María Luisa Navarro-Pérez

Medical device-associated infections represent a significant healthcare challenge, as sterilization of the biomaterial often necessitates device removal. The most frequently isolated microorganism in these infections is Staphylococcus epidermidis, a skin commensal capable of causing a wide range of nosocomial infections. The primary virulence factor of S. epidermidis is biofilm formation, which decreases antibiotic efficacy and host immune response. However, additional factors play crucial roles in infection establishment. Understanding the interplay between virulence factors is essential to developing preventive strategies that inhibit microbial adhesion and biofilm development. In this study, we analyzed the presence of genes associated with adhesion and biofilm formation (ica-dependent and ica-independent pathways) in 25 clinical isolates of S. epidermidis and four control strains: ATCC 12228, ATCC 35983, ATCC 35984, and the HAM 892 mutant. Resistance profile was determined, and biofilm quantification and composition of matrix was performed using multiple methodologies. Additionally, parameters associated with initial adherence as cell surface hydrophobicity (CSH) were investigated. A strong correlation was observed among different methods for measuring biofilm formation and matrix composition. The 14 icaADBC+ isolates exhibited higher prevalence of the aap, bhp, mecA, and IS256 genes, with polysaccharide intercellular adhesin (PIA) identified as the main matrix component. In contrast, icaADBC− biofilm-producing strains formed biofilms rich in other polysaccharides and proteins. The 15 non-biofilm-producing isolates showed significantly higher hydrophobicity levels, suggesting that this factor plays a critical role in initial adhesion and colonization. This study highlights the diverse mechanisms underlying biofilm formation in S. epidermidis and identifies hydrophobicity as a potential pathogenicity factor contributing to its virulence.

La revisión de material de angiospermas conservado en el herbario UNEX y de recolecciones recientes en Extremadura han revelado 13 novedades florísticas. Concretamente, respecto de taxones autóctonos, tres son nuevos para la región (Gagea bohemica, Rumex spinosus, Thrincia maroccana), uno para la provincia de Cáceres (Anthyllis vulneraria subsp. gandogeri) y tres para la de Badajoz (Rorippa sylvestris, Oenanthe pimpinelloides, Torilis arvensis subsp. recta). También se resaltan seis especies alóctonas, de las cuales tres son nuevas para Extremadura (Chasmanthe floribunda, Oxalis bowiei, Ludwigia grandiflora), una para la provincia de Badajoz (Cercis siliquastrum) y dos para la de Cáceres (Physalis isocarpa, Solanum bonariense).

Faced with the current situation of high rates of microbial resistance, together with the scarcity of new antibiotics, it is necessary to search for and identify new antimicrobials, preferably natural, to alleviate this situation. The aim of this work was to evaluate the antibacterial activity of carvacrol (CAR), a phenolic compound of essential oils, against pathogenic microorganisms causing oral infections, such as Streptococcus mutans and S. sanguinis, never evaluated before. The minimum inhibitory and the minimum bactericidal concentration were 93.4 μg/mL and 373.6 μg/mL, respectively, for the two strains. The growth kinetics under different concentrations of CAR, as well as the bactericidal power were determined. The subinhibitory concentrations delayed and decreased bacterial growth. Its efficacy on mature biofilms was also tested. Finally, the possible hemolytic effect of CAR, not observable at the bactericidal concentrations under study, was evaluated. Findings obtained point to CAR as an excellent alternative agent to safely prevent periodontal diseases. In addition, it is important to highlight the use of an experimental methodology that includes dual-species biofilm and subinhibitory concentration models to determine optimal CAR treatment concentrations. Thus, CAR could be used preventively in mouthwashes or biomaterials, or in treatments to avoid existing antibiotic resistance.

The new and simple numerical procedure presented in this paper to analyze bacterial growth will possibly allow the identification of true differences in efficacy among antimicrobial drugs for their applications in human health, food security, and the environment, among others. It further provides insight into predictive microbiology, likely helping in the development of proper mathematical models to predict the course of bacterial growth under diverse circumstances.

Increased bacterial resistance to traditional antimicrobial agents has prompted the use of natural products with antimicrobial properties such as propolis, extensively employed since ancient times. However, the chemical composition of propolis extracts is extremely complex and has been shown to vary depending on the region and season of collection, due to variations in the flora from which the pharmacological substances are obtained, being therefore essential for their antimicrobial activity to be checked before use. For this purpose, we evaluate the in vitro antimicrobial and anti-biofilm activity of a new and promising Spanish ethanolic extract of propolis (SEEP) on Streptococcus mutans and Streptococcus sanguinis, responsible, as dominant ‘pioneer’ species, for dental plaque. Results reveal that S. sanguinis is more sensitive to SEEP, slowing and retarding its growth considerably with lower concentrations than those needed to produce the same effect in S. mutans. SEEP presents concentration- and time-dependent killing activity and, furthermore, some of the subinhibitory concentrations employed increased biofilm formation even when bacterial growth decreased. Mono and dual-species biofilms were also inhibited by SEEP. Findings obtained clearly show the relevance of using biofilm and subinhibitory concentration models to determine optimal treatment concentrations.

Propolis is a natural product obtained from hives. Its chemical composition varies depending on the flora of its surroundings, but nevertheless, common for all types of propolis, they all exhibit remarkable biological activities. The aim of this study was to investigate the chemical composition and antimicrobial activity of a novel Spanish Ethanolic Extract of Propolis (SEEP). It was found that this new SEEP contains high amounts of polyphenols (205 ± 34 mg GAE/g), with unusually more than half of this of the flavonoid class (127 ± 19 mg QE/g). Moreover, a detailed analysis of its chemical composition revealed the presence of olive oil compounds (Vanillic acid, 1-Acetoxypinoresinol, p-HPEA-EA and 3,4-DHPEA-EDA) never detected before in propolis samples. Additionally, relatively high amounts of ferulic acid and quercetin were distinguished, both known for their important therapeutic benefits. Regarding the antimicrobial properties of SEEP, the minimal inhibitory and bactericidal concentrations (MIC and MBC) against Staphylococcus epidermidis strains were found at the concentrations of 240 and 480 µg/mL, respectively. Importantly, subinhibitory concentrations were also found to significantly decrease bacterial growth. Therefore, the results presented here uncover a new type of propolis rich in flavonoids with promising potential uses in different areas of human health.

Reproductive biology studies help us to understand how species’ reproductive characters contribute to reproductive success and thus population survival but cost considerable time and effort to conduct under field conditions. We investigated the reproductive system of natural populations of Scrophularia sambucifolia and S. grandiflora, two western Mediterranean endemics with large, colorful flowers that undergo mixed bird–insect pollination. We evaluated: (1) the importance of pollinators in the sexual reproduction of the two species, determining levels of fruit and seed set; (2) the species’ compatibility systems (self-compatible or self-incompatible); (3) the role of protogyny in their mating systems; and (4) the occurrence of unequal seed set along the inflorescence. A spontaneous self-pollination test demonstrated that floral protogyny minimizes autogamy and that pollinators are needed to ensure sexual reproduction. A hand-geitonogamous pollination test revealed that both species (especially S. grandiflora) are self-compatible and that the potential for geitonogamy extends throughout the flowering period but decreases as inflorescences age. Finally, seed set was similar in all whorls of the inflorescence of both species, possibly reflecting inflorescence architecture.