Modulation of Biofilm Growth by Sub‐Inhibitory Amounts of Antibacterial Substances

It is generally accepted that bacteria in biofilm are more resistant to antibacterials than their planktonic counterparts. For numerous antibiotics, it has been shown that minimal inhibitory concentrations (MICs) for bacteria grown in broth are much lower than the minimal biofilm inhibition concentrations. While sub‐inhibitory concentrations, that is, amounts of antibacterials below the MIC, do not either influence or suppress to some extent or other the bacterial growth in liquid media, these same amounts of drugs, natural substances, etc., may have diverse effects on bacterial biofilms, ranging from suppression to stimulation of the sessile growth and varying with regard to the bacterial species and strains. This is a source of additional risks for both biofilm infection of host tissues and contamination indwelling devices. When considering the data for biofilm modulation, differences in experimental protocols should be taken into account, as well as the strain‐specific mechanisms of biofilm formation

Cell response of Antarctic strain <i>Penicillium griseofulvum</i> against low temperature stress

During the evolution organisms are subjected to the continuous impact of environmental factors. In recent years an increasing number of studies have focused on the physicochemical limits of life on Earth such as temperature, pressure, drought, salt content, pH, heavy metals, etc. Extreme environmental conditions disrupt the most important interactions that support the function and structure of biomolecules. For this reason, organisms inhabiting extreme habitats have recently become of particularly great interest. Although filamentous fungi are an important part of the polar ecosystem, information about their distribution and diversity, as well as their adaptation mechanisms, is insufficient. In the present study, the fungal strain Penicillium griseofulvum isolated from an Antarctic soil sample was used as a study model. The fungal cellular response against short term exposure to low temperature was observed. Our results clearly showed that short-term low temperature exposure caused oxidative stress in fungal cells and resulted in enhanced level of oxidative damaged proteins, accumulation of reserve carbohydrates and increased activity of the antioxidant enzyme defence. Ultrastructural changes in cell morphology were analysed. Different pattern of cell pathology provoked by the application of two stress temperatures was detected. Overall, this study aimed to observe the survival strategy of filamentous fungi in extremely cold habitats, and to acquire new knowledge about the relationship between low temperature and oxidative stress

Cyclic enterobacterial common antigens fromEscherichia coliO157 as microbe-associated molecular patterns

In a previous study, we described 2 forms of cyclic enterobacterial common antigen (ECACYC), a tetramer and a pentamer, from Escherichia coli O157. ECACYC is present in several representatives of the Enterobacteriaceae. To date, functional studies on ECACYC are sparse. Cyclic oligosaccharides in other bacteria, like the cyclic -glucans in Rhizobiaceae, represent microbe-associated molecular patterns involved in host–bacteria interaction. This observation determined the aim of the present study: to test whether the tetrameric and pentameric ECACYC from E. coli O157 can be recognised by host humoral and cellular mechanisms. ELISA tests designed to compare the 2 ECACYC with the O157 lipopolysaccharide showed that both ECACYC were not recognised by polyclonal anti-O157 serum but were good ligands for mannan-binding lectin. The lectin had a higher affinity for the tetramer than the pentamer. ECACYC deposited more C3b than did the lipopolysaccharide. To examine the interactions with human circulating neutrophils, the antigens were loaded onto fluorescent latex beads and applied in a phagocytosis experiment. Spheres coated with the 2 ECACYC occasionally adhered to phagocyte surfaces but, unlike O157-loaded spheres, failed to induce free-radical release. The results show that the 2 ECACYC represent microbe-associated molecular patterns recognised by host humoral non-self-recognition mechanisms

Phenotypic characterization of an international Pseudomonas aeruginosa reference panel: strains of cystic fibrosis (CF) origin show less in vivo virulence than non-CF strains

Pseudomonas aeruginosa causes chronic lung infections in people with cystic fibrosis (CF) and acute opportunistic infections in people without CF. Forty-two P. aeruginosa strains from a range of clinical and environmental sources were collated into a single reference strain panel to harmonise research on this diverse opportunistic pathogen. To facilitate further harmonized and comparable research on P. aeruginosa, we characterized the panel strains for growth rates, motility, virulence in the Galleria mellonella infection model, pyocyanin and alginate production, mucoid phenotype, LPS pattern, biofilm formation, urease activity, and antimicrobial and phage susceptibilities. Phenotypic diversity across the P. aeruginosa panel was apparent for all phenotypes examined, agreeing with the marked variability seen in this species. However, except for growth rate, the phenotypic diversity among strains from CF versus non-CF sources was comparable. CF strains were less virulent in the G. mellonella model than non-CF strains (P = 0.037). Transmissible CF strains generally lacked O-antigen, produced less pyocyanin and had low virulence in G. mellonella. Furthermore, in the three sets of sequential CF strains, virulence, O-antigen expression and pyocyanin production were higher in the earlier isolate compared to the isolate obtained later in infection. Overall, this full phenotypic characterization of the defined panel of P. aeruginosa strains increases our understanding of the virulence and pathogenesis of P. aeruginosa and may provide a valuable resource for the testing of novel therapies against this problematic pathogen

Phenotypic characterisation of an international Pseudomonas aeruginosa reference panel: Strains of cystic fibrosis origin show less in vivo virulence than non-CF strains

Pseudomonas aeruginosa causes chronic lung infections in people with cystic fibrosis (CF) and acute opportunistic infections in people without CF. Forty two P. aeruginosa strains from a range of clinical and environmental sources were collated into a single reference strain panel to harmonise research on this diverse opportunistic pathogen. To facilitate further harmonized and comparable research on P. aeruginosa, we characterised the panel strains for growth rates, motility, virulence in the Galleria mellonella infection model, pyocyanin and alginate production, mucoid phenotype, lipopolysaccharide (LPS) pattern, biofilm formation, urease activity, antimicrobial and phage susceptibilities. Phenotypic diversity across the P. aeruginosa panel was apparent for all phenotypes examined agreeing with the marked variability seen in this species. However, except for growth rate, the phenotypic diversity among strains from CF versus non-CF sources was comparable. CF strains were less virulent in the G. mellonella model than non-CF strains (p=0.037). Transmissible CF strains generally lacked O antigen, produced less pyocyanin, and had low virulence in G. mellonella. Further, in the three sets of sequential CF strains, virulence, O-antigen expression and pyocyanin production were higher in the earlier isolate compared to the isolate obtained later in infection. Overall, full phenotypic characterization of the defined panel of P. aeruginosa strains increases our understanding of the virulence and pathogenesis of P. aeruginosa and may provide a valuable resource for the testing of novel therapies against this problematic pathogen.status: publishe