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Adhesion

Following the initial exposure, the pathogen adheres at the portal of entry. The term adhesion refers to the capability of pathogenic microbes to attach to the cells of the body using adhesion factors , and different pathogens use various mechanisms to adhere to the cells of host tissues.

Molecules (either proteins or carbohydrates) called adhesins are found on the surface of certain pathogens and bind to specific receptors (glycoproteins) on host cells. Adhesins are present on the fimbriae and flagella of bacteria, the cilia of protozoa, and the capsids or membranes of viruses. Protozoans can also use hooks and barbs for adhesion; spike proteins on viruses also enhance viral adhesion. The production of glycocalyces (slime layers and capsules) ( [link] ), with their high sugar and protein content, can also allow certain bacterial pathogens to attach to cells.

Biofilm growth can also act as an adhesion factor. A biofilm is a community of bacteria that produce a glycocalyx, known as extrapolymeric substance (EPS) , that allows the biofilm to attach to a surface. Persistent Pseudomonas aeruginosa infections are common in patients suffering from cystic fibrosis, burn wounds, and middle-ear infections (otitis media) because P. aeruginosa produces a biofilm. The EPS allows the bacteria to adhere to the host cells and makes it harder for the host to physically remove the pathogen. The EPS not only allows for attachment but provides protection against the immune system and antibiotic treatments, preventing antibiotics from reaching the bacterial cells within the biofilm. In addition, not all bacteria in a biofilm are rapidly growing; some are in stationary phase. Since antibiotics are most effective against rapidly growing bacteria, portions of bacteria in a biofilm are protected against antibiotics. D. Davies. “Understanding Biofilm Resistance to Antibacterial Agents.” Nature Reviews Drug Discovery 2 (2003):114–122.

Micrograph of round cells attached to a surface by long strands.
Glycocalyx produced by bacteria in a biofilm allows the cells to adhere to host tissues and to medical devices such as the catheter surface shown here. (credit: modification of work by Centers for Disease Control and Prevention)

Invasion

Once adhesion is successful, invasion can proceed. Invasion involves the dissemination of a pathogen throughout local tissues or the body. Pathogens may produce exoenzymes or toxins, which serve as virulence factors that allow them to colonize and damage host tissues as they spread deeper into the body. Pathogens may also produce virulence factors that protect them against immune system defenses. A pathogen’s specific virulence factors determine the degree of tissue damage that occurs. [link] shows the invasion of H. pylori into the tissues of the stomach, causing damage as it progresses.

Diagram of H. pylori invading the lining of the stomach. In the first image the H. pylori (an oval cell with 3 flagella is not able to penetrate the gastric mucin gel on top of the epithelial cells. Contact with stomach acid keeps the mucin lining the epithelial cell layer in a spongy gel-like state. This consistency is impermeable to the bacterium H. pylori. The second image shows the bacterium entering the lining. The bacterium releases urease, which neutralizes the stomach acid. This causes the mucin to liquefy and the bacterium can swim right through it.
H. pylori is able to invade the lining of the stomach by producing virulence factors that enable it pass through the mucin layer covering epithelial cells. (credit: modification of work by Zina Deretsky, National Science Foundation)

Intracellular pathogens achieve invasion by entering the host’s cells and reproducing. Some are obligate intracellular pathogens (meaning they can only reproduce inside of host cells) and others are facultative intracellular pathogens (meaning they can reproduce either inside or outside of host cells). By entering the host cells, intracellular pathogens are able to evade some mechanisms of the immune system while also exploiting the nutrients in the host cell.

Questions & Answers

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
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
The Day Jimmy"s Boa Ate the Wash by TRINKA HAKES NOBLE pictures by STEVEN KELLOGG
Alexia Reply
cytoplasmic membrane system in eukaryotes is called
Myerlyn Reply
I study in French,but I guess it's the same: we call it as the procaryotes "cytoplasme" but it's structure "cytosquelette" hope I helped.
BENNINI
hi bennini , I studied in English but I want to pursue in French .could u plz help me with French .thanks in advance
si
hi Si Yo, yes,of course how can I help you?
BENNINI
here can I download it where I could study it with relax dear
Irfan
hi
Ruth
ok
Francis
meaning of contagium vivum?
Royce Reply
explain transglutaminase cycle ?
Dilsath Reply
what a tropism in host
Khaliil Reply
HPV vaccine given to school children
Jayani Reply
Differentiation between electron, proton and neutron
Zainab Reply
proton .possitive charge electron . negative charge neutron . having no charge
Kifayat
proton positive charge. electron negative charge. And no charge of the neutron.
Saman
the nucleus is composed of electrons (-) charge and they turn around the Nucleon the Nucleon = neutron(no charge) + proton (+) a neutron can turn to a proton and vice versa (cuz they have the same mass=1)
BENNINI

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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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