The epidermis is the primary area of contact between the body and the environment, and it distinguishes between harmful exposures and those that should be tolerated. Discrimination between insults, ...and in particular the recognition of danger signals such as UVB, is mediated by innate immune receptors. Inflammasomes are one major innate mechanism that activate inflammatory caspases. In human keratinocytes, the importance of inflammasomes and the sensing of UVB and other danger signals are a matter of debate. Fenini et al. now provide evidence that the NLRP1 (rather than the NLRP3) inflammasome plays a key role in UVB sensing and subsequent IL-1β and -18 secretion by human keratinocytes.
The vast majority of systemic bacterial infections are caused by facultative, often antibiotic-resistant, pathogens colonizing human body surfaces. Nasal carriage of Staphylococcus aureus predisposes ...to invasive infection, but the mechanisms that permit or interfere with pathogen colonization are largely unknown. Whereas soil microbes are known to compete by production of antibiotics, such processes have rarely been reported for human microbiota. We show that nasal Staphylococcus lugdunensis strains produce lugdunin, a novel thiazolidine-containing cyclic peptide antibiotic that prohibits colonization by S. aureus, and a rare example of a non-ribosomally synthesized bioactive compound from human-associated bacteria. Lugdunin is bactericidal against major pathogens, effective in animal models, and not prone to causing development of resistance in S. aureus. Notably, human nasal colonization by S. lugdunensis was associated with a significantly reduced S. aureus carriage rate, suggesting that lugdunin or lugdunin-producing commensal bacteria could be valuable for preventing staphylococcal infections. Moreover, human microbiota should be considered as a source for new antibiotics.
The nasopharynx is the main ecological niche of the human pathogen Staphylococcus aureus. Although colonization of the nares is asymptomatic, nasal carriage is a known risk factor for endogenous ...staphylococcal infection. We quantified S. aureus mRNA levels in nose swabs of persistent carriers to gain insight into the regulatory adaptation of the bacterium to the nasal environment. We could elucidate a general response of the pathogen to the surrounding milieu independent of the strain background or the human host. Colonizing bacteria preferentially express molecules necessary for tissue adherence or immune-evasion whereas toxins are down regulated. From the analysis of regulatory loci we found evidence for a predominate role of the essential two-component system WalKR of S. aureus. The results suggest that during persistent colonization the bacteria are metabolically active with a high cell surface turnover. The increased understanding of bacterial factors that maintain the colonization state can open new therapeutic options to control nasal carriage and subsequent infections.
Staphylococci are commensals of human skin and mucous membranes, but some species can also cause serious infections. Host niches during both colonization and infection differ greatly and are ...characterized by specific environmental conditions (pH, temperature, oxygen, nutrient availability, and microbiota) that can affect gene expression and virulence of microbes. To successfully occupy extremely different habitats at different anatomical sites, Staphylococci are equipped with a variety of regulatory elements that allow specific adaptation to the changing environments. Not surprisingly, gene expression
in vivo
can be significantly different from the expression pattern observed
in vitro
. Niche specific stimuli that influence the bacterial ability to either cause infection or maintain colonization are only partially understood. Here, we describe habitat specific conditions and discuss the available literature analyzing staphylococcal gene expression, focusing on
Staphylococcus aureus
and
S. epidermidis
during colonization of the nose and skin.
All Staphylococcus aureus genomes contain a genomic island, which is termed νSaα and characterized by two clusters of tandem repeat sequences, i.e. the exotoxin (set) and 'lipoprotein-like' genes ...(lpl). Based on their structural similarities the νSaα islands have been classified as type I to IV. The genomes of highly pathogenic and particularly epidemic S. aureus strains (USA300, N315, Mu50, NCTC8325, Newman, COL, JH1 or JH9) belonging to the clonal complexes CC5 and CC8 bear a type I νSaα island. Since the contribution of the lpl gene cluster encoded in the νSaα island to virulence is unclear to date, we deleted the entire lpl gene cluster in S. aureus USA300. The results showed that the mutant was deficient in the stimulation of pro-inflammatory cytokines in human monocytes, macrophages and keratinocytes. Purified lipoprotein Lpl1 was further shown to elicit a TLR2-dependent response. Furthermore, heterologous expression of the USA300 lpl cluster in other S. aureus strains enhanced their immune stimulatory activity. Most importantly, the lpl cluster contributed to invasion of S. aureus into human keratinocytes and mouse skin and the non-invasive S. carnosus expressing the lpl gene cluster became invasive. Additionally, in a murine kidney abscess model the bacterial burden in the kidneys was higher in wild type than in mutant mice. In this infection model the lpl cluster, thus, contributes to virulence. The present report is one of the first studies addressing the role of the νSaα encoded lpl gene cluster in staphylococcal virulence. The finding that the lpl gene cluster contributes to internalization into non-professional antigen presenting cells such as keratinocytes highlights the lpl as a new cell surface component that triggers host cell invasion by S. aureus. Increased invasion in murine skin and an increased bacterial burden in a murine kidney abscess model suggest that the lpl gene cluster serves as an important virulence factor.
Healthy human skin is constantly exposed to sterile and microbial agents. The skin immune system plays an important role in immune surveillance between tolerance and immune activation. This is mainly ...mediated by neutrophils, macrophages and most importantly lymphocytes. Keratinocytes, which form the outer skin barrier (epidermis) are also critical for cutaneous homeostasis. Being a non-professional immune cell, recognition of danger signals in keratinocytes is mediated by innate immune receptors (pattern recognition receptors, PRR). While Toll-like receptors are located on the cell membrane or the endosomes, nucleotide-binding domain and leucine-rich repeat containing gene family receptors (NLR) are intracellular PRRs. Some of these, once activated, trigger the formation of inflammasomes. Inflammasomes are multiprotein complexes and serve as platforms that mediate the release of innate cytokines after successful recognition, thereby attracting immune cells. Moreover, they mediate the pro-inflammatory cell death pyroptosis. Best characterized is the NLRP3 inflammasome. The function of inflammasomes differs significantly between different cell types (keratinocytes versus immune cells) and between different species (human versus mouse). In recent years, great progress has been made in deciphering the activation mechanisms. Dysregulation of inflammasomes can lead to diseases with varying degrees of severity. Here we focus on the structure, function, and associated pathologies of the NLRP1 inflammasome, which is the most relevant inflammasome in keratinocytes.
The virulence factors of the opportunistic human pathogen
have been a main subject of research. In contrast, limited information is available on the mechanisms that allow the bacterium to accommodate ...to the conditions during carriage, a prerequisite for pathogenicity. Here, we tested the hypothesis that the adaptation of
at different anatomical sites is reflected by differential gene regulation. We used qPCR to profile
gene expression
in nose and skin swabs of 11 healthy individuals. Despite some heterogeneity between individuals, significant site-specific differences were detected. For example, expression of the
regulator
A was found similarly in the nose and on the skin of all individuals. Also, genes encoding colonization and immune evasion factors (
G,
C, and
A), as well as the sphingomyelinase encoding gene
, were expressed at both anatomical sites. In contrast, expression of the global regulator
was almost inactive in the nose but readily present on the skin. A similar site-specific expression profile was also identified for the putative chitinase-encoding SE0760. In contrast, expression of the autolysine-encoding gene
D and the wall teichoic acid (WTA) biosynthesis gene
B were more pronounced in the nose as compared to the skin. In summary, our analysis identifies site-specific gene expression patterns of
during colonization. In addition, the observed expression signature was significantly different from growth
. Interestingly, the strong transcription of sphingomyelinase together with the low expression of genes encoding the tricarboxylic acid cycle (TCA) suggests very good nutrient supply in both anatomical niches, even on the skin where one might have suspected a rather lower nutrient supply compared to the nose.
The healthy human epidermis provides physical protection and is impenetrable for pathogenic microbes. Nevertheless, commensal and pathogen bacteria such as
Staphylococcus aureus
are able to colonize ...the skin surface, which may subsequently lead to infection. To identify and characterize regulatory elements facilitating adaptation of
S. aureus
to the human skin environment we used
ex vivo
tissue explants and quantified
S. aureus
gene transcription during co-culture. This analysis provided evidence for a significant downregulation of the global virulence regulator
agr
upon initial contact with skin, regardless of the growth phase of
S. aureus
prior to co-culture. In contrast, the alternative sigma factor B (
sig
B) and the antimicrobial peptide-sensing system (
gra
RS) were expressed during early colonization. Consistently,
sig
B target genes such as the clumping factor A (
clf
A) and fibrinogen and fibronectin binding protein A (
fnb
A) were strongly upregulated upon skin contact. At later timepoints of the adhesion process, wall teichoic acid (WTA) synthesis was induced. Besides the expression of adhesive molecules, transcription of molecules involved in immune evasion were increased during late colonization (staphylococcal complement inhibitor and staphylokinase). Similar to nasal colonization, enzymes involved in cell wall metabolism (
sce
D and
atl
A) were highly transcribed. Finally, we detected a strong expression of proteases from all three catalytic classes during the entire colonization process. Taken together, we here present an
ex vivo
skin colonization model that allows the detailed characterization of the bacterial adaptation to the skin environment.
Abstract Staphylococcus aureus is a versatile pathogen that can be a commensal but also cause a wide range of different infections. This broad disease spectrum is a reflection of the complex ...regulation of a large collection of virulence factors that together with metabolic fitness allow adaptation to different niches. The alternative sigma factor SigB is one of the global regulators mediating this adaptation. However, even if SigB contributes to expression of many virulence factors its importance for successful infection greatly varies with the strain and the infection setting analyzed. We have recently established a proteomics workflow that combines high efficiency cell sorting with sensitive mass spectrometry and allows monitoring of global proteome adaptations with roughly one million bacterial cells. Thus, we can now approach the adaptation of pathogens to the intracellular milieu. In the current study this proteomics workflow was used in conjunction with qRT-PCR and confocal fluorescence microscopy to comparatively analyze the adaptation of the S. aureus wild type strain HG001 and its isogenic sigB mutant to the intracellular milieu of human S9 bronchial epithelial cells. The study revealed fast and transient activation of SigB following internalization by human host cells and the requirement of SigB for intracellular growth. Loss of SigB triggered proteome changes reflecting the different residual growth rates of wild type and sigB mutant, respectively, the resistance to methicillin, adaptation to oxidative stress and protein quality control mechanisms.
Highlights • Cyclosporine A (CsA) and Dimethylfumarate (DMF) are efficient in treating inflammatory skin diseases. • ATF3 suppresses IL-6 and inflammation, but also p53-mediated senescence, resulting ...in cell proliferation. • Both induce ATF3, but only CsA leads to increased squamous cell carcinoma. • ATF3 is upregulated in keratinocytes strongly by CsA, while DMF acts stronger in myeloid cells. • Different response of ATF3 induction in myeloid cells and keratinocytes might explain the carcinogenic effect of Cyclosporine A.
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