Lab 7: Diagnostic Microbiology - Enteric Bacteria Flashcards
What is the purpose of triple sugar iron agar (TSIA)?
To differentiate enteric bacteria based on their ability to ferment sugars, produce gas, and reduce sulfur
What sugars are present in TSIA?
Glucose (0.1%), lactose (1%), and sucrose (1%)
What is the function of Simmons citrate agar (SCA)?
To test if a bacterium can use citrate as the sole carbon source
What does EMB agar test for?
Selects for gram negative bacteria and differentiates lactose fermenters
What are the expected TSIA results for E. Coli?
A/A, no H2S, gas positive (acid slant and butt, vigorous fermenter)
What are the expected TSIA results for salmonella?
K/A, H2S positive, no gas (alkaline slant, acid butt, sulfur reduction)
What are the expected Simmons citrate agar results for E. Coli
Green (negative)
What are the expected Simmons citrate agar results for salmonella?
Blue (positive)
What does E. Coli look like on EMB agar?
Blue-black colonies with a green metallic sheen
What does salmonella look like on EMB agar?
Colorless or light pink colonies
Which enteric bacteria are typically motile?
Most are motile expect shigella and klebsiella
What type of flagella do motile enteric bacteria have?
Peritrichous flagella (distributed uniformly around the surface)
What gram reaction do enteric bacteria show?
Gram negative rods
How do you inoculate a TSIA tube?
Stab the needle into the butt, then streak the surface of the slant
How do you inoculate a Simmons citrate tube?
Streak only the surface of the slant, do not stab
What does black precipitate in the TSIA indicate?
H2S production from sulfur reduction (forms iron sulfide)
What happens if TSIA tubes are read too early or too late?
Too early = false positive
Too late = false negative due to reversion
Why do EMB dyes inhibit gram positive growth?
Eosin Y and methylene blue are slightly selective against gram positive bacteria
