Staphylococcus aureus produces autolysin-susceptible cell walls during growth in a high-NaCl and low-Ca2+ concentration medium

Insights into the Antimicrobial Activity of Hydrated Cobaltmolybdate Doped with Copper

Molybdates are biocidal materials that can be useful in coating surfaces that are susceptible to contamination and the spread of microorganisms. The aim of this work was to investigate the effects of copper doping of hydrated cobalt molybdate, synthesized by the co-precipitation method, on its antibacterial activity and to elucidate the structural and morphological changes caused by the dopant in the material. The synthesized materials were characterized by PXRD, Fourier Transformed Infrared (FTIR), thermogravimetric analysis/differential scanning calorimetry (TG/DSC), and SEM-Energy Dispersive Spectroscopy (SEM-EDS). The antibacterial response of the materials was verified using the Minimum Inhibitory Concentration (MIC) employing the broth microdilution method. The size of the CoMoO₄·1.03H₂O microparticles gradually increased as the percentage of copper increased, decreasing the energy that is needed to promote the transition from the hydrated to the beta phase and changing the color of material. CoMoO₄·1.03H₂O obtained better bactericidal performance against the tested strains of Staphylococcus aureus (gram-positive) than Escherichia coli (gram-negative). However, an interesting point was that the use of copper as a doping agent for hydrated cobalt molybdate caused an increase of MIC value in the presence of E. coli and S. aureus strains. The study demonstrates the need for caution in the use of copper as a doping material in biocidal matrices, such as cobalt molybdate.

High-throughput transposon sequencing highlights the cell wall as an important barrier for osmotic stress in methicillin resistant Staphylococcus aureus and underlines a tailored response to different osmotic stressors

Staphylococcus aureus is an opportunistic pathogen that can cause soft tissue infections but is also a frequent cause of foodborne illnesses. One contributing factor for this food association is its high salt tolerance allowing this organism to survive commonly used food preservation methods. How this resistance is mediated is poorly understood, particularly during long-term exposure. In this study, we used transposon sequencing (TN-seq) to understand how the responses to osmotic stressors differ. Our results revealed distinctly different long-term responses to NaCl, KCl and sucrose stresses. In addition, we identified the DUF2538 domain containing gene SAUSA300_0957 (gene 957) as essential under salt stress. Interestingly, a 957 mutant was less susceptible to oxacillin and showed increased peptidoglycan crosslinking. The salt sensitivity phenotype could be suppressed by amino acid substitutions in the transglycosylase domain of the penicillin-binding protein Pbp2, and these changes restored the peptidoglycan crosslinking to WT levels. These results indicate that increased crosslinking of the peptidoglycan polymer can be detrimental and highlight a critical role of the bacterial cell wall for osmotic stress resistance. This study will serve as a starting point for future research on osmotic stress response and help develop better strategies to tackle foodborne staphylococcal infections.

Ordering of lipid A-monophosphate clusters in aqueous solutions

In this investigation, a study of the self-assembly of electrostatically stabilized aqueous dispersions of nanometric lipid A-monophosphate clusters from Escherichia coli was carried out in three different volume-fraction regimes. The experimental techniques used in the investigation were osmotic pressure, static and quasielastic light scattering, scanning electron microscopy and transmission electron microscopy, and small-angle x-ray scattering. Experiments were carried out at low ionic strength (I=0.1-5.0 mM NaCl) at 25 degrees C. At volume fractions between 1.5x10(-4)<or=phi<or=5.4x10(-4), the lipid A-monophosphate clusters had an average rms hydrodynamic diameter of d=7.5 nm, and a weighted-average molecular weight of (1.78+/-0.23)x10(5) g mol(-1). Quasielastic light scattering (LS) experiments yield similar values for the particle size and particle size distribution compared to electron microscopy, small-angle x-ray scattering, and LS experiments. When the volume fraction was increased to a higher regime 5.4x10(-4)<or=phi<or=9.50x10(-4), much larger clusters of lipid A monophosphate formed. The clusters detected in this volume-fraction range were assembled from between 8 and 52 of the d=7.5 nm clusters and the assemblies are densely packed in such a way that colloidal crystals composed of the monodisperse microspheres are in physical contact with their nearest neighbors. Clusters that formed in volume fractions between 10.0x10(-4)<or=phi<or=40.0x10(-4) revealed a weighted-average molecular weight of (10.15+/-0.17)x10(6) g mol(-1) and a hydrodynamic diameter of approximately d=70.6 nm. The crossover volume fraction between the small and the large clusters appeared at phicr=5.05x10(-4). In the intermediate volume-fraction range, the scattered intensity I(Q) vs Q curves (light and x rays) showed asymptotic behavior. From the asymptotic curves, the scattered intensity, the relationship between the average mass and radius, and the fractal dimension df were determined. The df value, which was evaluated from the expression I(Q) proportional, RGdf, was found to be 1.67+/-0.03, a value that was virtually independent of the ionic strength (0.1-5.0 mM NaCl) at 25 degrees C. Even at a very low ionic strength (I=0.10 mM NaCl), lipid A monophosphate formed a number of differently shaped clusters. Electron microscope images showed that two types of self-assembled clusters existed at the lowest volume-fraction range studied and also dominated the images taken at the higher volume-fraction regimes. One type of cluster showed a cubic morphology and a size variation of 50-100 nm, while another type took on the appearance of a quadratic cylinder, with dimensions of 50x150 nm2. The other clusters appeared in various shapes: dimers, trimers, and distorted tetramers, which were quite different from the ones previously observed for lipid A diphosphate. Small-angle x-ray diffraction experiments on lipid A-monophosphate clusters suspended in water, containing 5 mM NaCl (25 degrees C), indicated the existence of long-range order of d=7.5 nm. At low polydispersity, two distinct types of lipid A-monophosphate colloidal clusters were able to form at low polydispersity and were subsequently identified using light scattering, small-angle x-ray scattering, and selected-area electron diffraction. From an analysis of experimental results obtained from these clusters, distinct peaks could be assigned to a body-centered cubic (bcc) lattice, with a=49.5+/-1.8 nm. The solution structure found for lipid A diphosphate at volume fractions of 3.75x10(-4)<or=phi<or=4.15x10(-4) also exhibited a (bcc)-type lattice; however, a=36.1 nm [C. A. Faunceet al. J. Phys. Chem. 107, 2214 (2003)]. Using the particle and cluster properties determined from small-angle x-ray scattering, light scattering, and osmotic-pressure measurements as a function of volume fraction, good agreement was found between the directly measured osmotic-pressure values and those calculated from scattering experiments.

Stimulation of microbial autolytic system by tryptic casein hydrolysate

Antimicrobial activity of a tryptic casein hydrolysate (TCH), its mode of antimicrobial action and its efficacy in treatment using a newborn calf colibacillosis model are described. The antimicrobial activity of TCH activated the autolytic system of the microbial cell and was expressed mathematically as the autolysis activation index. TCH stimulated the autolytic enzyme system of the 19 bacterial and five fungal strains tested. The autolysis activation index for naturally-autolyzing microorganisms was 1.45-22.0. Autolysis in three bacterial and one fungal strain that did not lyse in the absence of TCH was increased in its presence by 3.9-56.7% showing activation of latent autolysis. The in vivo trials on 800 newborn calves revealed 93.0% therapeutic and 93.5% prophylactic efficacy for TCH. These levels were similar to the 95.0 and 95.5% attained when Fermosorb, an authorized antimicrobial drug, was used.