Thermodynamic Surface Analyses to Inform Biofilm Resistance

A pH-Gated Functionalized Hollow Mesoporous Silica Delivery System for Photodynamic Sterilization in Staphylococcus aureus Biofilm

Multidrug-resistant bacteria are increasing, particularly those embedded in microbial biofilm. These bacteria account for most microbial infections in humans. Traditional antibiotic treatment has low efficiency in sterilization of biofilm-associated pathogens, and thus the development of new approaches is highly desired. In this study, amino-modified hollow mesoporous silica nanoparticles (AHMSN) were synthesized and used as the carrier to load natural photosensitizer curcumin (Cur). Then glutaraldehyde (GA) and polyethyleneimine (PEI) were used to seal the porous structure of AHMSN by the Schiff base reaction, forming positively charged AHMSN@GA@PEI@Cur. The Cur delivery system can smoothly diffuse into the negatively charged biofilm of Staphylococcus aureus (S. aureus). Then Cur can be released to the biofilm after the pH-gated cleavage of the Schiff base bond in the slightly acidic environment of the biofilm. After the release of the photosensitizer, the biofilm was irradiated by the blue LED light at a wavelength of 450 nm and a power of 37.4 mV/cm² for 5 min. Compared with the control group, the number of viable bacteria in the biofilm was reduced by 98.20%. Therefore, the constructed pH-gated photosensitizer delivery system can efficiently target biofilm-associated pathogens and be used for photodynamic sterilization, without the production of antibiotic resistance.

Multiple surface interaction mechanisms direct the anchoring, co-aggregation and formation of dual-species biofilm between Candida albicans and Helicobacter pylori

Introduction

Polymicrobial biofilms have a significant impact on pathogenesis of infectious microorganisms. Many human diseases are affected by colonization of multi-species communities affecting negatively the treatments and increase the risks for the health. In particular, in the epithelium of the stomach co-existence between C. albicans and H. pylori has been described, which has been associated to a synergistic effect on ulcer pathogenesis.

Objective

The objective of this work was to advance in the understanding of surface interaction between H. pylori and C. albicans for the formation of polymicrobial biofilms.

Methods

Studies of microbial surfaces both bacterium, yeast and co-cultures of them were carried out by infrared spectroscopy, deconvolution analysis, transmission and scanning electron microscopies, and optic microscopy. Additional methods were used to contrast the results as dynamic light scattering, contact angle, agarose gel electrophoresis and gene amplification.

Results

Several surface interaction mechanisms promote the anchoring of H. pylori on C. albicans, cell co-aggregation, and polymicrobial biofilm formation, main identified interactions were: (i) hydrophobic interactions between non-polar peptide chains and lipid structures, characterized by θ_w among 84.9 ± 1.6 (γ = 22.78 mJ/m² with 95.3 of dispersive contribution) and 76.6 ± 3.8 (γ = 17.34 mJ/m², 40.2 of dispersive contribution) for C. albicans and H. pylori, respectively, (ii) hydrogen bonds between surface components of yeast and bacterium (e.g., -S-H⋅⋅⋅NH₂- or -S-H⋅⋅⋅O[bond, double bond]CO-) and (iii) thiol-mediated surface interactions identified by displacements to lower wavenumbers (Δv = 5 cm^-1). Evidence of internalization and electrostatic interactions were not evidenced. All observations were congruent with the biofilm formation, including the identification of small-size biostructures (i.e., 122-459 nm) associated with extracellular proteins, extracellular DNA, or outer membrane vesicles were observed characteristic of biofilm formation.

Conclusion

It is concluded that biofilm is formed by co-aggregation after anchoring of H. pylori on C. albicans. Several surface interactions were associated with the prevalence of H. pylori, the possibility to find C. albicans in the stomach epithelium infected by H. pylori, but also, strength interactions could be interfering in experimental observations associated with bacterial-DNA detection in culture mixtures.

Modeling Bacterial Attachment Mechanisms on Superhydrophobic and Superhydrophilic Substrates

Superhydrophilic and superhydrophobic substrates are widely known to inhibit the attachment of a variety of motile and/or nonmotile bacteria. However, the thermodynamics of attachment are complex. Surface energy measurements alone do not address the complexities of colloidal (i.e., bacterial) dispersions but do affirm that polar (acid-base) interactions (ΔGAB) are often more significant than nonpolar (Lifshitz-van der Waals) interactions (ΔGLW). Classical DLVO theory alone also fails to address all colloidal interactions present in bacterial dispersions such as ΔGAB and Born repulsion (ΔGBorn) yet accounts for the significant electrostatic double layer repulsion (ΔGEL). We purpose to model both motile (e.g., P. aeruginosa and E. coli) and nonmotile (e.g., S. aureus and S. epidermidis) bacterial attachment to both superhydrophilic and superhydrophobic substrates via surface energies and extended DLVO theory corrected for bacterial geometries. We used extended DLVO theory and surface energy analyses to characterize the following Gibbs interaction energies for the bacteria with superhydrophobic and superhydrophilic substrates: ΔGLW, ΔGAB, ΔGEL, and ΔGBorn. The combination of the aforementioned interactions yields the total Gibbs interaction energy (ΔGtot) of each bacterium with each substrate. Analysis of the interaction energies with respect to the distance of approach yielded an equilibrium distance (deq) that seems to be independent of both bacterial species and substrate. Utilizing both deq and Gibbs interaction energies, substrates could be designed to inhibit bacterial attachment.

Quantifying interfacial substrate interactions via surface energy analyses

Determination of a substrate’s surface energy profile is a facile and inexpensive method to indicate the substrate’s interfacial thermodynamics with another substance (e.g., microorganisms, biomacromolecules, medical devices, etc). The following protocol details a goniometric method to calculate a substrate’s surface energy profile which (1) directly correlates to a substrate’s interfacial Gibbs energy (ΔG) and (2) predicts the interfacial interactions with other substances. We also provide a calculation template using advanced mathematics to expedite surface energy profile determination.

For complete details on the use and execution of this protocol, please refer to Cavitt et al. (2020).

•

Surface energy (SE) describes interfacial substrate interactions

•

Every material or biological substrate has a unique, five-component (5K) SE profile

•

The 5K SE profile may be experimentally determined goniometrically

•

A calculation template helps determine the 5K SE profile from contact angle data