Micro Lab Flashcards
What is a coliform? Which organisms belong to this group?
Lac+ Enterobacteriaceae E. coli, Klebsiella, Enterobacter, Citrobacter, Serratia
All gram - fermenters can ferment:
Glucose
Name 4 gram - fermenters
Enterobactericeae, Campylobacter, Aeromonas
Endocarditis in IV drug user
Pseudomonas
Idole -, Methyl Red -, Voges-Proskauer +, Citrate +
Klebsiella or Enterobacter
Name 2 opportunistic gram - non-fermenters
Pseudomonas, Actinomyces
Describe tube 0 and give a Ddx
Slant and butt are red = no fermentation
Pseudomonas, Actinomyces (gram - nonfermenters)
Describe tube 1 and give a Ddx
Butt is yellow = glucose fermented; slant is red = lactose NOT fermented
Shigella
Describe tube D and give a DDx
Butt is black = H2S formed; Slant is red = lactose NOT fermented; cracks = gas/H2 produced
Proteus, Salmonella, Citrobacter
Describe tube E and give a DDx
Slant is yellow = ferments lactose; butt is yellow = ferments glucose; cracks = gas/H2 formed
Klebsiella, E. coli, Enterobacter
Which could be Shigella?
Middle tube
(Yellow butt + red slant + no cracks = ferments glucose only)
Which could be Salmonella?
Last tube
(Black butt + gas = H2S and H2 formed)
Contamination of burns
Pseudomonas + S. aureus
Which organisms could produce the KAI finding in tube 1?
E. coli, Klebsiella, Enterobacter
(Yellow slant + butt + gas = lactose fermented)
Which could be Proteus?
Second to last tube
(Black = H2S formed; cracks = gas/H2 formed)
What would E. coli show on an IMViC test? Why would we do this?
Idole +, Methyl Red +, Voges-Proskauer -, Citrate -
Test for fecal contamination of water = must differentiate E. coli from Klebsiella and Enterobacter which can naturally grow in water so don’t necessarily mean fecal contamination if present
Corneal infections when abraded by contacts
Pseudomonas
A glucose-only fermenter, like ____, would produce which tube?
Shigella
Tube 1
(Red slant + yellow butt = only ferments glucose)
External ear infections (swimmer’s ear)
Pseudomonas
Which could be Pseudomonas?
Tube 2
(Red slant + red butt = no fermentation)
Idole +, Methyl Red +, Voges-Proskauer -, Citrate -
E. coli
Which would be Enterobacter? Citrobacter?
Enterobacter = tube 4 (yellow butt + slant + cracks = lactose fermenter)
Citrobacter = tube 4 (black + cracks = H2S and H2 formed)
Indole test converts ___ to ___ + ____
Tryptophan to indole + ammonia
Dx?
Shigella, E. coli
(Red layer on top = indole +)
Which is the positive reaction? Which organisms can produce such reaction?
Left = agglutination
Salmonella and shigella
(Positive serological testing = agglutination)
On this MacConkey agar medium, name 5 enteric bacteria that could be grown on the left and 7 that could be grown on the right.
Red = lac+ = E. coli, Klebsiella, Enterobacter, Citrobacter, Serratia
White = lac- = Shigella, Salmonella, Proteus, Morganella, Yersinia, Edwardsiella, Hafnia
Cystic fibrosis patients are prone to lung infections with:
Pseudomonas
What causes infection in infants and intoxication in adults?
C. botulinum
Describe the basis for serological testing? For which organisms is this method used, albeit uncommonly?
Antiserum w/ antibodies + suspension of organisms –> antigen present –> antibodies bind bacteria –> agglutination of bacterial cells
Shigella and Salmonella
____ and ____ are non-motile
Shigella and Klebsiella
This finding was revealed during surgery after an 11 year old boy presented with fever, RLQ pain, and diarrhea with cramping. Bug?
Yersinia
(Acute mesenteric lymphadenitis)
Oxidase +
Pseudomonas
Neonatal meningitis
E. coli
What would Klebsiella or Enterobacter show on IMViC testing? When would we do this test?
Idole -, Methyl Red -, Voges-Proskauer +, Citrate +
Test for fecal contamination of water = must differentiate E. coli from Klebsiella and Enterobacter which can naturally grow in water so don’t necessarily mean fecal contamination if present
This organism was grown on MacConkey agar with sorbitol instead of lactose. Dx?
EHEC
(Can’t ferment sorbitol = white)
Red pigmentation
Serratia
Non-lactose fermenters
Shigella (gluc only)
Salmonella, Proteus, Morganella
Yersinia, Edwardsiella, Hafnia
3 ways in which Pseudomonas can be distinguished from enterobacteriaceae species
- Pseudomonas is oxidase +
- Pseudomonas is a non-fermenter = red slant + red butt
- Pseudomonas grows blue-green, fruity-smelling colonies on BAP
How can one tell a water supply has fecal contamination?
MacConkey plating of water will show E. coli
One must distinguish ____ from ____ and ___ to determine fecal contamination of water because _____. How is this done?
E. coli from Klebsiella and Enterobacter
Klebsiella and Enterobacter can grow in water, so their presence doesn’t always mean fecal contamination
IMViC test
What does IMViC stand for? What does each test test for?
Indole (conversion of tryptophan to indole)
Methyl red (production of acid from glucose)
Voges-Proskauer (conversion of glucose to acetylmethylcarbinol)
Citrate (utilization)
Contents of MacConkey agar
Bile salts, lactose, pH indicator, crystal violet
What is the purpose of the bile salts in MacConkey agar?
Kills off G+ bugs
What is the purpose of the lactose and pH indicator in MacConkey agar?
Differentiates lac+ (red) from lac- (white) enterics
(i.e. E. coli from Shigella and Salmonella)
Which organism could produce the result on the right?
Pseudomonas
On special MacConkey agar medium, lactose can be replaced with ____ to help ID ____
Sorbitol
EHEC
(EHEC can’t ferment sorbitol like the rest of the E. coli so it would be white on sorbitol MacConkey agar)
Which 3 enteric flora cause GI disease? Describe the disease(s) caused by each.
- C. perfringens - food-borne diarrhea, Abx-assc enterocolitis
- C. diff - Abx-assc pseudomembranous colitis, water diarrhea + vomiting
- C. botulinum - descending flaccid paralysis
Why would you incubate feces in a microaerobic environment?
To grow Campylobacter
(Microaerobic = low O2 tension; H. pylori also grows in microaerobic environment)
Why must urine be stored at 4 degrees before culture?
Prevent growth of bacteria and false +
An EMB agar contains ___ and ___, which serve what function?
Eosin and methylene blue, which inhibit G+ bacteria
Dx based on this EMB agar?
E. coli
(Green with metallic sheen due to acid precipitation of methylene blue by lac+ organisms)
Dx based on this EMB agar?
Klebsiella
(Weakly fermentating bacteria show up as purple)
Dx based on this EMB agar?
Salmonella
(Non-fermenters are white)
Salmonella Shigella agar contains ____ which functions to ____.
High concetration of bile salts
Inhibits most coliforms (lac+ enterics) and all G+ bacteria so Shigella and Salmonella grow
ID each bacteria grown on these Salmonella Shigella plates.
Top/white = Shigella (non-lactose fermenter)
Bottom left/black = Salmonella (H2S production)
Bottom right/red = E. coli (lactose fermenter; not inhibited by bile salts)
We use Salmonella Shigella agar to differentiate between the lac - bacteria. However, we do not usually differentiate between the lac+ bacteria. Explain.
The only lac+ enteric that causes pathology is E. coli
Lac- enterics can grow to some degree in enteric media, so we have to distinguish Salmonella from Shigella
____ will only show motility at the top of an agar because:
Pseudomonas
It’s a strict aerobe and this is where oxygen is plentiful
Some species of ____ are only motile at room temp
Yersinia
What is swarming? Which organisms do it?
High motility
Proteus and Morganella
List two ways in which to differentiate Salmonella and Shigella
SS agar (Sal = black; Shig = white)
Serological testing (will also give you subgroup)
Descending paralysis + bilateral facial nerve palsy
Botulism
