Subinhibitory Concentrations of Thymol Reduce Enterotoxins A and B and α-Hemolysin Production in Staphylococcus aureus Isolates

BACKGROUND: Targeting bacterial virulence factors is now gaining interest as an alternative strategy to develop new types of anti-infective agents. It has been shown that thymol, when used at low concentrations, can inhibit the TSST-1 secretion in Staphylococcus aureus. However, there are no data on the effect of thymol on the production of other exotoxins (e.g., alpha-hemolysin and enterotoxins) by S. aureus. METHODOLOGY/PRINCIPAL FINDINGS: Secretion of alpha-hemolysin, SEA and SEB in both methicillin-sensitive and methicillin-resistant S. aureus isolates cultured with graded subinhibitory concentrations of thymol was detected by immunoblot analysis. Hemolysin and tumor necrosis factor (TNF) release assays were performed to elucidate the biological relevance of changes in alpha-hemolysin, SEA and SEB secretion induced by thymol. In addition, the influence of thymol on the transcription of hla, sea, and seb (the genes encoding alpha-hemolysin, SEA and SEB, respectively) was analyzed by quantitative RT-PCR. Thymol inhibited transcription of hla, sea and seb in S. aureus, resulting in a reduction of alpha-hemolysin, SEA and SEB secretion and, thus, a reduction in hemolytic and TNF-inducing activities. CONCLUSIONS/SIGNIFICANCE: Subinhibitory concentrations of thymol decreased the production of alpha-hemolysin, SEA and SEB in both MSSA and MRSA in a dose-dependent manner. These data suggest that thymol may be useful for the treatment of S. aureus infections when used in combination with beta-lactams and glycopeptide antibiotics, which induce expression of alpha-hemolysin and enterotoxins at subinhibitory concentrations. Furthermore, the structure of thymol may potentially be used as a basic structure for development of drugs aimed against these bacterial virulence factors

Effect of 17α-methyltestosterone (MT) on osmoregulatory responses and apoptosis in genetically improved farmed tilapia (GIFT), Oreochromis niloticus (L.)

361-368Androgenic compounds can affect osmoregulatory response and apoptosis in fish. In the present study, we exposed genetically improved farmed tilapia (GIFT) Oreochromis niloticus (L.) to 17α-methyltestosterone (MT, 0.5 and 5 mg/L) for 7, 14 and 21 days for understanding the phenomenon. The activities of Na+/K+ ATPase (NKA) and Ca2+/Mg2+ ATPase (CMA) were measured in the gill, kidney and intestine to evaluate the change in osmoregulation of GIFT, and genotoxicity was also detected. Results showed that organic NKA were significantly decreased in 5 mg/L MT exposure groups. The intestine NKA was significantly increased (0.5 mg/L MT). MT exposures increased the CMA of kidney and intestine (0.5 mg/L), together with gill CMA (5 mg/L MT). The results of genotoxicity assay showed gill atp1a1a and nkcc2 transcripts significantly increased, while intestine atp1a1a and fxyd7 transcripts revealed significant increases for MT exposure groups. Caspases proteins demonstrated significant increases at 7th and 21st day, and their transcripts were enhanced in 0.5 mg/L MT exposure groups. The results have evidently demonstrated that chronic exposure of MT could result in organic osmoregulatory response and hepatic apoptosis in GIFT O. niloticus

Effect of 17α-methyltestosterone (MT) on osmoregulatory responses and apoptosis in genetically improved farmed tilapia (GIFT), Oreochromis niloticus (L.)

Androgenic compounds can affect osmoregulatory response and apoptosis in fish. In the present study, we exposed genetically improved farmed tilapia (GIFT) Oreochromis niloticus (L.) to 17α-methyltestosterone (MT, 0.5 and 5 mg/L) for 7, 14 and 21 days for understanding the phenomenon. The activities of Na+/K+ ATPase (NKA) and Ca2+/Mg2+ ATPase (CMA) were measured in the gill, kidney and intestine to evaluate the change in osmoregulation of GIFT, and genotoxicity was also detected. Results showed that organic NKA were significantly decreased in 5 mg/L MT exposure groups. The intestine NKA was significantly increased (0.5 mg/L MT). MT exposures increased the CMA of kidney and intestine (0.5 mg/L), together with gill CMA (5 mg/L MT). The results of genotoxicity assay showed gill atp1a1a and nkcc2 transcripts significantly increased, while intestine atp1a1a and fxyd7 transcripts revealed significant increases for MT exposure groups. Caspases proteins demonstrated significant increases at 7th and 21st day, and their transcripts were enhanced in 0.5 mg/L MT exposure groups. The results have evidently demonstrated that chronic exposure of MT could result in organic osmoregulatory response and hepatic apoptosis in GIFT O. niloticus

Subinhibitory Concentrations of Perilla Oil Affect the Expression of Secreted Virulence Factor Genes in Staphylococcus aureus

BACKGROUND: The pathogenicity of staphylococcus aureus is dependent largely upon its ability to secrete a number of virulence factors, therefore, anti-virulence strategy to combat S. aureus-mediated infections is now gaining great interest. It is widely recognized that some plant essential oils could affect the production of staphylococcal exotoxins when used at subinhibitory concentrations. Perilla [Perilla frutescens (L.) Britton], a natural medicine found in eastern Asia, is primarily used as both a medicinal and culinary herb. Its essential oil (perilla oil) has been previously demonstrated to be active against S. aureus. However, there are no data on the influence of perilla oil on the production of S. aureus exotoxins. METHODOLOGY/PRINCIPAL FINDINGS: A broth microdilution method was used to determine the minimum inhibitory concentrations (MICs) of perilla oil against S. aureus strains. Hemolysis, tumour necrosis factor (TNF) release, Western blot, and real-time RT-PCR assays were performed to evaluate the effects of subinhibitory concentrations of perilla oil on exotoxins production in S. aureus. The data presented here show that perilla oil dose-dependently decreased the production of α-toxin, enterotoxins A and B (the major staphylococcal enterotoxins), and toxic shock syndrome toxin 1 (TSST-1) in both methicillin-sensitive S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA). CONCLUSIONS/SIGNIFICANCE: The production of α-toxin, SEA, SEB, and TSST-1 in S. aureus was decreased by perilla oil. These data suggest that perilla oil may be useful for the treatment of S. aureus infections when used in combination with β-lactam antibiotics, which can increase exotoxins production by S. aureus at subinhibitory concentrations. Furthermore, perilla oil could be rationally applied in food systems as a novel food preservative both to inhibit the growth of S. aureus and to repress the production of exotoxins, particularly staphylococcal enterotoxins

Capsaicin Protects Mice from Community-Associated Methicillin-Resistant Staphylococcus aureus Pneumonia

BACKGROUND: α-toxin is one of the major virulence factors secreted by most Staphylococcus aureus strains, which played a central role in the pathogenesis of S. aureus pneumonia. The aim of this study was to investigate the impact of capsaicin on the production of α-toxin by community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) strain USA 300 and to further assess its performance in the treatment of CA-MRSA pneumonia in a mouse model. METHODOLOGY/PRINCIPAL FINDINGS: The in vitro effects of capsaicin on α-toxin production by S. aureus USA 300 were determined using hemolysis, western blot, and real-time RT-PCR assays. The influence of capsaicin on the α-toxin-mediated injury of human alveolar epithelial cells was determined using viability and cytotoxicity assays. Mice were infected intranasally with S. aureus USA300; the in vivo protective effects of capsaicin against S. aureus pneumonia were assessed by monitoring the mortality, histopathological changes and cytokine levels. Low concentrations of capsaicin substantially decreased the production of α-toxin by S. aureus USA 300 without affecting the bacterial viability. The addition of capsaicin prevented α-toxin-mediated human alveolar cell (A549) injury in co-culture with S. aureus. Furthermore, the in vivo experiments indicated that capsaicin protected mice from CA-MRSA pneumonia caused by strain USA 300. CONCLUSIONS/SIGNIFICANCE: Capsaicin inhibits the production of α-toxin by CA-MRSA strain USA 300 in vitro and protects mice from CA-MRSA pneumonia in vivo. However, the results need further confirmation with other CA-MRSA lineages. This study supports the views of anti-virulence as a new antibacterial approach for chemotherapy

Hijacking of the Host Ubiquitin Network by Legionella pneumophila

Protein ubiquitination is critical for regulation of numerous eukaryotic cellular processes such as protein homeostasis, cell cycle progression, immune response, DNA repair, and vesicular trafficking. Ubiquitination often leads to the alteration of protein stability, subcellular localization, or interaction with other proteins. Given the importance of ubiquitination in the regulation of host immunity, it is not surprising that many infectious agents have evolved strategies to interfere with the ubiquitination network with sophisticated mechanisms such as functional mimicry. The facultative intracellular pathogen Legionella pneumophila is the causative agent of Legionnaires' disease. L. pneumophila is phagocytosed by macrophages and is able to replicate within a niche called Legionella-containing vacuole (LCV). The biogenesis of LCV is dependent upon the Dot/Icm type IV secretion system which delivers more than 330 effector proteins into host cytosol. The optimal intracellular replication of L. pneumophila requires the host ubiquitin-proteasome system. Furthermore, membranes of the bacterial phagosome are enriched with ubiquitinated proteins in a way that requires its Dot/Icm type IV secretion system, suggesting the involvement of effectors in the manipulation of the host ubiquitination machinery. Here we summarize recent advances in our understanding of mechanisms exploited by L. pneumophila effector proteins to hijack the host ubiquitination pathway

The Herbal Compound Thymol Protects Mice From Lethal Infection by Salmonella Typhimurium

Type III secretion system (T3SS) is an essential pathogenic determinant for many important bacterial pathogens; it functions to thwart immune defense by delivering effectors into host cells. Because of its essential role in bacterial virulence, this machinery is an important target in the development of novel anti-virulence therapeutics. By using an effector-lactamase fusion reporter, we identified thymol, a monoterpene phenol derivative of cymene, as an effective inhibitor of the T3SS-1 of Salmonella Typhimurium. Our results indicate that thymol effectively protected mice against S. Typhimurium-induced mortality and pathological damages, suggesting that this compound can be developed for the control of infections caused by Salmonella species

Effect of Chronic Exposure to Pesticide Methomyl on Antioxidant Defense System in Testis of Tilapia (Oreochromis niloticus) and Its Recovery Pattern

The chronic effect of environmental methomyl on the antioxidant system in testis of Nile tilapia (Oreochromis niloticus) and its recovery pattern was investigated. Tilapia were exposed to sublethal concentrations of 0.2, 2, 20 and 200 μgL−1 methomyl for 30 days and thereafter moved to methomyl-free water for 18 days. Antioxidant levels in testis, including glutathione peroxidase, catalase, glutathione-S-transferase, glutathione reductase, superoxide dismutase, reduced glutathione, oxidized glutathione were measured every 6 days during the period of exposure, and at 18 days after being transferred to methomyl-free water. The results showed that lower methomyl concentration (0.2 μgL−1) had no effect on the above antioxidants, thus 0.2 μgL−1 could be seen as NOAEL for methomyl to tilapia. However, higher methomyl concentration of 2, 20 and 200 μgL−1 could significantly influence the above antioxidants. Glutathione peroxidase and oxidized glutathione increased significantly. On the contrary, reduced glutathione decreased significantly. Catalase, superoxide dismutase, glutathione reductase, glutathione-S-transferase increased at lower methomyl (2 and 20 μgL−1), but decreased at higher methomyl (200 μgL−1). The recovery test showed that oxidative damage caused by lower methomyl of 2 and 20 μgL−1 was reversible, and oxidative damage caused by higher methomyl of 200 μgL−1 was irreversible within 18 days of recovery period