Medicine (MD/DO)

Master Penicillin with Picmonic for Medicine

With Picmonic, facts become pictures. We've taken what the science shows - image mnemonics work - but we've boosted the effectiveness by building and associating memorable characters, interesting audio stories, and built-in quizzing.


Recommended Picmonics

picmonic thumbnail
Aminopenicillin Mechanisms
picmonic thumbnail
Aminopenicillin Uses
picmonic thumbnail
Ampicillin and Amoxicillin
picmonic thumbnail
Beta-Lactamase Inhibitors
picmonic thumbnail
Cephalosporins Overview


Penicillin, derived from the Penicillium fungi, is the first antibiotic that successfully treated previously deemed critical diseases such as syphilis, staphylococcus and streptococcus infections. There are different forms of penicillin such as penicillin G, penicillin V, benzathine penicillin, etc. All penicillins are beta-lactam antibiotics, and they are still widely used today for gram-positive organisms and spirochetes.Penicillin works via a few different mechanisms. First, it binds to the penicillin-binding protein (PBP), which is also known as the enzyme transpeptidase, to disrupt normal bacterial cell wall synthesis. Penicillin blocks transpeptidase (PBP), a critical enzyme involved in the peptidoglycan cross-linking in the bacterial cell wall. This causes bacterial death from osmotic pressure induced cytolysis. Penicillin’s small size allows it to penetrate deeply into the cell wall. Another mechanism is that penicillin activates autolytic enzymes in the bacteria to cause cell death. This antibiotic is classified as bactericidal because it actually causes bacterial cell death. Common adverse reactions from penicillin include hypersensitivity reactions. High doses of penicillin can also induce immune-mediated hemolysis due to a hapten mechanism, which is when the antibodies target the combination of penicillin in association with the red blood cells and activate complements to induce hemolysis and removal of red blood cells.
Gram Positive
Graham-cracker Positive-angel

Gram-positive organisms are bacteria that are able to retain crystal violet stain due to relatively high amount of peptidoglycan in the cell wall. Because penicillin inhibits the formation of peptidoglycan cross-linking in the bacterial cell wall, penicillin is bactericidal for many gram-positive organisms.


Spirochetes are bacteria with a long, helical coiled structure. Penicillin remains the drug of choice for many spirochete infections including syphilis.

Bind PBPs

Penicillin-binding protein (PBP), also known as the enzyme transpeptidase, is a component of many bacterial cell walls and is important for cell wall synthesis. Beta-lactam antibiotics in general bind to this protein which leads to abnormal cell wall structure and cell death.

Block Transpeptidase Cross-linking of Cell Wall
Transformer-peptide character Cross Linking the Walls

Transpeptidase, also known as PBP, is a critical enzyme in bacteria that cross-links peptidoglycan to form the cell wall. Penicillin blocks this enzyme and therefore inhibits bacterial cell wall synthesis.

Activate Autolytic Enzymes
Auto-lights with Enzyme

This is the third mechanism of penicillin which activates autolytic enzymes in the bacteria to cause cell death.


Unlike bacteriostatic agents, which simply stop bacteria from reproducing, bactericidal agents actually cause bacterial cell death.

Hypersensitivity Reactions

Penicillin hypersensitivity reactions are characterized by an overreaction of the body's immune response to a penicillin antibiotic. Common symptoms include rashes, hives, itchy eyes, and swollen tongue or face. Some individuals can have an anaphylactic reaction.

Hemolytic Anemia
Hemolysing-RBCs from Anemone

Penicillin in high doses can induce an immune mediated hemolysis of red blood cells. This occurs via the hapten mechanism in which antibodies are targeted against the combination of penicillin attached to red blood cells. This leads to complement activation and removal of red blood cells by the spleen.

Beta-lactamase Sensitive
(B lac) Black Beta-fish crying

Beta-lactamase is an enzyme that is produced by some bacteria to cleave beta-lactam antibiotics rendering them ineffective. Antibiotics that are beta-lactamase sensitive are susceptible to cleavage by beta-lactamases and are therefore likely to be ineffective against beta-lactamase producing bacteria.


Take the Penicillin Quiz

Picmonic's rapid review multiple-choice quiz allows you to assess your knowledge.

It's worth every penny

Our Story Mnemonics Increase Mastery and Retention

Memorize facts with phonetic mnemonics

Unforgettable characters with concise but impactful videos (2-4 min each)

Memorize facts with phonetic mnemonics

Ace Your Medicine (MD/DO) Classes & Exams with Picmonic:

Over 1,900,000 students use Picmonic’s picture mnemonics to improve knowledge, retention, and exam performance.

Choose the #1 Medicine (MD/DO) student study app.

Picmonic for Medicine (MD/DO) covers information that is relevant to your entire Medicine (MD/DO) education. Whether you’re studying for your classes or getting ready to conquer the USMLE Step 1, USMLE Step 2 CK, COMLEX Level 1, or COMLEX Level 2, we’re here to help.

Works better than traditional Medicine (MD/DO) flashcards.

Research shows that students who use Picmonic see a 331% improvement in memory retention and a 50% improvement in test scores.