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Learning objectives

  • Identify the most common bacteria that can cause infections of the upper and lower respiratory tract
  • Compare the major characteristics of specific bacterial diseases of the respiratory tract

The respiratory tract can be infected by a variety of bacteria, both gram positive and gram negative. Although the diseases that they cause may range from mild to severe, in most cases, the microbes remain localized within the respiratory system. Fortunately, most of these infections also respond well to antibiotic therapy.

Streptococcal infections

A common upper respiratory infection, streptococcal pharyngitis ( strep throat ) is caused by Streptococcus pyogenes . This gram-positive bacterium appears as chains of cocci, as seen in [link] . Rebecca Lancefield serologically classified streptococci in the 1930s using carbohydrate antigens from the bacterial cell walls. S. pyogenes is the sole member of the Lancefield group A streptococci and is often referred to as GAS, or group A strep.

Micrograph of chains of spheres.
This scanning electron micrograph of Streptococcus pyogenes shows the characteristic cellular phenotype resembling chains of cocci. (credit: modification of work by U.S. Centers for Disease Control and Prevention - Medical Illustrator)

Similar to streptococcal infections of the skin, the mucosal membranes of the pharynx are damaged by the release of a variety of exoenzymes and exotoxins by this extracellular pathogen. Many strains of S. pyogenes can degrade connective tissues by using hyaluronidase , collagenase and streptokinase . Streptokinase activates plasmin, which leads to degradation of fibrin and, in turn, dissolution of blood clots, which assists in the spread of the pathogen. Released toxins include streptolysin s that can destroy red and white blood cells. The classic signs of streptococcal pharyngitis are a fever higher than 38 °C (100.4 °F); intense pharyngeal pain; erythema associated with pharyngeal inflammation; and swollen, dark-red palatine tonsils, often dotted with patches of pus; and petechiae (microcapillary hemorrhages) on the soft or hard palate (roof of the mouth) ( [link] ). The submandibular lymph nodes beneath the angle of the jaw are also often swollen during strep throat.

Some strains of group A streptococci produce erythrogenic toxin . This exotoxin is encoded by a temperate bacteriophage (bacterial virus) and is an example of phage conversion (see The Viral Life Cycle ). The toxin attacks the plasma membranes of capillary endothelial cells and leads to scarlet fever (or scarlatina), a disseminated fine red rash on the skin, and strawberry tongue , a red rash on the tongue ( [link] ). Severe cases may even lead to streptococcal toxic shock syndrome (STSS) , which results from massive superantigen production that leads to septic shock and death.

S. pyogenes can be easily spread by direct contact or droplet transmission through coughing and sneezing. The disease can be diagnosed quickly using a rapid enzyme immunoassay for the group A antigen. However, due to a significant rate of false-negative results (up to 30% WL Lean et al. “Rapid Diagnostic Tests for Group A Streptococcal Pharyngitis: A Meta-Analysis.” Pediatrics 134, no. 4 (2014):771–781. ), culture identification is still the gold standard to confirm pharyngitis due to S. pyogenes . S. pyogenes can be identified as a catalase-negative, beta hemolytic bacterium that is susceptible to 0.04 units of bacitracin. Antibiotic resistance is limited for this bacterium, so most β-lactams remain effective; oral amoxicillin and intramuscular penicillin G are those most commonly prescribed.

Questions & Answers

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
proton positive charge. electron negative charge. And no charge of the neutron.
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)
what are the roles of microorganisms in human being
Buhari Reply
some causes disease, others are not disease causing
they're necessary in our digestive system+the skin,everywhere actually the number of them in the human body alone is higher(by millions)than the number of humans cells,they're indispensable in the food industry,others are fundamental to make medicines and more,what exactly are you asking about ?
What are the natural occurring elements found in organisms on earth?
Otu Reply
some of the naturally occurring elements found in organisms are carbon, nitrogen, hydrogen, oxygen
some of them are carbon, oxygen, nitrogen, hydrogen, phosphorus and sulfur
what is Zika virus?
Somali Reply
Zika virus is a mosquito-borne flavivirus that was first identified in Uganda in 1947 in monkeys. 
in pregnancy it can cause the unborn child's head to underdevelop so that it does not grow along with the rest of the body
intracellular vesicles are found in
Akshay Reply
how do i report widal slide results
Isaac Reply
how food can be used as a substrate for the growth of microorganisms
Ashi Reply
what is the importance of understanding chemistry in the field of microbiology and food technology?
Charmaine Reply
What is different between eukaryotes and prokcaryotic
Abia Reply
main difference is that eukaryotic cells possess membrane bound organelles
prokaryotes are primitive organisms that doesn't contain membrane bound nucleus or any orgenelle while in eukaryotes membrane bound orgenelles and nucleus is present
what s anatomy
jane Reply
its mean body structure, function, and systems
study of internal structure of living things
anatomy is the study structure of the made human
anotomy is the actual study of body internally and externally Which include how itis made. for what and what is need of this
la science anatomie c'est la science qui nous aide à étudier l'homme
Ancestor are they real
Rapheal Reply
yes of course
yes please
50 50, depending on the accuracy of the clan records.
Why protist is not a kingdom of Linnaeus 'S taxonomy?
Neha Reply
I dont know
Linnaeus used Aristotle's criteria for dividing living organisms into kingdoms. Plants are immobile and insensitive, while animals are mobile and sensitive. the creatures he saw through the microscope were mobile, so he attributed them to animals.
name the different types of media use in lab to detect the micro organisms
Shehzadi Reply
The different types of media used in the lab to detect the microorganisms is known as cell culture..
solid media or broth is used to grow and detect microorganisms
what is microbiology
the study of large living organisms
the study of organisms which are micro in range
what is autoclaving?
process for sterilization
is a machine used on the process of sterilisation
what is difference between hot air oven and autoclave as they both are used for sterilization ?
autoclave basically do moist heat sterilization while hot air oven do sterilization by dry heat.....
what is the microbe
which method out of these two is best?
why human have microbe
hi to all
depends on what to sterilize
what is knowledge
well idea

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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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