Distal Colonization Research Articles

The deubiquitinase USP15 drives malignant progression of gastric cancer through glucose metabolism remodeling

BackgroundUbiquitin-specific protease 15 (USP15) exhibits amplifications in various tumors, including gastric cancer (GC), yet its biological function and mechanisms in GC progression remain elusive.MethodsHere, we established stable USP15 knockdown or overexpression GC cell lines and explored the potential mechanism of USP15 in GC. Besides, we also identified interacting targets of USP15.ResultsUSP15 knockdown significantly impeded cell proliferation, invasion, epithelial-mesenchymal transition, and distal colonization in xenograft models, while enhancing oxaliplatin's antitumor effect. USP15 was involved in ubiquitination modification of glycolytic regulators. Silencing of USP15 suppressed glycolytic activity and impaired mitochondrial functions. Interference with USP15 expression reversed tumor progression and distal colonization in vivo. HKDC1 and IGF2BP3 were found as core interacting targets of USP15, and HKDC1 was identified as a substrate for ubiquitination modification by USP15, whereby USP15 regulated glucose metabolism activity by inhibiting the ubiquitination degradation of HKDC1.ConclusionsOur study unveiled aberrantly high expression of USP15 in GC tissues, correlating with malignant progression and nonresponse to neoadjuvant therapy. USP15 inhibitors, if developed, could be effective in promoting chemotherapy through glucose metabolism remodeling.

In situ hydrogel enhances non-efferocytic phagocytosis for post-surgical tumor treatment

Post-surgical efferocytosis of tumor associated macrophages (TAMs) originates an immunosuppressive tumor microenvironment and facilitates abscopal metastasis of residual tumor cells. Currently, few strategies could inhibit efferocytosis while recovering the tumor-eliminative phagocytosis of TAMs. Herein, we developed an in situ hydrogel that contains anti-CD47 antibody (aCD47) and apocynin (APO), an inhibitor of nicotinamide adenine dinucleotide phosphate oxidase. This hydrogel amplifies the non-efferocytic phagocytosis of TAMs by (1) blocking the extracellular “Don’t eat me” signal of efferocytosis with aCD47, which enhances the receptor-mediated recognition and engulfment of tumor cells by TAMs in the post-surgical tumor bed, and (2) by utilizing APO to dispose of tumor debris in a non-efferocytic manner, which prevents acidification and maturation of efferosomes and allows for M1-polarization of TAMs, leading to improved antigen presentation ability. With the complementary intervention of extracellular and intracellular, this hydrogel reverses the immunosuppressive effects of efferocytosis, and induces a potent M1-associated Th1 immune response against tumor recurrence. In addition, the in situ detachment and distal colonization of metastatic tumor cells were efficiently restrained due to the intervention of efferocytosis. Collectively, the hydrogel potentiates surgery treatment of tumor by recovering the tumor-elimination ability of post-surgical TAMs.

Porphyromonas gingivalis Gingipains Destroy the Vascular Barrier and Reduce CD99 and CD99L2 Expression To Regulate Transendothelial Migration.

Porphyromonas gingivalis is an important periodontal pathogen that can cause vascular injury and invade local tissues through the blood circulation, and its ability to evade leukocyte killing is critical to its distal colonization and survival. Transendothelial migration (TEM) is a series of that enable leukocytes to squeeze through endothelial barriers and migrate into local tissues to perform immune functions. Several studies have shown that P. gingivalis-mediated endothelial damage initiates a series of proinflammatory signals that promote leukocyte adhesion. However, whether P. gingivalis is involved in TEM and thus influences immune cell recruitment remains unknown. In our study, we found that P. gingivalis gingipains could increase vascular permeability and promote Escherichia coli penetration by downregulating platelet/endothelial cell adhesion molecule 1 (PECAM-1) expression in vitro. Furthermore, we demonstrated that although P. gingivalis infection promoted monocyte adhesion, the TEM capacity of monocytes was substantially impaired, which might be due to the reduced CD99 and CD99L2 expression on gingipain-stimulated endothelial cells and leukocytes. Mechanistically, gingipains mediate CD99 and CD99L2 downregulation, possibly through the inhibition of the phosphoinositide 3-kinase (PI3K)/Akt pathway. In addition, our in vivo model confirmed the role of P. gingivalis in promoting vascular permeability and bacterial colonization in the liver, kidney, spleen, and lung and in downregulating PECAM-1, CD99, and CD99L2 expression in endothelial cells and leukocytes. IMPORTANCE P. gingivalis is associated with a variety of systemic diseases and colonizes in distal locations in the body. Here, we found that P. gingivalis gingipains degrade PECAM-1 to promote bacterial penetration while simultaneously reducing leukocyte TEM capacity. A similar phenomenon was also observed in a mouse model. These findings established P. gingivalis gingipains as the key virulence factor in modulating the permeability of the vascular barrier and TEM processes, which may provide a new rationale for the distal colonization of P. gingivalis and its associated systemic diseases.

The Infectivity Gene bbk13 Is Important for Multiple Phases of the Borrelia burgdorferi Enzootic Cycle.

ABSTRACTLyme disease is a multistage inflammatory disease caused by the spirochete Borrelia burgdorferi transmitted through the bite of an infected Ixodes scapularis tick. We previously discovered a B. burgdorferi infectivity gene, bbk13, that facilitates mammalian infection by promoting spirochete population expansion in the skin inoculation site. Initial characterization of bbk13 was carried out using an intradermal needle inoculation model of mouse infection, which does not capture the complex interplay of the pathogen-vector-host triad of natural transmission. Here, we aimed to understand the role of bbk13 in the enzootic cycle of B. burgdorferi. B. burgdorferi spirochetes lacking bbk13 were unable to be acquired by naive larvae fed on needle-inoculated mice. Using a capsule feeding approach to restrict tick feeding activity to a defined skin site, we determined that delivery by tick bite alleviated the population expansion defect in the skin observed after needle inoculation of Δbbk13 B. burgdorferi. Despite overcoming the early barrier in the skin, Δbbk13 B. burgdorferi remained attenuated for distal tissue colonization after tick transmission. Disseminated infection by Δbbk13 B. burgdorferi was improved in needle-inoculated immunocompromised mice. Together, we established that bbk13 is crucial to the maintenance of B. burgdorferi in the enzootic cycle and that bbk13 is necessary beyond early infection in the skin, likely contributing to host immune evasion. Moreover, our data highlight the critical interplay between the pathogen, vector, and host as well as the distinct molecular genetic requirements for B. burgdorferi to survive at the pathogen-vector-host interface and achieve productive disseminated infection.

Myeloid-derived suppressor cell and macrophage exert distinct angiogenic and immunosuppressive effects in breast cancer.

The immunosuppressive tumor microenvironment is a key obstacle to hinder a cancer immunotherapy. Myeloid-derived suppressor cells (MDSCs) have been considered as a major player in immunosuppression. In this study, we find that tumor-infiltrating MDSCs (tiMDSCs) are less immunosuppressive than tumor-associated macrophages (TAMs) in multiple murine orthotopic breast tumor models. Compared to TAMs, tiMDSCs produce higher levels of pro-inflammatory factors and lower levels of anti-inflammatory factors. Furthermore, tiMDSCs are preferentially located in hypoxic areas and are more pro-angiogenic than TAMs. Consistent with these functional disparities, a shift from tiMDSCs to TAMs is observed during the progression of breast cancer. Moreover, infiltration of tiMDSCs is also noted in distal colonization of breast cancer cells in the lung. Taken together, our findings indicate that tiMDSCs are more pro-angiogenic and promote tumor initiation, while TAMs are more immunosuppressive and facilitate tumor immune evasion. This study suggests that selectively targeting on TAMs could alleviate the immunosuppressive tumor microenvironment and potentiate cancer immunotherapy.

Abstract 1134: Slug promotes survival during metastasis through suppression of Puma-mediated apoptosis

Abstract Tumor cells must overcome apoptosis to survive throughout metastatic dissemination and distal organ colonization. Here we show in the Polyoma Middle T mammary tumor model that N-cadherin causes Slug upregulation, which promotes carcinoma cell survival. Slug was dramatically upregulated in distant metastases relative to primary tumors. Consistent with a role in metastasis, Slug knockdown in metastatic carcinoma cells suppressed pulmonary colonization, due to reducing cell survival, but had no effect on tumor cell invasion or extravasation. In support of a role in cell survival, Slug inhibition by shRNA, sensitized tumor cells to apoptosis by genotoxic stress, resulting in caspase-3 activation and PARP cleavage. Furthermore, the effects of Slug on cell survival were due to direct repression of the pro-apoptotic gene, Puma. Importantly, the survival function of the SLUG-PUMA axis was confirmed in human breast cancer cells, where Slug knockdown increased Puma expression and inhibited lung colonization. Thus, our study demonstrates a pivotal role for Slug in cell survival, which is beyond its role in epithelial-to-mesenchymal transition, implying that disruption of the SLUG-PUMA axis may impinge on the survival of metastatic cancer cells. Citation Format: Rachel Hazan. Slug promotes survival during metastasis through suppression of Puma-mediated apoptosis. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1134. doi:10.1158/1538-7445.AM2014-1134

Slug promotes survival during metastasis through suppression of Puma-mediated apoptosis.

Tumor cells must overcome apoptosis to survive throughout metastatic dissemination and distal organ colonization. Here, we show in the Polyoma Middle T mammary tumor model that N-cadherin (Cdh2) expression causes Slug (Snai2) upregulation, which in turn promotes carcinoma cell survival. Slug was dramatically upregulated in metastases relative to primary tumors. Consistent with a role in metastasis, Slug knockdown in carcinoma cells suppressed lung colonization by decreasing cell survival at metastatic sites, but had no effect on tumor cell invasion or extravasation. In support of this idea, Slug inhibition by shRNA sensitized tumor cells to apoptosis by DNA damage, resulting in caspase-3 and PARP cleavage. The prosurvival effect of Slug was found to be caused by direct repression of the proapoptotic gene, Puma (Bbc3), by Slug. Consistent with a pivotal role for a Slug-Puma axis in metastasis, inhibition of Puma by RNA interference in Slug-knockdown cells rescued lung colonization, whereas Puma overexpression in control tumor cells suppressed lung metastasis. The survival function of the Slug-Puma axis was confirmed in human breast cancer cells, where Slug knockdown increased Puma expression and inhibited lung colonization. This study demonstrates a pivotal role for Slug in carcinoma cell survival, implying that disruption of the Slug-Puma axis may impinge on the survival of metastatic cells.

Bacteriophage antimicrobial-lock technique for staphylococcus aureus central venous catheter-related infection: an in-vivo evaluation

Purpose Bacteriophages are viruses that selectively infect and kill bacteria. The purpose of this project was to determine whether a bacteriophage antimicrobial lock technique can reduce bacterial colonization and biofilm formation on indwelling central venous catheters in a rabbit model. Materials and Methods This study was performed in 10 female New Zealand white rabbits (weight range 3-4 kg). Broviac catheters (4.2 French, BARD access systems, NJ) were inserted into the jugular vein under image guidance and tunneled in an intrascapular position. Catheters were then inoculated for 24h with broth culture of Methicillin sensitive staphylococcus aureus (0.5 McFarland standard). The inoculate was aspirated and rabbits were randomized into two equal groups for 24h: (i) untreated controls (heparinized saline lock), (ii) Bacteriophage antimicrobial-lock (Staphylococcal Bacteriophage K, propagated titer > 10 8 ). At the completion of the experiment blood cultures were obtained via peripheral veins, the catheters were removed for quantitative culture and scanning electron microscopic analyses, and the animals were sacrificed. Statistical testing for substantial differences in distal catheter segment colonization was carried out using the rank sum test. Results Mean distal catheter segment colony forming units (CFU) per cm 2 as a measure of biofilm was significantly decreased in experimental animals compared to controls (control 1.2 × 10 5 CFU/cm 2 , experimental 7.58 × 10 3 , P=0.016). Scanning electron microscopic analysis of the catheter segments demonstrated qualitative reduction of biofilm in treated catheter segments compared to untreated controls. Blood culture results were not significantly different between the groups (control 3/5 positive (60%), experimental 4/5 positive (80%), (p=1.0). Conclusion In a rabbit model, treatment of infected central venous catheters with a bacteriophage antimicrobial-lock technique significantly reduced bacterial colonization and biofilm presence. Our data suggests that bacteriophage lock solution may be a feasible strategy for prevention and treatment of central venous catheter infections.

Beta Defensin-2 Is Reduced in Central but Not in Distal Airways of Smoker COPD Patients

BackgroundAltered pulmonary defenses in chronic obstructive pulmonary disease (COPD) may promote distal airways bacterial colonization. The expression/activation of Toll Like receptors (TLR) and beta 2 defensin (HBD2) release by epithelial cells crucially affect pulmonary defence mechanisms.MethodsThe epithelial expression of TLR4 and of HBD2 was assessed in surgical specimens from current smokers COPD (s-COPD; n = 17), ex-smokers COPD (ex-s-COPD; n = 8), smokers without COPD (S; n = 12), and from non-smoker non-COPD subjects (C; n = 13).ResultsIn distal airways, s-COPD highly expressed TLR4 and HBD2. In central airways, S and s-COPD showed increased TLR4 expression. Lower HBD2 expression was observed in central airways of s-COPD when compared to S and to ex-s-COPD. s-COPD had a reduced HBD2 gene expression as demonstrated by real-time PCR on micro-dissected bronchial epithelial cells. Furthermore, HBD2 expression positively correlated with FEV1/FVC ratio and inversely correlated with the cigarette smoke exposure. In a bronchial epithelial cell line (16 HBE) IL-1β significantly induced the HBD2 mRNA expression and cigarette smoke extracts significantly counteracted this IL-1 mediated effect reducing both the activation of NFkB pathway and the interaction between NFkB and HBD2 promoter.ConclusionsThis study provides new insights on the possible mechanisms involved in the alteration of innate immunity mechanisms in COPD.

Neuregulin 1 Type III/ErbB Signaling Is Crucial for Schwann Cell Colonization of Sympathetic Axons

Analysis of Schwann cell (SC) development has been hampered by the lack of growing axons in many commonly used in vitro assays. As a consequence, the molecular signals and cellular dynamics of SC development along peripheral axons are still only poorly understood. Here we use a superior cervical ganglion (SCG) explant assay, in which axons elongate after treatment with nerve growth factor (NGF). Migration as well as proliferation and apoptosis of endogenous SCG-derived SCs along sympathetic axons were studied in these cultures using pharmacological interference and time-lapse imaging. Inhibition of ErbB receptor tyrosine kinases leads to reduced SC proliferation, increased apoptosis and thereby severely interfered with SC migration to distal axonal sections and colonization of axons. Furthermore we demonstrate that SC colonization of axons is also strongly impaired in a specific null mutant of an ErbB receptor ligand, Neuregulin 1 (NRG1) type III. Taken together, using a novel SC development assay, we demonstrate that NRG1 type III serves as a critical axonal signal for glial ErbB receptors that drives SC development along sympathetic axons.

The Consistency and Clinical Significance between Bronchoscopic Samples and Endotracheal or Tracheostomic Aspirates in Severe Pneumonia Under Mechanical Ventilation

Background: Distal airway bacterial colonization occurs more frequently in patients with endotracheal tubes or tracheostomy of intensive care units (ICU) care. In general, bronchoscopic samples are considered more accurate than transtracheal aspirates. In this study, we evaluated the consistency and clinical significance between bronchoscopic samples and transtracheal aspirates (TTA) in severe pneumonia under mechanical ventilation. Methods: We investigated the consistency between bronchoscopic samples and transtracheal aspirates among patients with endotracheal tubes or tracheostomy, retrospectively. Fiberoptic bronchoscopy was performed in 212 patients with mechanical ventilation via endotracheal tube or tracheostomy between January 1st, 2004 and December 31th, 2008 in ICU at Ewha Womans University Hospital. We evaluated consistency in terms of true pathogen according to the arbitrary ICU days progress. Results: Among the 212 enrolled patients, 113 (53%) had consistency between bronchoscopic samples and transtracheal aspirates. When evaluated alteration trends in consist ency according to ICU stay, the consistency was maintained for 5 to 9 ICU days with statistical significance (p ＜ 0.05) since adjusting for age, sex, and combined risk factors. Consistency in sampling status between the endotracheal tube and tracheostomy was also evaluated, however, there was no statistical significance (OR 1.9 vs. 1, 95% CI = 0.997−3.582, p = 0.051). Conclusions: Shorter hospital stay (within 9 d ays of ICU stay) had higher probability of consistency between bronchoscopic samples and TTA samples. TTA may be as confident as bronchoscopic samples in patients of pneumonia under mechanical ventilation with shorter ICU stays, especially less than 10 days.

Distal Airways Bacterial Colonization and Inflammatory Pattern in Children With Chronic Lung Diseases

Distal Airways Bacterial Colonization and Inflammatory Pattern in Children With Chronic Lung Diseases

Temporally Distinct Requirements for Endothelin Receptor B in the Generation and Migration of Gut Neural Crest Stem Cells

Loss of Endothelin-3/Endothelin receptor B (EDNRB) signaling leads to aganglionosis of the distal gut (Hirschsprung's disease), but it is unclear whether it is required primarily for neural crest progenitor maintenance or migration. Ednrb-deficient gut neural crest stem cells (NCSCs) were reduced to 40% of wild-type levels by embryonic day 12.5 (E12.5), but no further depletion of NCSCs was subsequently observed. Undifferentiated NCSCs persisted in the proximal guts of Ednrb-deficient rats throughout fetal and postnatal development but exhibited migration defects after E12.5 that prevented distal gut colonization. EDNRB signaling may be required to modulate the response of neural crest progenitors to migratory cues, such as glial cell line-derived neurotrophic factor (GDNF). This migratory defect could be bypassed by transplanting wild-type NCSCs directly into the aganglionic region of the Ednrb sl/sl gut, where they engrafted and formed neurons as efficiently as in the wild-type gut.

The consequences of suppression of anaerobic bacteria.

Anaerobic bacteria such as Bacteroides fragilis, Peptostreptococcus species, and Fusobacterium species, when accompanied by aerobic bacteria or in the presence of dead tissue, can cause severe infections. This article discusses the most common type of anaerobic infection, i.e., infection after colonic contamination of the abdominal cavity and soft tissues. Colonic anaerobes rarely cause infections as solitary pathogens. Mixed infections of aerobes and anaerobes are treated by source control, surgical drainage and debridement, and combination antibiotic therapy. Antimicrobial treatment should cover both anaerobes and aerobes; treatment of mixed infections with anti-anaerobic agents alone is likely to result in abscess formation. Recent trends toward cost cutting and the advent of antibiotics with good coverage of both aerobes and relevant pathogenic anaerobes have led to increased single-agent therapy with cefoxitin, cefotetan, ampicillin/sulbactam, imipenem/cilastatin, ticarcillin/clavulanate, trovafloxacin/alatrofloxacin, and piperacillin/tazobactam. In the past 15 years, research has begun to focus on the gut barrier, particularly on the beneficial effects of anaerobic microflora. Directing antibiotic therapy against the anaerobe when it is involved in clinical infection is important; however, the negative consequences of anti-anaerobic antibiotic therapy on the beneficial effects of normal distal gut colonization must also be considered.

Outbreak of nosocomial urinary tract infections due to Pseudomonas aeruginosa in a paediatric surgical unit associated with tap-water contamination

An outbreak of 14 cases of urinary tract infections by Pseudomonas aeruginosa, including six symptomatic infections, occurred from September to November 1994 in a paediatric surgical unit. During the outbreak, urine samples from patients and multiple samples from the environment of patients were tested for the presence of P. aeruginosa. Bacterial isolates were studied by pulsed field gel electrophoresis. Genotypic analysis showed that most of the isolates from children were different. Multiple P. aeruginosa isolates were also found in the tap water, as the only putative source of contamination. Two of these isolates were identified in two infected patients, indicating possible direct contamination of patients via tap water and this was related to the distal colonization of faucets. Bacteria were eradicated from tap water by replacement of taps. The cluster of cases of P. aeruginosa urinary infection was, therefore, related to multiple contaminations through tap water. These results illustrate an unexpected risk of nosocomial infection and emphasizes the importance of checking tap water to prevent bacterial contamination through handwashing in contaminated water.

Eradicating Legionella From Hospital Water

<h3>To the Editor.</h3> —The report by the Centers for Disease Control and Prevention (CDC) on transmission of nosocomial legionnaires disease¹documents failure to eradicate<i>Legionella</i>organisms from the water distribution systems of 2 hospitals despite the use of hyperchlorination, thermal disinfection, and/ or metal ionization. The efficacy of these decontamination methods can be compromised by a variety of factors. The duration of thermal decontamination (160°F/71°C at the tap) used in hospital Y was only 5 minutes. The original report on the use of this method specified a 30-minute flush at the tap.²Thus, failure to maintain the elevated temperature for a sufficient period undoubtedly contributed to this failure to eradicate<i>Legionella</i>. In fact, when one California hospital applied thermal eradication with a flush time of 5 minutes, as recommended by the CDC, distal site colonization by<i>Legionella</i>organisms was unaffected. When the process was repeated using a 30-minute flush

Bacterial colonization of distal airways in healthy subjects and chronic lung disease: a bronchoscopic study.

In contrast to the healthy population, distal airway bacterial colonization may occur in patients with chronic lung diseases, who often have altered pulmonary defences. However, the information dealing with this issue is insufficient and is based mainly on nonspecific samples, such as sputum cultures. Using quantitative cultures of bronchoscopic protected specimen brush (PSB) and bronchoalveolar lavage (BAL) samples, we studied the bacterial colonization of distal airways in 16 healthy subjects, 33 patients with bronchogenic carcinoma, 18 with chronic obstructive pulmonary disease (COPD), 17 with bronchiectasis, and 32 with a long-term tracheostomy due to laryngeal carcinoma. All patients were without exacerbation, and free from antibiotic treatment at least 1 month before the study protocol. Thresholds for quantitative cultures to define colonization were > or = 10(2) colony-forming units (cfu) x mL(-1) for PSB and > or = 10(3) cfu x mL(-1) for BAL. Only one healthy subject was colonized by a potential pathogenic microorganism (PPM) (Staphylococcus aureus 4x10(2) cfu x mL(-1) in a PSB culture). Colonization was observed in 14 (42%) bronchogenic carcinoma patients (19 non-PPMs, and 10 PPMs); in 15 (83%) COPD patients (22 non-PPMs and 7 PPMs); in 15 (88%) bronchiectasis patients (20 non-PPMs and 13 PPMs); and in 15 (47%) long-term tracheostomy patients (5 non-PPMs and 13 PPMs). The two most frequent non-PPMs isolated in all groups studied were Streptococcus viridans and Neisseria spp. Haemophilus spp., Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis were the most frequent PPMs isolated in bronchogenic carcinoma, COPD, bronchiectasis and long-term tracheostomized patients, respectively. Pseudomonas aeruginosa colonization was infrequent in all the groups. Our results show that distal airway bacterial colonization is a frequent feature in stable patients with chronic lung diseases and also in patients with long-term tracheostomy. However, the pattern of colonization differs among groups studied. The knowledge of different colonization patterns may be important for future antibiotic prophylactic strategies and for the empirical antibiotic regimens when exacerbations occur in these patients.

An experimental analysis of the developmental capacities of distal parts of avian leg buds

The development, differentiation, and pattern formation of isolated distal parts of avian leg buds that had grown ectopically on the chorioallantoic membrane (CAM) or in the coelomic cavity were studied. The grafts grown on the CAM invariably gave rise to cartilage and soft connective tissue. In some cases muscle tissue was also found. The CAM grafts did not undergo overt morphogenesis and pattern formation. A high percentage of grafts grown in the coelomic cavity showed a close approximation to normal limbs. The presence of proximal structures depended on the stage of development of the donor at the time of the operation, on the size of the grafts, and on the site to which the graft was attached within the coelom. The presence of anteroposterior structures depended on the shape of the graft. The pattern formation of this axis was found to be independent of the presence of the zone of polarizing activity at the proximal posterior border of the bud. The distance from the tip of the bud to the line of most distal colonization by myogenic cells was determined. The speed of migration of the myogenic cells can be considered to be constant. In muscleless legs, tendons developed at the levels of the phalanges and the tarsometatarse. They degenerated, however, in the absence of muscle from day 9 on, from proximal to distal areas. CAM grafts as well as coelomic grafts were well vascularized. The endothelial cells of the blood vessels were of host origin. In coelomic grafts, nerves were present with Schwann cells of host origin. The nerves and blood vessels showed a distribution that resembled that in normal legs.

Inoculum potential of Gaeumannomyces Graminis var. tritici and disease potential of wheat roots

The effects of pathogen-determined factors on the progressive colonization of seminal roots of wheat by Gaeumannomyces graminis var. tritici were monitored for 18 days following direct inoculation of the roots by uniform, artificial inoculum units. The factors examined were secondary infection of an infected root, variation of the inoculum dose at the site of inoculation, and variation of the period of inoculum contact with roots. Secondary infections spread more slowly along roots than proximal, primary infections. Greater age of the host plant at the time of inoculation as well as the presence of primary infections contributed to the slower progress of these later infections. Secondary infections did not affect the course of primary infections but growth of infected roots ceased soon after the second inoculation. Trebling the inoculum dose at the sites of inoculation resulted in faster proximal colonization of the host roots but distal colonization and the advance of dark stelar discolouration were unaffected. By contrast, reducing the time of contact between inoculum and roots from 18 days to 3 days not only resulted in reduced proximal colonization by superficial runner hyphae but also led to a substantial reduction in distal colonization. Removal of inoculum units after 3 days also reduced the proportion of inoculations achieving dark discolouration of the stele during the period of observation. The effects of the treatments are discussed in relation to the concepts of inoculum potential and disease potential.