Success through diversity - how Staphylococcus epidermidis establishes as a nosocomial pathogen.

Staphylococcus epidermidis normally is a commensal inhabitant of the healthy human skin and mucosa, but also a common nosocomial pathogen in immunocompromised patients. Living at the edge between commensalism and pathogenicity, S. epidermidis has developed interesting strategies to conquer the hospital environment as a novel ecological niche and to transform into a notorious pathogen. Recent progress in genome analysis and molecular epidemiology gave interesting insights into the enormous flexibility by which these bacteria generate continuously novel phenotypic and genotypic variants. Recent multilocus sequence typing studies identified S. epidermidis as a highly diverse species that evolves mainly by recombination and acquires readily mobile genetic elements. With respect to healthcare-associated isolates, a limited number of epidemic clonal lineages were found to have emerged and established in hospital settings worldwide. These isolates are characterised by the carriage of various SCCmec gene cassettes, conferring methicillin resistance, and by a striking ability to form biofilms on medical devices. Moreover, nosocomial S. epidermidis strains typically harbour multiple copies of the insertion sequence element IS256 in their genomes. Nosocomial S. epidermidis strains vary virulence- and resistance-associated gene expression in the course of an infection to a remarkably high degree. Heterogenous gene expression in S. epidermidis is achieved, on the one hand, by complex regulatory pathways. On the other hand, it is associated with genetic mechanisms that were found to be mediated by the action of the IS256 element which obviously represents an important driving force for the flexibility of the S. epidermidis genome. The data accumulated so far suggest that recombination along with the frequent acquisition of mobile genetic elements are crucial factors for the success of S. epidermidis as a nosocomial pathogen.

Anti-parasitic compounds from Streptomyces sp. strains isolated from Mediterranean sponges.

Actinomycetes are prolific producers of pharmacologically important compounds accounting for about 70% of the naturally derived antibiotics that are currently in clinical use. In this study, we report on the isolation of Streptomyces sp. strains from Mediterranean sponges, on their secondary metabolite production and on their screening for anti-infective activities. Bioassay-guided isolation and purification yielded three previously known compounds namely, cyclic depsipeptide valinomycin, indolocarbazole alkaloid staurosporine and butenolide. This is the first report of the isolation of valinomycin from a marine source. These compounds exhibited novel anti-parasitic activities specifically against Leishmania major (valinomycin IC(50) < 0.11 microM; staurosporine IC(50) 5.30 microM) and Trypanosoma brucei brucei (valinomycin IC(50) 0.0032 microM; staurosporine IC(50) 0.022 microM; butenolide IC(50) 31.77 microM). These results underscore the potential of marine actinomycetes to produce bioactive compounds as well as the re-evaluation of previously known compounds for novel anti-infective activities.

Identification of specific genes in Staphylococcus aureus strains associated with bovine mastitis.

Staphylococcus aureus is a common cause of bovine mastitis that is responsible for the main economic loss to the dairy industry. For identification of putative, bovine-specific molecular marker a genome comparison between bovine S. aureus strain RF122 and 52 previously sequenced S. aureus isolates associated with human infections using genome viewer, annotation tool Artemis Comparison Tool (ACT), KEGG and NCBI BLAST databases was carried out. This led to the identification of 16 unique RF122 gene sequences that may be used as molecular marker to distinguish bovine from human strains. The distribution of these genes was analyzed in a collection of bovine mastitis strains from the Netherlands and human clinical isolates by PCR and Southern blotting. Only four genes within the pathogenicity island SaPIbov3 (sab1890, sab1891, sab1892, sab1893) were present in the majority of isolates from cattle but were absent from human clinical S. aureus isolates. These results suggest that there is no gene/ORF uniformly shared by all bovine S. aureus strains that could be uniformly used as a diagnostic marker gene.

Recombination between ccrC genes in a type V (5C2&5) staphylococcal cassette chromosome mec (SCCmec) of Staphylococcus aureus ST398 leads to conversion from methicillin resistance to methicillin susceptibility in vivo.

Various types of the staphylococcal cassette chromosome mec (SCCmec) are known to confer methicillin resistance on the human pathogen Staphylococcus aureus. Such cassettes are not always stably maintained. The present studies were aimed at identifying the mechanism underlying the in vivo conversion of methicillin-resistant S. aureus (MRSA) to methicillin-susceptible S. aureus (MSSA) derivatives as encountered in two patients suffering from pneumonia and an umbilicus infection, respectively. All MRSA and MSSA isolates identified belong to multilocus sequence type (MLST) 398, have spa type t034, and are Panton-Valentine leukocidin positive. Sequencing of 27,616 nucleotides from the chromosomal SCCmec insertion site in orfX to the hsdR gene for a restriction enzyme revealed a type V (5C2&5) SCCmec. Sequence comparisons show that parts of the cassette are highly similar to sequences within SCCmec elements from coagulase-negative staphylococci, indicating a possible common origin. The cassette investigated contains ccrC-carrying units on either side of its class C2b mec gene complex. In vivo loss of the mec gene complex was caused by recombination between the recombinase genes ccrC1 allele 8 and ccrC1 allele 10. In vitro, the SCCmec was very stable, and low-frequency MRSA-to-MSSA conversion was only observed when MRSA isolates were cultivated at 41 degrees C for prolonged periods of time. In this case also, loss of the mec complex was due to ccrC gene recombination. Interestingly, the MRSA and MSSA isolates studied displayed no detectable differences in competitive growth and virulence, suggesting that the presence of the intact type V (5C2&5) SCCmec has no negative bearing on staphylococcal fitness under the conditions used.

Streptomyces axinellae sp. nov., isolated from the Mediterranean sponge Axinella polypoides (Porifera).

An actinomycete strain, isolated from the marine sponge Axinella polypoides collected from Banyuls-sur-Mer, France, was characterized using a polyphasic approach. Based on its chemotaxonomic and morphological characteristics, strain Pol001(T) belongs to the genus Streptomyces. The strain is characterized by ll-diaminopimelic acid in the cell wall, menaquinones MK-9(H(4), H(6), H(8)) and a DNA G+C content of 71.0 mol%. It forms a separate phyletic line based on phylogenetic analyses of the nearly complete 16S rRNA gene sequence. Strain Pol001(T) could be differentiated from other closely related Streptomyces species with validly published names by phenotypic and genotypic analysis. DNA-DNA hybridization between strain Pol001(T) and closely related reference strains further confirmed that strain Pol001(T) represents a novel taxon of the genus Streptomyces. Therefore, it is proposed that strain Pol001(T) represents a novel species in the genus Streptomyces, Streptomyces axinellae sp. nov.; the type strain is Pol001(T) (=DSM 41948(T) =CIP 109838(T)).

Bioactive metabolites from the endophytic fungus Ampelomyces sp. isolated from the medicinal plant Urospermum picroides.

Extracts of cultures grown in liquid or on solid rice media of the fungal endophyte Ampelomyces sp. isolated from the medicinal plant Urospermum picroides exhibited considerable cytotoxic activity when tested in vitro against L5178Y cells. Chromatographic separation yielded 14 natural products that were unequivocally identified based on their 1H and 13C NMR as well as mass spectra and comparison with previously published data. Six compounds (2, 4, 5, 7, 9 and 11) were natural products. Both fungal extracts differed considerably in their secondary metabolites. The extract obtained from liquid cultures afforded a pyrone (2) and sulfated anthraquinones (7 and 9) along with the known compounds 1, 3, 6 and 8. When grown on solid rice medium the fungus yielded three compounds 4, 5 and 11 in addition to several known metabolites including 6, 8, 10, 12, 13 and 14. Compounds 4, 8 and 10 showed the strongest cytotoxic activity against L5178Y cells with EC50 values ranging from 0.2-7.3microg/ml. Furthermore, 8 and 10 displayed antimicrobial activity against the Gram-positive pathogens, Staphylococcus aureus, S. epidermidis and Enterococcus faecalis at minimal inhibitory concentrations (MIC) of 12.5microg/ml and 12.5-25microg/ml, respectively. Interestingly, 6 and 8 were also identified as constituents of an extract derived from a healthy plant sample of the host plant U. picroides thereby indicating that the production of bioactive natural products by the endophyte proceeds also under in situ conditions within the host plant.