Murine gastrointestinal tract as a portal of entry in experimental Pseudomonas aeruginosa infections

Effects of the Sex Steroid Hormone Estradiol on Biofilm Growth of Cystic Fibrosis Pseudomonas aeruginosa Isolates

Women with cystic fibrosis (CF) have a significantly lower life expectancy compared to men, which is indicated by an earlier impairment of lung function due to chronic colonization with biofilm formed by Pseudomonas aeruginosa. There is growing evidence that blood serum concentrations of the steroid sex hormone estradiol (E₂) correlate with the occurrence of pulmonary exacerbations in CF but also play a role in the mucoid switch of P. aeruginosa. This study aims to shed light on possible microbiological reasons for sexual dimorphism in CF by investigating the influence of E₂ on biofilm formation of P. aeruginosa CF isolates. For this purpose, 10 CF isolates of the respiratory tract derived from different CF patients have been treated with E₂ in a microtiter plate biofilm model. Biofilms have been examined by crystal violet assays, field emission scanning electron microscopy (FE-SEM), 3D laser scanning microscopy (LSM), and quorum sensing (QS) reporter assays of the supernatants taken from biofilms. This allowed us to simultaneously investigate the effects of E₂ on attached biofilm mass, biofilm ultrastructure, and QS activity. Upon E₂ treatment, six out of 10 investigated CF isolates showed an increase of attached biofilm mass, whereas biofilms from two tested non-CF laboratory strains (PAO1 and ATCC19660) did not. Moreover, FE-SEM and 3D LSM analyses of the E₂ responsive CF biofilms revealed ultrastructural remodeling of biofilm structure at different scales with increased formation of prominent biofilm spots, enhanced coverage with extracellular polymeric substance (EPS), and extended average surface roughness. QS activity measurements performed in biofilm supernatants via luminescence acyl homoserine lactone (AHL) reporter assays further showed that E₂ treatment may also modulate QS signaling, as shown in an E₂ sensitive CF isolate. Together, our results suggest the biofilm modulating effects of E₂ on various clinical CF isolates that are documented by both biomass and ultrastructural changes of biofilms. The gained new insight into the influence of steroid hormones on P. aeruginosa biofilm phenotypes might pave the way for novel future approaches in personalized medicine based on the patients’ sex and hormonal status.

Can the Cecal Ligation and Puncture Model Be Repurposed To Better Inform Therapy in Human Sepsis?

A recent report by the National Institutes of Health on sepsis research has implied there is a trend to move away from mouse models of sepsis. The most commonly used animal model to study the pathogenesis of human sepsis is cecal ligation and puncture (CLP) in mice. The model has been the mainstay of sepsis research for decades and continues to be considered the gold standard to inform novel pathways of sepsis physiology and its therapeutic direction. As there have been many criticisms of the model, particularly regarding its relevance to human disease, how this model might be repurposed to be more reflective of the human condition begs discussion. In this piece, we compare and contrast the mouse microbiome of the CLP model to the emerging science of the microbiome of human sepsis and discuss the relevance for mice to harbor the specific pathogens present in the human microbiome during sepsis, as well as an underlying disease process to mimic the characteristics of those patients with undesirable outcomes. How to repurpose this model to incorporate these "human factors" is discussed in detail and suggestions offered.

Assessing the Groundwater Quality at a Saudi Arabian Agricultural Site and the Occurrence of Opportunistic Pathogens on Irrigated Food Produce

This study examines the groundwater quality in wells situated near agricultural fields in Saudi Arabia. Fruits (e.g., tomato and green pepper) irrigated with groundwater were also assessed for the occurrence of opportunistic pathogens to determine if food safety was compromised by the groundwater. The amount of total nitrogen in most of the groundwater samples exceeded the 15 mg/L permissible limit for agricultural irrigation. Fecal coliforms in densities > 12 MPN/100 mL were detected in three of the groundwater wells that were in close proximity to a chicken farm. These findings, coupled with qPCR-based fecal source tracking, show that groundwater in wells D and E, which were nearest to the chicken farm, had compromised quality. Anthropogenic contamination resulted in a shift in the predominant bacterial phyla within the groundwater microbial communities. For example, there was an elevated presence of Proteobacteria and Cyanobacteria in wells D and E but a lower overall microbial richness in the groundwater perturbed by anthropogenic contamination. In the remaining wells, the genus Acinetobacter was detected at high relative abundance ranging from 1.5% to 48% of the total groundwater microbial community. However, culture-based analysis did not recover any antibiotic-resistant bacteria or opportunistic pathogens from these groundwater samples. In contrast, opportunistic pathogenic Enterococcus faecalis and Pseudomonas aeruginosa were isolated from the fruits irrigated with the groundwater from wells B and F. Although the groundwater was compromised, quantitative microbial risk assessment suggests that the annual risk incurred from accidental consumption of E. faecalis on these fruits was within the acceptable limit of 10⁻⁴. However, the annual risk arising from P. aeruginosa was 9.55 × 10⁻⁴, slightly above the acceptable limit. Our findings highlight that the groundwater quality at this agricultural site in western Saudi Arabia is not pristine and that better agricultural management practices are needed alongside groundwater treatment strategies to improve food safety.

Interkingdom adenosine signal reduces Pseudomonas aeruginosa pathogenicity

Pseudomonas aeruginosa is becoming recognized as an important pathogen in the gastrointestinal (GI) tract. Here we demonstrate that adenosine, derived from hydrolysis of ATP from the eucaryotic host, is a potent interkingdom signal in the GI tract for this pathogen. The addition of adenosine nearly abolished P. aeruginosa biofilm formation and abolished swarming by preventing production of rhamnolipids. Since the adenosine metabolite inosine did not affect biofilm formation and since a mutant unable to metabolize adenosine behaved like the wild-type strain, adenosine metabolism is not required to reduce pathogenicity. Adenosine also reduces production of the virulence factors pyocyanin, elastase, extracellular polysaccharide, siderophores and the Pseudomonas quinolone signal which led to reduced virulence with Caenorhabditis elegans. To provide insights into how adenosine reduces the virulence of P. aeruginosa, a whole-transcriptome analysis was conducted which revealed that adenosine addition represses genes similar to an iron-replete condition; however, adenosine did not directly bind Fur. Therefore, adenosine decreases P. aeruginosa pathogenicity as an interkingdom signal by causing genes related to iron acquisition to be repressed.

The neuroendocrine hormone norepinephrine increases Pseudomonas aeruginosa PA14 virulence through the las quorum-sensing pathway

It has been proposed that the gastrointestinal tract environment containing high levels of neuroendocrine hormones is important for gut-derived Pseudomonas aeruginosa infections. In this study, we report that the hormone norepinephrine increases P. aeruginosa PA14 growth, virulence factor production, invasion of HCT-8 epithelial cells, and swimming motility in a concentration-dependent manner. Transcriptome analysis of P. aeruginosa exposed to 500 microM, but not 50 microM, norepinephrine for 7 h showed that genes involved in the regulation of the virulence determinants pyocyanin, elastase, and the Pseudomonas quinolone signal (PQS, 2-heptyl-3-hydroxy-4-quinolone) were upregulated. The production of rhamnolipids, which are also important in P. aeruginosa infections, was not significantly altered in suspension cultures upon exposure to 500 microM norepinephrine but decreased on semisolid surfaces. Swarming motility, a phenotype that is directly influenced by rhamnolipids, was also decreased upon 500 microM norepinephrine exposure. The increase in the transcriptional activation of lasR but not that of rhlR and the increase in the levels of PQS suggest that the effects of norepinephrine are mediated primarily through the las quorum-sensing pathway. Together, our data strongly suggest that norepinephrine can play an important role in gut-derived infections by increasing the pathogenicity of P. aeruginosa PA14.

The re-emerging role of the intestinal microflora in critical illness and inflammation: why the gut hypothesis of sepsis syndrome will not go away

Recent advances in the ability to genetically interrogate microbial communities within the intestinal tract of humans have revealed many striking findings. That there may be as many as 300 unculturable and unclassified microbes within the human intestinal tract opens the possibility that yet-unidentified microbes may play a role in various human diseases [( 1) ]. Technologically, the regional and spatial aspects of intestinal microbial communities can now be better appreciated by emerging genetic and in vivo imaging systems using a bioinformatics approach [( 2) ]. Finally, in situ PCR of tissues and blood now allows the detection of microbes at concentrations that would otherwise remain undetected by culture alone [( 3) ]. In the aggregate, these studies have empowered clinicians to readdress the issue of how our microbial partners are affected by extreme states of physiologic stress and antibiotic use through the course of critical illness. The role of microbes in systemic inflammatory states, such as systemic inflammatory response syndrome, as well as in primary intestinal mucosal diseases, such as necrotizing enterocolitis, inflammatory bowel disease, and ischemia-reperfusion injury, can now be more completely defined, and the microbial genes that mediate the immune activation during these disorders can be identified. The 2008 roadmap initiative at the National Institutes of Health to fully define the human microbiome is further testament to the power of this technology and the importance of understanding how intestinal microbes, their genes, and their gene products affect the course of human disease and inflammation.

Acute and "chronic" phase reaction-a mother of disease

The world is increasingly threatened by a global epidemic of chronic diseases. Almost half of the global morbidity and almost two thirds of global mortality is due to these diseases-approximately 35 million die each year from chronic diseases. And they continue to increase. Increasing evidence suggest that these diseases are associated with lifestyle, stress, lack of physical exercise, over-consumption of calorie-condensed foods rich in saturated fat, sugar and starch, but also under-consumption of antioxidant-rich fruits and vegetables. As a result the function of the innate immune system is severe impaired. This review discusses the changes induced in response to mental and physical stress and their association with the subsequent development of metabolic syndrome, and its association with various chronic diseases. The endothelial cells and their function appears to be of great importance, and the function of their cellular membranes of special importance to the function of the underlying cells; their ability to obtain nutrients and antioxidants and to eliminate waste products. The abdominal adipocytes seen to play a key role, as they have the ability to in stressful situations release much of proinflammatory cytokines, PAI-1 and free fatty acids compared to elsewhere in the body. The load on the liver of these various substances in often of greater magnitude than the liver can handle. Some of the most common chronic diseases and their potential association with acute and "chronic" phase response, and with metabolic syndrome are discussed separately. The need for studies with lifestyle modifications is especially emphasized.

Pseudomonas aeruginosa expresses a lethal virulence determinant, the PA-I lectin/adhesin, in the intestinal tract of a stressed host: the role of epithelia cell contact and molecules of the Quorum Sensing Signaling System

OBJECTIVE

We have previously demonstrated that P. aeruginosa can have profound effects on the intestinal epithelial barrier via one of its virulence factors, the PA-I lectin/adhesin. The aims of the present study were to further characterize the interaction of P. aeruginosa and the intestinal epithelium using both in vitro and in vivo approaches.

METHODS

In vitro assays examining the effect of bacterial growth phase, epithelial cell contact, and butanoyl homoserine lactone (C4-HSL), a quorum sensing signaling molecule know to affect various extracellular virulence factors in P. aeruginosa, on PA-I expression in P. aeruginosa were performed. In vivo studies were carried out by modeling catabolic stress in mice using a 30% surgical hepatectomy and direct introduction of P. aeruginosa and various virulence components into the cecum. The effect of this model on PA-I expression in P. aeruginosa was determined.

RESULTS

Results demonstrated that PA-I expression in P. aeruginosa is affected by its phase of growth, its contact to the intestinal epithelium, and its exposure to the quorum sensing molecule, C4-HSL. Furthermore, data from the present study suggest that the PA-I lectin/adhesin of P. aeruginosa may be increased in vivo by local factors within the cecum of mice in response to surgical stress.

CONCLUSIONS

These data indicate that multiple factors present in the intestinal microenvironment of a stressed host may induce certain opportunistic pathogens to express key virulence factors leading to a state of lethal gut-derived sepsis.

Use of some pre-, pro- and synbiotics in critically ill patients

Maintenance of the gut environment is a key factor in determining outcome in the care of critically ill and postoperative patients. It is especially important to maintain both gastrointestinal secretions, full of anti-infectious and anti-inflammatory compounds, and the gut flora. Prebiotics, usually polysaccharides, exhibit strong bio-activity and the ingestion of prebiotics has been shown to reduce the rate of infection and restore health in sick and postoperative patients. Probiotics may have at least five functions, all of great importance to the sick patients: the reduction or elimination of potentially pathogenic micro-organisms of various kinds; the reduction or elimination of various toxins, mutagens, carcinogens, etc.; modulation of the innate and adaptive immune defence mechanisms; the promotion of apoptosis; and the release of numerous nutrient, antioxidant, growth, coagulation and other factors necessary for recovery. A combination of pre- and probiotics is referred to as 'synbiotics'. Our experience of synbiotic treatment in critically ill patients is limited, but cutting-edge results from studies of severe acute pancreatitis, chronic hepatitis and liver transplantation offer great hope for the future. This is especially important as pharmaceutical treatment, including the use of antibiotics, has largely failed, and the medical world is in much need of new treatment paradigms.

Influence of the critically ill state on host-pathogen interactions within the intestine: gut-derived sepsis redefined

Severe and prolonged states of catabolic stress have been shown to have profound effects on the intestinal tract microflora and intestinal function. Gut-derived sepsis is a term used to describe a state of systemic inflammation with organ dysfunction after severe catabolic stress hypothesized to be initiated and perpetuated by the intestinal tract microflora. Popular notions of the mechanism of this process have suggested that stress promotes the translocation of intestinal bacteria or their toxins into the systemic compartment resulting in the release of proinflammatory cytokines which participate in the systemic inflammatory response syndrome. This review is an attempt to redefine the mechanism of gut-derived sepsis by focusing on molecular events that result from host-pathogen interactions within the intestinal tract itself. This evidence-based review posits that gut-derived bacteremia, even with potent nosocomial pathogens, is an event of low proinflammatory potential and, itself, is an insufficient stimulus for the systemic inflammatory response and organ failure state typically seen after severe and prolonged catabolic stress. Mechanisms of this apparent paradox are discussed.

Gut-derived sepsis occurs when the right pathogen with the right virulence genes meets the right host: evidence for in vivo virulence expression in Pseudomonas aeruginosa

OBJECTIVE

To define the putative role of the PA-I lectin/adhesin, a binding protein of Pseudomonas aeruginosa, on lethal gut-derived sepsis after surgical stress, and to determine if this protein is expressed in vivo in response to physical and chemical changes in the local microenvironment of the intestinal tract after surgical stress.

SUMMARY BACKGROUND DATA

Previous work from the authors' laboratory has established that lethal gut-derived sepsis can be induced after the introduction of P. aeruginosa into the cecum of mice after a 30% hepatectomy. This effect does not occur when P. aeruginosa is introduced into the cecum of sham operated control mice. Previous experiments further established that the mechanism of this effect is due to the presence of the PA-I lectin/adhesin of P. aeruginosa, which induces a permeability defect to a lethal cytotoxin of P. aeruginosa, exotoxin A.

METHODS

Three strains of P. aeruginosa, one lacking functional PA-I, were tested in two complementary systems to assess virulence. Strains were tested for their ability to adhere to and alter the permeability of cultured human colon epithelial cells, and for their ability to induce mortality when injected into the cecum of mice after a 30% hepatectomy. To determine if PA-I is "in vivo expressed" when present in the cecal environment after hepatectomy, strains were retrieved from the cecum of sham-operated and hepatectomy-treated mice 24 and 48 hours after their introduction into the cecum and their PA-I expression was assessed.

RESULTS

Results indicated that PA-I plays a putative role in lethal gut-derived sepsis in the mouse, because strains lacking functional PA-I had an attenuated effect on cultured human epithelial cells, and were nonlethal when injected into the cecum of mice after 30% surgical hepatectomy. Furthermore, surgical stress in the form of hepatectomy significantly altered the intestinal microenvironment, resulting in an increase in luminal norepinephrine associated with an increase in PA-I expression in retrieved strains of P. aeruginosa. Co-incubation of P. aeruginosa with norepinephrine increased PA-I expression in vitro, suggesting that norepinephrine plays a role in the observed response in vivo.

CONCLUSIONS

Lethal gut-derived sepsis may occur when intestinal pathogens express virulence determinants in response to environmental signals indicating host stress. In this regard, the PA-I lectin/adhesin of P. aeruginosa appears to be a specific example of in vivo virulence expression in colonizing pathogens in the intestinal tract in response to surgical stress.

The key role of Pseudomonas aeruginosa PA-I lectin on experimental gut-derived sepsis

OBJECTIVE

To examine the effect of Pseudomonas aeruginosa on intestinal barrier function and its lethal potential when introduced into the intestinal tract of mice.

SUMMARY BACKGROUND DATA

The mere presence of P. aeruginosa in the intestinal tract of critically ill patients is associated with a threefold increase in death compared with matched cohorts without this pathogen. Whether this effect is a cause or a consequence of the critically ill state has not been previously addressed.

METHODS

Transepithelial electrical resistance, a measure of tight junction permeability, was evaluated in Caco-2 intestinal epithelial cells cells apically inoculated with live P. aeruginosa, exotoxin A, or purified PA-I lectin, an adhesin of P. aeruginosa. Lethality studies to P. aeruginosa were carried out in mice undergoing 30% surgical hepatectomy by injecting the bacteria or its various components directly into the cecum.

RESULTS

Only cells exposed to P. aeruginosa or its PA-I lectin developed alterations in barrier function. P. aeruginosa or the combination of PA-I and exotoxin A was lethal to mice when injected into the cecum after partial hepatectomy. Alterations in epithelial barrier function and death in mice were prevented when Pseudomonas was pretreated with N-acetyl D-galactosamine (GalNAc), a binder of PA-I.

CONCLUSIONS

P. aeruginosa may act as a pathogen in the gastrointestinal tract, resulting in altered epithelial barrier function and death in a susceptible host. The PA-I lectin of P. aeruginosa may play a key role in its pathogenicity to the intestinal epithelium by inducing a permeability defect to its cytotoxic exoproducts such as exotoxin A.