lactose fermenting gram negative rods on macconkey

After 24 hours of incubation, small colonies with a large zone of beta hemolysis are growing on the blood agar plate. The specimen is plated to standard microbiology media, including blood agar (trypticase soy agar enriched with 5% sheep blood). The patient is scheduled for surgical debridement of the wound, and during the procedure a tissue sample is collected and sent to the microbiology laboratory for culture. The patient has a fever, and the incision site is leaking purulent drainage. Microbiology Case Studies Using Differential & Selective Media Case 1Ī 28-year-old patient arrives at the emergency room with complaints of redness, pain and streaking along the site of a surgical incision on the leg. aureus) or the inability to ferment mannitol ( S. For example, mannitol salt agar is used to select for halophiles (e.g., Staphylococcus), while also visually differentiating species of staph based on mannitol fermentation ( S.

One of the most powerful applications of these types of media is combining both selective and differential characteristics into a single type of media. For example, NaCl media selects for halophiles (salt lovers) versus non-halophiles. Likewise, other chemicals can be addedto media to create a selective environment. For example, if a certain microbe is resistant to aparticular antibiotic (e.g., novobiocin), then that antibiotic can be added to the medium in order to prevent other organisms, which are not resistant, from growing. Selective media are used to select for the growth of a particular 'selected' microorganism. Notice non-mannitol fermenting clear colonies growing as well.īasic solid agar or liquid broth can also be enriched with various compounds specific for an organism of interest's needs (e.g. aureus is seen producing yellow colonies on mannitol salt agar. This allows for the rapid identification of organisms of interest, which is especially important for heavily mixed cultures, such as stool. The organisms interact with the added compounds (e.g., blood, sugars) in ways that make them visually distinct amongst other bacterial types on a plate. In contrast, differential media allow several different types of bacteria to grow, but also contain compounds that allow microbial genera (or even species) to be visually differentiated. Media that support the growth of many different microorganisms without distinguishing genera or species are nutritive. Primary culture media for clinical microbiology are divided into 3 primary categories - nutritive, differential and selective media. Differential Media and Selective Media: What Are They and What's the Difference?Ī culture medium is simply water and nutrients that support microbial growth.

Lactose fermenting gram negative rods on macconkey