Micro Exam 3 Flashcards
What are the metabolic products being tested for in the MRVP test?
Methyl red
Voges-Proskauer
What does methyl red contain?
Mixed acids (lactic, acetic, formic, and succinic)
What does Voges-Proskauer contain?
Acetoin and 2,3-butanediol
What is the positive reaction for a MRVP test?
formation of red color in the liquid medium, peptone base with dextrose (clear light yellow color)
What tests would you use to identify gram negative rods?
Oxidase test, gram stain, maconkey agar, can tell us if the microorganism is gram + or -
TSI, IMViCdetermine the type of gram - negative rod they are
What does the positive reaction in a MRVP test indicate about the fermentation?
It is a carbohydrate fermentation
Describe a Simmons Citrate Agar Slant
A solid medium with a sodium citrate, ammonium salt, bromthymol blue and agar with the medium being a forest green color
What is the function of the citrate slant test?
To see if the organism can use citrate as its only carbon source and ammonium salt as its only nitrogen source
What represents a positive citrate test?
Turns blue (negative is when it remains green)
Describe a SIM medium deep
It is a semi-solid, non-selective, differential agar medium with iron salt, thiosulfate, and peptone
What is the SIMs test used to indicate?
used to determine 3 tests in gram negative rods: Sulfide, Indole, Motility
What are the three tests in the SIMs Medium Deep and what are the positive results?
Hydrogen sulfide - blackening shows positive
- determines if the bacteria can break down sulfur into hydrogen sulfide gas
Indole Production - pink is positive
- checks whether the bacteria can break down tryptophan, an amino acid, to produce indole
Motility - cloudy or turbid growth from the stab is positive
What tests does the IMViC testing process include?
Indole, MR, VP, Citrate
Whats the first basic test used to differentiate fermenters from nonfermenters? What does a positive reaction look like?
Oxidase test, blue color means its positive which means its a nonfermenter and produces cytochrome
How can we get a false positive or false negative oxidase test?
False positive by a metal loop or
False negative when sampling with an older culture
Name the bacterium that are lactose fermenters and oxidase negative
Klebsiella pneumoniae, E. Coli, E. aerogenes
Define enterics
group of gram-negative rods that inhabit the intestinal tract
What are the oxidase test and MacConkey agar results for Pseudomonas aeruginosa?
Oxidase positive so its a nonfermenter
Clear = negative on Mac
Describe a MacConkey agar
a differential and selective medium used for detecting gram negative rods due to the crystal violet and bile salts that inhibit the growth of gram +
What results does lactose fermenters show on a Maconkey agar?
Pink
Name the contents in a Triple Sugar Iron Agar Slant (TSI)
a solid slant with glucose, lactose, sucrose, sulfur, sodium thiosulfate, ferrous sulfate, and phenol red and the pH indicator
Describe a TSI test and what it is used for
non-selective and differential medium, used to differentiate enteric, gram-negative bacteria based on their ability to reduce sulfur and ferment carbohydrates
What are the test results of a TSI?
Yellow is an acid color (A) and means its a carb fermentator
Red is alkaline because there was no change (K)
H2S production positive would show blackening of agar
Gas production positive shows bubbles in the medium
What is the Kirby Bauer sensitivity test used for?
Its a method used to see how a specific drug will effect/kill a patient’s bacterium
What is the physician looking for in a Kirby Bauer sensitivity test?
They are looking for the drug that will kill the bacteria the most easily without negative effects to the patient
Name the disk symbol and their antibiotic in the Kirby Bauer test
GM - Gentamicin
TMP- Trimethoprim
VA- Vancomycin
Name the zone sizes for each antibiotic
Resistant, Intermediate, Sensitive
GM Disk content: 10 ug
<=12 13-14 >=15
TMP Disk content: 5 ug
<=10 11-15 >=16
VA Disk content 30 ug
<=14 None >=15
Who are the disk content values standardized by?
CLSI, Clinical Laboratory Standards
If the antibiotic results are sensitive, does that mean it will cure the patient?
No, the drug might not react the same in the in vivo as in vitro. It can be TOO sensitive to the point of toxicity or it might not even be able to reach the appropriate body part
Whats an example of a sensitive antibiotic that could negatively impact hearing?
Aminoglycosides
What is Cary Blair media?
A liquid transport media that will preserve pathogenic bacteria in stool cultures
What are the host defense mechanisms of the GI tract?
High stomach acidity, normal flora that colonizes tract and makes it difficult for pathogens to intrude
Name the bacterial pathogens of the GI tract
Salmonella, Shigella, Campylobacter, Aeromonas, Pleisiomonas, shiga toxin, E.coli 0157
Describe and name the pathogen for Pseudomembranous colitis
Clostridium difficile’s toxins and is usually associated by using heavy amounts of antibiotics
What would you use to clean a patients room who had pseudomembranous colitis?
We would use bleach as this disease is easily spread nosocomially
What are the two bacterial toxins that are released by bacteria?
A Component (Enterotoxin)
B Component (Cytotoxin)
B Component (Cytotoxin)
the toxin is responsible for binding to the host cell, facilitating the entry or enhancing the effect of the active “A” component
A Component (Enterotoxin)
The active part of the toxin responsible for the specific effect inside host cells, often interfering with cellular functions. The “A” part typically disrupts the regulation of ion transport in intestinal cells, leading to water loss and diarrhea. Enterotoxins specifically affect the gut
Describe Proctitis and name the pathogen associated
Inflammation of rectal mucosa and is associated with sexually transmitted diseases like:
Neisseria gonorrhea (GC), Chlamydia
Syphilis (Treponema pallidum)
Describe Cholera and name the pathogen associated
associated with watery and profuse stools caused by Vibrio cholera
Name the viruses that cause Viral gastroenteritis
Norovirus (adults), Rotavirus (children)
Name common parasites that can cause GI tract diseases
Entamoeva histolytica
Giardia
Cyclospora
Cryptosporidium
Describe a Eosin Methylene Blue agar (EMB)
a selective and differential culture medium used to isolate pathogenic gram - bacteria found in GI tract
Name test results for Salmonella
MacConkey - Clear colonies / +
Citrate - Blue / +
EMB - Clear / - (they look for lactose fermenter pathogens and salmonella is not one)
TSI - K/A G H2S
Whats the mode of transmission for Salmonella?
contamined foods most common
Name the test results for Shigella
MAC - Clear / +
TSI - K/A
Citrate- Green / -
Hemolytic uremic syndrome
(DIC) the blood does not clot, causes kidney failure, severe complication and life threatening condiiton
Who does the hemolytic uremic syndrome happen to?
About 10% of people infected with a shiga toxin
What organism can cause hemolytic uremic syndrome and releases the shiga toxin?
E.coli 0157:H7
What should patients with E.coli 0157:H7 be treated with?
Only should be treated with supportive therapy like fluids
Never antibiotics
What is the Disk Diffusion Method of Kirby Bauer Sensitivity?
It is a manual way of doing a sensitivity test
Describe the steps of a sensitivity test the manual way
An inoculum of bacteria is placed on a Mueller Hinton plate. Paper disks impregnated with a standard concentration of antibiotic are placed on the surface. The antibiotic diffuses out from the disk. The zone around the antibiotic, the kill zone, determines how effective the antibiotic is.
Remember: The disk diffusion test is not a perfect indicator of how the drug will behave in vivo or in the patient’s body
Describe the positive results of a catalase reaction and how to trigger a false positive
Bubbles = positive
False positive = taking an organism from blood agar plate
Name the organism: beta hemolytic, A antigen positive, aka strep group A
Streptococcus pyogenes
Name the organism: Non-hemolytic, D antigen positive, aka Group D strep
Enterococcus faecalis
Name the organism: Staphaurex/Rapid Staph Latex positive
Staphylococcus aureus
Name the organism: Stapaurex/rapid staph latex negative
Staphylococcus epidermidis
Steps on a strep typing
Use white card
2 drops of Reagent 1 in tube
2 drops of Reagent 2 in tube
Pick up organism with Stick (4-6 colonies)
Mix in reagents 1 and 2
Add 4 drops Reagent 3
Use Beryl pipette to place organism on disposable card
Add appropriate strep typing reagent
Mix with stick; rock
Agglutination is positive; no agglutination is negative
Steps to do a Staph typing
Use smaller card
Drop of staphaurex on slide
Add bug with stick and mix
Rock
Agglutination is positive; no agglutination is negative
What toxin is also known as “rice water stools”
Vibrio Cholera
What is the substrate for indole?
Tryptophan
Test results for Klebsiella pneumoniae
MAC - pink/positive
Mucoid - has a capsule
Gram stain - pink rods/negative
Oxidase - clear/negative
SIMS - negative
TSI - K/K gas
Citrate - +
What type of specimen is Klebsiella pneumoniae?
sputum from an alocholic
Test results for Pseudomonas aeruginosa
MAC- clear colonies /+
Blood agar - green and grapey
Oxidase - blue / positive
Gram stain - pink rods
SIMS - positive for motility
Citrate - blue / positive
TSI - K/K
