resistance phenotype remains largely unknown. Here, culturable bacterial aerosol samples were collected from polluted air in Beijing using a portable high volume sampler (1000 L/min). Antimicrobial susceptibility testing was conducted to explore the antibiotic sensitivity of culturable bacterial aerosols to seven widely used antibiotics. As a comparison, ARG distribution and expression in two human respiratory pathogenic bacterial strains (Pseudomonas aeruginosa and Methicillin-resistant Staphylococcus aureus) and a non-pathogenic bacterial strain (Pseudomonas fluorescens) were also studied. Relative abundances of 39 ARG subtypes in three bacterial strains including Haemophilus influenzae were investigated by high throughput real-time qPCR platform. Surprisingly, 24.66% of the culturable bacterial aerosols in polluted air were resistant to vancomycin-the most powerful antibiotics to date, while 53.05% of airborne culturable bacteria were susceptible to ampicillin (β-lactams). Different bacteria demonstrated very different ARG distribution patterns of more or less skewed toward certain one ARG type. On the other hand, the vancomycin resistance gene vanB was detected both in H. influenza and P. fluorescens, however these bacteria did not exhibit anti-vancomycin phenotype. Furthermore, the resistance to ciprofloxacin (quinolones) was not observed in P. aeruginosa and P. fluorescens although these bacteria harbor abundant quinolone resistance gene qepA. Experimental data from this work show that air represents an important active reservoir of diverse ARGs, and some bacterial aerosols are harboring vancomycin resistance gene though not expressed. Results from human respiratory pathogens have further demonstrated similar findings. This work underscores the serious concern of airborne dissemination of ARBs including those resistant to vancomycin in polluted ambient environments, while revealing abundances and patterns of various ARGs in both pathogenic and non-pathogenic bacteria.

The Effect of Conjugation with Octaarginine, a Cell-Penetrating Peptide on Antifungal Activity of Imidazoacridinone Derivative.

Acridine cell-penetrating peptide conjugates are an extremely important family of compounds in antitumor chemotherapy. These conjugates are not so widely analysed in antimicrobial therapy, although bioactive peptides could be used as nanocarriers to smuggle antimicrobial compounds. An octaarginine conjugate of an imidazoacridinone derivative (Compound 1-R8) synthetized by us exhibited high antifungal activity against reference and fluconazole-resistant clinical strains (MICs ≤ 4 μg mL−1). Our results clearly demonstrate the qualitative difference in accumulation of the mother compound and Compound 1-R8 conjugate into fungal cells. Only the latter was transported and accumulated effectively. Microscopic and flow cytometry analysis provide some evidence that the killing activity of Compound 1-R8 may be associated with a change in the permeability of the fungal cell membrane. The conjugate exhibited low cytotoxicity against human embryonic kidney (HEK-293) and human liver (HEPG2) cancer cell lines. Nevertheless, the selectivity index value of the conjugate for human pathogenic strains remained favourable and no hemolytic activity was observed. The inhibitory effect of the analysed compound on yeast topoisomerase II activity suggested its molecular target. In summary, conjugation with R8 effectively increased imidazoacridinone derivative ability to enter the fungal cell and achieve a concentration inside the cell that resulted in a high antifungal effect.

Characterization and biological activities of carotenoids produced by three haloarchaeal strains isolated from Algerian salt lakes.

Halophilic archaea represent a promising natural source of carotenoids. However, little information is available about these archaeal metabolites and their biological effects. In the present work, carotenoids of strains Haloferax sp. ME16, Halogeometricum sp. ME3 and Haloarcula sp. BT9, isolated from Algerian salt lakes, were produced, extracted and identified by high-performance liquid chromatography-diode array detector and liquid chromatography-mass spectrometry. Analytical results revealed a variation in the composition depending on the strain with a predominance of bacterioruberin. The evaluation of antioxidant capacity using ABTS [(2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)] and DPPH (2,2-diphenyl-1-picrylhydrazyl) assays showed that these extracts have a strong antioxidant potential, in particular those of Haloferax sp. ME16 which displayed antioxidant power significantly higher than that of ascorbic acid used as standard. Antibacterial activity of carotenoid extracts against four human-pathogenic strains and four fish-pathogenic strains was evaluated by agar disk diffusion method. The results showed a good antibacterial activity. These findings suggest that the C50 carotenoids from the studied strains offer promising prospects for biotechnological applications.

First molecular detection of Anaplasma species in cattle from Kyrgyzstan; molecular identification of human pathogenic novel genotype Anaplasma capra and Anaplasma phagocytophilum related strain

Anaplasmosis is a rickettsial infection with significant effects on human and animal health, and the discovery of new species or genotypes with zoonotic potential in recent years has increased this importance. The aim of this study was to provide the first assessment of the molecular etiology and prevalence of bovine anaplasmosis in Kyrgyzstan (specifically in the Chuy, Talas, Djalal-Abad, Naryn, and Issyk-Kul regions). The prevalence of bovine anaplasmosis was determined as 1.7% (6/358). PCR and partial DNA sequencing results of the 16S ribosomal RNA (rRNA) gene revealed that Anaplasma centrale, A. phagocytophilum like-1, and the human pathogenic novel genotype A. capra are circulating in cattle herds in Kyrgyzstan. Six DNA nucleotide sequences obtained in this study were deposited in GenBank under the following accession numbers: A. centrale (MW672117, MW672118, MW672119, MW672120), A. phagocytophilum (MW672121), and A. capra (MW672115).

Assessment of antimicrobial properties of a lectin isolated from <em>Amaranthus cruentus</em> Linn

Lectins are diverse class of proteins which have the ability to bind carbohydrates with considerable specificity and involved in many biological processes like host pathogen interactions, cell targeting, cell- cell communications, cancer metastasis and differentiation. Plants are rich sources of lectins that have great implications in medicinal and therapeutic applications. The antimicrobial property of a lectin isolated from Amaranthus cruentus Linn seeds has been explored in this study. ACL (Amaranthus cruentus Linn lectin) was isolated, purified and characterised by hemagglutination assay with human ABO blood groups and the molecular weight was determined by SDS PAGE. ACL was subjected to evaluation for inhibition of microbial growth by disc diffusion against human pathogenic Gram positive and Gram negative bacterial strains and some fungal strains. MIC and MBC were assessed. The effects of ACL on biofilm forming bacterial strains was assessed using crystal violet assay. The isolated and purified ACL have a molecular weight of 60 KDa. The Hemagglutination activity of ACL was inhibited by N-acetyl galactosamine. ACL exhibited both antibacterial and antifungal activities with considerable zones of inhibition. Biofilm mass reduction was observed in ACL treated bacteria. These findings indicate that ACL is having therapeutic applications with great importance in clinical microbiology.

Ecological and Pharmacological Activities of Polybrominated Diphenyl Ethers (PBDEs) from the Indonesian Marine Sponge Lamellodysidea herbacea

Two known Polybrominated Diphenyl Ethers (PBDEs), 3,4,5-tribromo-2-(2′,4′-dibromophenoxy)phenol (1d) and 3,4,5,6-tetrabromo-2-(2′,4′-dibromophenoxy)phenol (2b), were isolated from the Indonesian marine sponge Lamellodysidea herbacea. The structure was confirmed using 13C chemical shift average deviation and was compared to the predicted structures and recorded chemical shifts in previous studies. We found a wide range of bioactivities from the organic crude extract, such as (1) a strong deterrence against the generalist pufferfish Canthigaster solandri, (2) potent inhibition against environmental and human pathogenic bacterial and fungal strains, and (3) the inhibition of the Hepatitis C Virus (HCV). The addition of a bromine atom into the A-ring of compound 2b resulted in higher fish feeding deterrence compared to compound 1d. On the contrary, compound 2b showed only more potent inhibition against the Gram-negative bacteria Rhodotorula glutinis (MIC 2.1 μg/mL), while compound 1d showed more powerful inhibition against the other human pathogenic bacteria and fungi. The first report of a chemical defense by compounds 1d and 2b against fish feeding and environmental relevant bacteria, especially pathogenic bacteria, might be one reason for the widespread occurrence of the shallow water sponge Lamellodysidea herbacea in Indonesia and the Indo-Pacific.

Cadmium(II) coordination polymer based on flexible dithiolate-polyamine binary ligands system: Crystal structure, Hirshfeld surface analysis, antimicrobial, and DNA cleavage potential

The mononuclear chelating complex [Cd(i-mnt)(tren)]n (1) fabricated from binary ligand systems 1,1-dicyanoethylene-2,2-dithiolate (i-mnt−2) and diethylenetriamine (tren) has been synthesized and structurally characterized by spectroscopic methods (IR, NMR). The single-crystal X-ray diffraction study reveals that Cd+2 has CdN3S3 coordination kernel having distorted trigonal prism geometry (TP) [twist angle (θ) 37.6(11)0] and the secondary ligand tren influences the ligation pattern of i-mnt−2 towards metal center in the formation of 1D polymeric chain where asymmetric units linked by bridging thiolate S2-atom of each i-mnt−2. The N H···N, N H···S type hydrogen bonds link the 1D polymeric chains in a 3D stacked chain supramolecular arrangement with apparent graph-set-motifs R118, C(4), and C(8). The Hirshfeld surface analysis corroborates well with X-ray data and explores all possible intermolecular interactions especially dominant N···H (16.6%) and H···S (7.3%) contacts. The MIC, MBC and in-vitro antibacterial study against Gram-positive (Staphylococcus aureus, Bacillus subtilis) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa) human pathogenic bacterial strains shows promising bactericidal activity. In-vitro antifungal study disclosing more activity against Aspergillus niger compared to Candida albicans at 50 mg/mL. DNA cleavage study (E. coli DNA) via Agarose gel electrophoresis shows DNA cleaving property of the title compound similar to that of H2O2 due to the suitable coordination of Cd(II) metal center.

A New Workflow to Generate Monoclonal Antibodies against Microorganisms

Monoclonal antibodies are used worldwide as highly potent and efficient detection reagents for research and diagnostic applications. Nevertheless, the specific targeting of complex antigens such as whole microorganisms remains a challenge. To provide a comprehensive workflow, we combined bioinformatic analyses with novel immunization and selection tools to design monoclonal antibodies for the detection of whole microorganisms. In our initial study, we used the human pathogenic strain E. coli O157:H7 as a model target and identified 53 potential protein candidates by using reverse vaccinology methodology. Five different peptide epitopes were selected for immunization using epitope-engineered viral proteins. The identification of antibody-producing hybridomas was performed by using a novel screening technology based on transgenic fusion cell lines. Using an artificial cell surface receptor expressed by all hybridomas, the desired antigen-specific cells can be sorted fast and efficiently out of the fusion cell pool. Selected antibody candidates were characterized and showed strong binding to the target strain E. coli O157:H7 with minor or no cross-reactivity to other relevant microorganisms such as Legionella pneumophila and Bacillus ssp. This approach could be useful as a highly efficient workflow for the generation of antibodies against microorganisms.

Cytotoxicity and antimicrobial activities of some soft corals inhabiting the red sea, Egypt.

Cancer and infectious diseases are notoriously known as deleterious health threats for the world, especially in the developing countries. The aim of the present study was to evaluate the cytotoxicity and antimicrobial activities of the methanolic extracts of the soft corals Nephthea elatensis, Heteroxenia fuscescens, Ellisella juncea, Dendronephthya mollis, and Sinularia hirta, that are native to the Red Sea in Egypt. The cytotoxicity assay was carried out by the enzymatic reduction of 3-[4,5-dimethylthiazole-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay against lung adenocarcinoma cell line (A549). Moreover, the antimicrobial activity was carried out against 11 human pathogenic bacterial and fungal strains using well-cut diffusion technique, while the Minimum Inhibitory Concentrations (MICs) were determined by microdilution method. Nephthea elatensis showed potent cytotoxicity [half maximal inhibitory concentration (IC50) 11.9 ± 1.2 µg/mL]. Also, it exhibited a potent antibacterial activity against Staphylococcus aureus(MIC 1.0 µg/mL). Sinularia hirta exhibited significant antimicrobial activities against Salmonella typhimurium and S. aureus (MIC 5.0 and 10.0 µg/mL, respectively). The results recommended N. elatensis and S. hirta as promising sources for new anticancer and antibiotic natural candidates.

Synthesis of New Series Bis-3-Chloro-β-Lactam Derivatives from Symmetrical Bis-Schiff Bases as Effective Antimicrobial Agents with Molecular Docking Studies

Endeavoring to find a new type of antimicrobial agents, a new sequence of bis-Schiff bases and bis-3-cholro-β-lactams are synthesized. An astonishing class of strained compounds is part of the symmetrical bis-Schiff bases that has widespread applications and building blocks for the combination of bis-3-cholro-β-lactams antibiotics. Bis-3-cholro-β-lactams are synthesized through (Staudinger) [2+2] ketene-imine cycloaddition reaction. Structures of the produced compounds are deduced by 1H, 13C-NMR, and FT-IR spectroscopies. All produced compounds are shown moderate to good antimicrobial activity compared to human pathogenic bacteria strains (Escherichia coli and Staphylococcus aureus), also compared to Aspergillus Niger and Trichophyton mentagrophytes fungi through the broth microdilution technique. A molecular docking study is used for showing the active sides and binding affinity of the products with the target proteins or receptors of E. coli (PDB ID: 3GI9).

The rise of the hepatitis E virus

It took 40 years for the hepatitis E virus (HEV) to grow from a suspected waterborne agent of hepatitis outbreaks in India,1 to the most common cause of acute viral hepatitis worldwide, and a crucial issue for the European Association for the Study of the Liver.2 HEV belongs to the Hepeviridae: a family of viruses that can infect mammals, birds, and fish. Human pathogenic strains are found within the Orthohepevirus A species divided in genotypes: HEV-1 and -2 are restricted to humans; HEV-3 and -4 infect both humans and animals, and pigs are the main reservoir, along with deer, wild boars, and rabbits.

Complete Genome Sequencing of Leptospira interrogans Isolates from Malaysia Reveals Massive Genome Rearrangement but High Conservation of Virulence-Associated Genes.

The ability of Leptospirae to persist in environments and animal hosts but to cause clinically highly variable disease in humans has made leptospirosis the most common zoonotic disease. Considering the paucity of data on variation in complete genomes of human pathogenic Leptospirae, we have used a combination of Single Molecule Real-Time (SMRT) and Illumina sequencing to obtain complete genome sequences of six human clinical L. interrogans isolates from Malaysia. All six contained the larger (4.28–4.56 Mb) and smaller (0.34–0.395 Mb) chromosome typical of human pathogenic Leptospirae and 0–7 plasmids. Only 24% of the plasmid sequences could be matched to databases. We identified a chromosomal core genome of 3318 coding sequences and strain-specific accessory genomes of 49–179 coding sequences. These sequences enabled detailed genomic strain typing (Genome BLAST Distance Phylogeny, DNA–DNA hybridization, and multi locus sequence typing) and phylogenetic classification (whole-genome SNP genotyping). Even though there was some shared synteny and collinearity across the six genomes, there was evidence of major genome rearrangement, likely driven by horizontal gene transfer and homologous recombination. Mobile genetic elements were identified in all strains in highly varying numbers, including in the rfb locus, which defines serogroups and contributes to immune escape and pathogenesis. On the other hand, there was high conservation of virulence-associated genes including those relating to sialic acid, alginate, and lipid A biosynthesis. These findings suggest (i) that the antigenic variation, adaption to various host environments, and broad spectrum of virulence of L. interrogans are in part due to a high degree of genomic plasticity and (ii) that human pathogenic strains maintain a core set of genes required for virulence.

Bacteriophage-Mediated Risk Pathways Underlying the Emergence of Antimicrobial Resistance via Intrageneric and Intergeneric Recombination of Antibiotic Efflux Genes Across Natural populations of Human Pathogenic Bacteria

Antimicrobial resistance continues to be a significant and growing threat to global public health, being driven by the emerging drug-resistant and multidrug-resistant strains of human and animal bacterial pathogens. While bacteriophages are generally known to be one of the vehicles of antibiotic resistance genes (ARGs), it remains largely unclear how these organisms contribute to the dissemination of the genetic loci encoding for antibiotic efflux pumps, especially those that confer multidrug resistance, in bacteria. In this study, the in-silico recombination analyses provided strong statistical evidence for bacteriophage-mediated intra-species recombination of ARGs, encoding mainly for the antibiotic efflux proteins from the MF superfamily, as well as from the ABC and RND families, in Salmonella enterica, Staphylococcus aureus, Staphylococcus suis, Pseudomonas aeruginosa, and Burkholderia pseudomallei. Events of bacteriophage-driven intrageneric recombination of some of these genes could be also elucidated among Bacillus thuringiensis, Bacillus cereus and Bacillus tropicus natural populations. Moreover, we could also reveal the patterns of intergeneric recombination, involving the MF superfamily transporter-encoding genetic loci, induced by a Mycobacterium smegmatis phage, in natural populations of Streptomyces harbinensis and Streptomyces chartreusis. The SplitsTree- (fit: 100; bootstrap values: 92.7-100; Phi p ≤ 0.2414), RDP4- (p ≤ 0.0361), and GARD-generated data strongly supported the above genetic recombination inferences in these in-silico analyses. Thus, based on this pilot study, it can be suggested that the above mode of bacteriophage-mediated recombination plays at least some role in the emergence and transmission of multidrug resistance across a fairly broad spectrum of bacterial species and genera including human pathogens.

Distribution of Vibrio parahaemolyticus in Farmed Shrimp Penaeus vannamei, Farm Water and Sediment

The halophilic marine bacterium Vibrio parahaemolyticus is a zoonotic pathogen associated with wild-caught and farmed shrimp. The bacterium is an important cause of gastroenteritis associated with the consumption of raw or undercooked seafood. In the present study, the prevalence and human pathogenic potential of Vibrio parahaemolyticus in Penaeus vannamei (tissue and hepatopancreas) and the farm environment (water and sediment) was investigated by conventional culture and molecular techniques. The total Vibrio counts of P. vannamei ranged from <1 CFU/mL in hemolymph to 7.61 log CFU/g in the hepatopancreas. The sediment samples consistently showed the counts of 6-7 log CFU/g, while the pond water had Vibrio counts in the range of 2-3 log CFU/ml. Of 120 Vibrio isolates identified, 87 were confirmed as V. parahaemolyticus based on the toxR and tlh gene-specific PCR. The virulence marker gene tdh was not detected in any of the isolates, while the trh gene was detected in 3 (3.6%) isolates. Although the incidence of pathogenic V. parahaemolyticus in farmed P. vannamei is low, the high numbers of total vibrios and V. parahaemolyticus demand constant monitoring of animals and the farm environment for human pathogenic strains of V. parahaemolyticus.

Synthesis, characterization, biological evaluation, and molecular docking approach of nickel (II) complexes containing O, N‐donor chelation pattern of sulfonamide‐based Schiff bases

AbstractA series of Schiff bases (L1–L4) that possess in their structure bioactive sulfonamide group and their nickel (II) complexes have been synthesized. Microanalytical analyses, various spectroscopic methods such as Fourier transform infrared spectroscopy (FT‐IR), 1H nuclear magnetic resonance (NMR), 13C NMR, UV–Vis, and MS, are used to explore the nature of bonding and to elucidate the chemical structures. The analytical and magnetic values suggest a range of stoichiometries 1:1, 1:2, and 2:1 (M:L) for the synthesized complexes of almost square planar geometry. The spectral comparative interpretation reveals that L1 and L2 coordinate to the central Ni (II) in tetradentate ONON donor sequence, whereas L3 and L4 in bidentate ON pattern through deprotonated phenolic‐O and the azomethine‐N. Density functional theory (DFT) and MOE‐docking approaches are used to evaluate the molecular parameters and the binding propensity of the synthesized ligands and their complexes with 3s7s protein and to signify their inhibition strength. Besides, the anticancer, antimicrobial and antifungal activities have been screened against number of tumor cells and human pathogen strains. These in vitro studies reveal that Schiff base L4 and its complex, [Ni(L4‐H)(OAc)(H2O)], have superior activities reflecting the importance of inserting bioactive pendant substituents such as thiazole ring and 3‐fluorophenylazo to the pharmacophoric sulfonamide moiety. Moreover, some of the synthesized Ni (II) complexes display promising therapeutic effects as novel non‐platinum antitumor agents after further preclinical investigations.

Antibiofilm and Antifungal Activities of Laurelia sempervirens (Chilean laurel) Essential Oil

Background: Laurelia sempervirens, better known as Chilean laurel, is endemic to Chile. For many years, the leaves and branches of this plant have been popularly used as medicinal agents. However, its antifungal properties and antibiofilm activity against bacterial strains have not been studied. Objectives: To determine antibiofilm and antimicrobial properties of Chilean laurel essential oil on human pathogenic strains. Methods: The antifungal and antibacterial activities of Chilean laurel essential oil were evaluated through the agar diffusion method, and its minimum inhibitory concentration was determined using the standard microdilution method. Antibiofilm activity was examined based on the formation and disruption of bacterial biofilms and evidenced by the crystal violet technique. Results: The results showed important antimicrobial activity against human pathogenic yeast strains, and the minimum inhibitory concentration of Chilean laurel essential oil was 64 µg mL-1 against Candida albicans. The essential oil also showed an important inhibitory effect against the formation of biofilms produced by Staphylococcus aureus, since it inhibited the formation of biofilms by over 50% at the concentration of 64 µg mL-1. With increasing the essential oil’s concentration to 128 µg mL-1, its antibiofilm activity increased by 60%. Conclusions: These results approve the domestic use of Chilean laurel essential oil as an antimicrobial agent and provide knowledge about the antibiofilm and antifungal properties of L. sempervirens.

Biological insights into the piericidin family of microbial metabolites.

Extensively produced by members of the genus Streptomyces, piericidins are a large family of microbial metabolites, which consist of main skeleton of 4-pyridinol with methylated polyketide side chain. Nonetheless, these metabolites show differences in their bioactive potentials against micro-organisms, insects and tumour cells. Due to its close structural similarity with coenzyme Q, piericidins also possess an inhibitory activity against NADH dehydrogenase as well as Photosystem II. This review studied the latest research progress of piericidins, covering the chemical structure and physical properties of newly identified members, bioactivities, biosynthetic pathway with gene clusters and future prospect. With the increasing incidence of drug-resistant human pathogen strains and cancers, this review aimed to provide clues for the development of either new potential antibiotics or anti-tumour agents.

Novel staphylococci nucH taxonomical marker used in identification of human-associated Staphylococcus succinus subsp. casei.

The aim of our study was to assess the sequencing of unique nucH gene fragment based on performed bioinformatics analysis as a novel diagnostic method for the identification of difficult to identify staphylococcal human pathogenic strains. Initially, PCR-RFLP-rrn analysis specific to the spacers between 16SrDNA and 23SrDNA followed by HhaI restriction analysis was performed. Further, sequencing of nucH and 16S rDNA genes fragments was carried out. Blast analysis from the NCBI showed 99% similarity of nucH gene fragment with reference genomic DNA for S. succinus with the accession no. CP018199. This result was also confirmed by MALDI-TOF analysis. Sequencing analysis of 16S rDNA gene fragment allowed for 100% identification of two strains isolated from human samples as Staphylococus succinus subsp. casei. Sequencing of identified unique nucH gene fragment seems to be a promising diagnostic assay for the identification of Staphylococcus species. Based on our results, we can assume that probably other Staphylococcus species originated from different clinical samples could be identified using nucH gene sequencing method we developed. However, an extension of the genetic databases with a substantially bigger number of reference staphylococcal species for nucH gene is needed to make this method better than widely used standard 16S rDNA sequencing assay. To the best of our knowledge, it is the second published isolation of S. succinus subsp. casei from human clinical specimens. Moreover, possibility of decreasing the number of dimensions from multi-PCR-bands results using ribotyping analysis is also described.

The Influence of Cellulose-Type Formulants on Anti-Candida Activity of the Tyrocidines.

Candida species are highly adaptable to environmental changes with their phenotypic flexibility allowing for the evasion of most host defence mechanisms. Moreover, increasing resistance of human pathogenic Candida strains has been reported against all four classes of available antifungal drugs, which highlights the need for combinational therapies. Tyrocidines are cyclic antimicrobial peptides that have shown synergistic activity with antifungal drugs such as caspofungin and amphotericin B. However, these cyclodecapeptides have haemolytic activity and cytotoxicity, but they have been used for decades in the clinic for topical applications. The tyrocidines tend to form higher-order structures in aqueous solutions and excessive aggregation can result in variable or diminished activity. Previous studies have shown that the tyrocidines prefer ordered association to celluloses. Therefore, a formulation with soluble cellulose was used to control the oligomer stability and size, thereby increasing the activity against Candida spp. Of the formulants tested, it was found that commercial hydroxy-propyl-methyl cellulose, E10M, yielded the best results with increased stability, increased anti-Candida activity, and improved selectivity. This formulation holds promise in topical applications against Candida spp. infections.

Insights into the acquisition of the pks island and production of colibactin in the Escherichia coli population.

The pks island codes for the enzymes necessary for synthesis of the genotoxin colibactin, which contributes to the virulence of Escherichia coli strains and is suspected of promoting colorectal cancer. From a collection of 785 human and bovine E. coli isolates, we identified 109 strains carrying a highly conserved pks island, mostly from phylogroup B2, but also from phylogroups A, B1 and D. Different scenarios of pks acquisition were deduced from whole genome sequence and phylogenetic analysis. In the main scenario, pks was introduced and stabilized into certain sequence types (STs) of the B2 phylogroup, such as ST73 and ST95, at the asnW tRNA locus located in the vicinity of the yersiniabactin-encoding High Pathogenicity Island (HPI). In a few B2 strains, pks inserted at the asnU or asnV tRNA loci close to the HPI and occasionally was located next to the remnant of an integrative and conjugative element. In a last scenario specific to B1/A strains, pks was acquired, independently of the HPI, at a non-tRNA locus. All the pks-positive strains except 18 produced colibactin. Sixteen strains contained mutations in clbB or clbD, or a fusion of clbJ and clbK and were no longer genotoxic but most of them still produced low amounts of potentially active metabolites associated with the pks island. One strain was fully metabolically inactive without pks alteration, but colibactin production was restored by overexpressing the ClbR regulator. In conclusion, the pks island is not restricted to human pathogenic B2 strains and is more widely distributed in the E. coli population, while preserving its functionality.