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PubMed1990

Gene-for-gene complementarity in plant-pathogen interactions.

The cloning of avirulence genes has greatly aided our understanding of plant-pathogen specificity. It has proven that the gene-for-gene relationship first noted by Flor is correct--single avirulence gene encoding single protein products indeed are the genetic elements that interact with plant disease resistance genes. Furthermore, firm genetic evidence has provided insight into how two cloned avirulence genes (the TMV coat gene and avrD) cause the HR. The differences in structure of pathogen elicitors also indicates that plants have evolved diverse recognitional mechanisms to detect pathogens. It is appealing to speculate, therefore, that elicitors represent the plant equivalent of antigens in vertebrates. Another consequence of these results has been the establishment of firm genetic and biochemical evidence supporting the elicitor-receptor model for recognition of incompatible pathogen races by plants. In both TMV and bacterial pathogens, we are also beginning to understand how avirulence genes are altered to confound plant recognition of the pathogen. The next few years should yield additional information on avirulence gene structure as well as the important questions of their function in the pathogen and the molecular mechanisms whereby plant recognition occurs. The marked successes in cloning avirulence genes underscore only more forcefully the pressing need to clone and characterize plant disease resistance genes. Certainly an understanding of these genes is required to further our basic knowledge of active defense in plants and to permit their manipulation for improved control of plant diseases in practical agriculture.

Cloning, Molecular↗

PubMed2001

New (and used) approaches to the study of fungal pathogenicity.

The fungi are the most economically important plant pathogens and continue to be the focus of extensive research with a wide variety of methodologies. Enhancements in microscopy techniques have increased our ability to visualize the intimate interaction of fungi and their host plants. Improving methods allow pharmacological inhibition and genetic dissection of the determinants of fungal pathogenicity in a gene-by-gene approach. Identification and analysis of genes differentially transcribed in ways pertinent to pathogenicity continues to be a frequent research approach. Genome-wide analysis is gaining favor in biological research and fungal plant pathogens are no exception. Several industrial research groups are exploring fungal plant pathogenesis based on genomic sequence data and genome-wide mutagenesis. In March 2001 the first publicly available complete genome of a filamentous fungus (Neurospora crassa) was released. N. crassa is of course a saprophyte and there is no complete sequence available for a plant pathogenic fungus in public databases. However, freely accessible entire genome sequences for both plant pathogenic fungi and their hosts are on the horizon. Sequence availability promises to revolutionize the rate at which data relevant to disease processes will be accrued. In this review we describe approaches currently applied to the study of plant pathogenic fungi and explore developments of potential future benefit with existing technologies not yet applied to this group of important organisms.

Fungi↗

PubMed2006

The dawn of fungal pathogen genomics.

Recent advances in sequencing technologies have led to a remarkable increase in the number of sequenced fungal genomes. Several important plant pathogenic fungi are among those that have been sequenced or are being sequenced. Additional fungal pathogens are likely to be sequenced in the near future. Analysis of the available genomes has provided useful information about genes that may be important for plant infection and colonization. Genome features, such as repetitive sequences, telomeres, conserved syntenic blocks, and expansion of pathogenicity-related genes, are discussed in detail with Magnaporthe oryzae (M. grisea) and Fusarium graminearum as examples. Functional and comparative genomic studies in plant pathogenic fungi, although still in the early stages and limited to a few pathogens, have enormous potential to improve our understanding of the molecular mechanisms involved in host-pathogen interactions. Development of advanced genomics tools and infrastructure is critical for efficient utilization of the vast wealth of available genome sequence information and will form a solid foundation for systems biology studies of plant pathogenic fungi.

Fungi↗

PubMed2006

Comparative genomics reveals what makes an enterobacterial plant pathogen.

The bacterial family Enterobacteriaceae contains some of the most devastating human and animal pathogens, including Escherichia coli, Salmonella enterica and species of Yersinia and Shigella. These are among the best-studied of any organisms, yet there is much to be learned about the nature and evolution of interactions with their hosts and with the wider environment. Comparative and functional genomics have fundamentally improved our understanding of their modes of adaptation to different ecological niches and the genes that determine their pathogenicity. In addition to animal pathogens, Enterobacteriaceae include important plant pathogens, such as Erwinia carotovora subsp. atroseptica (Eca), the first plant-pathogenic enterobacterium to be sequenced. This review focuses on genomic comparisons between Eca and other enterobacteria, with particular emphasis on the differences that exemplify or explain the plant-associated lifestyle(s) of Eca. Horizontal gene transfer in Eca may directly have led to the acquisition of a number of determinants that mediate its interactions, pathogenic or otherwise, with plants, offering a glimpse into its evolutionary divergence from animal-pathogenic enterobacteria.

Enterobacteriaceae↗

PubMed2025

Diversification of an emerging bacterial plant pathogen; insights into the global spread of Xanthomonas euvesicatoria pv. perforans.

Emerging and re-emerging plant diseases continue to present multifarious threats to global food security. Considerable recent efforts are therefore being channeled towards understanding the nature of pathogen emergence, their spread and evolution. Xanthomonas euvesicatoria pv. perforans (Xep), one of the causal agents of bacterial spot of tomato, rapidly emerged and displaced other bacterial spot xanthomonads in many tomato production regions around the world. In less than three decades, it has become a dominant xanthomonad pathogen in tomato production systems across the world and presents a compelling example for understanding diversification of recently emerged bacterial plant pathogens. Although Xep has been continuously monitored in Florida since its discovery, the global population structure and evolution at the genome-scale is yet to be fully explored. The objectives of this work were to determine genetic diversity globally to ascertain if different tomato production regions contain genetically distinct Xep populations, to examine genetic relatedness of strains collected in tomato seed production areas in East Asia and other production regions, and to evaluate variation in type III secretion effectors, which are critical pathogenicity and virulence factors, in relationship to population structure. We used genome data from 270 strains from 13 countries for phylogenetic analysis and characterization of type III effector gene diversity among strains. Our results showed notable genetic diversity in the pathogen. We found genetically similar strains in distant tomato production regions, including seed production regions, and diversification over the past 100 years, which is consistent with intercontinental dissemination of the pathogen in hybrid tomato production chains. Evolution of the Xep pangenome, including the acquisition and loss of type III secreted effectors, is apparent within and among phylogenetic lineages. The apparent long-distance movement of the pathogen, together with variants that may not yet be widely distributed, poses risks of emergence of new variants in tomato production.

Xanthomonas↗

PubMed2003

Serious bacterial infections in febrile infants younger than 90 days of age: the importance of ampicillin-resistant pathogens.

BACKGROUND: Intrapartum antibiotic prophylaxis against group B Streptococcus (GBS) has reduced the occurrence of serious bacterial infections (SBI) in young infants caused by GBS. Recommendations for initial antibiotic therapy for the febrile infant 1 to 90 days old were developed when infections with GBS were common and antibiotic resistance was rare. OBJECTIVE: To document the pathogens responsible for SBI in recent years in febrile infants 1 to 90 days old and the antibiotic susceptibility of these organisms. METHODS: The results of bacterial cultures from infants 1 to 90 days old evaluated for fever at Primary Children's Medical Center in Salt Lake City, Utah, between July 1999 and April 2002 were analyzed. Antibiotic susceptibility profiles were collected and patient records were reviewed to determine if initial antibiotic therapy was changed following the identification of the organism. RESULTS: Of 1298 febrile infants enrolled from the Primary Children's Medical Center emergency department, 105 (8%) had SBI. The mean age of the infants with SBI was 39 days (range 2-82 days) and 2 (2%) were <7 days. SBI included urinary tract infection (UTI; 67%), bacteremia (16%), bacteremia and UTI (6%), bacteremia and meningitis (5%), meningitis (2%), abscess (2%), meningitis and UTI (1%), and meningitis and gastroenteritis (1%). Eighty-three (79%) of 105 episodes of SBI were caused by Gram-negative bacteria, including 92% of UTI, 54% of bacteremia, and 44% of meningitis cases. The most common pathogen was Escherichia coli (61%). Other Gram-negative pathogens were responsible for 19% of SBI. Staphylococcus aureus was the most common Gram-positive pathogen, causing 8% of SBI. GBS accounted for 6% of SBI. Of the 105 pathogens, 56 (53%) were resistant to ampicillin. Of the pathogens causing meningitis, UTI, and bacteremia, 78%, 53%, and 50%, respectively, were resistant to ampicillin. Antibiotic therapy was changed in 54% of cases of SBI following identification of the organism. CONCLUSIONS: In Utah, ampicillin-resistant Gram-negative bacteria are the most common cause of SBI in febrile infants <90 days old. This finding impacts antibiotic selection, especially in cases of meningitis. Local surveillance of pathogens and antibiotic susceptibility patterns is critical to determine appropriate antibiotic therapy.

Ampicillin Resistance↗

PubMed1994

Molecular and cellular basis for pathogenicity of autoantibodies.

Using two different kinds of monoclonal autoantibodies, anti-mouse RBC (MRBC) autoantibodies and IgG3 rheumatoid factor (RF) cryoglobulins, we have attempted to better define the molecular and cellular basis of the pathogenicity of autoantibodies. Among eight anti-MRBC monoclonal antibodies (mAbs) obtained from NZB mice, only five of them are able to cause anemia. The distinct differences in specificity between pathogenic and non-pathogenic anti-MRBC mAbs emphasize the importance of autoantibody specificity for the pathogenesis of autoimmune hemolytic anemia. Histological examination has revealed that Fc gamma receptor-mediated erythrophagocytosis and sequestration of agglutinated RBC in spleens and livers are the major pathogenic mechanisms of hemolytic anemia. This indicates that the affinity of autoantibodies for the Fc gamma receptors of phagocytes and/or the ability to cause hemagglutination, both of which vary among immunoglobulin isotypes, are additional factors determining the pathogenic activity of anti-MRBC autoantibodies. Studies on a panel of anti-IgG2a RF mAbs derived from MRL-lpr/lpr mice have demonstrated that only the IgG3 isotypes of RF mAb are able to generate cryoglobulins and to induce skin leukocytoclastic vasculitis and glomerulonephritis in normal mice. Although the cryoglobulin activity of RF mAb associated with the IgG3 isotype has been shown to be solely responsible for the generation of glomerular lesions (both RF and cryoglobulin activities are necessary for cutaneous vascular lesions), the absence of nephritogenic activity by some IgG3 monoclonal cryoglobulins supports the idea that qualitative features of cryoglobulins are critical to determine their pathogenic activities. Of interest, IgG3 autoantibodies lacking the cryoglobulin activity may not be harmful, but even protective against the development of IgG3 cryoglobulin-mediated tissue lesions, because they inhibit the cryoglobulin formation of pathogenic IgG3 autoantibodies as a result of their nonspecific IgG3 Fc-Fc interaction. Our results on monoclonal autoantibodies clearly indicate the importance of certain subpopulations of autoantibodies in the pathogenesis of autoantibody-mediated cellular and tissue injuries.

Anemia, Hemolytic, Autoimmune↗

PubMed1991

Survival of pathogenic micro-organisms and parasites in excreta, manure and sewage sludge.

The causative agents of many infectious diseases are excreted by the faecal route and also with other excretions or secretions of the body. Some pathogens are also excreted from clinically healthy animals, from those with latent infections and in cases of transmissible multifactorial diseases. In all types of livestock housing, the pathogens finally reach the floor with the installations for collecting manure as a solid or liquid. Under these conditions livestock owners do not realise that manure may contain pathogens, and therefore do not take precautions against possible spread of diseases by utilisation of manure. The pathogens do not survive very long in stored farmyard manure because of the temperatures and biological and biochemical activities prevailing in the middens. But the conditions in slurry are different because the temperature does not rise and biochemical activity is low. Therefore the pathogens survive for rather long periods in slurry. To avoid disease transfer by utilisation of manure and slurry as fertilisers, certain precautions are necessary and these are described in detail. The agricultural utilisation of municipal sewage sludge is common in many countries. However, these sludges contain pathogens which are excreted by the human population served by the sewers and sewage treatment plants. In the sewage purification processes most of the pathogens are reduced in number but not completely eliminated. They are enriched by sedimentation processes in the sewage sludge. To protect the livestock of farms utilising sewage sludge as fertiliser or for amending soils it is necessary to sanitise hygienically dubious sludges prior to their use. The epidemiological aspects of agricultural sludge utilisation are discussed and details of the available sanitation technologies are given.

Animals↗

PubMed2004

Effect of pathogen-specific clinical mastitis on milk yield in dairy cows.

Our objective was to estimate the effects of the first occurrence of pathogen-specific clinical mastitis (CM) on milk yield in 3071 dairy cows in 2 New York State farms. The pathogens studied were Streptococcus spp.,Staphylococcus aureus, Staphylococcus spp., Escherichia coli, Klebsiella spp., Arcanobacterium pyogenes, other pathogens grouped together, and "no pathogen isolated." Data were collected from October 1999 to July 2001. Milk samples were collected from cows showing signs of CM and were sent to the Quality Milk Production Services laboratory at Cornell University for microbiological culture. The SAS statistical procedure PROC MIXED, with an autoregressive covariance structure, was used to quantify the effect of CM and several other control variables (herd, calving season, parity, month of lactation, J-5 vaccination status, and other diseases) on weekly milk yield. Separate models were fitted for primipara and multipara, because of the different shapes of their lactation curves. To observe effects of mastitis, milk weights were divided into several periods both pre- and postdiagnosis, according to when they were measured in relation to disease occurrence. Another category contained cows without the type of CM being modeled. Because all pathogens were modeled simultaneously, a control cow was one without CM. Among primipara, Staph. aureus, E. coli, Klebsiella spp., and "no pathogen isolated" caused the greatest losses. Milk yield generally began to drop 1 or 2 wk before diagnosis; the greatest loss occurred immediately following diagnosis. Mastitic cows often never recovered their potential yield. Among older cows, Streptococcus spp., Staph. aureus, A. pyogenes, E. coli, and Klebsiella spp. caused the most significant losses. Many multipara that developed CM were actually higher producers before diagnosis than their nonmastitic herd-mates. As in primipara, milk yield in multipara often began to decline shortly before diagnosis; the greatest loss occurred immediately following diagnosis. Milk loss persisted until at least 70 d after diagnosis for Streptococcus spp., Klebsiella spp., and A. pyogenes. The tendency for higher producing cows to contract CM may mask its impact on cow health and production. These findings provide dairy producers with more information on which pathogen-specific CM cases should receive treatment and how to manage these cows, thereby reducing CM impact on cow well being and profitability.

Actinomycetaceae↗

PubMed2006

Prevalence of mastitis pathogens and their resistance against antimicrobial agents in dairy cows in Brandenburg, Germany.

The primary objective of this study was to determine management practices concerning mastitis in Brandenburg, Germany, the prevalence of mastitis pathogens in dairy cows, and their resistance to selected antimicrobial agents. A further objective was to study the potential effect of parity and stage of lactation on the resistance of Staphylococcus aureus isolates against ampicillin. Milk samples for microbiological culture were collected from 4 groups of clinically healthy cows (first lactation, >1 lactation, >50 d in milk, and >250 d in milk; 8 cows/group) in 80 dairy herds. Resistance of gram-positive pathogens against 6 antimicrobial agents was tested using the broth microdilution method. Mastitis pathogens were isolated from 26.4% of the milk samples. Coagulase-negative staphylococci (CNS, 9.1% of quarters) and Corynebacterium bovis (7.3%) were the pathogens most frequently isolated. Among the major pathogens, Staph. aureus (5.7%) and Streptococcus uberis (1.0%) had the highest prevalence. Streptococcus agalactiae was isolated in samples from 29% of the herds. Although the prevalence of most pathogens was higher in older cows, the prevalence of CNS was higher in primiparous cows. Results of the mastitis control questionnaire showed that cows with clinical mastitis were transferred to a sick cow pen in 70% of the herds. Cephalosporins were the drug of first choice for treatment of clinical mastitis cases followed by fixed combinations of antimicrobial agents, beta-lactamase-resistant penicillins, and penicillin. Most farmers treated cows 3 to 4 times per case. Cloxacillin, alone or in combination, and penicillin were most often used for dry-cow therapy. Antimicrobial resistance of the pathogens was within the range of other reports. Resistance of Staph. aureus to ampicillin increased significantly during the first lactation. Further research is required to determine the factors that lead to the selection of Staph. aureus strains that are resistant to ampicillin during the first lactation.

Ampicillin Resistance↗

PubMed2003

Cutting edge: carbohydrate profiling identifies new pathogens that interact with dendritic cell-specific ICAM-3-grabbing nonintegrin on dendritic cells.

Dendritic cells (DC) are instrumental in handling pathogens for processing and presentation to T cells, thus eliciting an appropriate immune response. C-type lectins expressed by DC function as pathogen-recognition receptors; yet their specificity for carbohydrate structures on pathogens is not fully understood. In this study, we analyzed the carbohydrate specificity of DC-specific ICAM-3-grabbing nonintegrin (SIGN)/CD209, the recently documented HIV-1 receptor on DC. Our studies show that DC-SIGN binds with high affinity to both synthetic mannose- and fucose-containing glycoconjugates. These carbohydrate structures are abundantly expressed by pathogens as demonstrated by the affinity of DC-SIGN for natural surface glycans of the human pathogens Mycobacterium tuberculosis, Helicobacter pylori, Leishmania mexicana, and Schistosoma mansoni. This analysis expands our knowledge on the carbohydrate and pathogen-specificity of DC-SIGN and identifies this lectin to be central in pathogen-DC interactions.

Animals↗

PubMed2001

Evaluation of universal preenrichment broth for growth of heat-injured pathogens.

Universal preenrichment broth (UPB) was developed to enable enrichment of injured foodborne pathogens of different genera simultaneously in lieu of having to undergo separate simultaneous enrichment cultures for subsequent detection or isolation of each pathogen. Enrichment conditions in UPB for growth of injured pathogens to populations that will enable pathogen detection by rapid immuno-based or polymerase chain reaction (PCR)-based assays have not been defined. Hence, studies were done to determine recovery and growth rates of heat-injured Escherichia coli O157:H7, Salmonella enterica ser. Typhimurium, Salmonella enterica ser. Enteritidis. and Listeria monocytogenes in UPB. Bacterial cells were heat injured in tryptic phosphate broth at 57.2 degrees C and inoculated at populations of ca. 0.17 to 63 injured cells per ml with raw ground beef, fresh chicken, lettuce, and environmental sponge samples. Enrichment cultures were sampled at 1, 2, 3, 4, 5, 6, and 24 h at 37 degrees C postinoculation, and pathogens were enumerated on appropriate selective media. Results revealed that recovery and growth of pathogens during the first 6 h of enrichment were not sufficient to ensure adequate numbers of bacteria (> 10(3) CFU/ ml) for detection by most immunoassays or PCR assays. Cells often required 3 to 4 h for recovery before growth was initiated. Salmonella Typhimurium, Salmonella Enteritidis, E. coli O157:H7, or L. monocytogenes cell populations in enrichment cultures with ground beef or lettuce at 6 h were 0.5 to 2.9 log10 CFU/ml. At 24 h of incubation, cell counts of enrichment samples for the three pathogens from all food and environmental sponge samples ranged from 4.0 to 8.3 log10 CFU/ml. Enrichment in UPB at 37 degrees C of foods or environmental sponge samples containing heat-injured cells of Salmonella Typhimurium, Salmonella Enteritidis, E. coli O157:H7, or L. monocytogenes reliably provides at 24 h of incubation-but not at 6 h-sufficient cell populations for detection by rapid immunoassay or PCR assay procedures that can detect at least 4 log10 CFU/ml. These results raise questions regarding the sensitivity of rapid detection methods that employ an abbreviated enrichment protocol of 6 h or less.

Animals↗

PubMed1991

Branhamella (Moraxella) catarrhalis: pathogenic significance in respiratory infections.

OBJECTIVES: To assess the pathogenic significance of Branhamella catarrhalis isolates in patients with respiratory infections and to define the clinical characteristics of such patients. DESIGN AND SETTING: Respiratory specimens were assessed in a three-year prospective study performed in a Brisbane metropolitan hospital. Assessment of the pathogenic significance of isolates of B. catarrhalis was based on four predetermined criteria: (i) clinical evidence of respiratory infection based on history, examination and chest x-ray; (ii) isolation of B. catarrhalis as the sole potential pathogen; (iii) absence of antibiotic treatment in the previous two weeks; and (iv) subsequent clinical response to an antibiotic to which the isolate was sensitive. RESULTS: B. catarrhalis was identified in 118 respiratory samples, 92 (78%) being from patients less than 10 years old. Infection with B. catarrhalis was more commonly seen in winter months and was community-acquired in two-thirds of cases. Isolation of this organism was associated with a broad variety of upper and lower respiratory tract syndromes. Isolates were considered to be of pathogenic significance (all four above criteria satisfied) in 35% of cases and of possible significance (the first and fourth criteria satisfied) in a further 15% of cases. Isolates were more likely to be of pathogenic significance in older patients and in those with pre-existing cardiorespiratory disease; however, a number of serious infections were observed in previously-well children. Expectorated sputum and tracheal aspirates were more likely to yield a clinically significant isolate than nasopharyngeal aspirates. Production of beta-lactamase was demonstrated in 88% of isolates. CONCLUSION: B. catarrhalis causes respiratory infection more frequently than is generally appreciated. Isolation of this organism from the respiratory tract had pathogenic significance or possible pathogenic significance in 50% of our patients. If therapy is indicated in patients with respiratory infection caused by this organism, traditional beta-lactam regimens cannot be relied upon, as shown by the high rate of beta-lactamase production in this study; a tetracycline, erythromycin, a second or third generation cephalosporin, or the combination of a penicillin derivative and beta-lactamase inhibitor should be considered.

Adolescent↗

PubMed1975

[Experimental pathogenicity of "Yersinia enterocolitica" for athymic nude mice (author's transl)].

Amongst the 4,500 strains of our collection of Yersinia enterocolitica usually non-pathogenic for laboratory animals, 5 or 6 strains appeared to be naturally pathogenic for mice. Using these strains and non-pathogenic strains representing more than 90 per cent of human isolates in the world (biotype 4, serotype 0:3, phagocyte VIII; biotype 2, serotype 0:9, phagotype X3), the pathogenicity for cyclophosphamid treated mice and athymic Nude mice has been tested. Highly pathogenic strains killed conventional as well as cyclophosphamid treated mice. Non-pathogenic strains for conventional mice did not show any pathogenicity for cyclophosphamid treated mice (strain IP161 excepted) but killed 30 athymic Nude mice inoculated with 5 x 10(8) and 5 x 10(5) organisms by the oral or intraperitoneal routes. Nude mice infected intragastrically or intraperitoneally showed signs of enteritis and bronchopneumonia followed by a septicemia. Abscesses were found in the liver, the spleen and the ileal wall. The infection of Nude mice with Y. enterocolitica resembles naturally acquired human infection where 2/3 of the cases are enteritis among under 4-year-old children and where septicemia occurs among immunologically deficient adults. The role of T-lymphocytes and of immune functions in Y. enterocolitica infection is discussed through our model.

Animals↗

PubMed2003

[Incidence and pathogens of nosocomial bacteremia in China].

OBJECTIVE: To investigate the incidence and pathogens of nosocomial bacteremia (NB) in China. METHODS: The data of incidence and pathogens of NB reported from Jun 1998 to Dec 2001 by the hospitals of the Chinese nosocomial infections surveillance system (CNISS) were collected and analyzed. RESULTS: A total of 4882364 patients were surveyed and 2 371 cases of NB were reported. The incidence rate of NB was 48.6/100000, accounting for 1.3% of nosocomial infection. The incidence of bacteremia was higher in units of hematology, infectious disease, neonatology, and burns, and among the surgical patients with contaminated wound. 1757 strains of pathogens had been isolated, among which 585 (33.3%) were gram-positive bacteria, 962 (54.8%) gram-negative bacteria, 186 (10.6%) fungi, and 24 (1.4%) other pathogens. The most common pathogens were Escherichia coli (17.2%), Coagulase negative staphylococcus (CoNS 13.4%), fungi (10.6%), Klebsiella (9.1%), Staphylococcus aureus (8.1%), Pseudomonas aeruginosa (6.8%), and Enterobactor (6.3%) spp. CONCLUSION: Patients in unit of hematology, infectious diseases, burns and neonatology and surgical patients with class III incision have higher incidence of nosocomial bacteremia. Gram-negative bacteria were the prominent pathogens, the most common pathogens were E. coli, CoNS, fungi, Klebsiella, S. aureus, P. aeruginosa, and Enterobactor spp.

Adult↗

PubMed1992

Phagocytosis and proteinase activity are not related to pathogenicity of Entamoeba histolytica.

To examine the relationship between phagocytosis, proteinase activity and pathogenicity of axenically grown trophozoites of E. histolytica of strain HM-1:IMSS four different cultures were used: 1) a culture preserved in our laboratory for over 4 years, that lost its pathogenicity 3 years ago; 2) a culture passaged several times through hamster liver, that lost its pathogenicity recently; 3) a highly virulent culture supplied by another laboratory; and 4) amebas recovered from hamster liver abscesses caused by the latter culture. Phagocytosis was measured as erythrophagocytosis. Proteinase activity was determined on azocasein. Pathogenicity was defined as the capacity to cause liver abscesses in hamsters. A negative correlation was found between phagocytic activity and pathogenicity, since amebas unable to cause liver abscesses had the highest phagocytic activity whereas those recovered from liver abscesses had the lowest phagocytic activity. The percent of phagocytic amebas increased progressively in all cultures through a 2-month observation period. No correlation was found between the level of proteinase activity and pathogenicity. It is concluded that neither phagocytosis nor proteinase activity are adequate markers of amebic pathogenicity.

Animals↗

PubMed1992

[Recent findings on the pathogenicity of Entamoeba histolytica].

Entamoeba histolytica is the causative agent of human amoebiasis. During recent years, research in amoebiasis has concentrated on two subjects: 1. the dual manifestation of the infection as harmless colonization of the intestinal cavity or pathogenic tissue invasion and 2. the molecular analysis of functions of E. histolytica that are considered essential for pathogenicity. Besides epidemiological studies and isoenzyme analyses, molecular genetics have revealed additional evidence that two genetically distinct forms of E. histolytica do exist, named "pathogenic" and "nonpathogenic" forms, respectively. Both can infect humans but only the "pathogenic" form is able to invade the tissue and cause disease whereas the "nonpathogenic" is not. Questions remain open about the mechanism that triggers "pathogenic" E. histolytica to become invasive and about the molecules that are involved. Current data indicate that at least three functions of the amoebae are considered essential for pathogenic tissue invasion. Pathogenicity is viewed as a result of 1. adherence of the amoeba to host cells, predominantly mediated by a galactose- and N-acetylgalactosamine-inhibitable lectin, 2. killing of host cells by a pore-forming peptide known as amoebapore, and 3. proteolysis of the host's extracellular matrix mediated by cysteine proteinases. Structural detailed molecular analysis including cloning of the corresponding genes have led to a better understanding of the function of these proteins.

Animals↗

PubMed2004

Reduction of microbial pathogens during apple cider production using sodium hypochlorite, copper ion, and sonication.

Sodium hypochlorite (100 ppm), copper ion water (1 ppm), and sonication (22 to 44 kHz and 44 to 48 kHz) were assessed individually and in combination for their ability to reduce populations of Escherichia coli O157:H7 and Listeria monocytogenes on apples and in apple cider. Commercial unpasteurized cider was inoculated to contain approximately 10(6) CFU/ml of either pathogen and then sonicated at 44 to 48 kHz, with aliquots removed at intervals of 30 to 60 s for up to 5 min and plated to determine numbers of survivors. Subsequently, whole apples were inoculated by dipping to contain approximately 10(6) CFU/g E. coli O157:H7 or L. monocytogenes, held overnight, and then submerged in 1 ppm copper ion water with or without 100 ppm sodium hypochlorite for 3 min with or without sonication at 22 to 44 kHz and examined for survivors. Treated apples were also juiced, with the resulting cider sonicated for 3 min. Populations of both pathogens decreased 1 to 2 log CFU/ml in inoculated cider following 3 min of sonication. Copper ion water alone did not significantly reduce populations of either pathogen on inoculated apples. However, when used in combination with sodium hypochlorite, pathogen levels decreased approximately 2.3 log CFU/g on apples. Sonication of this copper ion-sodium hypochlorite solution at 22 to 44 kHz did not further improve pathogen reduction on apples. Numbers of either pathogen in the juice fraction were approximately 1.2 log CFU/ml lower after being juiced, with sonication (44 to 48 kHz) of the expressed juice decreasing L. monocytogenes and E. coli O157:H7 populations an additional 2 log. Hence, a 5-log reduction was achievable for both pathogens with the use of copper ion water in combination with sodium hypochlorite followed by juicing and sonication at 44 to 48 kHz.

Beverages↗