Human neutrophil chemotaxis is modulated by capsule and O antigen from an extraintestinal pathogenic Escherichia coli strain

Predictors of Comorbidity of Malaria and Septicemia in Children Living in Malaria-Endemic Communities in Nigeria

PURPOSE

The study attempted to identify possible overlap between serum cell-reactive proteins (C-rp) and hematological indices as predictors of comorbidity of malaria and septicemia among children attending primary healthcare facilities in Ilorin, Nigeria.

METHODS

One hundred and ninety-three children (aged: ≤ 1-15 years) presenting with symptoms suggestive of malaria were enrolled. Blood specimens were collected and screened for: Romanowsky, culture, serum C-RP and hematological indices.

RESULTS

One hundred and fifteen (59.6%) children had Plasmodium falciparum infections (female 69.0% and male 34.1%). Septicemia was common among 52 (26.9%), but malaria and septicemia co-infection was 42 (36.5%). C-rp levels were low (< 10 mg/L) in 41 (35.7%, OR 4.594, CI 2.463-8.571) and high (> 10 mg/L) in 74 (64.3%, OR 2.519, CI 1.681-3.775) among the malaria positives (p < 0.05). Children with low C-rp, 8 (15.4%, OR 9.413, CI 4.116-21.531) were positive for septicemia and high C-RP 44 (84.6%, OR 1.694, CI 1.396-2.055), but without malaria, respectively. Similarly, increased C-rp levels were significantly associated with clinical malaria; > 10,000 parasites/μL (OR 1.486, CI 1.076-2.054, P < 0.001). Malaria-positive versus negative showed that PCV, C-rp, hemoglobin, platelet, WBC, and neutrophil were statistically significant (P < 0.05). Two bacteria species were identified, viz; Staphylococcus aureus 39 (54.9%) and Escherichia coli 32 (45.1%). The trade-off between sensitivity and specificity occurred at 16.475 cut-off using C-rp and degree of malaria severity as the standard for AUROC.

CONCLUSION

C-rp are inflammatory markers, though non-specificity may be associated with malaria prognosis and severity during malaria-septicemia co-infection.

The role of O-polysaccharide chain and complement resistance of Escherichia coli in mammary virulence

Mastitis, inflammation of the mammary gland, is a common disease of dairy animals. The disease is caused by bacterial infection ascending through the teat canal and mammary pathogenic Escherichia coli (MPEC) are common etiology. In the first phase of infection, virulence mechanisms, designated as niche factors, enable MPEC bacteria to resist innate antimicrobial mechanisms, replicate in milk, and to colonize the mammary gland. Next, massive replication of colonizing bacteria culminates in a large biomass of microbe-associated molecular patterns (MAMPs) recognized by pattern recognition receptors (PRRs) such as toll-like receptors (TLRs) mediating inflammatory signaling in mammary alveolar epithelial cells (MAEs) and macrophages. Bacterial lipopolysaccharides (LPSs), the prototypical class of MAMPs are sufficient to elicit mammary inflammation mediated by TLR4 signaling and activation of nuclear factor kB (NF-kB), the master regulator of inflammation. Using in vivo mastitis model, in low and high complements mice, and in vitro NF-kB luminescence reporter system in MAEs, we have found that the smooth configuration of LPS O-polysaccharides in MPEC enables the colonizing organisms to evade the host immune response by reducing inflammatory response and conferring resistance to complement. Screening a collection of MPEC field strains, we also found that all strains were complement resistant and 94% (45/48) were smooth. These results indicate that the structure of LPS O-polysaccharides chain is important for the pathogenesis of MPEC mastitis and provides protection against complement-mediated killing. Furthermore, we demonstrate a role for complement, a key component of innate immunity, in host-microbe interactions of the mammary gland.

The probiotic strain Escherichia coli Nissle 1917 prevents papain-induced respiratory barrier injury and severe allergic inflammation in mice

Allergic asthma is characterized by a strong Th2 and Th17 response with inflammatory cell recruitment, airways hyperreactivity and structural changes in the lung. The protease allergen papain disrupts the airway epithelium triggering a rapid eosinophilic inflammation by innate lymphoid cell type 2 (ILC2) activation, leading to a Th2 immune response. Here we asked whether the daily oral administrations of the probiotic Escherichia coli strain Nissle 1917 (ECN) might affect the outcome of the papain protease induced allergic lung inflammation in BL6 mice. We find that ECN gavage significantly prevented the severe allergic response induced by repeated papain challenges and reduced lung inflammatory cell recruitment, Th2 and Th17 response and respiratory epithelial barrier disruption with emphysema and airway hyperreactivity. In conclusion, ECN administration attenuated severe protease induced allergic inflammation, which may be beneficial to prevent allergic asthma.

The Vi capsular polysaccharide enables Salmonella enterica serovar typhi to evade microbe-guided neutrophil chemotaxis

Salmonella enterica serovar Typhi (S. Typhi) causes typhoid fever, a disseminated infection, while the closely related pathogen S. enterica serovar Typhimurium (S. Typhimurium) is associated with a localized gastroenteritis in humans. Here we investigated whether both pathogens differ in the chemotactic response they induce in neutrophils using a single-cell experimental approach. Surprisingly, neutrophils extended chemotactic pseudopodia toward Escherichia coli and S. Typhimurium, but not toward S. Typhi. Bacterial-guided chemotaxis was dependent on the presence of complement component 5a (C5a) and C5a receptor (C5aR). Deletion of S. Typhi capsule biosynthesis genes markedly enhanced the chemotactic response of neutrophils in vitro. Furthermore, deletion of capsule biosynthesis genes heightened the association of S. Typhi with neutrophils in vivo through a C5aR-dependent mechanism. Collectively, these data suggest that expression of the virulence-associated (Vi) capsular polysaccharide of S. Typhi obstructs bacterial-guided neutrophil chemotaxis.

Uropathogenic Escherichia coli

The urinary tract is among the most common sites of bacterial infection, and Escherichia coli is by far the most common species infecting this site. Individuals at high risk for symptomatic urinary tract infection (UTI) include neonates, preschool girls, sexually active women, and elderly women and men. E. coli that cause the majority of UTIs are thought to represent only a subset of the strains that colonize the colon. E. coli strains that cause UTIs are termed uropathogenic E. coli (UPEC). In general, UPEC strains differ from commensal E. coli strains in that the former possess extragenetic material, often on pathogenicity-associated islands (PAIs), which code for gene products that may contribute to bacterial pathogenesis. Some of these genes allow UPEC to express determinants that are proposed to play roles in disease. These factors include hemolysins, secreted proteins, specific lipopolysaccharide and capsule types, iron acquisition systems, and fimbrial adhesions. The current dogma of bacterial pathogenesis identifies adherence, colonization, avoidance of host defenses, and damage to host tissues as events vital for achieving bacterial virulence. These considerations, along with analysis of the E. coli CFT073, UTI89, and 536 genomes and efforts to identify novel virulence genes should advance the field significantly and allow for the development of a comprehensive model of pathogenesis for uropathogenic E. coli.Further study of the adaptive immune response to UTI will be especially critical to refine our understanding and treatment of recurrent infections and to develop vaccines.

In vivo imaging and quantitative analysis of leukocyte directional migration and polarization in inflamed tissue

Directional migration of transmigrated leukocytes to the site of injury is a central event in the inflammatory response. Here, we present an in vivo chemotaxis assay enabling the visualization and quantitative analysis of subtype-specific directional motility and polarization of leukocytes in their natural 3D microenvironment. Our technique comprises the combination of i) semi-automated in situ microinjection of chemoattractants or bacteria as local chemotactic stimulus, ii) in vivo near-infrared reflected-light oblique transillumination (RLOT) microscopy for the visualization of leukocyte motility and morphology, and iii) in vivo fluorescence microscopy for the visualization of different leukocyte subpopulations or fluorescence-labeled bacteria. Leukocyte motility parameters are quantified off-line in digitized video sequences using computer-assisted single cell tracking. Here, we show that perivenular microinjection of chemoattractants [macrophage inflammatory protein-1alpha (MIP-1alpha/Ccl3), platelet-activating factor (PAF)] or E. coli into the murine cremaster muscle induces target-oriented intravascular adhesion and transmigration as well as polarization and directional interstitial migration of leukocytes towards the locally administered stimuli. Moreover, we describe a crucial role of Rho kinase for the regulation of directional motility and polarization of transmigrated leukocytes in vivo. Finally, combining in vivo RLOT and fluorescence microscopy in Cx3CR1(gfp/gfp) mice (mice exhibiting green fluorescent protein-labeled monocytes), we are able to demonstrate differences in the migratory behavior of monocytes and neutrophils.Taken together, we propose a novel approach for investigating the mechanisms and spatiotemporal dynamics of subtype-specific motility and polarization of leukocytes during their directional interstitial migration in vivo.

Extraintestinal pathogenic Escherichia coli-induced acute necrotizing pneumonia in cats

Extraintestinal pathogenic Escherichia coli (ExPEC) are pathogens involved in several disease conditions, ranging from urinary tract infection to meningitis in humans and animals. They comprise epidemiologically and phylogenetically distinct strains, affecting most species and involving any organ or anatomical site. Here, we report fatal cases of necrotizing pneumonia in cats. Over a 1-week period, 13 cats from an animal shelter in Stamford, Connecticut were presented for necropsy. All had a clinical history of acute respiratory disease. The gross and microscopic findings for all the cats were consistent. Escherichia coli was uniformly isolated from the lungs of all the tested cats. All the isolates were haemolytic, genetically related as determined by enterobacterial repetitive intergenic consensus PCR, and harboured genes encoding for cytotoxic necrotizing factor-1 and fimbriae and adhesions that are characteristic of ExPEC, implying a point source clonal outbreak. As cats are common household pets, this report raises concerns regarding zoonotic potential (in either direction) for these ExPEC strains.

Capsule and O-antigen from an extraintestinal isolate of Escherichia coli modulate cytokine levels in rat macrophages in vitro and in a rat model of pneumonia

Gram-negative pneumonia results in significant morbidity, mortality, and cost to the healthcare system. Previously the authors demonstrated that capsule and O-antigen, virulence factors of the extraintestinal Escherichia coli isolate CP9, modulate pulmonary neutrophil influx in a rat pneumonia model. In this report, the authors utilized CP9 and mutants deficient in O-antigen (CP921), capsule (CP9.137), or both (CP923) to test the hypothesis that modulation of cytokine levels by capsule and/or O-antigen may be a contributory mechanism. Effects of capsule and O-antigen on cytokine levels in rats in vivo and in isolated pulmonary macrophages in vitro were assessed. In vivo, capsule and O-antigen had no significant effect on tumor necrosis factor (TNF)-alpha levels in bronchoalveolar lavage fluid (BALF), but both were associated with significant increases in the levels of interleukin (IL)-1beta and Cytokine-induced neutrophil Chemoattractant-1 (CINC-1). However, potential difficulties in interpreting data occurred because challenge bacterial strains exhibited differential growth, and clearance characteristics and mixed cell populations were present. Therefore, added mechanistic studies investigated specific interactions of capsule and O-antigen with pulmonary macrophages purified from normal rats and exposed to CP9, CP921, CP9.137, or CP923 in vitro. Results indicated that the presence of capsule led to significantly increased levels of TNF-alpha, IL-1beta, and CINC-1, whereas O-antigen significantly decreased macrophage-associated levels of these mediators. These findings support the hypothesis that CP9 capsule is proinflammatory for macrophage-induced neutrophil recruitment, whereas O-antigen attenuates macrophage production of proinflammatory mediators in pneumonia. These results expand our understanding on the mechanisms by which these virulence traits may contribute to the inflammatory pathogenesis of pneumonia.

Extraintestinal pathogenic Escherichia coli survives within neutrophils

Extracellular pathogenic Escherichia coli (ExPEC) strains are common causes of a variety of clinical syndromes, including urinary tract infections, abdominal infections, nosocomial pneumonia, neonatal meningitis, and sepsis. ExPEC strains are extracellular bacterial pathogens; therefore, the innate immune response (e.g., professional phagocytes) plays a crucial role in the host defense against them. Studies using the model ExPEC strain CP9 demonstrated that it is relatively resistant to neutrophil-mediated bactericidal activity. Although this could be due to resistance to phagocytosis, the ability of CP9 to survive the intracellular killing mechanisms of neutrophils is another possibility. Using a variation of the intracellular invasion assay, we studied the survival of CP9 within peripheral blood-derived human neutrophils. Our results indicated that CP9 did survive within human neutrophils, but we were unable to demonstrate that intracellular replication occurred. This finding was not unique to CP9, since when a conservative assessment of survival was used, four of six additional ExPEC strains, but not an E. coli laboratory strain, were also capable of survival within neutrophils. Initial studies in which we began to decipher the mechanisms by which CP9 is able to successfully survive intracellular neutrophil-mediated bactericidal activity demonstrated that CP9 was at least partially susceptible to the neutrophil oxidative burst. Therefore, absolute resistance to the oxidative burst is not a mechanism by which ExPEC survives within neutrophils. In addition, electron microscopy studies showed that CP9 appeared to be present in phagosomes within neutrophils. Therefore, avoidance of phagosomal uptake or subsequent escape from the phagosome does not appear to be a mechanism that contributes to CP9's survival. These findings suggest that survival of ExPEC within neutrophils may be an important virulence mechanism.

E. colivirulence factor hemolysin induces neutrophil apoptosis and necrosis/lysis in vitro and necrosis/lysis and lung injury in a rat pneumonia model

Enteric gram-negative bacilli, such as Escherichia coli are the most common cause of nosocomial pneumonia. In this study a wild-type extraintestinal pathogenic strain of E. coli (ExPEC)(CP9) and isogenic derivatives deficient in hemolysin (Hly) and cytotoxic necrotizing factor (CNF) were assessed in vitro and in a rat model of gram-negative pneumonia to test the hypothesis that these virulence factors induce neutrophil apoptosis and/or necrosis/lysis. As ascertained by in vitro caspase-3/7 and LDH activities and neutrophil morphology, Hly mediated neutrophil apoptosis at lower E. coli titers (1 × 105–6cfu) and necrosis/lysis at higher titers (≥1 × 107cfu). Data suggest that CNF promotes apoptosis but not necrosis or lysis. We also demonstrate that annexin V/7-amino-actinomycin D staining was an unreliable assessment of apoptosis using live E. coli. The use of caspase-3/7 and LDH activities and neutrophil morphology supported the notion that necrosis, not apoptosis, was the primary mechanism by which neutrophils were affected in our in vivo gram-negative pneumonia model using live E. coli. In addition, in vivo studies demonstrated that Hly mediates lung injury. Neutrophil necrosis was not observed when animals were challenged with purified lipopolysaccharide, demonstrating the importance of using live bacteria. These findings establish that Hly contributes to ExPEC virulence by mediating neutrophil toxicity, with necrosis/lysis being the dominant effect of Hly on neutrophils in vivo and by lung injury. Whether Hly-mediated lung injury is due to neutrophil necrosis, a direct effect of Hly, or both is unclear.

IL-8 is a key chemokine regulating neutrophil recruitment in a new mouse model of Shigella-induced colitis

The lack of a mouse model of acute rectocolitis mimicking human bacillary dysentery in the presence of invasive Shigella is a major handicap to study the pathogenesis of the disease and to develop a Shigella vaccine. The inability of the mouse intestinal mucosa to elicit an inflammatory infiltrate composed primarily of polymorphonuclear leukocytes (PMN) may be due to a defect in epithelial invasion, in the sensing of invading bacteria, or in the effector mechanisms that recruit the PMN infiltrate. We demonstrate that the BALB/cJ mouse colonic epithelium not only can be invaded by Shigella, but also elicits an inflammatory infiltrate that, however, lacks PMN. This observation points to a major defect of mice in effector mechanisms, particularly the lack of expression of the CXC chemokine, IL-8. Indeed, this work demonstrates that the delivery of recombinant human IL-8, together with Shigella infection of the colonic epithelial surface, causes an acute colitis characterized by a strong PMN infiltrate that, by all criteria, including transcription profiles of key mediators of the innate/inflammatory response and histopathological lesions, mimics bacillary dysentery. This is a major step forward in the development of a murine model of bacillary dysentery.