Enterics Flashcards
Enterics:
1) Gram stain
2) Morphology
3) Identifying traits
1) Gram negative bacilli
2) Rods
3) Oxidase negative, catalase positive, aerobic or facultative anaerobic
What is the difference between the pathogenic strains and opportunistic strains?
Pathogenic strains will most likely always cause infection while opportunistic strains will only cause infections in those who are immunocompromised or when allows to enter the body through a wound or other means of entry
What are the examples of disease that E. coli can cause?
E. coli most commonly causes UTIs especially in young women of childbearing age, all strains cause gastroenteritis
What are the examples of diseases the pathogenic strains can cause? What are the symptoms of the diseases caused by each pathogenic enteric?
- Salmonella: typhoid fever, salmonellosis, UTIs (other salmonella species)
- Shigella: shigellosis, dysentary
Symptoms: - Typhoid fever: high fever, headaches, gastroenteritis, profuse sweating, and non-bloody diarrhea
- Salmonellosis (food poisoning, enteritis, typhoid-like-disease septicemia)
- Shigellosis: diarrhea with cramps, abdominal pains, headache, and fever; diarrhea often contains blood and mucus
What type of media is MacConkey Agar? Why did we use this plate for this lab? What types of enterics can it differentiate and how?
MacConkey agar is a selective media for only gram-negative bacteria. We used it in this lab because it is differential for coliforms (E. coli and other opportunisits) and other enteric bacilli such as Salmonella and Shigella. It can differentiate enterics by the color of the colonies that grow on it: coliforms ferment lactose to acid resulting in pink colonies and other enterics (Salmonella & Shigella) do not ferment lactose resulting in colorless colonies.
What type of media is the HE (Hektoen Enteric Agar) Plate? What is the biochemical mechanism of this plate? What type of enterics can it differentiate and how?
The HE Plate is selective media and selects for gram-negative bacteria. Biochemically, coliforms ferment sugars resulting in salmon-orange-colored colonies. Salmonella and Shigella do not ferment sugars resulting in blueish-green colonies. It also detects H2S production - colonies with a black center. It differentiates for gram-negative bacilli because the presence of bile salts and dyes inhibits most gram-positive organisms.
What does an ODC (Ornithine decarboxylase) Plate tell you? What is a positive result? What is biochemical reaction?
ODC Plates detect the production of the enzyme ornithine decarboxylase. A positive result is the color changing from yellow-orange to red. The microbe will be able to use the amino acid ornithine as a source of carbon and energy for growth through the enzyme ornithine decarboxylase.
What is general biochemical mechanism of TSI (Triple Sugar Iron) Agar? What type of enterics can it differentiate and how? How do you interpret the results of this test?
TSI Agar looks for glucose, lactose, and sucrose fermentation (also checks for H2S production/sulfur reduction). Glucose is in low concentration so if the organism ferments only glucose, it will exhaust the glucose supply. If the organism can ferment glucose and lactose/sucrose, the entire media will turn yellow. H2S production only occurs in the acid conditions, meaning the organism that produces it must also be positive for fermentation. It differentiates Enterobacteriaceae from other gram-negative rods by sugar fermentation.
- Yellow slant/yellow butt = glucose + lactose/sucrose fermentation
- Red slant/yellow butt = glucose only
- Red slant/red butt = no fermentation
- Red slant/no change in butt = no fermentation
- No change in slut and butt = organism is growing slowly or not at all
- Black precipitate in agar = sulfur reduction
- Cracks in or lifting of agar = gas production
What is the general biochemical mechanism of BG Sulfa Agar? What makes this media selective and what makes it differential? Know the expected results for a Salmonella spp. Compared to a different enteric.
BG Sulfa Agar differentiates coliforms based on lactose/sucrose fermentation with phenol red pH indicator. Sodium pyridine and brilliant green cause the media to be selective and the sugars make it differential. Salmonella is expected to form pink colonies on red agar.
How do we read the slant/slant butt of KIA and LIA Slants? What do the changes in each area of the media tell us? What is the general biochemical mechanism? What type of enterics can it differentiate and how? Know how to interpret the results of a test if given sample.
If the organism can ferment glucose the butt will turn yellow due to acid production. If the organism can ferment both glucose and lactose the butt and the slant turn yellow due to acid production. H2S production means the color will change to black. The organism will ferment glucose or lactose resulting in the color of the slant, butt, or both of the media. It differentiates Enterobacteriaceae from other gram-negative bacilli by sugar fermentation
What is the general biochemical reaction of Motility Nitrate Agar Deep? What type of media is this?
The pink and red color develops through the breakdown of nitrate to nitrite. TYPE OF MEDIA????
What does Simmon’s Cirate Agar Slant test for? What is the biochemical mechanism? What does a positive result look like?
Simmon’s Citrate Agar Slant tests if the organism can use citrate as its only source of carbon. Citrate utilization produces NH3 resulting in basic conditions. A positive result is blue.
Understand which medias we used to differentiate pathogenic enterics from the opportunistic enterics. How did they work?
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