chemistry

Quellung reaction

Quellung reaction is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Quellung reaction rather than just read about it. In short: The quellung reaction, also called the Neufeld reaction, is a biochemical reaction in which antibodies bind to the bacterial capsule of Streptococcus pneumoniae, Klebsiella pneumoniae, Neisseria meningitidis, Bacillus anthracis, Haemophilus influenzae, Escherichia coli, and Salmonella. The antibody reaction allows these species to be visualized under a microscope.

Key takeaways

Quellung reaction belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Quellung reaction to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Quellung reaction from memory before moving on to harder problems.

Reference excerpt

The quellung reaction, also called the Neufeld reaction, is a biochemical reaction in which antibodies bind to the bacterial capsule of Streptococcus pneumoniae, Klebsiella pneumoniae, Neisseria meningitidis, Bacillus anthracis, Haemophilus influenzae, Escherichia coli, and Salmonella. The antibody reaction allows these species to be visualized under a microscope. If the reaction is positive, the capsule becomes opaque and appears to enlarge.

Quellung is the German word for "swelling" and describes the microscopic appearance of pneumococcal or other bacterial capsules after their polysaccharide antigen has combined with a specific antibody. The antibody usually comes from serum taken from an immunized laboratory animal. As a result of this combination, and precipitation of the large, complex molecule formed, the capsule appears to swell, because of increased surface tension, and its outlines become demarcated. The pneumococcal quellung reaction was first described in 1902 by the scientist Fred Neufeld, and applied only to Streptococcus pneumoniae, both as microscopic capsular swelling and macroscopic agglutination (clumping visible with the naked eye). It was initially an intellectual curiosity more than anything else, and could distinguish only the three pneumococcal serotypes known at that time. However, it acquired an important practical use with the advent of serum therapy to treat certain types of pneumococcal pneumonia in the 1920s because selection of the proper antiserum to treat an individual patient required correct identification of the infecting pneumococcal serotype, and the quellung reaction was the only method available to do this. Dr. Albert Sabin made modifications to Neufeld's technique so that it could be done more rapidly, and other scientists expanded the technique to identify 29 additional serotypes. Application of Neufeld's discoveries to other important areas of research came when Fred Griffith showed that pneumococci could transfer information to transform one serotype into another. Oswald Avery, Colin MacLeod, and Maclyn McCarty later showed that the transforming factor was deoxyribonucleic acid, or DNA. Serum therapy for infectious diseases was displaced by antibiotics in the 1940s, but identification of specific serotypes remained important as the understanding of the epidemiology of pneumococcal infections still required their identification to determine where different serotypes spread, as well as the variable invasiveness of different serotypes. Understanding the prevalence of various serotypes was also critical to the development of pneumococcal vaccines to prevent invasive infections. The quellung reaction has been used to identify the 93 known capsular serotypes of Streptococcus pneumoniae in diagnostic settings, but in recent years it has been challenged by the latex agglutination method, and further by molecular typing techniques such as the polymerase chain reaction, which detect DNA and therefore target genetic differences between serotypes. Currently, there are >100 known capsular serotypes.

References

Further reading Park, I. H., Pritchard, D., Cartee, R., Brandao, A., Brandileone, M. and Nahm, M. Discovery of a new capsular serotype (6C) within serogroup 6 of Streptococcus pneumoniae. Journal of Clinical Microbiology. 2007;45:1225–1233. Pai, R; Gertz, R. E.; Beall, B. (2006). "Sequential multiplex PCR approach for determining capsular serotypes of Streptococcus pneumoniae isolates". Journal of Clinical Microbiology. 44: 124–131. CiteSeerX 10.1.1.510.8589. doi:10.1128/jcm.44.1.124-131.2006. PMID 16390959. S2CID 86648528. {{cite journal}}: Cite uses deprecated parameter |citeseerx= (help) Austrian, R (1976). "The Quellung Reaction, a Neglected Microbiologic Technique". Mount Sinai Journal of Medicine. 43 (6): 699–709. PMID 13297.

Illustrations

Worked examples

Example 1 — a first encounter with Quellung reaction

Start with the simplest possible case. Write down what Quellung reaction claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Quellung reaction before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Quellung reaction ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Quellung reaction

In research: Quellung reaction appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Quellung reaction in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Quellung reaction is common in secondary-school and first-year university syllabi. It links to neighbouring topics 1902 in biology, 1902 introductions, Biochemistry methods, so understanding it makes those chapters shorter.
In everyday life: Look for Quellung reaction outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Quellung reaction in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Quellung reaction means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Quellung reaction out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Quellung reaction in simple terms?

Why does Quellung reaction matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Quellung reaction?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Quellung reaction.