Kris Honraet

Eradication of Propionibacterium acnes biofilms by plant extracts and putative identification of icariin, resveratrol and salidroside as active compounds.

Propionibacterium acnes is a Gram-positive bacterium that plays an important role in the pathogenesis of acne vulgaris. This organism is capable of biofilm formation and the decreased antimicrobial susceptibility of biofilm-associated cells may hamper efficient treatment. In addition, the prolonged use of systemic antibiotic therapy is likely to lead to the development and spread of antimicrobial resistance. In the present study we investigated whether P. acnes biofilms could be eradicated by plant extracts or their active compounds, and whether other mechanisms besides killing of biofilm cells could be involved. Out of 119 plant extracts investigated, we identified five with potent antibiofilm activity against P. acnes (extracts from Epimedium brevicornum, Malus pumila, Polygonum cuspidatum, Rhodiola crenulata and Dolichos lablab). We subsequently identified icariin, resveratrol and salidroside as active compounds in three of these extracts. Extracts from E. brevicornum and P. cuspidatum, as well as their active compounds (icariin and resveratrol, respectively) showed marked antibiofilm activity when used in subinhibitory concentrations, indicating that killing of microbial cells is not their only mode of action.

In Vitro Inhibition of Streptococcus mutans Biofilm Formation on Hydroxyapatite by Subinhibitory Concentrations of Anthraquinones

ABSTRACT We report that certain anthraquinones (AQs) reduce Streptococcus mutans biofilm formation on hydroxyapatite at concentrations below the MIC. Although AQs are known to generate reactive oxygen species, the latter do not underlie the observed effect. Our results suggest that AQs inhibit S. mutans biofilm formation by causing membrane perturbation.

Biofilms in skin infections: Propionibacterium acnes and acne vulgaris.

It is generally accepted that many human infections are biofilm-related and that sessile (biofilm-grown) cells are highly resistant against antimicrobial agents. Propionibacterium acnes plays a role in the pathogenesis of acne vulgaris, a common disorder of the pilosebaceous follicles and it has been suggested that P. acnes cells residing within the follicles grow as a biofilm. Although P. acnes biofilms have not been observed directly in the pilosebaceous unit, the observation that P. acnes readily forms biofilm in vitro as well as on various medical devices in vivo, combined with the high resistance of sessile P. acnes cells and the increased production of particular virulence factors and qourum sensing molecules in sessile cells point in this direction. In addition, in vitro and in vivo biofilm formation has also been demonstrated for other microorganisms involved in skin diseases (including Staphylococcus aureus and Streptococcus pyogenes).

Recurrent colonization of successively implanted tracheoesophageal vocal prostheses by a member of the Fusarium solani species complex.

ABSTRACT Tracheoesophageal vocal prostheses (TVP) in laryngectomized patients commonly deteriorate due to overgrowth by yeasts, particularly Candida species. We describe the first case of colonization of such devices by a member of the Fusarium solani species complex in a patient with a history of glottal carcinoma. Three isolates, from three prostheses, were found morphologically consistent with the traditional picture of F. solani. Ribosomal sequence analysis showed that the isolates belonged to a distinct, as yet apparently unnamed phylogenetic species within the F. solani species complex. This species, one of two distinct genetic types (genotype 2) traditionally considered part of the plant-pathogenic subtaxon Fusarium solani f. sp. radicicola, has not previously been identified as an agent of human or animal disease, although it is closely related to a known etiologic agent of mycetoma, an Acremonium-like species recently renamed Fusarium falciforme. Sequence and multisatellite M13 polymorphism analysis revealed no distinctions among the case isolates. Production of cyclosporine was detected for all three case isolates.

Effect of a buccal bioadhesive nystatin tablet on the lifetime of a Provox™ silicone tracheoesophageal voice prosthesis

Conclusion. Daily application of a buccal bioadhesive slow-release nystatin tablet (100 000 IU per tablet) significantly increased the voice prosthesis lifetime in laryngectomized patients compared to conventional local cleaning of the prosthesis with an antimicrobial agent on a brush. Objective. To investigate the effect of a buccal bioadhesive nystatin tablet on the lifetime of a Provox™ tracheoesophageal voice prosthesis in post-laryngectomy patients. Material and methods. A buccal bioadhesive tablet, based on a spray-dried Amioca®/Carbopol® 974P mixture containing 10% (w/w) Carbopol® 974P, was loaded with 100 000 IU of nystatin. Patients were included in the study when replacement of their voice prosthesis was required and were divided into three groups. Conventional daily local cleaning of the voice prosthesis by means of an oral nystatin suspension on a brush (Group 1; n=7) was compared with application of one nystatin buccal bioadhesive tablet per day, after breakfast, on the gingiva above the upper canine (Group 2; n=7). The control group (n=5) used no antimicrobial agents. The lifetime of the prosthesis was followed and expressed in days. Results. The lifetime of the voice prosthesis was significantly increased in Group 2 compared to Group 1 (p<0.05; paired t-test), indicating that sustained release of nystatin in the oral cavity, by means of erosion of the tablet over a period of ≈8 h, is more effective at preventing microbial colonization of the prosthesis than local cleaning.

Screening of Repellents against Vespid Wasps.

Vespid wasps are ecologically beneficial, but they can be a nuisance and dangerous to people due to their tendency to sting. Here, the aim was to screen samples of volatiles (i.e., essential oils and pure chemicals) for their repellency against wasps. The number of wasps (mainly Vespula vulgaris) present in a glass box with attractant and 5 µL sample was compared to the number of wasps in a similar box with attractant only. Both boxes were connected to a large glass container harboring 18–35 wasps. Among 66 tested samples, some essential oils from Lamiaceae and Asteraceae, as well as some pure natural compounds such as the monoterpenes (−)-terpinen-4-ol and isopulegol showed a significant repellency against vespids. Our results corroborate the potential of (mixtures of) volatiles in repelling these insects.

In Vitro and In Vivo Evaluation of Infestation Deterrents Against Lice

ABSTRACT The human head louse is a cosmopolitan ectoparasite and frequently infests many people, particularly school-age children. Due to widespread pyrethroid resistance and the lack of efficient resistance management, there has been a considerable interest in the protection of uninfested people and prevention of reinfestation by disrupting lice transfer. In this study, two nonclinical model systems (in vitro and in vivo) were used to determine the efficacy of the infestation deterrents, Elimax lotion and Elimax shampoo, against human head lice or poultry chewing lice, respectively. With in vitro assessments, female head lice exhibited significantly higher avoidance responses to hair tufts treated with either of the test formulations, which led to significantly higher ovipositional avoidance when compared with female lice on control hair tufts. Additionally, both formulations were determined to be competent infestation deterrents in a competitive avoidance test in the presence of a known attractant (head louse feces extract). In in vivo assessments using a previously validated poultry model, Elimax shampoo was determined to be an efficacious deterrent against poultry chewing lice within Menopon spp. and Menacanthus spp.

The Acne Biofilm

Around the beginning of the nineteenth century, Unna isolated Corynebacterium acnes (now known as Propionibacterium acnes) from acne lesions in patients, establishing the link between acne and local P. acnes infection. However, later when P. acnes was also isolated from normal, healthy skin [1], its concept as a pathogen greatly declined. In 1963, Kirschbaum and Kligman [2] re-confirmed P. acnes as a factor involved in the complex pathogenesis of acne by showing that an injection of viable P. acnes into sterile steatocystomas (as a model for sterile acne comedones) could convert these quiescent cysts into inflammatory lesions. Since then research has revealed that P. acnes influences inflammation through a wide range of pathways, ranging from neutrophil chemotaxis by P. acnes lipase [3] to direct induction of Toll-like receptors in keratinocytes [4]. However, the question remains whether this commensal is capable of initiating inflammation in the sebaceous gland and if so, why colonization does not always result in inflammation. In other words, what triggers P. acnes to play its part in acne? The answer to this question may very well be found using the concept of microbial biofilms.