The plates are incubated overnight, and the zone of inhibition of bacterial growth is used as a measure of susceptibility (see below). Large zones of inhibition indicate that the organism is susceptible, while small or no zone of inhibition indicateresistance.

There are multiple factors that determine the size of a zone of inhibition in this assay, including drug solubility, rate of drug diffusion through agar, the thickness of the agar medium, and the drug concentration impregnated into the disk.

The natural penicillins have activity against non-beta-lactamase producing gram-positive cocci, including viridans streptococci, group A streptococci, Streptococcus pneumoniae, and anaerobic streptococcus (Peptostreptococcus, Peptococcus sp.). Enterococcus sp. is most susceptible to the natural penicillins.

Mueller Hinton Media contains Beef Extract, Acid Hydrolysate of Casein, Starch and Agar. Beef Extract and Acid Hydrolysate of Casein provide nitrogen, vitamins, carbon, amino acids, sulphur and other essential nutrients. Starch is added to absorb any toxic metabolites produced.

Mueller Hinton Agar is a solid medium originally designed for the isolation of pathogenic Neisseria species, now widely used for antibiotic susceptibility testing (including sulfonamides) of aerobic and facultatively anaerobic bacteria isolated from clinical specimens.

Results: The prevalence of multiple drug resistance as determined on Mueller-Hinton agar was 83.3% for Salmonella typhi and 80% for Staphylococcus aureus. For Salmonella typhi, resistance ranged from 6.7% (gentamicin and amikacin) to 83.3% (cotrimoxazole, ampicillin and chloramphenicol).

7.3 ± 0.1

Mueller-Hinton agar is superior to PDM blood agar for detection of methicillin-resistant Staphylococcus aureus. Clin Microbiol Infect.

Other media available for AST

• Brucella Blood agar.
• Mueller Hinton cloxa.
• Mueller Hinton Salt Etest®
• RPMI.
• BHI agar.

How to prepare nutrient agar?

1. Suspend 28g of nutrient agar powder (CM0003B) in 1L of distilled water.
2. Mix and dissolve them completely.
3. Sterilize by autoclaving at 121°C for 15 minutes.
4. Pour the liquid into the petri dish and wait for the medium to solidify.

The only difference between broth and agar media is that broths do not contain an agar component. We use broth tubes primarily for specific assays, or (rarely) for bacteria that will not form colonies on a solid surface. Unlike preparation of agar plates, tubes are prepared with media already in the incubation vessel.

When taken by mouth: Agar is POSSIBLY SAFE for most adults when taken with at least one 8-ounce glass of water. If it is not taken with enough water, agar can swell and block the esophagus or bowel.