Gastrointestinal

digestion, metabolism, immune system

•Less than 10 to the 4 organisms/ml of secretions
•Gastric acid in stomach
•Rapid movement of food through the small intestine - peristalsis

Primarily the colon
Up to 10 to the 11 bacteria per gram of feces
Most are commensals
Mutualistic relationship with host
Vitamins:
K, biotin, folic acid, etc.

ingestion of contaminated food or water
Importance of good sanitation/hygiene practices

Large intestine consists primarily of anaerobes
Most fecal contamination is associated with G- facultative anaerobes
Enteric family (Enterobacteriaceae)
Lactose fermenters (coliforms) vs. non-lactose fermenters (pathogens such as Salmonella and Shigella spp.)

biopsy

Stool
Presence of mucus, blood, etc.
Color and consistency can be observed
May require selective and differential media
Salmonella, Shigella spp. may require enrichment
Can also look for parasites and test for viral infections
Rectal swab
Sometimes blood cultures
Typhoid fever resulting from Salmonella infection

-Selective: Bile salts and crystal violet inhibit G+ organisms
-Differential: pH indicator and lactose differentiate lactose fermenters
•Fermentation - breakdown of a sugar that results in the generation of acid and can result in gas production (not always)
•Neutral red-pH indicator responds to the drop in pH that accompanies the acid produced from fermentation and changes color
-Lactose fermenters produce pink/red colonies

Commonly used to identify members of the genus Enterococcus
Bile inhibits the growth of Gram-positive bacteria other than Enterococcus and some Streptococcus spp.
Many Gram-negative bacteria will grow on this media
Differentiates the ability to hydrolyze esculin
If an organism can hydrolyze esculin in the presence of bile, the product esculetin is formed. Esculetin reacts with ferric citrate (component within the medium), which turns the slant a dark brown or black color
NOTE - some organisms may grow on this media but not be able to hydrolyze esculin (no color change)
Media starts as a pale brown color and will turn dark brown/black if positive for the ability to hydrolyze esculin to esculetin