Commensal bacteria are known to inhibit pathogen colonization; however, complex host-microbe and microbe-microbe interactions have made it difficult to gain a detailed understanding of the mechanisms involved in the inhibition of colonization. Here we show that the serine protease Esp secreted by a subset of Staphylococcus epidermidis, a commensal bacterium, inhibits biofilm formation and nasal colonization by Staphylococcus aureus, a human pathogen. Epidemiological studies have demonstrated that the presence of Esp-secreting S. epidermidis in the nasal cavities of human volunteers correlates with the absence of S. aureus. Purified Esp inhibits biofilm formation and destroys pre-existing S. aureus biofilms. Furthermore, Esp enhances the susceptibility of S. aureus in biofilms to immune system components. In vivo studies have shown that Esp-secreting S. epidermidis eliminates S. aureus nasal colonization. These findings indicate that Esp hinders S. aureus colonization in vivo through a novel mechanism of bacterial interference, which could lead to the development of novel therapeutics to prevent S. aureus colonization and infection.

Abstract-We examined the effect of ␣ 1 -adrenoceptor subtype-specific stimulation on L-type Ca 2ϩ current (I Ca ) and elucidated the subtype-specific intracellular mechanisms for the regulation of L-type Ca 2ϩ channels in isolated rat ventricular myocytes. We confirmed the protein expression of ␣ 1A -and ␣ 1B -adrenoceptor subtypes at the transverse tubules (T-tubules) and found that simultaneous stimulation of these 2 receptor subtypes by nonsubtype selective agonist, phenylephrine, showed 2 opposite effects on I Ca (transient decrease followed by sustained increase). However, selective ␣ 1A -adrenoceptor stimulation (Ն0.1 mol/L A61603) only potentiated I Ca , and selective ␣ 1B -adrenoceptor stimulation (10 mol/L phenylephrine with 2 mol/L WB4101) only decreased I Ca . The positive effect by ␣ 1A -adrenoceptor stimulation was blocked by the inhibition of phospholipase C (PLC), protein kinase C (PKC), or Ca 2ϩ /calmodulin-dependent protein kinase II (CaMKII). The negative effect by ␣ 1B -adrenoceptor stimulation disappeared after the treatment of pertussis toxin or by the prepulse depolarization, but was not attriburable to the inhibition of cAMP-dependent pathway. The translocation of PKC␦ and to the T-tubules was observed only after ␣ 1A -adrenoceptor stimulation, but not after ␣ 1B -adrenoceptor stimulation. Immunoprecipitaion analysis revealed that ␣ 1A -adrenoceptor was associated with G q/11 , but ␣ 1B -adrenoceptor interacted with one of the pertussis toxin-sensitive G proteins, G o . These findings demonstrated that the interactions of ␣ 1 -adrenoceptor subtypes with different G proteins elicit the formation of separate signaling cascades, which produce the opposite effects on I Ca . The coupling of ␣ 1A -adrenoceptor with G q/11 -PLC-PKC-CaMKII pathway potentiates I Ca . In contrast, ␣ 1B -adrenoceptor interacts with G o , of which the ␤␥-complex might directly inhibit the channel activity at T-tubules. he ␣ 1 -adrenoceptor (AR) stimulation has an important role for the regulation of mammalian cardiac muscle contraction. [1][2][3][4] We have previously shown that ␣ 1 -AR stimulation modulates the function of voltage-gated L-type Ca 2ϩ channels (VLCC) which is one of the important regulatory factors in cardiac excitation-contraction coupling. 5 The effects of ␣ 1 -AR stimulation on cardiac Ca 2ϩ current through VLCC (I Ca ) can be classified into 2 opposite effects (negative and positive effects): the positive effect is dependent on protein kinase C (PKC) and Ca 2ϩ /calmodulin-dependent protein kinase II (CaMKII) activity, but the negative effect is not. 5 Although we have proposed this novel model for understanding the molecular mechanisms underlying the modulation of VLCC by ␣ 1 -AR stimulation, 2 important questions remain to be solved: (1) What is the molecular mechanism which simultaneously induces two opposite effects during ␣ 1 -AR stimulation?; (2) What are the molecular components for evoking the negative effect on I Ca by ␣ 1 -AR stimulation? We postulated that these 2 opposite effects simul...

Neutrophils play a crucial role in the host response to infection with Staphylococcus aureus, which is a major human pathogen capable of causing life-threatening disease. Interleukin-8 (IL-8) is a potent chemoattractant and activator of neutrophils. We previously reported that S. aureus secretes a factor that suppresses IL-8 production by human endothelial cells. Here we isolated an inhibitor of IL-8 production from the supernatant and identified it as staphylococcal beta-hemolysin. Beta-hemolysin reduced IL-8 production without cytotoxicity to endothelial cells. Pretreatment with beta-hemolysin decreased the expression of both IL-8 mRNA and protein induced by tumor necrosis factor alpha (TNF-␣). Migration of neutrophils across TNF-␣-activated endothelium was also inhibited by beta-hemolysin. In contrast, beta-hemolysin had no effect on intercellular adhesive molecule 1 expression in activated endothelial cells. These results showed that beta-hemolysin produced by S. aureus interferes with inflammatory signaling in endothelial cells and may help S. aureus evade the host immune response.

Fibronectin-binding protein A (FnBPA) and FnBPB are important adhesins for Staphylococcus aureus infection. We constructed fnbA and/or fnbB mutant strains from S. aureus SH1000, which possesses intact rsbU, and studied the role of these adhesins in in vitro and in vivo infections. In intravenous infection, all fnb mutants caused a remarkable reduction in the colonization rate in kidneys and the mortality rate of mice. fnbB mutant caused a more severe decrease in body weight than that caused by fnbA mutant. Serum levels of interleukin-6 and nuclear factor B (NF-B) activation in spleen cells were remarkably reduced in fnbA or fnbA fnbB mutant infections; however, there was no significant reduction in fnbB mutant infections. In in vitro cellular infection, FnBPA was shown to be indispensable for adhesion to and internalization by nonprofessional phagocytic cells upon ingestion by inflammatory macrophages and NF-B activation. However, both FnBPs were required for efficient cellular responses. The results showed that FnBPA is more important for in vitro and in vivo infections; however, cooperation between FnBPA and FnBPB is indispensable for the induction of severe infection resulting in septic death.

In a recent report, ATP, which was possibly secreted by some intestinal bacteria, was shown to cause colitis in mice via Th17 cell differentiation. However, the ATP-secreting bacteria have not been isolated and identified. In the present study, we report that Enterococcus gallinarum, which is a vancomycin-resistant Gram-positive coccus isolated from mice and humans, secretes ATP.