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Members of the genus Staphylococcus and Streptococcus are the causative agnets of many human and animal diseases. Over the past decade the complete sequencing of many staphylococcal and streptococcal genomes has promoted a significant advance in our knowledge of these important pathogens. The pathogenicity of these bacteria is due to the expression of a large variety of virulence factors. Such determinants, which are cell wall-associated and secreted proteins, include adhesins that confer to the pathogen the ability to attach to extracellular matrix/plasma and host cell surfaces, proteins that contribute to host cell invasion and intracellular survival and soluble factors that decrease phagocytosis and modulate the immune response. Furthermore, these Gram-positive cocci in many natural environments (heart valve, lung, oral cavity, throat) and infections on implanted devices live in matrix-encased groups known as biofilms. Biofilms are specialized bacterial communities with high order organization analogous to that of a tissue in multicellular organism that adhere to abiotic or biological substrata and produce an exopolymeric matrix composed of polysaccarides, proteins, DNA or combination thereof. Bacteria within a biofilm persist in adverse conditions, show resistance to killing by antibiotics and to host immune defences and are difficult to eradicate and treat clinically. Therefore, understanding the mechanisms of biofilm development will allow us to effectively combat staphylococcal/streptococcal biofilm-based infections. This Research Topic will focus on the molecular components involved in biofilm formation by staphylococci and streptococci, the role they play in the development, maturation and dispersal of biofilm and on the regulatory aspects of such complex processes. The implication for the pathogenesis of infective diseases and potential therapeutic strategies against biofilm-based infections will be also discussed. The articles will highlight both the recent advances and future challenges inherent in this rapidly evolving area.

Staphylococcus --- Streptococcus --- Biofilm --- Pathogenesis --- colonization

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The dairy chain is an integral part of global food supply, with dairy food products a staple component of recommended healthy diets. The dairy food chain from production through to the consumer is complex, with various opportunities for microbial contamination of ingredients or food product, and as such interventions are key to preventing or controlling such contamination. Dairy foods often include a microbial control step in their production such as pasteurization, but in some cases may not, as with raw milk cheeses. Microbial contamination may lead to a deterioration in food quality due to spoilage organisms, or may become a health risk to consumers should the contaminant be a pathogenic microorganism. As such food safety and food production are intrinsically linked. This Research Topic eBook includes submissions on issues relating to the microbiological integrity of the dairy food chain, such as the ecology of pathogenic and spoilage organisms through the dairy farm to fork paradigm, their significance to dairy foods and health, and genomic analysis of these microorganisms.

Dairy --- Spoilage --- Pathogenic bacteria --- Coliforms --- Sporeformers --- Biofilm --- Microbiome

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The transmission route used by many bacterial pathogens of clinical importance includes a step outside the host; thereafter refer to as the non-clinical environment (NCE). Obvious examples include foodborne and waterborne pathogens and also pathogens that are transmitted by hands or aerosols. In the NCE, pathogens have to cope with the presence of toxic compounds, sub-optimal temperature, starvation, presence of competitors and predators. Adaptation of bacterial pathogens to such stresses affects their interaction with the host. This Research Topic presents important concept to understand the life of bacterial pathogens in the NCE and provides the reader with an overview of the strategies used by bacterial pathogens to survive and replicate outside the host.

Biofilm --- Persistence --- Viable but non culturable --- protozoa --- packaging --- Listeria --- Legionella --- Escherichia coli --- Clostridium botulinum --- Pseudomonas

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The oral cavity harbors an immense diversity of microorganisms, including bacteria, fungi, archaea, protozoa and viruses. At health, oral microbial community is thought to be in a state of homeostasis, even after numerous perturbations (e.g., toothbrushing, food intake) a day. The breach in this homeostasis can occur for instance if the perturbations become too excessive (e.g., frequent carbohydrate intake leading to acidification of the community) or the host is compromised (e.g., inadequate immune response resulting in persistent inflammation of periodontal tissue). Aggressive antimicrobial therapy (e.g., antibiotics in case of periodontal disease or preventive antibiotic therapy before and after dental extractions) is commonly applied with all the negative consequences of this approach. So far little is known on the interplay between the environmental, host and microbial factors in maintaining an ecological balance. What are the prerequisites for a healthy oral ecosystem? Can we restore an unbalanced oral microbiome? How stable is the oral microbiome through time and how robust it is to external perturbations? Gaining new insights in the ecological factors sustaining oral health will lead to conceptually new therapies and preventive programs. Recent advances in high throughput technologies have brought microbiology as a science to a new era, allowing an open-ended approach instead of focusing on few opportunistic pathogens. With this topic we would like to integrate the current high-throughput ‘omics’ tools such as metagenomics, metatranscriptomics, metaproteomics or metabolomics with biochemical, physiological, genetic or clinical parameters within the oral microbial ecosystem. We aim to address questions underlying the regulation of the ecological balance in the oral cavity by including the following areas: • Ecology of oral microbiome at health • Ecology of oral microbiome under oral diseases • Ecology of oral microbiome during non-oral diseases • Shifts in the oral microbiome by therapeutic approaches (e.g., antimicrobials, replacement therapy, pre- and probiotics) • Modeling of oral ecological shifts (e.g., animal models, in vitro microcosm models) • Complex inter- and intra-kingdom interactions (e.g., bacterial-fungal-host) related to oral ecology • Environmental (e.g., diet, tobacco), host-related (e.g., immune response, saliva composition and flow) and biotic (e.g., bacterial competition) factors influencing oral ecology • Geographic variation in oral microbial ecology and diversity

horizontal gene transfer --- Fungal bacterial interactions --- Quorum Sensing --- Immune System --- Dental Plaque --- Biofilm --- Oral ecology --- metatranscriptomics

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Streptococcus pneumoniae has been for decades the number one bacterial killer of children in the world. Although vaccination with pneumococcal vaccines [PCV7, PCV10, and PCV13 (children) or PPSV23 (adults)] has helped decrease the burden of pneumococcal disease (PD), mortality remains high. Therefore, pathogenesis studies are still key toward our understanding of PD and its control. The introduction of pneumococcal vaccines has also created a niche for vaccine-escape clones. Moreover, the rise of multi-drug resistant clones around the world has also posed a serious threat in recent years. The proposed special issue of Frontiers in Cellular and Infection Microbiology highlights many of the recent advances that have been made in pneumococcal pathogenesis, colonization and antibiotic resistance by groups in Latino America, Europe, and the USA.

Streptococcus pneumoniae --- pathogenesis --- gene regulation --- biofilm --- co-infection --- drug resistance --- microbial --- macrophages