Encapsulated Staphylococcus aureus strains vary in adhesiveness assessed by atomic force microscopy

Clinical, Epidemiologic, and Laboratory Aspects of Methicillin-Resistant Staphylococcus aureus Infections

Oxacillin-resistant Staphylococcus aureus (abbreviated MRSA for historical reasons) is a major pathogen responsible for both hospital- and community-onset disease. Resistance to oxacillin in most clinical isolates of S. aureus is mediated by PBP2a, a penicillin-binding protein with low affinity to beta-lactams, encoded primarily by the mecA gene. Rapid and accurate methods of susceptibility testing of S. aureus isolates to identify MRSA infections are important tools to limit the spread of this organism. This review focuses on the clinical significance of MRSA infections and new approaches for the laboratory diagnosis and epidemiologic typing of MRSA strains.

Fosfomycin and Staphylococcus aureus: transcriptomic approach to assess effect on biofilm, and fate of unattached cells

Interest has been rekindled in the old antibiotic fosfomycin, partly because of its ability to penetrate biofilm. Using a transcriptomic approach, we investigated the modifications induced by fosfomycin in sessile cells of a clinical Staphylococcus aureus isolated from a device-associated infection. Cells still able to form biofilm after 4 h of incubation in the presence of subinhibitory concentrations of fosfomycin and cells from 24-h-old biofilm later submitted to fosfomycin had 6.77% and 9.41%, respectively, of differentially expressed genes compared with their antibiotic-free control. Fosfomycin induced mostly downregulation of genes assigned to nucleotide, amino acid and carbohydrate transport, and metabolism. Adhesins and capsular biosynthesis proteins encoding genes were downregulated in fosfomycin-grown biofilm, whereas the murein hydrolase regulator lgrA and a D-lactate dehydrogenase-encoding gene were upregulated. In fosfomycin-treated biofilm, the expression of genes encoding adhesins, the cell wall biosynthesis protein ScdA, and to a lesser extent the fosfomycin target MurA was also decreased. Unattached cells surrounding fosfomycin-grown biofilm showed greater ability to form aggregates than their counterparts obtained without fosfomycin. Reducing their global metabolism and lowering cell wall turnover would allow some S. aureus cells to grow in biofilm despite fosfomycin stress while promoting hyperadherent phenotype in the vicinity of the fosfomycin-treated biofilm.

Dynamics of mono- and dual-species biofilm formation and interactions between Staphylococcus aureus and Gram-negative bacteria

Microorganisms are not commonly found in the planktonic state but predominantly form dual- and multispecies biofilms in almost all natural environments. Bacteria in multispecies biofilms cooperate, compete or have neutral interactions according to the involved species. Here, the development of mono- and dual-species biofilms formed by Staphylococcus aureus and other foodborne pathogens such as Salmonella enterica subsp. enterica serovar Enteritidis, potentially pathogenic Raoultella planticola and non-pathogenic Escherichia coli over the course of 24, 48 and 72 h was studied. Biofilm formation was evaluated by the crystal violet assay (CV), enumeration of colony-forming units (CFU cm-2 ) and visualization using confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). In general, Gram-negative bacterial species and S. aureus interacted in a competitive manner. The tested Gram-negative bacteria grew better in mixed dual-species biofilms than in their mono-species biofilms as determined using the CV assay, CFU ml-2 enumeration, and CLSM and SEM visualization. In contrast, the growth of S. aureus biofilms was reduced when cultured in dual-species biofilms. CLSM images revealed grape-like clusters of S. aureus and monolayers of Gram-negative bacteria in both mono- and dual-species biofilms. S. aureus clusters in dual-species biofilms were significantly smaller than clusters in S. aureus mono-species biofilms.

Influence of biomaterial nanotopography on the adhesive and elastic properties of Staphylococcus aureus cells

Despite the well-known beneficial effects of biomaterial nanopatterning on host tissue integration, the influence of controlled nanoscale topography on bacterial colonisation and infection remains unknown.

Infectious and immunologic phenotype of MECP2 duplication syndrome

MECP2 (methyl CpG binding protein 2) duplication causes syndromic intellectual disability. Patients often suffer from life-threatening infections, suggesting an additional immunodeficiency. We describe for the first time the detailed infectious and immunological phenotype of MECP2 duplication syndrome. 17/27 analyzed patients suffered from pneumonia, 5/27 from at least one episode of sepsis. Encapsulated bacteria (S.pneumoniae, H.influenzae) were frequently isolated. T-cell immunity showed no gross abnormalities in 14/14 patients and IFNy-secretion upon ConA-stimulation was not decreased in 6/7 patients. In 6/21 patients IgG₂-deficiency was detected – in 4/21 patients accompanied by IgA-deficiency, 10/21 patients showed low antibody titers against pneumococci. Supra-normal IgG₁-levels were detected in 11/21 patients and supra-normal IgG₃-levels were seen in 8/21 patients – in 6 of the patients as combined elevation of IgG₁ and IgG₃. Three of the four patients with IgA/IgG₂-deficiency developed multiple severe infections. Upon infections pronounced acute-phase responses were common: 7/10 patients showed CRP values above 200 mg/l. Our data for the first time show systematically that increased susceptibility to infections in MECP2 duplication syndrome is associated with IgA/IgG₂-deficiency, low antibody titers against pneumococci and elevated acute-phase responses. So patients with MECP2 duplication syndrome and low IgA/IgG₂ may benefit from prophylactic substitution of sIgA and IgG.

Clinical, epidemiologic, and laboratory aspects of methicillin-resistant Staphylococcus aureus infections

Methicillin-resistant Staphylococcus aureus (MRSA) is a major pathogen responsible for both hospital and community onset disease. Resistance to methicillin in S. aureus is mediated by PBP2a, a penicillin-binding protein with low affinity to beta-lactams, encoded by the mecA gene. Accurate susceptibility testing of S. aureus isolates and screening of patients for colonization with MRSA are important tools to limit the spread of this organism. This review focuses on the clinical significance of MRSA infections and new approaches for the laboratory diagnosis and epidemiologic typing of MRSA strains.

Atomic Force Microscopy and pharmacology: from microbiology to cancerology

BACKGROUND

Atomic Force Microscopy (AFM) has been extensively used to study biological samples. Researchers take advantage of its ability to image living samples to increase our fundamental knowledge (biophysical properties/biochemical behavior) on living cell surface properties, at the nano-scale.

SCOPE OF REVIEW

AFM, in the imaging modes, can probe cells morphological modifications induced by drugs. In the force spectroscopy mode, it is possible to follow the nanomechanical properties of a cell and to probe the mechanical modifications induced by drugs. AFM can be used to map single molecule distribution at the cell surface. We will focus on a collection of results aiming at evaluating the nano-scale effects of drugs, by AFM. Studies on yeast, bacteria and mammal cells will illustrate our discussion. Especially, we will show how AFM can help in getting a better understanding of drug mechanism of action.

MAJOR CONCLUSIONS

This review demonstrates that AFM is a versatile tool, useful in pharmacology. In microbiology, it has been used to study the drugs fighting Candida albicans or Pseudomonas aeruginosa. The major conclusions are a better understanding of the microbes' cell wall and of the drugs mechanism of action. In cancerology, AFM has been used to explore the effects of cytotoxic drugs or as an innovative diagnostic technology. AFM has provided original results on cultured cells, cells extracted from patient and directly on patient biopsies.

GENERAL SIGNIFICANCE

This review enhances the interest of AFM technologies for pharmacology. The applications reviewed range from microbiology to cancerology.

Cell surface hydrophobicity of colistin-susceptible vs resistant Acinetobacter baumannii determined by contact angles: methodological considerations and implications

Contact angle analysis of cell surface hydrophobicity (CSH) describes the tendency of a water droplet to spread across a lawn of filtered bacterial cells. Colistin-induced disruption of the Gram-negative outer membrane necessitates hydrophobic contacts with lipopolysaccharide (LPS). We aimed to characterize the CSH of Acinetobacter baumannii using contact angles, to provide insight into the mechanism of colistin resistance. Contact angles were analysed for five paired colistin-susceptible and resistant Ac. baumannii strains. Drainage of the water droplet through bacterial layers was demonstrated to influence results. Consequently, measurements were performed 0·66s after droplet deposition. Colistin-resistant cells exhibited lower contact angles (38·8±2·8-46·8±1·3°) compared with their paired colistin-susceptible strains (40·7±3·0-48·0±1·4°; anova; P<0·05). Contact angles increased at stationary phase (50·3±2·9-61·5±2·5° and 47·4±2·0-50·8±3·2°, susceptible and resistant, respectively, anova; P<0·05) and in response to colistin 32mgl(-1) exposure (44·5±1·5-50·6±2·8° and 43·5±2·2-48·0±2·2°, susceptible and resistant, respectively; anova; P<0·05). Analysis of complemented strains constructed with an intact lpxA gene, or empty vector, highlighted the contribution of LPS to CSH. Compositional outer-membrane variations likely account for CSH differences between Ac. baumannii phenotypes, which influence the hydrophobic colistin-bacterium interaction. Important insight into the mechanism of colistin resistance has been provided. Greater consideration of contact angle methodology is necessary to ensure accurate analyses are performed.

ELECTRICALLY CONDUCTIVE POLYMER NANOTUBES WITH ANTI-BACTERIAL PROPERTIES

Nanotubes (NT) composed of the electrically active polymer poly (3,4-ethylenedioxythiophene) (PEDOT) have been used for photothermal ablation of both gram-positive (Staphylococcus aureus) and gram-negative (Escherichia coli) bacteria. Since infrared absorption of PEDOT is dominated by bipolarons strongly coupled to phonons, we hypothesize that nonradiative decay of these states leads to heat generation. Photothermal death of bacteria by PEDOT NT was compared to single-wall carbon nanotubes (SWNT). Complete eradication of bacterial colonies incubated with 100 ug/ml of either PEDOT NT or SWNT occurred with a single exposure to 1064 nm light (3.8 W/cm2) for 60 s. PEDOT NT were also shown to elicit a mild antibacterial response upon incubation with bacteria and no infrared exposure. PEDOT NT have the same capacity for photothermal ablation of bacteria as compared to SWNT; therefore, they represent an exciting new class of polymer based nanoparticles for medically-relevant photothermal therapies.

Polymorphisms in fibronectin binding protein A of Staphylococcus aureus are associated with infection of cardiovascular devices

Medical implants, like cardiovascular devices, improve the quality of life for countless individuals but may become infected with bacteria like Staphylococcus aureus. Such infections take the form of a biofilm, a structured community of bacterial cells adherent to the surface of a solid substrate. Every biofilm begins with an attractive force or bond between bacterium and substratum. We used atomic force microscopy to probe experimentally forces between a fibronectin-coated surface (i.e., proxy for an implanted cardiac device) and fibronectin-binding receptors on the surface of individual living bacteria from each of 80 clinical isolates of S. aureus. These isolates originated from humans with infected cardiac devices (CDI; n = 26), uninfected cardiac devices (n = 20), and the anterior nares of asymptomatic subjects (n = 34). CDI isolates exhibited a distinct binding-force signature and had specific single amino acid polymorphisms in fibronectin-binding protein A corresponding to E652D, H782Q, and K786N. In silico molecular dynamics simulations demonstrate that residues D652, Q782, and N786 in fibronectin-binding protein A form extra hydrogen bonds with fibronectin, complementing the higher binding force and energy measured by atomic force microscopy for the CDI isolates. This study is significant, because it links pathogenic bacteria biofilms from the length scale of bonds acting across a nanometer-scale space to the clinical presentation of disease at the human dimension.