Grazing Management Effects on Sediment, Phosphorus, and Pathogen Loading of Streams in Cool-Season Grass Pastures

Erosion and runoff from pastures may lead to degradation of surface water. A 2-yr grazing study was conducted to quantify the effects of grazing management on sediment, phosphorus (P), and pathogen loading of streams in cool-season grass pastures. Six adjoining 12.1-ha pastures bisected by a stream in central Iowa were divided into three treatments: continuous stocking with unrestricted stream access (CSU), continuous stocking with restricted stream access (CSR), and rotational stocking (RS). Rainfall simulations on stream banks resulted in greater (P \u3c 0.10) proportions of applied precipitation and amounts of sediment and P transported in runoff from bare sites than from vegetated sites across grazing treatments. Similar differences were observed comparing vegetated sites in CSU and RS pastures with vegetated sites in CSR pastures. Bovine enterovirus was shed by an average of 24.3% of cows during the study period and was collected in the runoff of 8.3 and 16.7% of runoff simulations on bare sites in CSU pastures in June and October of 2008, respectively, and from 8.3% of runoff simulations on vegetated sites in CSU pastures in April 2009. Fecal pathogens (bovine coronavirus [BCV], bovine rotavirus group A, andEscherichia coli O157:H7) shed or detected in runoff were almost nonexistent; only BCV was detected in feces of one cow in August of 2008. Erosion of cut-banks was the greatest contributor of sediment and P loading to the stream; contributions from surface runoff and grazing animals were considerably less and were minimized by grazing management practices that reduced congregation of cattle by pasture streams

Grazing Management Effects on Sediment, Phosphorus, and Pathogen Loading of Pasture Streams

In order to quantify the sources of sediment, phosphorus (P), and pathogen loading of pasture streams, six 30-acre pastures, bisected by a stream, were stocked with 15 fall-calving cows from mid-May through midOctober of two years by continuous stocking with unrestricted stream access (CSU), continuous stocking with stream access restricted to 16-foot wide stabilized crossings (CSR), or rotational stocking (RS). Cows in RS pastures excreted less fecal P than cows in the CSU and CSR pastures. The proportion of water applied and the amounts of sediment and P in precipitation runoff during rainfall simulations were greater from bare sites on the stream banks of CSU or RS pastures than vegetated sites of CSU, RS, or CSR pastures. Amounts of stream bank erosion did not differ between grazing management treatments. When sources of sediment and P were compared, stream bank erosion contributed 99.5 and 94.4% of the sediment and P loading of the stream. At the stocking rate used in this experiment, direct fecal deposition in the pasture stream contributed more P than transport in precipitation runoff. The incidence of fecal pathogens E. coli O157:H7, bovine coronavirus, and bovine rotavirus shedding in the feces of the cows in this experiment as well as in the runoff from the rainfall simulations was extremely low. These results suggest that the major source of sediment and P loading of pasture streams is stream bank erosion primarily associated with stream hydrology. Grazing management practices that reduce congregation of grazing cattle near pasture streams will reduce sediment and nutrient loading resulting from direct fecal deposition or transport in precipitation runoff. While fecal pathogens may be potential pollutants of pasture streams, pathogen loading of pasture streams by grazing cattle is infrequent and dependent upon the pathogen shedding, temporal\spatial distribution of grazing cattle, and surface runoff from stream banks, in respective order

The Spectrin Cytoskeleton Is Crucial for Adherent and Invasive Bacterial Pathogenesis

Various enteric bacterial pathogens target the host cell cytoskeletal machinery as a crucial event in their pathogenesis. Despite thorough studies detailing strategies microbes use to exploit these components of the host cell, the role of the spectrin-based cytoskeleton has been largely overlooked. Here we show that the spectrin cytoskeleton is a host system that is hijacked by adherent (Entropathogenic Escherichia coli [EPEC]), invasive triggering (Salmonella enterica serovar Typhimurium [S. Typhimurium]) and invasive zippering (Listeria monocytogenes) bacteria. We demonstrate that spectrin cytoskeletal proteins are recruited to EPEC pedestals, S. Typhimurium membrane ruffles and Salmonella containing vacuoles (SCVs), as well as sites of invasion and comet tail initiation by L. monocytogenes. Spectrin was often seen co-localizing with actin filaments at the cell periphery, however a disconnect between the actin and spectrin cytoskeletons was also observed. During infections with S. Typhimurium ΔsipA, actin-rich membrane ruffles at characteristic sites of bacterial invasion often occurred in the absence of spectrin cytoskeletal proteins. Additionally, early in the formation of L. monocytogenes comet tails, spectrin cytoskeletal elements were recruited to the surface of the internalized bacteria independent of actin filaments. Further studies revealed the presence of the spectrin cytoskeleton during SCV and Listeria comet tail formation, highlighting novel cytoplasmic roles for the spectrin cytoskeleton. SiRNA targeted against spectrin and the spectrin-associated proteins severely diminished EPEC pedestal formation as well as S. Typhimurium and L. monocytogenes invasion. Ultimately, these findings identify the spectrin cytoskeleton as a ubiquitous target of enteric bacterial pathogens and indicate that this cytoskeletal system is critical for these infections to progress

VAMP8 mucin exocytosis attenuates intestinal pathogenesis by Entamoeba histolytica

The intestinal mucosa encounters a barrage of ingested insults within the host yet under homeostasis elegantly facilitates nutrient absorption and sustenance of the commensal microbiota. An essential defence mechanism employed by the host is limiting the spatial niche various microbes may occupy as executed by the fluid mucus layer. Pathogens that violate their restricted niche within the intestinal mucosa are first expelled by robust mucus secretion from goblet cells thus by-passing the need for an immune response. Surprisingly, while many pathogens are known to exert hyper-secretion of mucus from goblet cells, the mechanisms governing this event remain elusive. In a recent report by Cornick et al (MBio 8: e01323-17), we nominate SNARE-mediated exocytosis as the putative mechanism responsible for pathogen-induced mucus secretion from goblet cells. The vesicle SNARE VAMP8 on mucin granules within goblet cells is specifically activated following infection with the protozoan parasite Entamoeba histolytica that is known to induce potent hyper-secretion and coordinates mucin exocytosis. This secretion event is critical in fending off a pathogen, as cells lacking VAMP8 are prone to increased E. histolytica colonization and cytolysis through apoptosis. Failing coordinated mucus exocytosis and subsequent epithelial barrier destruction, the host mounts an immune response as a last line of defence

<i>Entamoeba histolytica</i> Cysteine Proteinase 5 Evokes Mucin Exocytosis from Colonic Goblet Cells via αvβ3 Integrin

<div><p>Critical to the pathogenesis of intestinal amebiasis, <i>Entamoeba histolytica</i> (<i>Eh</i>) induces mucus hypersecretion and degrades the colonic mucus layer at the site of invasion. The parasite component(s) responsible for hypersecretion are poorly defined, as are regulators of mucin secretion within the host. In this study, we have identified the key virulence factor in live <i>Eh</i> that elicits the fast release of mucin by goblets cells as cysteine protease 5 (<i>Eh</i>CP5) whereas, modest mucus secretion occurred with secreted soluble <i>Eh</i>CP5 and recombinant CP5. Coupling of <i>Eh</i>CP5-αvβ3 integrin on goblet cells facilitated outside-in signaling by activating SRC family kinases (SFK) and focal adhesion kinase that resulted in the activation/phosphorlyation of PI3K at the site of <i>Eh</i> contact and production of PIP3. PKCδ was activated at the <i>Eh</i>CP5-αvβ3 integrin contact site that specifically regulated mucin secretion though the trafficking vesicle marker myristoylated alanine-rich C-kinase substrate (MARCKS). This study has identified that <i>Eh</i>CP5 coupling with goblet cell αvβ3 receptors can initiate a signal cascade involving PI3K, PKCδ and MARCKS to drive mucin secretion from goblet cells critical in disease pathogenesis.</p></div