Final answer:
Hektoen enteric (HE) agar is both a selective and differential media, designed to favor certain bacteria and differentiate among bacterial types based on growth characteristics and colony color changes.
Step-by-step explanation:
The Hektoen enteric (HE) agar is both a selective and differential media. This media tipo is designed to favor the growth of certain microorganisms, particularly the Enterobacteriaceae, while inhibiting the growth of others, which is a characteristic of selective media. Additionally, HE agar can differentiate between organisms based on the color change in the colonies or the medium, which is typical of differential media.
Selective media are formulated to support the growth of particular bacteria while suppressing others. For instance, MacConkey agar is another type of selective medium which contains substances like bile salts and crystal violet that inhibit the growth of many gram-positive bacteria, promoting the growth of gram-negative bacteria.
Differential media are used to differentiate among bacteria. These media have compounds that indicate differences in growth patterns or biochemical activities of different bacterial types, presenting visual cues like color changes.
Enrichment media are used to foster the preferential growth of a specific organism, enhancing the likelihood of its detection, especially when present in small numbers. Enrichment media, however, are not typically used in distinguishing between different types of bacteria, but rather to promote the growth of a desired microorganism.
In summary, Hektoen enteric (HE) agar is both selective, by inhibiting certain types of bacteria, and differential, by allowing the differentiation of bacteria based on their growth characteristics on the medium.