The Role of Pectobacterium atrosepticum Exopolysaccharides in Plant–Pathogen Interactions

The phytopathogenic bacterium Pectobacterium atrosepticum (Pba), one of the members of the soft rot Pectobacteriaceae, forms biofilm-like structures known as bacterial emboli when colonizing the primary xylem vessels of the host plants. The initial extracellular matrix of the bacterial emboli is composed of the host plant’s pectic polysaccharides, which are gradually substituted by the Pba-produced exopolysaccharides (Pba EPS) as the bacterial emboli “mature”. No information about the properties of Pba EPS and their possible roles in Pba-plant interactions has so far been obtained. We have shown that Pba EPS possess physical properties that can promote the maintenance of the structural integrity of bacterial emboli. These polymers increase the viscosity of liquids and form large supramolecular aggregates. The formation of Pba EPS aggregates is provided (at least partly) by the acetyl groups of the Pba EPS molecules. Besides, Pba EPS scavenge reactive oxygen species (ROS), the accumulation of which is known to be associated with the formation of bacterial emboli. In addition, Pba EPS act as suppressors of the quantitative immunity of plants, repressing PAMP-induced reactions; this property is partly lost in the deacetylated form of Pba EPS. Overall, our study shows that Pba EPS play structural, protective, and immunosuppressive roles during Pba–plant interactions and thus should be considered as virulence factors of these bacteria.

Abstract TP284: Association of Hemorrhagic Stroke with Recurrence Stroke caused by Infective Endocarditis

Objective: Infective endocarditis causes not only brain infarcts and infection triggered by bacterial emboli, but also hemorrhagic stroke by inflamed arteries or aneurysms prone to rupture, when we make the requisite open-heart surgery delayed. We examined if hemorrhagic stroke caused by infective endocarditis and complicated microbleeds were associated with subsequent recurrent stroke. Methods: We conducted the observational study on 36 consecutive patients (19 men, aged 18-84, median 53) with acute symptomatic stroke caused by definite or possible infective endocarditis according to the Duke University criteria from October 2005 to April 2012. Brain hemorrhage/infarcts responsible for neurological signs and asymptomatic microbleeds were verified by CT and diffusion/T2*-weighted MRI. We had followed each patient as for recurrent symptomatic stroke for 3 months. Results: Out of 36, hemorrhagic stroke was noted in 15 patients, 13 of whom had simultaneous infarcts, and the other 21 patients showed pure ischemic stroke and TIA. Fifteen patients had asymptomatic microbleeds. Fourteen patients experienced recurrent stroke, which consisted of SAH in 4, hematoma/massive hemorrhagic transformation from infarcts in 4 and pure infarction in 6. Ten patients (71%) in the recurrent group had hemorrhagic stroke for initial attack, while 5 in 22 (23%) of the non-recurrent group did (p<0.01). The recurrent group had a higher average age (18-82 years, median 68 years) than the non-recurrent group (23-75 years, median 51 years). No statistically significant differences between the non-recurrent and the recurrent groups were observed of a proportion of patients that were female and had, infarction, microbleeds, hypertension, diabetes, antithrombotic treatment, attachment of 10-mm or larger vegetations to damaged valves, isolation of staphylococcus aureus from blood, embolization to other organs than the brain and complication of meningitis/abscess. Conclusions: Hemorrhagic stroke, but not asymptomatic microbleeds, was associated with recurrent stroke after infective endocarditis. Duration of waiting for the safe heart operation after symptomatic hemorrhagic stroke can be in face of recurrent stroke.

Streptococcal Bacterial Endocarditis in Chickens

Nineteen of 20 chickens with bacterial endocarditis characterized by well-developed vegetations on valves of the left side of the heart had lesions in the central nervous system. Anhemolytic streptococci were implicated as etiologic agents in 11 spontaneous cases, and S. faecalis var. liquefaciens was used to produce the disease experimentally in the 9 other birds. The CNS lesions were related to bacterial emboli, and included multifocal segmental inflammation of arteries, arterioles, and capillaries, with associated perivascular and intracerebral inflammatory foci, infarcts of brain tissue, and leptomeningitis.

About Endocarditis lenta with multiple septic skin lesions

One of the most permanent and very important features in the clinical picture of endocarditis lenta is, as you know, a tendency to embolism in various organs. Emboli can be carried by the blood stream into various organs: the spleen, kidneys, brain, etc., as a result of which a complex symptom complex with the participation of a number of organs is obtained, which is so characteristic of the clinical picture of protracted septic endocarditis. Embolism in any organ and the symptoms caused by it are often the cause of those complaints with which the patient first goes to the doctor, but often embolism in the organs important for life, for example, the brain, serves as the last blow that interrupts the life of these patients. From numerous works devoted in recent years to the etiology, clinic and pathological and anatomical picture of endocarditis lenta (Hess, Stahl, Zimnitsky, Nevyadomsky, Mindlin, Th. Horder, etc.), it can be seen that embolism in the spleen and kidney is most often observed, less often into the brain, limbs, retina and very rarely into the skin. In this case, the participation of the skin in the picture of the disease is reduced mainly to the presence of hemorrhages, which are an essential symptom of this clinical form. These hemorrhages in the skin and mucous membranes are closely related to the toxic changes in the vessels present in this disease, which entail their slight vulnerability (Zimintsky, Strazhesko, Skulsky, Mindlin), and do not depend, as was previously thought, on bacterial emboli (Stahl ). Real septic metastases with the formation of multiple purulent foci in the skin itself are evidently extremely rare. At least, in the literature available to me, I could not find a single such case. In view of this, we observed in the clinic prof. Luria's case of multiple septic skin lesions in endocarditis tenta is, as it seems to us, of known clinical interest.

STUDIES IN GLOMERULONEPHRITIS

Repeated injections into the blood stream of streptococci and stapnylococci derived from cases of scarlet fever, and of Bacillus coli communior failed to produce typical glomerulonephritis even when immune antibodies could be demonstrated in the serum in high dilutions. Bacteriolysis of streptococci was not found by the usual tests in intro or by the Pfeiffer procedure. It is therefore concluded that the weight of evidence is against the theory that glomerulonephritis is due to immune bacteriolysis of streptococci. The experiments also failed to give any support to the hypothesis of allergy or. of sensitization as a factor in the production of the disease. Evidence is presented to show that bacterial emboli are rapidly removed from the glomerular capillaries by leukocytes, and that this embolism, even after injections of enormous quantities of bacteria, affects but a small proportion of the glomeruli. It is again suggested that a circulating poison in the soluble state is responsible directly for the disease in question.

TOXIN AND ANTITOXIN OF AND PROTECTIVE INOCULATION AGAINST BACILLUS WELCHII

Five cultures of Bacillus welchii have been studied and compared Four came from infected wounds in the western theatre of war, and one was obtained from a personal article of clothing. Each culture possesses the essential characteristics ascribed to that group of bacteria. The infectious processes caused by the five cultures in rabbits, guinea pigs, and pigeons, are local in character; and very few or no bacilli enter or are found in the general blood stream during life or immediately after death. Glucose broth cultures, injected intravenously, are fatal to rabbits. Death occurs, almost immediately or after a few hours. Agglutinative bacterial emboli have been ruled out as the cause of death, as has been an acid intoxication. The fluid part of the culture acts in the same manner as the full culture and irrespective of neutralization with sodium hydroxide. The full cultures and supernatant fluid are hemolytic when injected directly into the circulation of rabbits and pigeons, and the acute death produced may be ascribed to a massive destruction of red corpuscles. The passage of the fluid portion of glucose broth cultures through Berkefeld filters reduces materially the hemolytic and poisonous effects. Cultures of the Welch bacilli in plain broth to which sterile pigeon or rabbit muscle is added are highly toxic, and the toxicity is not noticeably diminished by Berkefeld filtration. The filtrates are hemolytic when injected intravenously and inflaming and necrotizing when injected subcutaneously and intramuscularly. The local lesions produced in the breast muscles of the pigeon closely resemble those caused by infection with the bacilli. The toxicity of these filtrates is not affected by neutralization with sodium hydroxide, but is materially reduced by heating to 62°C. and entirely removed by heating to 70°C. for 30 minutes. Successive injections of carefully graded doses of this toxic filtrate in pigeons and rabbits give rise to active immunity. The blood taken from the immunized rabbits is capable of neutralizing the toxic filtrate in vivo and in vitro. The filtrate has therefore been designated as toxin and the immune serum as antitoxin. The antitoxin neutralizes the toxin in multiple proportions. Hence the latter would seem to possess the properties of an exotoxin. Moreover, it neutralizes the hemolytic as well as the locally .injurious toxic constituent. Antitoxic serum prepared from a given culture of Bacillus welchii is neutralizing for the toxins yielded by the other four cultures of that microorganism. The antitoxin is protective and curative against infection with the spore and the vegetative stages of Bacillus welchii in pigeons. The limits of the protective and curative action are now under investigation.

GLOMERULAR LESIONS OF SUBACUTE BACTERIAL ENDOCARDITIS

1. In most cases of chronic or subacute bacterial endocarditis due to the endocarditis coccus (Streptococcus viridans), there exists a distinctive pathological lesion in some of the glomeruli due to bacterial emboli. 2. The salient features of the pathological picture are first, the involvement of one or more loops of a variable number of glomeruli; secondly, the absence of any visible disease in the uninvolved glomeruli and in the uninvolved portions of affected glomeruli; and thirdly, the association in most of the bacterial cases of all the various stages of the glomerular process often seen in a single microscopical section. 3. The lesion does not occur in cases of acute endocarditis, and up to the present time it has been absent in cases of subacute bacterial endocarditis due to organisms other than the endocarditis coccus. 4. In a group of cases having vegetations that are typical of those in the active stage of subacute endocarditis (except that they are free from bacteria and healing or healed), the healed stage of this distinctive glomerular lesion is present, although it is less extensive than in the active bacterial cases. 5. These cases, therefore, are most probably examples of subacute bacterial endocarditis due originally to the endocarditis coccus, but in which the endocardial vegetations have become free from bacteria rather early in their course and are now healing or healed, as claimed by Harbitz and Libman. 6. During the active bacterial stage of the disease, if the glomerular lesions are not too numerous, the only symptoms produced will be an almost constant hematuria, usually demonstrable only microscopically. If the glomerular lesions are very numerous, symptoms resembling those of subacute hemorrhagic nephritis may occur and may even cause a fatal issue. If the glomerular lesions are very numerous but not sufficient to cause death, and the cardiac lesion should go on to healing, a contracted kidney, secondary to the glomerular lesion, may subsequently ensue and produce the typical symptoms and death. In such a case, the finding of the healed or healing lesion of subacute bacterial endocarditis will be accidental.