chemistry

Mupirocin

Mupirocin 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 Mupirocin rather than just read about it. In short: Mupirocin, sold under the brand name Bactroban among others, is a topical antibiotic useful against superficial skin infections such as impetigo or folliculitis. It may also be used to get rid of methicillin-resistant S. aureus (MRSA) when present in the nose without symptoms.

Key takeaways

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

Reference excerpt

Mupirocin, sold under the brand name Bactroban among others, is a topical antibiotic useful against superficial skin infections such as impetigo or folliculitis. It may also be used to get rid of methicillin-resistant S. aureus (MRSA) when present in the nose without symptoms. Out of concerns of developing resistance, use for greater than ten days is not recommended. It is used as a cream or ointment applied to the skin. Common side effects include itchiness and rash at the site of application, headache, and nausea. Long-term use may result in increased growth of fungi. Use during pregnancy and breastfeeding appears to be safe. Mupirocin is chemically a carboxylic acid. It works by blocking a bacterium's ability to make protein, which usually results in bacterial death. Mupirocin was initially isolated in 1971 from Pseudomonas fluorescens. It is on the World Health Organization's List of Essential Medicines. In 2023, it was the 171st most commonly prescribed medication in the United States, with more than 2 million prescriptions. It is available as a generic medication.

Medical uses

Mupirocin is used as a topical treatment for bacterial skin infections (for example, boils, impetigo, or open wounds), which are typically due to infection by Staphylococcus aureus or Streptococcus pyogenes. It is also useful in the treatment of superficial methicillin-resistant Staphylococcus aureus (MRSA) infections. Mupirocin is inactive for most anaerobic bacteria, mycobacteria, mycoplasma, chlamydia, yeast, and fungi. Intranasal mupirocin before surgery is effective for prevention of post-operative wound infection with Staphylcoccus aureus and preventative intranasal or catheter-site treatment is effective for reducing the risk of catheter site infection in persons treated with chronic peritoneal dialysis.

Resistance Shortly after the clinical use of mupirocin began, strains of Staphylococcus aureus that were resistant to mupirocin emerged, with nares clearance rates of less than 30% success. Two distinct populations of mupirocin-resistant S. aureus were isolated. One strain possessed low-level resistance (MuL: MIC = 8–256 mg/L), and another possessed high-level resistance (MuH: MIC > 256 mg/L). Resistance in the MuL strains is probably due to mutations in the organism's wild-type isoleucyl-tRNA synthetase (IleS). In E. coli IleS, a single amino acid mutation was shown to alter mupirocin resistance. MuH is linked to the acquisition of a separate Ile synthetase gene, MupA. Mupirocin is not a viable antibiotic against MuH strains. Other antibiotic agents, such as azelaic acid, nitrofurazone, silver sulfadiazine, and ramoplanin, have been shown to be effective against MuH strains. Most strains of Cutibacterium acnes, a causative agent in the skin disease acne vulgaris, are naturally resistant to mupirocin. Most strains of Pseudomonas fluorescens are also resistant to mupirocin as they produce the antibiotic and it's possible other species of Pseudomonas may be resistant as well. The mechanism of action of mupirocin differs from other clinical antibiotics, rendering cross-resistance to other antibiotics unlikely. However, the MupA gene may co-transfer with other antibacterial resistance genes. This has been observed already with resistance genes for triclosan, tetracycline, and trimethoprim. It may also result in overgrowth of non-susceptible organisms. A second type of high-level resistant synthetase was discovered in 2012 and termed MupB. It was found in a Canadian MRSA isolate "MUP87" and is probably located on a nonconjugative plasmid.

Mechanism of action Pseudomonic acid (mupirocin) inhibits isoleucine—tRNA ligase in bacteria, leading to depletion of isoleucyl-tRNA and accumulation of the corresponding uncharged tRNA. Depletion of isoleucyl-tRNA results in inhibition of protein synthesis. The uncharged form of the tRNA binds to the aminoacyl-tRNA binding site of ribosomes, triggering the formation of (p)ppGpp, which in turn inhibits RNA synthesis. The combined inhibition of protein synthesis and RNA synthesis results in bacteriostasis. This mechanism of action is shared with furanomycin, an analog of isoleucine. Inhibition of the tRNA ligase/synthase is brought by the structural similarity between the molecule's monic acid "head" part and isoleucyl-adenylate (Ile-AMS). The unique 9-hydroxynonanoic acid "tail" wraps around the enzyme and further stabilizes the complex, keeping the catalytic part stuck. Mupirocin is able to bind to bacterial and archaeal versions of the enzyme, but not eukaryotic versions.

Biosynthesis

Mupirocin is a mixture of several pseudomonic acids, with pseudomonic acid A (PA-A) constituting greater than 90% of the mixture. Also present in mupirocin are pseudomonic acid B with an additional hydroxyl group at C8, pseudomonic acid C with a double bond between C10 and C11, instead of the epoxide of PA-A, and pseudomonic acid D with a double bond at C4' and C5' in the 9-hydroxy-nonanoic acid portion of mupirocin.

Biosynthesis of pseudomonic acid A The 74 kb mupirocin gene cluster contains six multi-domain enzymes and twenty-six other peptides (Table 1). Four large multi-domain type I polyketide synthase (PKS) proteins are encoded, as well as several single function enzymes with sequence similarity to type II PKSs. Therefore, it is believed that mupirocin is constructed by a mixed type I and type II PKS system. The mupirocin cluster exhibits an atypical acyltransferase (AT) organization, in that there are only two AT domains, and both are found on the same protein, MmpC. These AT domains are the only domains present on MmpC, while the other three type I PKS proteins contain no AT domains. The mupirocin pathway also contains several tandem acyl carrier protein doublets or triplets. This may be an adaptation to increase the throughput rate or to bind multiple substrates simultaneously. Pseudomonic acid A is the product of an esterification between the 17C polyketide monic acid and the 9C fatty acid 9-hydroxy-nonanoic acid. The possibility that the entire molecule is assembled as a single polyketide with a Baeyer-Villiger oxidation inserting an oxygen into the carbon backbone has been ruled out because C1 of monic acid and C9' of 9-hydroxy-nonanoic acid are both derived from C1 of acetate.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Mupirocin

Start with the simplest possible case. Write down what Mupirocin 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 Mupirocin 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 Mupirocin 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 Mupirocin

In research: Mupirocin 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 Mupirocin 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: Mupirocin is common in secondary-school and first-year university syllabi. It links to neighbouring topics Antibiotics, Carboxylate esters, Drugs developed by GSK plc, so understanding it makes those chapters shorter.
In everyday life: Look for Mupirocin 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 Mupirocin in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Mupirocin 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 Mupirocin out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Mupirocin in simple terms?

Why does Mupirocin 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 Mupirocin?

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 Mupirocin.