Salmonella enterica serovar Typhimurium requires nonsterol precursors of the cholesterol biosynthetic pathway for intracellular proliferation

Modifiers of symptomatic embolic risk in infective endocarditis

OBJECTIVE

To ascertain the impact of prior antiplatelet and statin therapy on symptomatic embolic events in [corrected] infective endocarditis (IE).

PATIENTS AND METHODS

We studied a retrospective cohort of adult patients with a diagnosis of IE who presented to Mayo Clinic (Rochester, MN) from January 1, 2003, to December 31, 2006. Patients were grouped into those who received treatment before infection or controls who did not receive treatment for both antiplatelet therapy and, separately, statin therapy. Because of the retrospective study design and thus the nonrandomized treatment groups, a propensity score approach was used to account for the confounding factors that may have influenced treatment allocation. Antiplatelet therapy included aspirin, dipyridamole, clopidogrel, ticlopidine or any combination of these agents. Statin therapy included atorvastatin, simvastatin, pravastatin, lovastatin, rosuvastatin, or fluvastatin. The primary end point was a symptomatic embolic event that occurred before or during hospitalization. Multivariable logistic regression was used to assess the propensity-adjusted effects of continuous daily therapy with antiplatelet and statin agents on risk of symptomatic emboli. Likewise, Cox proportional hazards regression was used to test for an independent association with 6-month mortality for each of the treatments.

RESULTS

The study cohort comprised 283 patients with [corrected] IE. Twenty-eight patients (24.1%) who received prior continuous antiplatelet therapy developed a symptomatic embolic event compared with 66 (39.5%) who did not receive such treatment. After adjusting for propensity to treat, the effect of antiplatelet therapy on embolic risk was not statistically significant (odds ratio, 0.71; 95% confidence interval [CI], 0.37-1.36; P=.30). Only 14 patients (18.2%) who received prior continuous statin therapy developed a symptomatic embolic event compared with 80 (39.4%) of the 203 patients who did not. After adjusting for propensity to treat with statin therapy, the benefit attributable to statins was significant (odds ratio, 0.30; 95% CI, 0.14-0.62; P=.001). The 6-month mortality rate of the entire cohort was 28% (95% CI, 23%-34%). No significant difference was found in the propensity-adjusted rate of 6-month mortality between patients who had and had not undergone prior antiplatelet therapy (P=.91) or those who had and had not undergone prior statin therapy (P=.87).

CONCLUSION

The rate of symptomatic emboli associated with IE was reduced in patients who received continuous daily statin therapy before onset of IE. Despite fewer embolic events observed in patients who received antiplatelet agents, a significant association was not found after adjusting for propensity factors. A continued evaluation of these drugs and their potential impact on subsequent embolism among IE patients is warranted.

Plasma membrane cholesterol plays a critical role in the Salmonella-induced anti-inflammatory response in intestinal epithelial cells

Our recent study demonstrated that a phosphatidylinositol-3 kinase (PI3K)/Akt-dependent anti-inflammatory pathway was activated by Salmonella in intestinal epithelial cells. Salmonella virulence is dependent on the ability of the bacterium to invade nonphagocytic host cells and then survive and replicate within modified Salmonella-containing vacuoles where cholesterol accumulates. In addition, cholesterol in membrane lipid rafts is frequently a platform for the activation of downstream signaling pathways, including the PI3K/Akt pathway. However, the role of plasma membrane cholesterol in the Salmonella-induced anti-inflammatory response in intestinal epithelial cells has not been elucidated. Here, we show that the effect of plasma membrane cholesterol depletion on the inhibition of Akt activation allows sustained ERK activation and the subsequent upregulation of IL-8 expression. These results demonstrate that plasma membrane cholesterol plays a critical role in the PI3K-dependent anti-inflammatory pathway activated by Salmonella in intestinal epithelial cells.

Statins enhance formation of phagocyte extracellular traps

Statins are inhibitors of 3-hydroxy 3-methylglutaryl coenzyme A (HMG-CoA) reductase, the rate-limiting enzyme in cholesterol biosynthesis. Recent clinico-epidemiologic studies correlate patients receiving statin therapy with having reduced mortality associated with severe bacterial infection. Investigating the effect of statins on the innate immune capacity of phagocytic cells against the human pathogen Staphylococcus aureus, we uncovered a beneficial effect of statins on bacterial clearance by phagocytes, although, paradoxically, both phagocytosis and oxidative burst were inhibited. Probing instead for an extracellular mechanism of killing, we found that statins boosted the production of antibacterial DNA-based extracellular traps (ETs) by human and murine neutrophils and also monocytes/macrophages. The effect of statins to induce phagocyte ETs was linked to sterol pathway inhibition. We conclude that a drug therapy taken chronically by millions alters the functional behavior of phagocytic cells, which could have ramifications for susceptibility and response to bacterial infections in these patients.

Plasmodium salvages cholesterol internalized by LDL and synthesized de novo in the liver

Our previous morphological studies illustrated the association of sterols with Plasmodium infecting hepatocytes. Because malaria parasites cannot synthesize sterols, they must scavenge these lipids from the host. In this paper, we have examined the source/s of sterols for intrahepatic Plasmodium and evaluated the importance of sterols for liver stage development. We show that Plasmodium continuously diverts cholesterol from hepatocytes until release of merozoites. Removal of plasma lipoproteins from the medium results in a 70% reduction of cholesterol content in hepatic merozoites but these parasites remain infectious in animals. Plasmodium salvages cholesterol that has been internalized by low-density lipoprotein but reduced expression of host low-density lipoprotein receptors by 70% does not influence liver stage burden. Plasmodium is also able to intercept cholesterol synthesized by hepatocytes. Pharmacological blockade of host squalene synthase or downregulation of the expression of this enzyme by 80% decreases by twofold the cholesterol content of merozoites without further impacting parasite development. These data enlighten that, on one hand, malaria parasites have moderate need of sterols for optimal development in hepatocytes and, on the other hand, they can adapt to survive in cholesterol-restrictive conditions by exploitation of accessible sterols derived from alternative sources in hepatocytes to maintain proper infectivity.

Lovastatin protects against experimental plague in mice

BACKGROUND

Plague is an ectoparasite-borne deadly infection caused by Yersinia pestis, a bacterium classified among the group A bioterrorism agents. Thousands of deaths are reported every year in some African countries. Tetracyclines and cotrimoxazole are used in the secondary prophylaxis of plague in the case of potential exposure to Y. pestis, but cotrimoxazole-resistant isolates have been reported. There is a need for additional prophylactic measures. We aimed to study the effectiveness of lovastatin, a cholesterol-lowering drug known to alleviate the symptoms of sepsis, for plague prophylaxis in an experimental model.

METHODOLOGY

Lovastatin dissolved in Endolipide was intraperitoneally administered to mice (20 mg/kg) every day for 6 days prior to a Y. pestis Orientalis biotype challenge. Non-challenged, lovastatin-treated and challenged, untreated mice were also used as control groups in the study. Body weight, physical behavior and death were recorded both prior to infection and for 10 days post-infection. Samples of the blood, lungs and spleen were collected from dead mice for direct microbiological examination, histopathology and culture. The potential antibiotic effect of lovastatin was tested on blood agar plates.

CONCLUSIONS/SIGNIFICANCE

Lovastatin had no in-vitro antibiotic effect against Y. pestis. The difference in the mortality between control mice (11/15; 73.5%) and lovastatin-treated mice (3/15; 20%) was significant (P<0.004; Mantel-Haenszel test). Dead mice exhibited Y. pestis septicemia and inflammatory destruction of lung and spleen tissues not seen in lovastatin-treated surviving mice. These data suggest that lovastatin may help prevent the deadly effects of plague. Field observations are warranted to assess the role of lovastatin in the prophylaxis of human plague.

Atorvastatin as a potential anti-malarial drug: in vitro synergy in combinational therapy with quinine against Plasmodium falciparum

Background

Quinine (QN) remains the first line anti-malarial drug for the treatment of complicated malaria in Europe and Africa. The emergence of QN resistance has been documented. QN resistance is not yet a significant problem, but there is an urgent need to discover partners for use in combination with QN. The aim of the study was to assess the in vitro potentiating effects of atorvastatin (AVA), a 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor, in combination with QN against Plasmodium falciparum and to evaluate whether the effects of AVA could be associated with gene copy number or mutations in genes involved in QN resistance, such as pfcrt, pfmdr1, pfmrp and pfnhe.

Methods

The susceptibilities to combination of AVA with QN were assessed against 21 parasite strains using the in vitro isotopic microtest. Genotypes and gene copy number were assessed for pfcrt, pfmdr1, pfmdr2, pfmrp genes. In addition, the number of DNNND, DDNHNDNHNN repeats in pfnhe-1 ms4760 and the ms4760 profile were determined for each strains of P. falciparum.

Results

AVA demonstrated synergistic effects in combination with QN against 21 P. falciparum strains. The QN IC₅₀ was reduced by 5% (0% to 15%; 95%CI: 1%-8%), 10% (3% to 23%; 95%CI: 7%-14%) and 22% (14% to 40%; 95%CI: 19%-25%) in presence of AVA at concentrations of 0.1, 0.5 and 1.0 μM, respectively. These reductions were all significant (p < 0.009). The reduction in the QN IC₅₀ in presence of AVA was not significantly correlated with the QN IC₅₀ (r = 0.22, P = 0.3288) or the AVA IC₅₀ (r = 0.03, P = 0.8946). The synergistic effect of AVA in combination with QN was not significantly associated with polymorphisms in the pfcrt, pfmdr1, pfmrp, and pfnhe-1 genes that could be involved in QN resistance. The synergistic effect of AVA on QN responses was not significantly associated with pfmdr1 copy number (P = 0.0428).

Conclusion

The synergistic effect of AVA in combination with QN was found to be unrelated to mutations occurring in transport protein genes involved in QN drug resistance. The different mechanisms of drug uptake and/or mode of action for AVA compared to the other anti-malarial drugs, as well as the AVA-mediated synergy of the anti-malarial effect of QN, suggests that AVA will be a good candidate for combinatorial malaria treatment. All of these observations support calls for both an in vivo evaluation with pharmacokinetic component and clinical trials of AVA as an anti-malarial therapy.

Atorvastatin is a promising partner for antimalarial drugs in treatment of Plasmodium falciparum malaria

Atorvastatin (AVA) is a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor. AVA exposure resulted in the reduced in vitro growth of 22 Plasmodium falciparum strains, with the 50% inhibitory concentrations (IC(50)s) ranging from 2.5 microM to 10.8 microM. A significant positive correlation was found between the strains' responses to AVA and mefloquine (r = 0.553; P = 0.008). We found no correlation between the responses to AVA and to chloroquine, quinine, monodesethylamodiaquine, lumefantrine, dihydroartemisinin, atovaquone, or doxycycline. These data could suggest that the mechanism of AVA uptake and/or the mode of action of AVA is different from those for other antimalarial drugs. The IC(50)s for AVA were unrelated to the occurrence of mutations in the transport protein genes involved in quinoline antimalarial drug resistance, such as the P. falciparum crt, mdr1, mrp, and nhe-1 genes. Therefore, AVA can be ruled out as a substrate for the transport proteins (CRT, Pgh1, and MRP) and is not subject to the pH modification induced by the P. falciparum NHE-1 protein. The absence of in vitro cross-resistance between AVA and chloroquine, quinine, mefloquine, monodesethylamodiaquine, lumefantrine, dihydroartemisinin, atovaquone, and doxycycline argues that these antimalarial drugs could potentially be paired with AVA as a treatment for malaria. In conclusion, the present observations suggest that AVA is a good candidate for further studies on the use of statins in association with drugs known to have activities against the malaria parasite.

Cholesterol-dependent anaplasma phagocytophilum exploits the low-density lipoprotein uptake pathway

In eukaryotes, intracellular cholesterol homeostasis and trafficking are tightly regulated. Certain bacteria, such as Anaplasma phagocytophilum, also require cholesterol; it is unknown, however, how this cholesterol-dependent obligatory intracellular bacterium of granulocytes interacts with the host cell cholesterol regulatory pathway to acquire cholesterol. Here, we report that total host cell cholesterol increased >2-fold during A. phagocytophilum infection in a human promyelocytic leukemia cell line. Cellular free cholesterol was enriched in A. phagocytophilum inclusions as detected by filipin staining. We determined that A. phagocytophilum requires cholesterol derived from low-density lipoprotein (LDL), because its replication was significantly inhibited by depleting the growth medium of cholesterol-containing lipoproteins, by blocking LDL uptake with a monoclonal antibody against LDL receptor (LDLR), or by treating the host cells with inhibitors that block LDL-derived cholesterol egress from late endosomes or lysosomes. However, de novo cholesterol biosynthesis is not required, since inhibition of the biosynthesis pathway did not inhibit A. phagocytophilum infection. The uptake of fluorescence-labeled LDL was enhanced in infected cells, and LDLR expression was up-regulated at both the mRNA and protein levels. A. phagocytophilum infection stabilized LDLR mRNA through the 3′ UTR region, but not through activation of the sterol regulatory element binding proteins. Extracellular signal–regulated kinase (ERK) was up-regulated by A. phagocytophilum infection, and inhibition of its upstream kinase, MEK, by a specific inhibitor or siRNA knockdown, reduced A. phagocytophilum infection. Up-regulation of LDLR mRNA by A. phagocytophilum was also inhibited by the MEK inhibitor; however, it was unclear whether ERK activation is required for LDLR mRNA up-regulation by A. phagocytophilum. These data reveal that A. phagocytophilum exploits the host LDL uptake pathway and LDLR mRNA regulatory system to accumulate cholesterol in inclusions to facilitate its replication.

Maintenance of the cholesterol amount and transport within cells are essential for healthy human cell functions. Most bacteria do not need cholesterol, but certain bacteria that infect human cells are dependent on host cell cholesterol for their infection. How infected human cells deal with these cholesterol-robbing bacteria, and in turn how these bacteria hijack host cholesterol, are intriguing questions. Anaplasma phagocytophilum is a bacterium that lives inside white blood cells, and causes the disease human granulocytic anaplasmosis (HGA). A. phagocytophilum needs host cholesterol to live. Here, we discovered that A. phagocytophilum infection increases the amount of cholesterol in host cells and sequesters the majority of cholesterol in A. phagocytophilum inclusions inside host cells. Human cells acquire cholesterol from two sources: receptor-mediated endocytosis of cholesterol-containing low-density lipoprotein (LDL) from the circulating blood, and synthesis of cholesterol inside the cells. Since A. phagocytophilum depends on cholesterol derived from LDL, it coaxes the host cell to take up more LDL by increasing LDL receptor, through inhibition of LDL receptor mRNA degradation. A. phagocytophilum infection may serve as a model to improve our understanding of the cellular cholesterol regulation in white blood cells, and may provide insight regarding new therapeutic target for treatment of HGA.

Statins as potential antimalarial drugs: low relative potency and lack of synergy with conventional antimalarial drugs

The in vitro sensitivity of Plasmodium falciparum to atorvastatin and rosuvastatin was assessed using chloroquine-sensitive and chloroquine-resistant strains. Although atorvastatin was more potent, it had weak activity (mean 50% inhibitory concentration of > or = 17 microM) and an indifferent interaction with chloroquine and dihydroartemisinin. Bioassay of plasma from an atorvastatin-treated subject showed similar results.

Maintenance of the Salmonella-containing vacuole in the juxtanuclear area: a role for intermediate filaments

Until recently, intermediate filaments (IF) were thought to be only involved in resistance to physical stress and mechanical integrity of cells and tissues. Recent data indicate that IF play a much more important role in cellular physiology including organelle structure and positioning within the cell. Here, we show that Salmonella enterica serovar Typhimurium (S. typhimurium) induces in epithelial cells and macrophages the formation of an aggresome-like structure with a dramatic remodelling of cytoplasmic IF (vimentin and cytokeratin) networks and the adaptor proteins 14-3-3 which are recruited around intracellular S. typhimurium microcolonies. These rearrangements are not necessary for bacterial replication. Depletion of vimentin and cytokeratin by siRNA indicates that IF remodelling is required to maintain Salmonella microcolonies in the juxtanuclear area.

Statins limit Rickettsia conorii infection in cells

Recent data suggest that statins may have a beneficial effect during sepsis. In this study, we tested the effect of lovastatin and pravastatin on the cellular culture of Rickettsia conorii using a quantitative plaque assay model associated with an original image analysis algorithm. Statins added at the time of infection did not modify plaque formation, whereas pre-incubation with statins for 48h resulted in a significant 30-68% plaque reduction, depending on the tested compounds and doses. These preliminary findings raise the hypothesis that statins may prevent or moderate rickettsial disease in exposed people.

Preoperative statins and infectious complications following cardiac surgery

PURPOSE

Recent observational studies have suggested that statins can decrease the incidence and severity of various infections including pneumonia and bacteremia. However, the effect of statins on post-cardiac surgery infection has not been adequately evaluated. Therefore we sought to determine whether preoperative statin use resulted in a reduction in infection following cardiac surgery.

METHODS

This was a cohort evaluation of all consecutive patients who underwent coronary artery bypass graft (CABG) and/or valve surgery at our institution between January 1, 2004 and August 31, 2006. Our primary outcome measure was the occurrence of at least one of the following postoperative infectious complications (pneumonia, bacteremia, sternal wound, leg vein harvest site infection, urinary tract infection, or tracheotomy site infection). We used multivariable logistic regression to control for potential confounding and to calculate adjusted odds ratios (AORs) and 95% confidence intervals (CIs).

RESULTS

A total of 1934 patients were included in this evaluation of which 1248 received a statin preoperatively and 686 did not. Our study population was 66.3 +/- 11.6 years of age, 71.3% male; 37.2% underwent complex surgery, 3.6% were morbidly obese, and 32.0% were diabetic (each being previously identified as an independent predictor of infection following cardiac surgery). Patients receiving a statin preoperatively and not receiving a statin preoperatively varied in respect to a number of important pre- and peri- operative characteristics. Patients receiving preoperative statin therapy were more likely to have had a history of diabetes, chronic obstructive pulmonary disease or high cholesterol and to be smokers, but less likely to be undergoing urgent/emergent surgery or surgery utilizing a cardiopulmonary bypass pump (p < 0.05 for all comparisons). In total, 151 (7.8%) patients developed an infectious complication. Upon multivariable logistic regression, preoperative statin use was associated with a significant reduction in the development of infection (AOR; 0.67 (95% CI 0.46-0.99), p = 0.04). The use of a statin was not associated with a statistically significant reduction in any individual infection on its own (p > 0.08 for all).

LIMITATIONS

Patients were not randomized to receive statins or not. We did not have adequate power to evaluate individual infections.

CONCLUSIONS

Preoperative statin use is associated with a reduction in patients' odds of developing a postoperative infection following cardiac surgery.

Exosomes released from macrophages infected with intracellular pathogens stimulate a proinflammatory response in vitro and in vivo

Intracellular pathogens and the molecules they express have limited contact with the immune system. Here, we show that macrophages infected with intracellular pathogens Mycobacterium tuberculosis, M bovis BCG, Salmonella typhimurium, or Toxoplasma gondii release from cells small vesicles known as exosomes which contain pathogen-associated molecular patterns (PAMPs). These exosomes, when exposed to uninfected macrophages, stimulate a proinflammatory response in a Toll-like receptor- and myeloid differentiation factor 88-dependent manner. Further, exosomes isolated from the bronchoalveolar lavage fluid (BALF) of M bovis BCG-infected mice contain the mycobacteria components lipoarabinomannan and the 19-kDa lipoprotein and can stimulate TNF-alpha production in naive macrophages. Moreover, exosomes isolated from M bovis BCG- and M tuberculosis-infected macrophages, when injected intranasally into mice, stimulate TNF-alpha and IL-12 production as well as neutrophil and macrophage recruitment in the lung. These studies identify a previously unknown function for exosomes in promoting intercellular communication during an immune response to intracellular pathogens, and we hypothesize that extracellular release of exosomes containing PAMPs is an important mechanism of immune surveillance.

Statins, bugs and prophylaxis: intriguing possibilities

Statin therapy may represent a potential prophylactic intervention in certain high-risk scenarios, for example in pandemic influenza and in those undergoing aggressive medical treatments. Emerging data indicate a potential prophylactic role in these high-risk groups.

Replication of Coxiella burnetii is inhibited in CHO K-1 cells treated with inhibitors of cholesterol metabolism

Coxiella burnetii directs the synthesis of a large parasitophorous vacuole (PV) that is required for its replication. While some lysosomal characteristics of the PV have been described, the origin and composition of the PV membrane remain largely undefined. Cholesterol is an essential component of mammalian membranes where it lends mechanical stability and serves as a platform for signaling proteins. Using infected Chinese hamster ovary cells as a model, we examined whether cholesterol is trafficked to the C. burnetii PV membrane and the effects of inhibitors of cholesterol metabolism on C. burnetii replication. When infected cells were stained with filipin, a fluorescent polyene antifungal agent that binds cholesterol, obvious staining of PV was observed indicating the PV membrane is cholesterol-rich. Furthermore, replication of C. burnetii was significantly inhibited in cells treated with the cholesterol metabolism inhibitors lovastatin, ketoconazole, imipramine, progesterone, and U18666A. These data suggest that cholesterol is an important component of the C. burnetii PV membrane and that normal cellular cholesterol metabolism is required for optimal C. burnetii replication.

Statins: panacea for sepsis?

Sepsis occurs when the immune system responds to a localised infection at a systemic level, thereby causing tissue damage and organ dysfunction. Statins have proven health benefits in many diseases involving vascular inflammation and injury. Recent animal data suggest that the administration of a statin before a sepsis-inducing insult reduces morbidity and improves survival. The immunomodulatory and anti-inflammatory effects of statins, collectively referred to as pleiotropic effects, lend biological plausibility to such findings. Limited human data hint at reduced mortality rates in bacteraemic patients, and a reduced risk of sepsis in patients with bacterial infections concurrently taking statins. These lines of evidence point to a potential new treatment and prevention modality for sepsis. The stage is set for randomised controlled clinical trials that will determine whether statins represent a safe and beneficial treatment in critically ill, septic patients and whether statins are effective at preventing sepsis in high-risk clinical settings.

Coxiella burnetii inhabits a cholesterol-rich vacuole and influences cellular cholesterol metabolism

Coxiella burnetii directs the synthesis of a large parasitophorous vacuole (PV) required for replication. While some lysosomal characteristics of the PV have been described, the origin and composition of the PV membrane is largely undefined. Cholesterol is an essential component of mammalian cell membranes where it plays important regulatory and structural roles. Here we investigated the role of host cholesterol in biogenesis and maintenance of the C. burnetii PV in Vero cells. The C. burnetii PV membrane stained with filipin and was positive for the lipid raft protein flotillin-1, suggesting PV membranes are enriched in cholesterol and contain lipid raft microdomains. C. burnetii infection increased host cell cholesterol content by 1.75-fold with a coincident upregulation of host genes involved in cholesterol metabolism. Treatment with U18666A, lovastatin, or 25-hydroxycholesterol, pharmacological agents that inhibit cholesterol uptake and/or biosynthesis, altered PV morphology and partially inhibited C. burnetii replication. Complete inhibition of C. burnetii PV development and replication was observed when infected cells were treated with imipramine or ketoconazole, inhibitors of cholesterol uptake and biosynthesis respectively. We conclude that C. burnetii infection perturbs host cell cholesterol metabolism and that free access to host cholesterol stores is required for optimal C. burnetii replication.

Peculiarities of host cholesterol transport to the unique intracellular vacuole containing Toxoplasma

The intracellular protozoan Toxoplasma gondii is auxotrophic for low-density lipoprotein (LDL)-derived cholesterol (C). We previously showed that T. gondii scavenges this essential lipid from host endolysosomal compartments and that C delivery to the parasitophorous vacuole (PV) does not require transit through host Golgi or endoplasmic reticulum. In this study, we explore the itinerary of C from the host endolysosomes to the PV. Labeled C incorporated into LDL is rapidly detected in intravacuolar parasites and partially esterified by the parasites. In contrast to diverse mammalian organelles, the post-endolysosomal transfer of C to the PV does not involve the host plasma membrane as an intermediate. Nevertheless, the PV membrane is accessible to extracellular sterol acceptors, suggesting C trafficking from intracellular parasites to host plasma membrane. C movement to the PV requires temperatures permissive for vesicular transport, metabolic energy and functional microtubules. Host caveolae vesicles and the sterol carrier protein-2 do not participate in this process. Proteolytic treatment of purified PV or free parasites abolishes C acquisition by the parasites. Altogether, these results support a vesicular transport system from host endolysosomes to the PV, and a requirement for PV membrane and parasite plasma membrane proteins in C delivery to T. gondii.

Effect of simvastatin, an established lipid-lowering drug, on pulmonary Chlamydia pneumoniae infection in mice

The effects of simvastatin treatment on Chlamydia pneumoniae lung infection, inflammation, and serum lipids in mouse model were studied. Simvastatin decreased viable chlamydial counts and increased inflammatory cell infiltrates in the lung tissue, suggesting that simvastatin treatment had both antichlamydial and immunomodulatory effects during an acute C. pneumoniae infection.

Cholesterol binding by the bacterial type III translocon is essential for virulence effector delivery into mammalian cells

A ubiquitous early step in infection of man and animals by enteric bacterial pathogens like Salmonella, Shigella and enteropathogenic Escherichia coli (EPEC) is the translocation of virulence effector proteins into mammalian cells via specialized type III secretion systems (TTSSs). Translocated effectors subvert the host cytoskeleton and stimulate signalling to promote bacterial internalization or survival. Target cell plasma membrane cholesterol is central to pathogen-host cross-talk, but the precise nature of its critical contribution remains unknown. Using in vitro cholesterol-binding assays, we demonstrate that Salmonella (SipB) and Shigella (IpaB) TTSS translocon components bind cholesterol with high affinity. Direct visualization of cell-associated fluorescently labelled SipB and parallel immunogold transmission electron microscopy revealed that cholesterol levels limit both the amount and distribution of plasma membrane-integrated translocon. Correspondingly, cholesterol depletion blocked effector translocation into cultured mammalian cells by not only the related Salmonella and Shigella TTSSs, but also the more divergent EPEC system. The data reveal that cholesterol-dependent association of the bacterial TTSS translocon with the target cell plasma membrane is essential for translocon activation and effector delivery into mammalian cells.

Bacterial interactions with the eukaryotic secretory pathway

Pathogenic bacteria exploit a wide variety of host cellular processes to adhere to, invade, replicate within and damage host cells. One such process is the eukaryotic secretory pathway, in which proteins and lipids are modified and transported from the endoplasmic reticulum through the Golgi network to the plasma membrane and other cellular destinations. Certain bacteria secrete toxins that utilise this transport pathway to reach their cellular targets. Some intracellular pathogens, including Legionella, Brucella and Chlamydia, engage other steps of the pathway to establish intracellular replicative organelles. Recent work has implicated specific virulence proteins of enterohaemorrhagic Escherichia coli and Salmonella enterica in secretory pathway interactions.