Host–pathogen interaction

Last updated

The host-pathogen interaction is defined as how microbes or viruses sustain themselves within host organisms on a molecular, cellular, organismal or population level. This term is most commonly used to refer to disease-causing microorganisms although they may not cause illness in all hosts. [1] Because of this, the definition has been expanded to how known pathogens survive within their host, whether they cause disease or not.

Contents

On the molecular and cellular level, microbes can infect the host and divide rapidly, causing disease by being there and causing a homeostatic imbalance in the body, or by secreting toxins which cause symptoms to appear. Viruses can also infect the host with virulent DNA, which can affect normal cell processes (transcription, translation, etc.), protein folding, or evading the immune response. [2]

Pathogenicity

Pathogen history

One of the first pathogens observed by scientists was Vibrio cholerae, described in detail by Filippo Pacini in 1854. His initial findings were just drawings of the bacteria but, up until 1880, he published many other papers concerning the bacteria. He described how it causes diarrhea as well as developed effective treatments against it. Most of these findings went unnoticed until Robert Koch rediscovered the organism in 1884 and linked it to the disease.

Giardia lamblia was discovered by Leeuwenhoeck in the 1600s [2] [3] but was not found to be pathogenic until the 1970s, when an EPA-sponsored symposium was held following a large outbreak in Oregon involving the parasite. Since then, many other organisms have been identified as pathogens, such as H. pylori and E. coli, which have allowed scientists to develop antibiotics to combat these harmful microorganisms.

Types of pathogens

Pathogens include bacteria, fungi, protozoa, parasitic worms (helminths), and viruses.

Each of these different types of organisms can then be further classified as a pathogen based on its mode of transmission. This includes the following: food borne, airborne, waterborne, blood-borne, and vector-borne. Many pathogenic bacteria, such as food-borne Staphylococcus aureus and Clostridium botulinum , secrete toxins into the host to cause symptoms. HIV and hepatitis B are viral infections caused by blood-borne pathogens. Aspergillus the most common pathogenic fungi, secretes aflatoxin, which acts as a carcinogen and contaminates many foods, especially those grown underground (nuts, potatoes, etc.). [4]

Transmission methods

Within the host, pathogens can do a variety of things to cause disease and trigger the immune response.

Microbes and fungi cause symptoms due to their high rate of reproduction and tissue invasion. This causes an immune response, resulting in common symptoms as phagocytes break down the bacteria within the host.

Some bacteria, such as H. pylori, can secrete toxins into the surrounding tissues, resulting in cell death or inhibition of normal tissue function.

Viruses, however, use a completely different mechanism to cause disease. Upon entry into the host, they can do one of two things. Many times, viral pathogens enter the lytic cycle; this is when the virus inserts its DNA or RNA into the host cell, replicates, and eventually causes the cell to lyse, releasing more viruses into the environment. The lysogenic cycle, however, is when the viral DNA is incorporated into the host genome, allowing it to go unnoticed by the immune system. Eventually, it gets reactivated and enters the lytic cycle, giving it an indefinite "shelf life" so to speak. [5]

Context-based host interactions

Types of interactions

There are three types of host-pathogen interactions based on how the pathogen interacts with the host. Commensalism is when the pathogen benefits while the host gains nothing from the interaction. An example of this is Bacteroides thetaiotaomicron, which resides in the human intestinal tract but provides no known benefits. [6] Mutualism occurs when both the pathogen and the host benefit from the interaction, as seen in the human stomach. Many of the bacteria aid in breaking down nutrients for the host, and in return, our bodies act as their ecosystem. [7] Parasitism occurs when the pathogen benefits from the relationship while the host is harmed. This can be seen in the unicellular Plasmodium falciparum parasite which causes malaria in humans. [8]

Pathogenic variability in hosts

Although pathogens do have the capability to cause disease, they do not always do so. This is described as context-dependent pathogenicity. Scientists believe that this variability comes from both genetic and environmental factors within the host. One example of this in humans is E. coli. Normally, this bacteria flourishes as a part of the normal, healthy microbiota in the intestines. However, if it relocates to a different region of the digestive tract or the body, it can cause intense diarrhea. So, while E. coli is classified as a pathogen, but it does not always act as such. [9] This example can also be applied to S. aureus and other common microbial flora in humans.

Current pathogenic treatment methods

Currently, antimicrobials are the primary treatment method for pathogens. These drugs are specifically designed to kill microbes or inhibit further growth within the host environment. Multiple terms can be used to describe antimicrobial drugs. Antibiotics are chemicals made by microbes that can be used against other pathogens, such as penicillin and erythromycin. Semi-synthetics are antimicrobials that are derived from bacteria, but they are enhanced to have a greater effect. In contrast to both of these, synthetic are strictly made in the lab to combat pathogenicity. Each of these three types of antimicrobials can be classified into two subsequent groups: bactericidal and bacteriostatic. Bactericidal substances kill microorganisms while bacteriostatic substances inhibit microbial growth. [10]

The main problem with pathogenic drug treatments in the modern world is drug resistance. Many patients don't take the full treatment of drugs, leading to the natural selection of resistant bacteria. One example of this is methicillin-resistant Staphylococcus aureus (MRSA). Because of antibiotic overuse, only the bacteria which have developed genetic mutations to combat the drug can survive. This reduces drug effectiveness and renders many treatments useless. [11]

Future directions

Thanks to network analysis of host–pathogen interactions and large-scale analyses of RNA sequencing data from infected host cells, [12] we know that pathogen proteins causing an extensive rewiring of the host interactome have a higher impact in pathogen fitness during infection. These observations suggest that hubs in the host–pathogen interactome should be explored as promising targets for antimicrobial drug design. [13] Dual-species proteomics could also be employed to study host-pathogen interactions by simultaneously quantifying proteins newly synthesized by the host and pathogen [14] . Currently, many scientists are aiming to understand genetic variability and how it contributes to pathogen interaction and variability within the host. They are also aiming to limit the transmission methods for many pathogens to prevent rapid spread in hosts. As we learn more about the host–pathogen interaction and the amount of variability within hosts, [15] the definition of the interaction needs to be redefined. Casadevall proposes that pathogenicity should be determined based on the amount of damage caused to the host, classifying pathogens into different categories based on how they function in the host. [16] However, in order to cope with the changing pathogenic environment, treatment methods need to be revised to deal with drug-resistant microbes.

See also

Related Research Articles

<span class="mw-page-title-main">Bacteriophage</span> Virus that infects and replicates within bacteria

A bacteriophage, also known informally as a phage, is a virus that infects and replicates within bacteria and archaea. The term was derived from "bacteria" and the Greek φαγεῖν, meaning "to devour". Bacteriophages are composed of proteins that encapsulate a DNA or RNA genome, and may have structures that are either simple or elaborate. Their genomes may encode as few as four genes and as many as hundreds of genes. Phages replicate within the bacterium following the injection of their genome into its cytoplasm.

<span class="mw-page-title-main">Immune system</span> Biological system protecting an organism against disease

The immune system is a network of biological systems that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as cancer cells and objects such as wood splinters, distinguishing them from the organism's own healthy tissue. Many species have two major subsystems of the immune system. The innate immune system provides a preconfigured response to broad groups of situations and stimuli. The adaptive immune system provides a tailored response to each stimulus by learning to recognize molecules it has previously encountered. Both use molecules and cells to perform their functions.

A human pathogen is a pathogen that causes disease in humans.

<span class="mw-page-title-main">Infection</span> Invasion of an organisms body by pathogenic agents

An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable disease, is an illness resulting from an infection.

<span class="mw-page-title-main">Koch's postulates</span> Four criteria showing a causal relationship between a causative microbe and a disease

Koch's postulates are four criteria designed to establish a causal relationship between a microbe and a disease. The postulates were formulated by Robert Koch and Friedrich Loeffler in 1884, based on earlier concepts described by Jakob Henle, and the statements were refined and published by Koch in 1890. Koch applied the postulates to describe the etiology of cholera and tuberculosis, both of which are now ascribed to bacteria. The postulates have been controversially generalized to other diseases. More modern concepts in microbial pathogenesis cannot be examined using Koch's postulates, including viruses and asymptomatic carriers. They have largely been supplanted by other criteria such as the Bradford Hill criteria for infectious disease causality in modern public health and the Molecular Koch's postulates for microbial pathogenesis.

Virulence is a pathogen's or microorganism's ability to cause damage to a host.

Mycoplasma pneumoniae is a very small cell wall-less bacterium in the class Mollicutes. It is a human pathogen that causes the disease mycoplasma pneumonia, a form of atypical bacterial pneumonia related to cold agglutinin disease. M. pneumoniae is characterized by the absence of a peptidoglycan cell wall and resulting resistance to many antibacterial agents. The persistence of M. pneumoniae infections even after treatment is associated with its ability to mimic host cell surface composition.

<i>Rickettsia rickettsii</i> Species of bacterium

Rickettsia rickettsii is a Gram-negative, intracellular, coccobacillus bacterium that was first discovered in 1902. Having a reduced genome, the bacterium harvests nutrients from its host cell to carry out respiration, making it an organoheterotroph. Maintenance of its genome is carried out through vertical gene transfer where specialization of the bacterium allows it to shuttle host sugars directly into its TCA cycle.

<span class="mw-page-title-main">Innate immune system</span> Immunity strategy in living beings

The innate immune system or nonspecific immune system is one of the two main immunity strategies in vertebrates. The innate immune system is an alternate defense strategy and is the dominant immune system response found in plants, fungi, prokaryotes, and invertebrates.

Virulence factors are cellular structures, molecules and regulatory systems that enable microbial pathogens to achieve the following:

<i>Aeromonas hydrophila</i> Species of heterotrophic, Gram-negative, bacterium

Aeromonas hydrophila is a heterotrophic, Gram-negative, rod-shaped bacterium mainly found in areas with a warm climate. This bacterium can be found in fresh or brackish water. It can survive in aerobic and anaerobic environments, and can digest materials such as gelatin and hemoglobin. A. hydrophila was isolated from humans and animals in the 1950s. It is the best known of the species of Aeromonas. It is resistant to most common antibiotics and cold temperatures and is oxidase- and indole-positive. Aeromonas hydrophila also has a symbiotic relationship as gut flora inside of certain leeches, such as Hirudo medicinalis.

Host tropism is the infection specificity of certain pathogens to particular hosts and host tissues. This explains why most pathogens are only capable of infecting a limited range of host organisms.

<span class="mw-page-title-main">Medical microbiology</span> Branch of medical science

Medical microbiology, the large subset of microbiology that is applied to medicine, is a branch of medical science concerned with the prevention, diagnosis and treatment of infectious diseases. In addition, this field of science studies various clinical applications of microbes for the improvement of health. There are four kinds of microorganisms that cause infectious disease: bacteria, fungi, parasites and viruses, and one type of infectious protein called prion.

<span class="mw-page-title-main">Pathogenic bacteria</span> Disease-causing bacteria

Pathogenic bacteria are bacteria that can cause disease. This article focuses on the bacteria that are pathogenic to humans. Most species of bacteria are harmless and are often beneficial but others can cause infectious diseases. The number of these pathogenic species in humans is estimated to be fewer than a hundred. By contrast, several thousand species are part of the gut flora present in the digestive tract.

<span class="mw-page-title-main">Microbial symbiosis and immunity</span>

Long-term close-knit interactions between symbiotic microbes and their host can alter host immune system responses to other microorganisms, including pathogens, and are required to maintain proper homeostasis. The immune system is a host defense system consisting of anatomical physical barriers as well as physiological and cellular responses, which protect the host against harmful microorganisms while limiting host responses to harmless symbionts. Humans are home to 1013 to 1014 bacteria, roughly equivalent to the number of human cells, and while these bacteria can be pathogenic to their host most of them are mutually beneficial to both the host and bacteria.

Pathogenomics is a field which uses high-throughput screening technology and bioinformatics to study encoded microbe resistance, as well as virulence factors (VFs), which enable a microorganism to infect a host and possibly cause disease. This includes studying genomes of pathogens which cannot be cultured outside of a host. In the past, researchers and medical professionals found it difficult to study and understand pathogenic traits of infectious organisms. With newer technology, pathogen genomes can be identified and sequenced in a much shorter time and at a lower cost, thus improving the ability to diagnose, treat, and even predict and prevent pathogenic infections and disease. It has also allowed researchers to better understand genome evolution events - gene loss, gain, duplication, rearrangement - and how those events impact pathogen resistance and ability to cause disease. This influx of information has created a need for bioinformatics tools and databases to analyze and make the vast amounts of data accessible to researchers, and it has raised ethical questions about the wisdom of reconstructing previously extinct and deadly pathogens in order to better understand virulence.

A neutralizing antibody (NAb) is an antibody that defends a cell from a pathogen or infectious particle by neutralizing any effect it has biologically. Neutralization renders the particle no longer infectious or pathogenic. Neutralizing antibodies are part of the humoral response of the adaptive immune system against viruses, bacteria and microbial toxin. By binding specifically to surface structures (antigen) on an infectious particle, neutralizing antibodies prevent the particle from interacting with its host cells it might infect and destroy.

In biology, a pathogen, in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ.

Host microbe interactions in <i>Caenorhabditis elegans</i>

Caenorhabditis elegans- microbe interactions are defined as any interaction that encompasses the association with microbes that temporarily or permanently live in or on the nematode C. elegans. The microbes can engage in a commensal, mutualistic or pathogenic interaction with the host. These include bacterial, viral, unicellular eukaryotic, and fungal interactions. In nature C. elegans harbours a diverse set of microbes. In contrast, C. elegans strains that are cultivated in laboratories for research purposes have lost the natural associated microbial communities and are commonly maintained on a single bacterial strain, Escherichia coli OP50. However, E. coli OP50 does not allow for reverse genetic screens because RNAi libraries have only been generated in strain HT115. This limits the ability to study bacterial effects on host phenotypes. The host microbe interactions of C. elegans are closely studied because of their orthologs in humans. Therefore, the better we understand the host interactions of C. elegans the better we can understand the host interactions within the human body.

The following outline is provided as an overview of and topical guide to concepts related to infectious diseases in humans.

References

  1. ↑ Casadevall A, Pirofski LA (December 2000). "Host–pathogen interactions: basic concepts of microbial commensalism, colonization, infection, and disease". Infection and Immunity. 68 (12): 6511–6518. doi:10.1128/IAI.68.12.6511-6518.2000. PMC   97744 . PMID   11083759.
  2. 1 2 Rendtorff RC (March 1954). "The experimental transmission of human intestinal protozoan parasites. II. Giardia lamblia cysts given in capsules". American Journal of Hygiene. 59 (2): 209–220. doi:10.1093/oxfordjournals.aje.a119634. PMID   13138586.
  3. ↑ Dobell C (1920). "The Discovery of the Intestinal Protozoa of Man". Proceedings of the Royal Society of Medicine. 13 (Sect Hist Med): 1–15. doi:10.1177/003591572001301601. PMC   2151982 . PMID   19981292.
  4. ↑ San-Blas G, Calderone RA (2008). Pathogenic fungi: Insights in molecular biology. Horizon Scientific Press.
  5. ↑ "How Pathogens Make Us Sick". Infectious Disease. The National Academies.
  6. ↑ Hooper LV, Gordon JI (May 2001). "Commensal host-bacterial relationships in the gut". Science. 292 (5519): 1115–1118. Bibcode:2001Sci...292.1115H. doi:10.1126/science.1058709. PMID   11352068. S2CID   44645045.
  7. ↑ Bäckhed F, Ley RE, Sonnenburg JL, Peterson DA, Gordon JI (March 2005). "Host-bacterial mutualism in the human intestine". Science. 307 (5717): 1915–1920. Bibcode:2005Sci...307.1915B. doi:10.1126/science.1104816. PMID   15790844. S2CID   6332272.
  8. ↑ Sato S (January 2021). "Plasmodium-a brief introduction to the parasites causing human malaria and their basic biology". Journal of Physiological Anthropology. 40 (1): 1. doi: 10.1186/s40101-020-00251-9 . PMC   7792015 . PMID   33413683.
  9. ↑ Clermont O, Bonacorsi S, Bingen E (October 2000). "Rapid and simple determination of the Escherichia coli phylogenetic group". Applied and Environmental Microbiology. 66 (10): 4555–4558. Bibcode:2000ApEnM..66.4555C. doi:10.1128/aem.66.10.4555-4558.2000. PMC   92342 . PMID   11010916.
  10. ↑ Brown, AE (2012). Benson's Microbiological Applications: Laboratory Manual in General Microbiology, Short Version (12th ed.). New York, U.S.: Mc-Graw-Hill.
  11. ↑ Neu HC (August 1992). "The crisis in antibiotic resistance". Science. 257 (5073): 1064–1073. Bibcode:1992Sci...257.1064N. doi:10.1126/science.257.5073.1064. PMID   1509257. S2CID   1261981.
  12. ↑ Chakravorty S, Yan B, Wang C, Wang L, Quaid JT, Lin CF, et al. (December 2019). "Integrated Pan-Cancer Map of EBV-Associated Neoplasms Reveals Functional Host-Virus Interactions". Cancer Research. 79 (23): 6010–6023. doi: 10.1158/0008-5472.CAN-19-0615 . PMC   6891172 . PMID   31481499.
  13. ↑ Crua Asensio N, Muñoz Giner E, de Groot NS, Torrent Burgas M (January 2017). "Centrality in the host–pathogen interactome is associated with pathogen fitness during infection". Nature Communications. 8: 14092. Bibcode:2017NatCo...814092C. doi:10.1038/ncomms14092. PMC   5241799 . PMID   28090086.
  14. ↑ Liu, Yang Sylvia; Zhang, Chengqian; Khoo, Bee Luan; Hao, Piliang; Chua, Song Lin (2024-09-02). "Dual-species proteomics and targeted intervention of animal-pathogen interactions". Journal of Advanced Research. doi:10.1016/j.jare.2024.08.038. ISSN   2090-1232.
  15. ↑ Avraham R, Haseley N, Brown D, Penaranda C, Jijon HB, Trombetta JJ, et al. (September 2015). "Pathogen Cell-to-Cell Variability Drives Heterogeneity in Host Immune Responses". Cell. 162 (6): 1309–1321. doi:10.1016/j.cell.2015.08.027. PMC   4578813 . PMID   26343579.
  16. ↑ Casadevall A, Pirofski LA (August 1999). "Host–pathogen interactions: redefining the basic concepts of virulence and pathogenicity". Infection and Immunity. 67 (8): 3703–3713. doi:10.1128/IAI.67.8.3703-3713.1999. PMC   96643 . PMID   10417127.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.