Selective and Differential Media & Intestinal Pathogens (Part 1)

is BOTH selective and differential.

Selective: contains the antibiotics colistin and nalidixic acid. INHIBITS the growth of G- bacteria

Differential: Contains Sheeps Blood differentiates G+ based on hemolysis pattern.

Isolate G+ organisms such as Staphylococci and Streptococci from specimens that include G- bacteria

Media: Columbia CNA agar

Molecule: Hemolysin

Indicators: Colistin & Nalidixic acid blood

Growth/ No Growth *Selective* Growth = G+

Hemolysis Pattern *Differential*:

Gamma- No hemolysis-colorless

Alpha- Partial hemolysis- greenish and drab

Beta - Complete hemolysis- colonies surrounded by clearing in media

Is BOTH selective and differential medium

Selective: Dyes eosin & methylene Blue

*INHIBITS growth of (most) G+ bacteria

Differential: lactose

~Fermentation of lactose in the medium leads to the presence of acid

~Eosin & Methylene Blue react w. acid to produce colorful colonies

To differentiate between G-, nonpathogenic intestinal Rods

Media: Levine EMB Agar

Molecule: Lactase

Indicators: Lactose, eosin and methylene Blue

Growth/No Growth *Selective*: Growth G- Bacteria

Lactose Fermentation Pattern *Differential*:

Non-Fermenters - Colonies colorless

Fermenters- Colonies are purple, black, or pink

Vigorous Fermenters -Colonies are metallic Green (OOO Shiny!)

Enterics- bacteria found in human and animal intestines

Salmonella typhimurium- Serotype of what causes typhoid fever. Can cause noninvasive gastroenteritis (my tummy hurts...run run hurries)

Shigella flexnari- other species cause shigellosis. Invasive gastroenteritis (tummy hurts, run run hurry, pray to the porcelain god, possibly need IV fluids)

*G- rods*

*E.coli can be pathogenic if strain produces enterotoxins (EIEC) but is mostly normal flora

To discriminate between Salmonella and Shigella based on fermentation patterns & H2S production

Media: HE Agar

Enzyme: Lactase & Sucrase, sulfur reductase

Indicator: Bile salts & dyes (Bromothymol blue & acid fuchsin), Ferric ammonium citrate

Both selective and differential

Selective: dyes bromothymol blue and acid fuchsin, inhibits growth of G+

Differential: lactose, sucrose, salicin & ferric ammonium citrate.

G- based on fermination pattern and H2S production

-reduce sulfur to H2S= black or green with black centered colonies

Bile salts & Dyes: Bromothymol blue & acid fuchsin; inhibits growth of most G+

Sugars: Lactose, sucrose, & salicin; Identifies fermenters and non-fermenters of sugar

Peptones: carbon source for non-fermenters so they can still grow on the media

Selective enrichment medium for Salmonella spp

Contains: sodium selenite inhibits growth of Enterococci and coliforms

Enterococci: spherical bacteria found in GI tract

Coliforms: G-, facultative or aerobic rods that ferment in lactose, produce acid & gas