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Optimize growth with the right antibiotics

We carry a wide variety of antibiotics and are here to help you find the best fit for your application. Learn about every antibiotic we offer in our ready-to-use culture media that comes pre-mixed to save you time and ensure consistent performance. We can also customize your formulation, combining up to five antibiotics in a single plate.





Understanding the mode of action of each of our many antibiotic options can help you get optimal results for your specific application, whether you are looking to prevent biological contamination or select for cells that contain your desired genetic modifications.


To ensure your plates perform as expected, check the unique characteristics of all the antibiotics we offer below, including molecular weight, stock solution, suggested working concentrations, resistance, and expected shelf life.

Molecular weight (g/mol)Stock solution (mg/mL)Working concentration (µg/mL)Estimated shelf lifeResistanceCrossover resistanceSpectrum Mode of actionClass
371.39Water: 50-100Bacteria in agar diffusion tests: 100-512 -20°C: 4-6 monthsResistance conferred by product of TEM-1 β-lactamase (bla) gene from Tn3 transposonNoneEffective against many Gram-positive and Gram-negative bacteria.Inhibits cell-wall synthesis by interfering with peptidoglycan cross-linking. Ampicillin is used with all plasmids carrying the beta-lactamase gene (bla) (e.g., pUC19, pBluescript, pGEM).Bactericidal
Low copy plasmids: 20
High copy plasmids: 50-100
Rich media: 50-100
Minimal media: 15 



TIP: When β-lactamase is produced at high levels, it reduces the effectiveness of ampicillin in the growth medium, which enables the growth of satellite colonies. These satellite colonies can be minimized by using a higher concentration of ampicillin. Alternatively, the use of TIMENTIN inhibits the growth of satellite colonies.

Molecular weight (g/mol)Stock solution (mg/mL)Working concentration (µg/mL)Estimated shelf lifeResistanceCrossover resistanceSpectrum Mode of actionClass
637.66Water: 100 Bacteria: 8-80°C: 1 yearResistance is conferred by an aminoglycoside 3-N-acetyltransferase type-IV enzyme (aac(3)-IV) or 16S rRNA m1A1408 methyltransferase (npmA) gene.The aac(3)-IV gene also confers reduced resistance to gentamycin and kanamycin.Active against some Gram-negative bacteria, particularly those resistant to other aminoglycosides.Binds to the 30S ribosomal subunit of the bacterium, it induces misreading of mRNA, resulting in the bacterium's incapability to create essential proteins crucial for its growth.Bactericidal



See our Apramycin products:

Molecular weight (g/mol)Stock solution (mg/mL)Working concentration (µg/mL)Estimated shelf lifeResistanceCrossover resistanceSpectrum Mode of actionClass
458.9Water and acetic acid: 5-10Bacteria: 50-1004°C: 1-2 weeksResistance is conferred by blasticidin-S deaminase (bsr) from  Bacillus cereus. In addition, it's conferred by the blastcidin S acetyltransferase gene (bls) from Streptoverticillum sp, and the blasticidin S deaminase gene (BSD) from Apergillus terreus.NoneActive against both prokaryotic and eukaryotic cells.Inhibitits the termination stage of translation and, to a lesser degree, the formation of peptide bonds by the ribosome. Consequently, cellular capacity to generate novel proteins via mRNA translation is impeded both prokaryotic and eukaryotic cells.Bactericidal
Yeast: 25-300-20°C: 6-8 weeks
Mammalian cells: 1-10 


TIP: Bacteria are not sensitive to blasticidin, but colonies resistant to blasticidin can be selected on low salt LB agar medium (pH 8) supplemented with 100 μg/ml blasticidin. High pH enhances the selective activity.



See our Blasticidin S products:

Molecular weight (g/mol)Stock solution (mg/mL)Working concentration (µg/mL)Estimated shelf lifeResistanceCrossover resistanceSpectrum Mode of actionClass
422.36Water: 50-100Bacteria-20°C: 6 monthsResistance conferred by product of TEM-1 β-lactamase (bla) gene from Tn3 transposon. NoneEffective against Gram-negative bacteria.Causes disruption of the final phase of cell wall synthesis in susceptible bacteria. It acylates the C-terminal domain of the transpeptidase and prevents the linkage formation between two linear peptidoglycan strands, thereby impeding the conclusive step in bacterial cell wall construction and cell lysis.Bactericidal
Low copy plasmids: 20 
High copy plasmids: 100

Molecular weight (g/mol)Stock solution (mg/mL)Working concentration (µg/mL)Estimated shelf lifeResistanceCrossover resistanceSpectrum Mode of actionClass
323.1Ethanol (or methanol): 34Bacteria-20°C: 1 yearResistance conferred by the product of the chloramphenicol acetyl transferase (cat) gene from Tn9 transposon.NoneBoth gram-positive and gram-negative bacteria, anaerobes, and some rickettsial pathogens.Inhibits microbial protein synthesis by binding to the 50 S subunit of the ribosome. This prevents the activity of peptidyl transferase enzyme, responsible for the formation of peptide bonds.Bacteriostatic
Low copy plasmids: 12.5 
High copy plasmids: 20-35
Rich media: 20
Minimal media: 5


See our Chloramphenicol products

Molecular weight (g/mol)Stock solution (mg/mL)Working concentration (µg/mL)Estimated shelf lifeResistanceCrossover resistanceSpectrum Mode of actionClass
1359.47Water: 10Bacteria: 50-100-20°C: 1 yearResistance conferred by nourseothricin acetyltransferase (nat1 or sat1) gene from Streptomyces noursei.NoneGram-positive and gram-negative bacteria, various fungi, and certain DNA and RNA viruses,  effective on higher eukaryotes.Inhibits protein synthesis by impeding mRNA translocation, leading to RNA misreads. Binds to bacterial ribosomal subunits, causing erroneous mRNA alignment and incorrect amino acid incorporation in the peptide chain.Bacteriostatic


TIP: Nourseothricin are inhibited by high salt concentrations. When working with bacteria, use low salt LB for optimal selection.



See our Nourseothricin products:

Molecular weight (g/mol)Stock solution (mg/mL)Working concentration (µg/mL)Estimated shelf lifeResistanceCrossover resistanceSpectrum Mode of actionClass
692.7Water: 50-200Bacteria: 100-200-20°C: 1 yearResistance to G418 is conferred by the neo gene from Tn5 transposon encoding an aminoglycoside 3′-phosphotransferase (apt 3′ II).NoneBoth gram-positive and gram-negative organisms but is particularly useful for the treatment of severe gram-negative infections.Inhibits protein synthesis, triggering the activation of phosphatidylinositol phospholipase C (resulting in the liberation of GPI-anchored proteins), and enhancing both dihydroxyacetone phosphate acyltransferase and peroxisomal β-oxidation activity.Bactericidal
Mammalian cells: 200-500 (200 for maintenance, 400-500 for selection)


Molecular weight (g/mol)Stock solution (mg/mL)Working concentration (µg/mL)Estimated shelf lifeResistanceCrossover resistanceSpectrum Mode of actionClass
575.67Water: 100 Bacteria: 15-20°C: 1 yearResistance conferred by product of gentamycin acetyltransferase and kanamycin phosphotransferase (aacA-aphD) gene from Tn4001 transposon, or  by the product of gentamycin acetyltransferase (aacC1) gene. aacC1 confers resistance to gentamycin only. aacA-aphD confers resistance to gentamycin and kanamycin in two separate domains. Many Gram-negative and some Gram-positive bacteria.Inhibits protein synthesis by binding to the 16S rRNA within the 30S ribosomal subunit. The binding interferes with mRNA translation, leading to the production of incomplete or non-functional proteins.Bactericidal
Yeast: 50
Mammalian cells: 50


Molecular weight (g/mol)Stock solution (mg/mL)Working concentration (µg/mL)Estimated shelf lifeResistanceCrossover resistanceSpectrum Mode of actionClass
527.54PBS: 50Bacteria: 50-10025°C: 3 monthsResistance conferred by the product of the hygromycin phosphotransferase (hphB) gene from Streptomyces hygroscopicus.NoneBacteria (gram-negative and gram-positive), fungi, and higher eukaryotic cells.Inhibits protein synthesis. It binds to the mRNA decoding center within the small (30S) ribosomal subunit of the 70S ribosome and prompts a localized conformational change.Bactericidal
HEPES, pH 7: 100 Yeast: 50-2004 °C and -20°C: 2 years
 Mammalian cells: 50-200Light-sensitive


TIP: Higher pH levels of media and low salt media such as LB demonstrate enhanced sensitivity. Hygromycin B is sensitive to high acid levels but can handle brief exposure to low concentrations of acids.



See our Hygromycin B products:

Molecular weight (g/mol)Stock solution (mg/mL)Working concentration (µg/mL)Estimated shelf lifeResistanceCrossover resistanceSpectrum Mode of actionClass
582.6Water: 50Bacteria-20°C: 1 year Light-sensitivePlasmid resistance is conferred by the product of the kanamycin phosphotransferase (aph) gene from Tn903 transposon, or kanamycin and neomycin phosphotransferase II (ntpII) from Tn5 transposon.Several versions of the aph gene exist, with crossover resistance to neomycin and gentamycin.Both Gram-negative and Gram-positive bacteria.Inhibits protein synthesis by attaching to the decoding site (A-site) of the minor ribosomal subunit (30S). This interference leads to mRNA misreading and results in the inhibition of translocation processes.Bactericidal
Low copy plasmids: 25 
High copy plasmids: 50-100
Rich media: 50
Minimal media: 12.5
Cosmids: 20


TIP: Resistance gene is not highly expressed in media below pH 7.2.



Molecular weight (g/mol)Stock solution (mg/mL)Working concentration (µg/mL)Estimated shelf lifeResistanceCrossover resistanceSpectrum Mode of actionClass
908.9Water: 5-50Bacteria: 50-100-20°C: 1 yearResistance is conferred by the neo gene from  transposon Tn5 encodes the enzyme neomycin phosphotransferase II (aph 3' II). Aph 3' II gene confers resistance to various aminoglycoside antibiotics, including kanamycin and G418.Both Gram-positive and Gram-negative bacteria.Binds to 30S ribosomal subunit and inhibits bacterial protein synthesis.Bactericidal
Mammalian cells: 100-200



See our Neomycin B products:

Molecular weight (g/mol)Stock solution (mg/mL)Working concentration (µg/mL)Estimated shelf lifeResistanceCrossover resistanceSpectrum Mode of actionClass
544.4Water: 50Bacteria: 100-125-20°C: 1 yearPuromycin N-acetyltransferase (pac) from Streptomyces alboninger.NoneUsed for selection in cell culture and molecular biology.Inhibits protein synthesis by acting as an analog of amino-acyl tRNA (causes premature chain termination).Bactericidal
Mammalian cells: 0.5-104°C: 3 months


TIP: Frozen stock solution can generate crystalline precipitate. If this occurs, heat the product to 37 °C using a thermomixer or water bath.  



See our Puromycin products:

Molecular weight (g/mol)Stock solution (mg/mL)Working concentration (µg/mL)Estimated shelf lifeResistanceCrossover resistanceSpectrum Mode of actionClass
495.35Water: 100Bacteria-20°C: 1 yearResistance is conferred by adenylyltransferase (aadA) from Enterococcus faecalis. AadA gene also confers resistance to streptomycin.Gram-negative bacteria, used to treat infections like gonorrhea.Inhibits bacterial protein synthesis by binding to 16S rRNA helix 34 of the 30S subunit of the bacterial ribosome, and blocking the translocation step of protein synthesis.Bacteriostatic
Rich media: 100-120
Minimal media: 50


TIP: Spontaneous mutations in the chromosome can yield resistant colonies. Use a 120 µg/mL working concentration for cloning to reduce the background.



Molecular weight (g/mol)Stock solution (mg/mL)Working concentration (µg/mL)Estimated shelf lifeResistanceCrossover resistanceSpectrum Mode of actionClass
1457.4Water: 50Bacteria-20°C: 1 yearResistance is conferred by adenylyltransferase (aadA) from Enterococcus faecalis. AadA gene also confers resistance to spectinomycin.Gram-negative and some Gram-positive bacteria, used to treat tuberculosis.Inhibits protein synthesis by binding to the S12 protein of the 30S ribosomal subunit and inhibiting proper translation.Bacteriostatic. Bactericidal at higher concentrations.
Rich media: 100-2005-15°C: 1 month
Minimal media: 100 


Molecular weight (g/mol)Stock solution (mg/mL)Working concentration (µg/mL)Estimated shelf lifeResistanceCrossover resistanceSpectrum Mode of actionClass
480.970% ethanol: 15Bacteria-20°C: 1 year  Light-sensitiveResistance conferred by tetracycline efflux protein (tetA) from RP1, RP4 or Tn1721, or tetracycline efflux protein (tetC) from pSC101 or pBR322.Note: tetA gene conveys stronger resistance than that from tetC.NoneGram-positive and gram-negative bacteria, atypical organisms such as chlamydiae, mycoplasmas, and rickettsiae, and protozoan parasites.Tetracycline inhibits protein synthesis by preventing binding of aminoacyl tRNA to the ribosome A site.Bacteriostatic
Water: 4Rich media: 10-20
 Minimal media: 5-10


TIP: Magnesium ions are inhibitors, do not use with minimal media (for example, M9).



Molecular weight (g/mol)Stock solution (mg/mL)Working concentration (µg/mL)Estimated shelf lifeResistanceCrossover resistanceSpectrum Mode of actionClass
290.3DMSO: 75Bacteria: 10-20°C: 1 yearResistance conferred by mutated II dihydrofolate reductase (DHFR) genes from Pseudomonas aeruginosaNoneWhen used in combination, it has a broad spectrum of activity against both Gram-negative and Gram-positive) bacteriaTrimethoprim and sulfamethoxazole block the production of tetrahydrofolic acid, which is an essential form of folic acid. This acid is needed as a helper molecule in creating thymidine, purines, and bacterial DNA.When used alone, trimethoprim is bacteriostatic, but it is bactericidal when combined with sulfonamides


See our Trimethoprim products:

Molecular weight (g/mol)Stock solution (mg/mL)Working concentration (µg/mL)Estimated shelf lifeResistanceCrossover resistanceSpectrum Mode of actionClass
1427.53Water: 100 Bacteria -20°C: 1 year Light-sensitiveResistance conferred by the product of the Sh ble gene from Streptoalloteichus hindustanusSh ble gene also confers resistance to PhleomycinToxicity against bacteria, fungi (including yeast), plants, and mammalian cellsZeocin intercalates into DNA, causing double-strand breaks which result in cell death. Bactericidal
Rich media: 50
Yeast: 50-300
Mammalian: 50-1000


TIP: Use a low salt media such as LB for optimal selection. Salt concentrations higher than 90 mm will inactivate Zeocin.



Frequently asked questions

You can find answers here for our most commonly asked questions. If you don't find the information you are looking for, get in touch with our team. We're here to help.

ClassExamplesMode of action
AminoglycosidesGentamicin and streptomycinInhibits protein synthesis in bacteria
AmphenicolsChloramphenicolInterferes with bacterial protein synthesis
Beta-lactamsPenicillins and cephalosporinsInhibits bacterial cell wall synthesis
CarbapenemsImipenemInhibits bacterial cell wall synthesis
Cyclic lipopeptidesDaptomycinDisrupts bacterial cell membrane integrity
GlycopeptidesVancomycinInhibits bacterial cell wall synthesis
LevamisoleAn anthelmintic agent used to treat parasitic worm infections
LincomycinInhibits bacterial protein synthesis
LincosamidesLincosamidesInhibits bacterial protein synthesis
MacrolidesErythromycin and azithromycinDisrupts bacterial protein synthesis
MonobactamsAztreonamEffective against gram-negative bacteria by inhibiting cell wall synthesis
OxazolidinonesLinezolidInhibits bacterial protein synthesis
OxfendazoleAn anthelmintic drug used to treat parasitic worm infections
QuinolonesCiprofloxacin and levofloxacinTargets bacterial DNA gyrase and topoisomerase IV, disrupting DNA replication and repair
SulfonamidesStructural analogs of para-aminobenzoic acid (PABA) that inhibit the synthesis of folic acid in bacteria
TetracyclinesDisrupt bacterial protein synthesis

Ampicillin is a beta-lactam antibiotic that inhibits bacterial cell wall synthesis. Bacteria need some time to replicate and divide, and ampicillin interferes with this process. It may take some time for ampicillin to affect bacterial growth and demonstrate antibiotic resistance.

Kanamycin is an aminoglycoside antibiotic that disrupts bacterial protein synthesis. It acts relatively quickly by binding to the bacterial ribosomes. The incubation time required to observe antibiotic resistance with kanamycin may be shorter compared to ampicillin.

One possible reason why your cells are not forming colonies could be the loss of selective pressure. In a selective medium containing antibiotics or other inhibitory substances, bacterial colonies will only form from cells that have acquired resistance to the selective agent. If the selective pressure is reduced or eliminated, non-resistant cells can also grow on the plate but won't form distinct colonies.


To help address this challenge, we have developed a rigorous performance growth testing process for our agar plates, handpicking 27 bacterial and 8 fungal strains to establish proprietary predictive growth patterns that include a variety of antibiotic combinations. We perform tests daily, screening the first and last plates in every lot for sterility and performance to help ensure batch-to-batch consistency so you get reproducible results. We also maintain retention samples for the lifespan of the product, so we can continually test its integrity.

Antibiotic susceptibility testing is a crucial process in determining the effectiveness of antibiotics against specific bacterial strains. There are several methods used to test antibiotic susceptibility, and your choice of method will depend on the type of bacteria being tested, and the timing of the test. Mueller-Hinton media is typically used for these tests due to its standardized composition and pH.


Here are some common methods for testing susceptibility:


MethodDescriptionTypical media used
Disk Diffusion Method (Kirby-Bauer)In this method, the susceptibility of bacterial strains to antibiotics is assessed by measuring the size of the zone of inhibition around antibiotic-impregnated paper disks placed on an agar plate. Larger zones indicate greater susceptibility. Mueller-Hinton Agar (MHA)
Broth Dilution MethodIn this method, bacterial isolates are exposed to varying concentrations of antibiotics in liquid broth. The minimum inhibitory concentration (MIC) is determined as the lowest antibiotic concentration that inhibits bacterial growth. Mueller-Hinton Broth (MHB)
E-Test (Epsilometer Test)The E-test combines aspects of both disk diffusion and broth dilution methods. It employs a strip with a gradient of antibiotic concentrations. The MIC is read where the bacterial growth intersects the strip. Mueller-Hinton Agar (MHA)
MIC Test Strips (Gradient Diffusion)Like the E-test, MIC test strips provide a gradient of antibiotic concentrations on an agar plate, allowing for the determination of MIC. Mueller-Hinton Agar (MHA)
Microdilution MethodIn this method, bacterial isolates are tested in a series of liquid media with decreasing antibiotic concentrations. The MIC is recorded as the lowest concentration at which no visible growth occurs.Cation-Adjusted Mueller-Hinton Broth (CAMHB)


Source: Patel, 2021

Many antibiotics are sensitive to heat and could potentially degrade if the media is too hot. These antibiotics are typically not recommended to be added until the media has cooled to an appropriate temperature (usually around 45-50°C or 113-122°F).


The degradation rates obtained for the model within a liquid matrix (water) at 100°C observed among different antibiotic classes and can be summarized as follows:


β-lactams = tetracyclines (most heat-labile) > lincomycin > amphenicols > sulfonamides > oxfendazole > levamisole (most heat-stable)


To help address this challenge we ofter a wide variety of pre-mixed solutions that already contain the anitbiotics you need. With over 27 years of experience making complex formulations, we have a well-established process in place to safely manufacture agar plates that include heat sensitive antibiotics.


Source: Tian L., Khalil S., Bayen S. Effect of Thermal Treatments on the Degradation of Antibiotic Residues in Food. Crit. Rev. Food Sci. Nutr. 2017;57:3760–3770

It has been demonstrated that no significant degradation occurs from UVA irradiation alone, however pH does have a substantial impact on antibiotic degradation. To address this and ensure consistent and accurate pH in our products, we follow a rigorous quality testing procedure for every lot to ensure variability is less than 0.04 pH from batch to batch. You can learn more in our guide for optimal pH.


Source: Elmolla, E. S., & Chaudhuri, M. (2010). Photocatalytic degradation of amoxicillin, ampicillin and cloxacillin antibiotics in aqueous solution using UV/TiO2 and UV/H2O2/TiO2 photocatalysis. Desalination, 252(1-3), 46-52.

Antibiotics used for selection in mammalian cells are toxic to mammalian cells lacking a particular resistance gene or marker. This selectivity ensures that only mammalian cells with the desired genetic modification survive and proliferate.


Antibiotics commonly used for mammalian cell selection include:


●      Zeocin (Blasticidin S): Mammalian cells expressing the zeocin resistance gene can survive and proliferate in the presence of Zeocin.

●      Puromycin: Puromycin is a protein synthesis inhibitor that is toxic to mammalian cells but has a limited effect on bacterial cells.

●      Hygromycin B: Hygromycin B is effective against a broad range of bacteria and fungi but can be safely used with mammalian cells expressing the hygromycin resistance gene. It interferes with protein synthesis in bacterial cells while allowing resistant mammalian cells to grow.

●      G418 (Geneticin): G418 is an antibiotic that selectively inhibits the growth of mammalian cells. Cells expressing the G418 resistance gene can survive and proliferate in the presence of G418.

●      Bleomycin: While Bleomycin can affect some bacterial strains, it is used less frequently for bacterial selection. It causes DNA damage in mammalian cells but can be tolerated by those expressing the bleomycin resistance gene.


Source: Curr.Protoc.Mol.Biol. 86:9.5.1-9.5.13. (2009)

The antibiotic kill curve is a dose-finding experiment in which mammalian cells are exposed to increasing concentrations of an antibiotic to determine the lowest and the most effective antibiotic concentration that kills the untransfected cells. To make a kill curve, typically, untransfected cells are plated in a 96-well plate at a low density so that on the day of antibiotic treatment, they reach ~50% confluency. Following the recommended concentration range for the antibiotic, the cells are treated at increasing concentrations in triplicates. The cells are then regularly observed under a light microscope over a 7- to 10-day period, replacing the medium every 2 to 3 days. Viable cells in each well are quantified directly (e.g., trypan blue) or indirectly (e.g., MTT, CellTiter Glo) and plotted against antibiotic concentrations to determine the lowest concentration effective at killing all the cells.



Sample dose-response plot with a non-linear regression fit, showcasing the cell viability of DU1245 and PC3 cells



Source: adapted from Oseni, 2021

Yes, you can absolutely have more than one antibiotic selection marker. However, you should be aware that some pairs of antibiotics can exhibit cross-reactivity due to shared resistance mechanisms or overlapping target sites in bacterial cells.


Some common examples of antibiotics with cross-reacting pairs include:


●      Ampicillin, Amoxicillin and Carbenicillin: both are β-lactam antibiotics that target bacterial cell wall synthesis and share similar resistance mechanisms. Bacterial strains resistant to one of these antibiotics may exhibit partial resistance to the other.

●      Kanamycin, Streptomycin, Gentamicin and Neomycin: all belong to the aminoglycoside class of antibiotics and can exhibit cross-resistance. They target bacterial protein synthesis.

●     Tetracycline and Doxycycline and Minocycline: cross-reactivity between these in bacterial culture is related to their shared mechanism of action, it does not imply a uniform response among all bacterial strains.


To ensure you get the right combinations of antibiotics, explore our wide variety of ready-made pre-poured plates that include anywhere from 1-5 antibiotics.

Both antibiotics share the same mechanism of action as they belong to the beta-lactam group. Ampicillin, a commonly used antibiotic in molecular biology, offers stability and cost-effectiveness but may lead to the formation of satellite colonies. On the other hand, Carbenicillin exhibits greater stability due to its enhanced tolerance for heat and acidity, making it a preferred choice when maintaining selective pressure. Furthermore, Carbenicillin is associated with a lower occurrence of satellite colonies, owing to its heightened stability and reduced susceptibility to inactivation by beta-lactamase enzymes. It's worth noting that Carbenicillin has a narrower antibacterial spectrum and is typically more expensive than Ampicillin.

The choice between Gentamicin and Streptomycin depends on the specific needs of your experiment or application. Gentamicin is preferred for its stability at low pH and effectiveness in controlling bacterial growth in tissue culture, especially when acidic conditions are involved, but it has a broader spectrum of activity. Streptomycin is a cost-effective option, suitable when increased stability is not a priority.