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Learning objectives

  • Describe virulence factors unique to fungi and parasites
  • Compare virulence factors of fungi and bacteria
  • Explain the difference between protozoan parasites and helminths
  • Describe how helminths evade the host immune system

Although fungi and parasites are important pathogens causing infectious diseases, their pathogenic mechanisms and virulence factors are not as well characterized as those of bacteria. Despite the relative lack of detailed mechanisms, the stages of pathogenesis and general mechanisms of virulence involved in disease production by these pathogens are similar to those of bacteria.

Fungal virulence

Pathogenic fungi can produce virulence factors that are similar to the bacterial virulence factors that have been discussed earlier in this chapter. In this section, we will look at the virulence factors associated with species of Candida , Cryptococcus, Claviceps, and Aspergillus .

Candida albicans is an opportunistic fungal pathogen and causative agent of oral thrush, vaginal yeast infections, and cutaneous candidiasis. Candida produces adhesins (surface glycoproteins) that bind to the phospholipids of epithelial and endothelial cells. To assist in spread and tissue invasion, Candida produces proteases and phospholipases (i.e., exoenzymes). One of these proteases degrades keratin, a structural protein found on epithelial cells, enhancing the ability of the fungus to invade host tissue. In animal studies, it has been shown that the addition of a protease inhibitor led to attenuation of Candida infection. K. Fallon et al. “Role of Aspartic Proteases in Disseminated Candida albicans Infection in Mice.” Infection and Immunity 65 no. 2 (1997):551–556. Similarly, the phospholipases can affect the integrity of host cell membranes to facilitate invasion.

The main virulence factor for Cryptococcus , a fungus that causes pneumonia and meningitis, is capsule production. The polysaccharide glucuronoxylomannan is the principal constituent of the Cryptococcus capsule. Similar to encapsulated bacterial cells, encapsulated Cryptococcus cells are more resistant to phagocytosis than nonencapsulated Cryptococcus , which are effectively phagocytosed and, therefore, less virulent.

Like some bacteria, many fungi produce exotoxins. Fungal toxins are called mycotoxin s . Claviceps purpurea , a fungus that grows on rye and related grains, produces a mycotoxin called ergot toxin, an alkaloid responsible for the disease known as ergotism . There are two forms of ergotism: gangrenous and convulsive. In gangrenous ergotism , the ergot toxin causes vasoconstriction, resulting in improper blood flow to the extremities, eventually leading to gangrene. A famous outbreak of gangrenous ergotism occurred in Eastern Europe during the 5th century AD due to the consumption of rye contaminated with C. purpurea . In convulsive ergotism , the toxin targets the central nervous system, causing mania and hallucinations.

The mycotoxin aflatoxin is a virulence factor produced by the fungus Aspergillus , an opportunistic pathogen that can enter the body via contaminated food or by inhalation. Inhalation of the fungus can lead to the chronic pulmonary disease aspergillosis , characterized by fever, bloody sputum, and/or asthma. Aflatoxin acts in the host as both a mutagen (a substance that causes mutations in DNA) and a carcinogen (a substance involved in causing cancer), and has been associated with the development of liver cancer . Aflatoxin has also been shown to cross the blood-placental barrier. C.P. Wild et al. “In-utero exposure to aflatoxin in west Africa.” Lancet 337 no. 8757 (1991):1602. A second mycotoxin produced by Aspergillus is gliotoxin . This toxin promotes virulence by inducing host cells to self-destruct and by evading the host’s immune response by inhibiting the function of phagocytic cells as well as the pro-inflammatory response. Like Candida , Aspergillus also produces several proteases. One is elastase , which breaks down the protein elastin found in the connective tissue of the lung, leading to the development of lung disease. Another is catalase , an enzyme that protects the fungus from hydrogen peroxide produced by the immune system to destroy pathogens.

Questions & Answers

what is the difference between biogenesis & abiogenesis
Mayuri Reply
what is mean by pasturation method?
Mayuri Reply
Pasteurization is a process that kills harmful bacteria and creates an extended shelf life for your milk. ... It's pretty simple—we take the milk from the cows, we rapidly heat it to a high enough temperature to kill the bacteria, and then we cool it back down before packaging and shipping it to you
Kaviya
tell me about abiogenessis &biogenesis
Mayuri
discribe aristol spontaneous generation theory in brif
Mayuri Reply
The Greek philosopher Aristotle (384–322 BC) was one of the earliest recorded scholars to articulate the theory of spontaneous generation, the notion that life can arise from nonliving matter. Aristotle proposed that life arose from nonliving material if the material contained pneuma (“vital heat”).
Kaviya
thank you 😊
Mayuri
No mention dear 😊
Kaviya
what is the hetropolysachharide 's monomeric units?
Hinal Reply
Homopolysaccharides contain only a single type of monomeric unit; heteropolysaccharides contain two or more different kinds of monomeric units.Some homopolysaccharides serve as storage forms of monosaccharides used as fuels; starch and glycogen are homopolysaccharides of this type.
Kaviya
Polysaccharides (glycans) are long chains of monosaccharides. Each monosaccharide is connected together via glycosidic bonds to form the polymeric structure known as polysaccharide. ... units in the chain; whereas, a heteropolysaccharide is composed of two or more types of monosaccharides.
Hetshree
They are polymer of different monosaccharide units...on hydrolysis, it yeilds different monosaccharides example; Mucopolysaccharide and Heparin.
Swetha
what is virulence plasmid
Harsh
Virulence plasmids are usually large (>40 kb) low copy elements and encode genes that promote host–pathogen interactions. Although virulence plasmids provide advantages to bacteria in specific conditions, they often impose fitness costs on their host.
Kaviya
can you suggest a good book for biotechnology
Harsh
In my point of view, u can refer A textbook of biotechnology by R C Dubey
Kaviya
Biotechnology by B. D. Singh
Microbiology
how psychrophiles live at such a low temperature that their proteins dont get denatured
Harsh Reply
anti freeze proteins are synthesized to prevent such denaturations..
Swetha
okay thank u
Harsh
can you suggest me a book for food microbiology
Harsh
and for industrial microbiology
Harsh
food microbiology by M.R Adam and M.O.Moss
Swetha
Industrial microbiology by L.E.casida.
Swetha
maam can you suggest a best book that have applied microbiology concepts
Harsh
mem can you suggest a best book of microscopy
for applied microbiology K.R.Aneja and other book by Allen Laskin
Swetha
for microscopy Kirsteen Roger.
Swetha
Define sterilization
Pramod Reply
Sterilization refers to any process that removes, kills, or deactivates all forms of life and other biological agents like prions present in a specific surface, object or fluid, for example food or biological culture media.
Kaviya
sterilization is the process of making an aseptic condition or microbe free environment to keep the objects from any kind of contamination.
Swetha
Cool. I work for a Sterilisation company in India. We do Gamma Radiation, Steam Sterilisation and Ethylene Oxide Sterilisation
Shanu
Explain the polymerization reaction of DNA polymerase enzyme?
Swetha Reply
I think in my opinion polymerization means monomers connects and produce large molecular chain
LEE
DNA polymerase I catalyzes the polymerization of dNTPs into DNA. This occurs by the addition of a dNTP (as dNMP) to the 3' end of a DNA chain, hence chain growth occurs in a 5' to 3' direction.Thus in this reaction, a phosphoanhydride bond in the dNTP is broken, and a phosphodiester is formed.
Kaviya
Thank you
Swetha
ok..Thank you
Swetha
Nicely explained
Shanu
Welcome 🙏
Kaviya
write a note of microbiology with definition
Lucky Reply
Microbiology is the study of all living organisms that are too small to be visible with the naked eye. This includes bacteria, archaea, viruses, fungi, prions, protozoa and algae, collectively known as 'microbes'.
si
write down the difference branches of microbiology
Lucky
Baccteriolog: the study of bactera. Immunology: the study of the immune system. It looks at the relationships between pathogens such as bacteria and viruses and their hosts. Mycology: the study of fungi, such as yeasts and molds. Nematology:the study of nematodes (roundworms).
Aashi
Bacteriology: the study of bacteria. Immunology: the study of the immune system. It looks at the relationships between pathogens such as bacteria and viruses and their hosts. Mycology: the study of fungi, such as yeasts and molds. Nematology: the study of nematodes (roundworms).
si
Parasitology :the study of parasites. Phycology: the study of algae. Protozoology : the study of protozoa, single-celled organisms like amoebae. Virology:the study of viruses.
Aashi
Parasitology: the study of parasites. Not all parasites are microorganisms, but many are. Protozoa and bacteria can be parasitic; the study of bacterial parasites is usually categorized as part of bacteriology. Phycology: the study of algae. Protozoology: the study of protozoa, single-celled organis
si
Virology: the study of viruses.
si
difference between gram negative and gram positive bacteria.
Hirut
the difference between gram negative and gram positive bacteria is the colour which is obtained after staining techniques.. Gram positive bacteria stain violet due to the presence of a thick layer of peptidoglycan in their cell walls, which retains the crystal violet these cells are stained with.
Kaviya
Father of paleobotany?
LEE
The father of paleobotany is Birbal Sahni...
Kaviya
It is the study and recovery of ancient plants and geological contents
Kaviya
Father of immunology
Kaviya
Louis pasture was really father of immunology,despite Edward jenner poineering by introducing the vaccine against smallpox.
TASAWAR
thank you anna
Kaviya
define a cell?
Swetha
thank you Kaviya
Hirut
Cells have many parts, each with a different function. Some of these parts, called organelles, are specialized structures that perform certain tasks within the cell.
Kaviya
cell is the basic structural and functional unit of life.
TASAWAR
In biology, a cell ([sɛl], ”plural: cells”) is defined as the structural, functional, and biological unit of all organisms. It is an autonomous self-replicating unit that may exist as a functional independent unit of life (as in the case of a unicellular organism), or as a sub-unit in a multicellula
si
thank you
Swetha
all bacterial cells have
Millie Reply
refamycin kills bacterial cell by acting on ...?
Yogesh Reply
monensin kills bacterial cell by acting on
Yogesh
genetic linkage cross over ratio ?
Yogesh
what is microbiology?
onuoha Reply
Hi!!! wants to know the meaning of microbiology
Christian Reply
Microbiology, study of microorganisms, or microbes, a diverse group of generally minute, simple life-forms that include bacteria, archaea, algae, fungi, protozoa, and viruses. The field is concerned with the structure, function, and classification of such organisms .
si
to study the life of microorganisms or microbes by knowing their characteristics types and relative species in lab
ayesha
Microbiology is simply the study of microbial world.
Shyamji
Microbiology is the branch of biology in which we study microorganisms those which cannot be seen with naked eye these are bacteria,fungi,viruses Protozoa etc.
Nisar
thanks for that information
Better
microbiology, is a study of microorganisms adiversegroup of generally, simple life,
Better
Thanks ever so much for the discussion.
Christian
Can anyone help with Organic Chemistry, and types?
Christian
which topic in organic chemistry
si
Introduction to organic chemistry.
Christian
Organic chemistry is the chemistry of carbon, an element that forms strong chemical bonds to other carbon atoms as well as to many other elements like hydrogen, oxygen, nitrogen, and the halogens. ... Many are composed of only carbon and hydrogen, collectively called hydrocarbons.
si
microbiology is the study of microorganisms like (bacteria ,viruses,fungi,protozoa and algae) their relationship to environment and their impact on environment .
TASAWAR
can one tell me what are reservoirs and their types with explanation.
onuoha
structure of protists
Rayyanu Reply
what is enzyme engineering
swati Reply
what is the difference between prokaryotes and eukaryotes?
Guirlaine Reply
Prokaryotes lack nucleus in their cells while eukaryotes have well defined nucleus in their cells
Ayo
Prokaryotes are organisms that consist of a single prokaryotic cell. Eukaryotic cells are found in plants, animals, fungi, and protists. They range from 10–100 μm in diameter, and their DNA is contained within a membrane-bound nucleus. Eukaryotes are organisms containing eukaryotic cells.
Pratibha
Practice MCQ 2

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Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
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