Microbial Adherence to Contact Lenses and Pseudomonas aeruginosa as a Model Organism for Microbial Keratitis

Microbial keratitis (MK), the infection of the cornea, is a devastating disease and the fifth leading cause of blindness and visual impairment around the world. The overwhelming majority of MK cases are linked to contact lens wear combined with factors which promote infection such as corneal abrasion, an immunocompromised state, improper contact lens use, or failing to routinely disinfect lenses after wear. Contact lens-related MK involves the adherence of microorganisms to the contact lens. Therefore, this review discusses the information currently available regarding the disease pathophysiology, the common types of microorganisms causing MK, physical and organic mechanisms of adhesion, material properties which are involved in adhesion, and current antimicrobial strategies. This review also concludes that Pseudomonas aeruginosa is a model organism for the investigation of contact lens microbial adherence due to its prevalence in MK cases, its extremely robust adhesion, antimicrobial-resistant properties, and the severity of the disease it causes.

Influence of Curing Time on the Microbiological Behavior of Bulk-Fill Nanohybrid Resin Composites

This in vitro study aimed to evaluate the influence of curing time on surface characteristics and microbiological behavior of three bulk-fill resin-based composites (RBCs). Materials were light-cured for either 10 s or 80 s, then finished using a standard clinical procedure. They were characterized by surface morphology (SEM), surface elemental composition (EDS), surface roughness (SR), and surface free energy (SFE). Microbiological behavior was assessed as S. mutans adherence (2 h) and biofilm formation (24 h) using a continuous-flow bioreactor. Statistical analysis included a two-way ANOVA and Tukey’s test (p < 0.05). Materials differed substantially as filler shape, dimension, elemental composition and resin matrix composition. Significant differences between materials were found for SR, SFE, and microbiological behavior. Such differences were less pronounced or disappeared after prolonged photocuring. The latter yielded significantly lower adherence and biofilm formation on all tested materials, similar to conventional RBCs. Improved photoinitiators and UDMA-based resin matrix composition may explain these results. No correlation between surface characteristics and microbiological behavior can explain the similar microbiological behavior of bulk-fill materials after prolonged photocuring. This different performance of bulk-fill materials compared with conventional RBCs, where surface characteristics, especially surface chemistry, influence microbiological behavior, may have important implications for secondary caries occurrence and restoration longevity.

Enterococcal Endocarditis: Hiding in Plain Sight

Enterococcus faecalis is a major opportunistic bacterial pathogen of increasing clinical relevance. A substantial body of experimental evidence suggests that early biofilm formation plays a critical role in these infections, as well as in colonization and persistence in the GI tract as a commensal member of the microbiome in most terrestrial animals. Animal models of experimental endocarditis generally involve inducing mechanical valve damage by cardiac catheterization prior to infection, and it has long been presumed that endocarditis vegetation formation resulting from bacterial attachment to the endocardial endothelium requires some pre-existing tissue damage. Here we review both historical and contemporary animal model studies demonstrating the robust ability of E. faecalis to directly attach and form stable microcolony biofilms encased within a bacterially-derived extracellular matrix on the undamaged endovascular endothelial surface. We also discuss the morphological similarities when these biofilms form on other host tissues, including when E. faecalis colonizes the GI epithelium as a commensal member of the normal vertebrate microbiome - hiding in plain sight where it can serve as a source for systemic infection via translocation. We propose that these phenotypes may allow the organism to persist as an undetected infection in asymptomatic individuals and thus provide an infectious reservoir for later clinical endocarditis.

Bacterial adherence to silk and expanded polytatrafluorethilene sutures: an in vivo human study

After oral surgery, bacterial adhesion to suture can cause surgical site infections and delay wound healing. Microbial adherence to the suture is influenced by its physical configuration and chemical structure. The aim of this study was to compare in vivo the bacterial adhesion to two suture materials used in oral surgery: silk and monofilament expanded polytetrafluoethilene (e-PTFE). After sinus lift surgery, 15 flaps were sutured with silk (nonabsorbable, organic, braided, 4.0) and 15 were sutured with e-PTFE (nonabsorbable, synthetic, monofilament, 4.0). Seven days after surgery, bacterial adherence, in terms of percentage of the surface covered, was evaluated for each suture material by scanning electron microscope (SEM). Onto silk suture, plaque consisted of a few cocci and a higher proportion of rods and filamentous-shaped bacteria, with some mineralized plaque. Onto e-PTFE speciments, only small colonies of a few cocci or no bacteria were observed, with empty spaces between the colonies and no plaque mineralization. The surface covered by bacteria on e-PTFE specimens was significantly lower than that of silk sutures. (22.1% ±4.96% vs 54.3% ± 7.9%; P =0.0001). The results of the present study suggest that multifilament structure of silk favours a greater bacterial adherence, proliferation, and persistence, so monofilament and e- PTFE suture should be preferred in oral surgery.

Glucan Binding Protein C of Streptococcus mutans Mediates both Sucrose-Independent and Sucrose-Dependent Adherence

The high-resolution structure of glucan binding protein C (GbpC) at 1.14 Å, a sucrose-dependent virulence factor of the dental caries pathogen Streptococcus mutans, has been determined. GbpC shares not only structural similarities with the V regions of AgI/II and SspB but also functional adherence to salivary agglutinin (SAG) and its scavenger receptor cysteine-rich domains (SRCRs). This is not only a newly identified function for GbpC but also an additional fail-safe binding mechanism for S. mutans Despite the structural similarities with S. mutans antigen I/II (AgI/II) and SspB of Streptococcus gordonii, GbpC remains unique among these surface proteins in its propensity to adhere to dextran/glucans. The complex crystal structure of GbpC with dextrose (β-d-glucose; Protein Data Bank ligand BGC) highlights exclusive structural features that facilitate this interaction with dextran. Targeted deletion mutant studies on GbpC's divergent loop region in the vicinity of a highly conserved calcium binding site confirm its role in biofilm formation. Finally, we present a model for adherence to dextran. The structure of GbpC highlights how artfully microbes have engineered the lectin-like folds to broaden their functional adherence repertoire.

Pathogenic microbial amyloids: Their function and the host response

Functional microbial amyloids are ubiquitous in nature and some contribute to the pathogenesis of infectious diseases. Three pathogenic microbial amyloids are compared and their contribution to the disease process explained. The recent demonstration and visualization of fungal amyloid in human invasive candidiasis is discussed. Moreover, the binding of host serum amyloid P component to Candida functional amyloid in invasive human disease is presented in light of its possible role of masking fungi from the host defenses.