Biological Sciences
Pathogenicity
Pathogenicity refers to the ability of a microorganism, such as a virus, bacterium, fungus, or parasite, to cause disease in a host organism. It involves the mechanisms by which the pathogen enters the host, evades the host's immune system, and causes damage to the host's cells and tissues. Understanding pathogenicity is crucial for developing strategies to prevent and treat infectious diseases.
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11 Key excerpts on "Pathogenicity"
eBook - PDF- Barbara H. Iglewski(Author)
- 1990(Publication Date)
- Academic Press(Publisher)
Part I Introduction This page intentionally left blank THE BACTERIA, VOL. XI CHAPTER 1 The Zen of Bacterial Pathogenicity STANLEY FALKOW Department of Microbiology and Immunology Stanford University Stanford, California 94305 I. Introduction 3 II. The Attributes of Microbial Pathogenicity 4 A. Entry 4 B. Finding a Niche 5 C. Avoiding Host Defense Mechanisms 5 III. Corollaries of Microbial Pathogenicity 6 A. The Clonal Nature of Bacterial Pathogens 6 B. Extrachromosomal Determinants of Pathogenicity 7 C. Regulation of Bacterial Virulence Factors 7 IV. Concluding Remarks 8 I. Introduction A pathogen is often defined as a microorganism that has the capacity to cause disease in a particular host. This definition reflects the past and present emphasis in medical microbiology and medicine with disease, the end product of the infectious process. Not unexpectedly, a good deal of research effort has been, and is, directed to the treatment and prevention of infectious diseases. However, over the past decade there has been an increasing emphasis to understand the funda-mental biology of microorganisms that cause human infection and disease. These studies of infectious bacterial agents have provided a slightly different view of microbial Pathogenicity; they also give new insights into the control and preven-tion of infectious diseases. A microbial pathogen is now recognized as a highly adapted microorganism that may cause disease (overt damage to a host) because its survival strategy includes a requirement for infection (persistence, usually by multiplication on or within another living organism). This view, from the standpoint of the micro-organism so to speak, emphasizes the point that disease is an inadvertent and unfavorable outcome of a microbial infection.
eBook - PDFThe Bacteria
Molecular Basis of Bacterial Pathogenesis
- Bozzano G Luisa(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
Part I I n t r o d u c t i o n This page intentionally left blank THE BACTERIA, VOL. XI CHAPTER 1 The Zen of Bacterial Pathogenicity STANLEY FALKOW Department of Microbiology and Immunology Stanford University Stanford, California 94305 I. Introduction II. The Attributes of Microbial Pathogenicity 3 4 4 B. Finding a Niche C. Avoiding Host Defense Mechanisms III. Corollaries of Microbial Pathogenicity A. The Clonal Nature of Bacterial Pathogens B. Extrachromosomal Determinants of Pathogenicity C. Regulation of Bacterial Virulence Factors IV. Concluding Remarks I. Introduction A pathogen is often defined as a microorganism that has the capacity to cause disease in a particular host. This definition reflects the past and present emphasis in medical microbiology and medicine with disease, the end product of the infectious process. Not unexpectedly, a good deal of research effort has been, and is, directed to the treatment and prevention of infectious diseases. However, over the past decade there has been an increasing emphasis to understand the funda-mental biology of microorganisms that cause human infection and disease. These studies of infectious bacterial agents have provided a slightly different view of microbial Pathogenicity; they also give new insights into the control and preven-tion of infectious diseases. A microbial pathogen is now recognized as a highly adapted microorganism that may cause disease (overt damage to a host) because its survival strategy includes a requirement for infection (persistence, usually by multiplication on or within another living organism). This view, from the standpoint of the micro-organism so to speak, emphasizes the point that disease is an inadvertent and unfavorable outcome of a microbial infection.
- C. H. Collins, A. J. Beale(Authors)
- 2015(Publication Date)
- Butterworth-Heinemann(Publisher)
5 Pathogenicity testing J. Hacker and M. Ott 1. Features of microbial Pathogenicity Microbial Pathogenicity has been defined as 'the biochemical mechanisms whereby microorganisms cause disease' (Finlay and Falkow, 1989). Thus, Pathogenicity enables bacteria of several species to cause different kinds of infections, e.g. in the urinary, respiratory and gastrointestinal tracts, and other sites (Mims, 1987). In contrast, virulence is referred to as the degree of the 'pathogenic potential' of special microbial strains which can be quantified by suitable animal tests like LD 50 measurements (see below). With the exception of a few cases of intoxication (e.g. diphtheria, tetanus) microbial Pathogenicity is a process which involves several factors known as 'virulence or Pathogenicity factors'. As indicated in Figure 5.1, microbial infections may start via a non-specific contact of the pathogen with the mucosa, through lesions of the skin or through the bite of an arthropod (Mims, 1987). These non-specific events that lead to an attachment of microorganisms include the occurrence of 'long distance attractive forces' or the action of non-specific adhesins such as the type I fimbriae produced by several enterobacterial species (Mirelman, 1986; Hacker, 1990). In recent years it became attractive to distinguish between extracellular and intracellular pathogens. The former organisms are able to colonize tissues and multiply outside the eukaryotic cells, e.g. Vibrio cholerae or Escherichia coli wild-type strains which cause diarrhoeal diseases (Finlay and Falkow, 1989). Extracellular pathogens mostly produce specific attachment factors which bind to distinct receptor molecules on the eukaryotic site. Such adhesins may consist of protein organelles termed fimbriae, which are produced by numerous Gram-negative bacteria, of exopolysac-charides found by Pseudomonas aeruginosa, as well as lipoteichoic acids or glucan polymers produced by streptococci (Mirelman, 1986).
- OECD(Author)
- 2016(Publication Date)
- OECD(Publisher)
Although “Pathogenicity” can be defined in terms of properties of a micro-organism, it is important to keep in mind that the concept of Pathogenicity is highly anthropomorphic, as it implies that a micro-organism would cause disease “on purpose”. A more realistic view is that the body is a habitat for micro-organisms to adapt to and use as a favourable environment for survival and growth. Some bacteria have developed a “lifestyle” that enables them to colonise this niche in symbiotic as well as in pathogenic ways (Wassenaar and Gaastra, 2001). Each body surface – skin, conjunctiva, mucous membranes of the upper and lower respiratory tract, intestinal tract, genital tract and so forth – harbors a characteristic commensal bacterial population which differs qualitatively from the population of other areas of the body. Bacteria with pathogenic 30 – I.1. BACTERIA: Pathogenicity FACTORS SAFETY ASSESSMENT OF TRANSGENIC ORGANISMS: OECD CONSENSUS DOCUMENTS, VOLUME 5 © OECD 2016 behaviour may establish a foothold in this microbial ecosystem. Once established, other pathogenic properties allow the pathogen to penetrate into deeper tissues, to avoid or counteract host defense mechanisms, and to multiply. As they pursue this strategy, pathogenic bacteria produce damage to the host. Virulence-associated factors may be defined as all factors that are essential for expressing Pathogenicity. Whether a host will develop disease is, however, not just determined by the pathogenic potential of the bacterium, but also by host factors. There is a formidable array of specific and non-specific host factors that affect the outcome of an encounter between a host and a pathogenic bacterium. For example, the normal commensal population plays an important role in protecting the host from invasion by pathogenic organisms.
eBook - ePub- Barron's Educational Series, Rene Kratz(Authors)
- 2011(Publication Date)
- Barrons Educational Services(Publisher)
20Pathogenicity ofMicroorganisms WHAT YOU WILL LEARNThis chapter takes a look at the various tools and tricks pathogens use in order to colonize the body and get past your defenses. As you study this chapter, you will: • examine how pathogens enter the body; • discover the importance of attachment; • learn how pathogens evade defenses like complement and phagocytosis; • explore how pathogens damage host tissues with toxins.SECTIONS IN THIS CHAPTER• Ability to Invade Tissues• Evasion of Host Defenses• Damage to the HostThe human body has amazing defenses against invasion by microorganisms. Most microbes we encounter are prevented from establishing an infection by our innate immunity (Chapter 18 ). Those that do establish an infection are usually defeated by our adaptive immunity (Chapter 19 ). So why is it that we get sick at all? How do some microbes manage to get around our defenses? Why does their presence in our bodies cause disease?The ability of a microorganism to cause disease is its Pathogenicity . A more familiar term might be virulence , which refers to the degree of Pathogenicity. For example, an organism that very easily causes disease would be considered highly virulent. Microorganisms that are highly virulent have the ability to colonize the host easily and disrupt the host physiology. Any molecules that a microorganism makes and that help them to cause disease are called virulence factors . In other words, virulence factors are like the tool kit of a pathogen. What makes one pathogen different from another is what they have in their tool kit.REMEMBERA virulence factor is any molecule that helps a pathogen cause disease.The ability of a pathogen to cause disease depends on three main issues. First, the pathogen must be able to invade the host. Second, it must be able to evade the host defenses. And finally, it may produce enzymes or toxins that damage host tissues and contribute to the signs and symptoms of disease. The different strategies that pathogens use to invade the human body are truly amazing, and understanding the details of these mechanisms can help us figure out new ways to prevent disease.
eBook - PDF- Nina Parker, Mark Schneegurt, Anh-Hue Thi Tu, Brian M. Forster, Philip Lister(Authors)
- 2016(Publication Date)
- Openstax(Publisher)
Chapter 15 Microbial Mechanisms of Pathogenicity Figure 15.1 Although medical professionals rely heavily on signs and symptoms to diagnose disease and prescribe treatment, many diseases can produce similar signs and symptoms. (credit left: modification of work by U.S. Navy) Chapter Outline 15.1 Characteristics of Infectious Disease 15.2 How Pathogens Cause Disease 15.3 Virulence Factors of Bacterial and Viral Pathogens 15.4 Virulence Factors of Eukaryotic Pathogens Introduction Jane woke up one spring morning feeling not quite herself. Her throat felt a bit dry and she was sniffling. She wondered why she felt so lousy. Was it because of a change in the weather? The pollen count? Was she coming down with something? Did she catch a bug from her coworker who sneezed on her in the elevator yesterday? The signs and symptoms we associate with illness can have many different causes. Sometimes they are the direct result of a pathogenic infection, but in other cases they result from a response by our immune system to a pathogen or another perceived threat. For example, in response to certain pathogens, the immune system may release pyrogens, chemicals that cause the body temperature to rise, resulting in a fever. This response creates a less-than-favorable environment for the pathogen, but it also makes us feel sick. Medical professionals rely heavily on analysis of signs and symptoms to determine the cause of an ailment and prescribe treatment. In some cases, signs and symptoms alone are enough to correctly identify the causative agent of a disease, but since few diseases produce truly unique symptoms, it is often necessary to confirm the identity of the infectious agent by other direct and indirect diagnostic methods. Chapter 15 | Microbial Mechanisms of Pathogenicity 657
eBook - PDF- Edward Bittar(Author)
- 1998(Publication Date)
- Elsevier Science(Publisher)
These diseases are caused by normal flora (e.g., urinary tract infections in women), or by microorganisms that reside in the environment (e.g., cholera). Zoonoses are dis- eases that primarily occur in animals but can be transmitted to humans (e.g., bubonic plague). The different routes of transmission of bacterial infection are shown in Table 2. PATHOGENIC MICROORGANISMS The development of disease after exposure to an infectious agent depends on properties of both the bacterium and the host. Microorganisms vary in their ability Principles of Bacterial Pathogenesis 89 to cause disease. Those that are successful are pathogens and the manner in which a disease originates is referred to as its pathogenesis. Bacterial characteristics that contribute to Pathogenicity are virulence factors. A pathogens' ability to cause disease in a given host varies due to individual differences in the host's defense mechanisms (immune response), and due to strain differences (these are sometimes referred to as differences in virulence or differences in Pathogenicity). If one could infect the same individual multiple times with different strains of the same species of bacteria (and the host did not develop an immune response to the infection), differences in the outcome of each infection would reflect differences in the pathogenic potential of each strain. The severity of the disease reflects the total of the expression of the virulence determinants of the infecting strain(s). These differences in the severity of the disease are due to differential expression of virulence determinants. Some commensal microorganisms are unable to cause disease when present alone in certain biological niches. However, when other strains are present, the two nonpathogens can interact and cause disease. This synergistic interaction is commonly seen in infections caused by anaerobic micro- organisms.
eBook - PDFPlant Disease: An Advanced Treatise
How Plants Defend Themselves
- James G. Horsfall(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
The range of possible interactions in a typical host-pathogen encoun-ter are diagrammed in Fig. 1. The diagram emphasizes that the sequence of events leading to successful infection are distinct from the sequence of events that may lead to disease. The diagram is not meant to imply that all four possible types of interaction exist in all disease systems. Also, the diagram should not be interpreted to imply a fixed or constant relationship between any of these categories. In some disease systems, for example, susceptibility and vulnerability are inextricably linked, while in other systems the two phenomena are separate and distinct from one another. The model emphasizes that vulnerability is the net result of a specific sequence of stimulus-response events, and not neces-sarily a straight-line consequence of successful infection. The model infers that disease tolerance results from specific, heritable attributes of the host. The mechanisms of tolerance may vary greatly from one host plant to another, but the one common characteristic of tolerance to biotic pathogens is the ability of the plant to produce useful produce while providing the necessary habitat for pathogen development. C. The Problem of Latent Infections Although superficially similar, the phenomena of tolerance are dis-tinct from the phenomena of latent infections. Both types of interactions involve relatively long periods of intimate contact between pathogen and host without gross damage to the host. In latent infections, however, the absence of symptoms is due to the host-induced quiescence of the pathogen. Quiescence may be induced by some aspect of host physiology, such as low p H or a deficiency of oxygen or sugar in infected tissues. When host physiology shifts in a manner that permits active develop-ment of the pathogen, such as in fruit ripening, the presence of the pathogen will become manifest by the rapid development of disease.
eBook - PDF- Dave Wessner, Christine Dupont, Trevor Charles, Josh Neufeld(Authors)
- 2020(Publication Date)
- Wiley(Publisher)
Gal-Mor, O., and B. B. Finlay. 2006. Pathogenicity islands: A molecu- lar toolbox for bacterial virulence. Cell Microbiol 8:1707–1719. Raskin, D. M., R. Seshadri, S. U. Pukatzki, and J. J. Mekalanos. 2006. Bacterial genomics and pathogen evolution. Cell 124:703–714. Rossetto, O., M. Pirazzini, and C. Montecucco. 2014. Botulism neuro- toxins: Genetic, structural and mechanistic insights. Nat Rev Micro- biol 12:535–549. Rutherford, S. T., and B. L. Bassler. 2012. Bacterial quorum sensing: Its role in virulence and possibilities for its control. Cold Spring Harb Perspect Med 2:a012427. Travis, J. 2003. All the world’s a phage: Viruses that eat bacteria abound—and surprise. Sci News 164:26–27. Zughaier, S. M., and P. Cornelis. 2018. Editorial: Role of iron in bac- terial pathogenesis. Front Cell Infect Microbiol 8:334. doi: 10.3389/ fcimb.2018.00344. 9. Production of antibody has not been found to be protective against Mycobacterium tuberculosis infection. Explain why this would be. 10. You encounter what appears to be a newly emerged strain of bac- teria. As you examine its DNA sequence, you determine it has genes for a type III secretion system. What would this sequence analysis tell you about the pathogenesis of these bacteria? 11. Enterotoxigenic strains of E. coli can cause diarrhea in travelers to regions where these strains exist as common gut inhabitants in local populations, yet they do not usually cause disease in local popu- lations. Suggest why these strains are a problem for travelers but not for the locals. 12. If you could design your vision of the ideal pathogenic bacterium that was able to gain access to a host, avoid immune destruction, and obtain nutrients, what virulence factor genes would you insert in its genome? Explain your reasoning for each. 782 We probably have all heard about “introduced species.” The term refers to species that are released into a non‐native envi- ronment.
eBook - PDF- George Agrios(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
Thus, in many cases, para-sitism is intimately associated w i th Pathogenicity , since the ability of the parasite to invade and become established in the h o st g e n e r a l ly r e s u l ts in the development of a diseased condition in the host. In s o me c a s es of parasitism , as w i th the root nodule b a c t e r ia of leg-ume plants, both the p l a nt and the microorganism are b e n e f i c i al to the other's development, and this phenomenon is known as symbiosis . In m o st p l a nt diseases , however, parasitis m a l o ne c a n n ot explain the a m o u nt of damage c a u s ed to plants, since this is often much g r e a t er t h an w o u ld be expected from the mere r e m o v al of n u t r i e n ts by the parasite . This additiona l damage r e s u l ts from substances secreted by the parasite or produced by the host in response to stimuli originat-ing in the parasite . T i s s u es affected by such substances m ay show in-c r e a s ed respiration , disintegration or collapse of c e l l s, wilting, abscis-s i o n, abnormal cell division and e n l a r g e m e n t, degeneration of specific c o m p o n e n ts such as chlorophyll, and other conditions which in them-s e l v es do not seem d i r e c t ly to i m p r o ve the welfare of the parasite . It w o u ld appear then that the degree of Pathogenicity exhibited by a parasite is not always porportional to the nutritional affiliation of the parasite and its h o s t. Pathogenicity m ay be more p r o p e r ly c o n s i d e r ed as the interference of the parasite w i th one or more of the essential f u n c t i o ns of the plant, w i th parasitis m playing, frequently, an i m p o r-tant, but not always the m o st important , role. Of the l a r ge number of groups of l i v i ng organisms , only a few mem-bers of a few groups can parasitiz e plants: fungi, bacteria, and parasiti c higher plants (all three belonging to the p l a nt k i n g d o m ), nematodes (of the animal k i n g d o m ), and viruses.
eBook - PDF- Anthony Pometto, Kalidas Shetty, Gopinadhan Paliyath, Robert E. Levin(Authors)
- 2005(Publication Date)
- CRC Press(Publisher)
In addition, the environment must allow exposure of the host to the pathogen, and for food borne pathogens, the most important environmental factors are dependent on how the food is produced, processed, stored, prepared, and consumed. Through development of new processing strategies and food handling systems, we have selected for many of the pathogens which potentially contaminate our foods. 2.5.4 Applications of Genetic and Molecular Understanding of Pathogenesis Research into the genetic and physiological basis of virulence is critical in improving our ability to detect dangerous pathogens and prevent disease. When the genes for a particular pathogen’s virulence factors are known, DNA based methods can be developed to quickly detect and identify that pathogen, to distinguish between virulent and avirulent strains of closely related bacteria, and to help develop vaccines specific to those virulence factors. Currently, DNA based methods have been most useful for diagnosis of infections caused by pathogens which are particularly difficult to culture (such as Mycobacterium tuberculosis , which causes tuberculosis, Bordetella pertussis , the cause of whooping cough, and a variety of viral diseases), but as automation and less expensive methods become more widely avail-able, DNA based molecular diagnostics are expected to become increasingly valuable tools in identifying a wide range of pathogens (112). Another important application of understanding the molecular mechanisms of patho-genesis is the development of DNA based subtyping methods. These methods allow rapid strain “fingerprinting” for epidemiological studies to assist in disease management and control. If an outbreak of disease is caused by a specific strain of a pathogen, and foods containing that specific strain can be found, it will allow epidemiologists to very precisely identify the source of the outbreak. Molecular subtyping has been an important tool used
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