Last min cram Flashcards
(23 cards)
What are the steps in a gram stain?
Bacterial smear on a glass slide
Crystal violet (primary stain)
Iodine solution (mordant)
Alcohol or acetone-alcohol (decolorizer)
Safranin (counterstain)
What is the primary stain used in Gram staining?
Crystal violet.
Crystal violet is a basic dye that stains all cells initially.
What is the role of iodine in the Gram stain?
Acts as a mordant to form a complex with crystal violet and fix the dye in the cell wall.
Iodine increases the affinity of the dye for the cell wall.
What does the decolorizer do in the Gram stain process?
Removes the crystal violet–iodine complex from Gram-negative cells.
Common decolorizers include alcohol or acetone.
What counterstain is used in Gram staining?
Safranin.
Safranin stains the Gram-negative bacteria pink after decolorization.
Why do Gram-positive bacteria retain the primary stain?
Their thick peptidoglycan layer traps the crystal violet–iodine complex.
This structural characteristic is key to their staining properties.
Why do Gram-negative bacteria lose the primary stain?
Their thin peptidoglycan layer and outer membrane allow the dye to be washed out.
The outer membrane is a significant difference between Gram-positive and Gram-negative bacteria.
What does specificity measure in a diagnostic test?
The ability of a test to correctly identify those without the disease (true negatives).
What is the formula for calculating specificity?
Specificity = True Negatives (TN) / (True Negatives (TN) + False Positives (FP)).
In a test with high specificity, what kind of error is minimized?
False positives.
What does sensitivity measure in a diagnostic test?
The ability of a test to correctly identify those with the disease (true positives).
What is the formula for calculating sensitivity?
Sensitivity = True Positives / (True Positives + False Negatives)
What does PPV (Positive Predictive Value) measure?
The probability that a person who tested positive actually has the disease.
What is the formula for calculating PPV?
PPV = True Positives / (True Positives + False Positives)
What does NPV (Negative Predictive Value) measure?
The probability that a person who tested negative truly does not have the disease.
What is the formula for calculating NPV?
NPV = True Negatives / (True Negatives + False Negatives)
How does disease prevalence affect the Negative Predictive Value (NPV) of a diagnostic test?
When disease prevalence is low, NPV is high because most people are disease-free, so a negative test is very likely true. When prevalence is high, NPV decreases because there are more diseased individuals, making a negative test less reliable.
What disease is caused by Vitamin B1 deficiency?
Beriberi (dry and wet types) and Wernicke-Korsakoff syndrome
Beriberi can be categorized into two types: dry, affecting the nervous system, and wet, affecting the cardiovascular system.
What are the key symptoms of Beriberi?
Dry: peripheral neuropathy, muscle weakness
Wet: heart failure, edema
Symptoms vary based on the type of Beriberi; dry focuses on neurological issues while wet involves cardiovascular complications.
What disease is caused by Vitamin B3 deficiency?
Pellagra
Pellagra is characterized by the three D’s: dermatitis, diarrhea, and dementia.
What are symptoms of Vitamin B6 deficiency?
Peripheral neuropathy, cheilitis, stomatitis, irritability, and seizures
Vitamin B6 is crucial for neurotransmitter synthesis and deficiency can lead to significant neurological issues.
What are symptoms of Vitamin B12 deficiency?
Megaloblastic anemia, peripheral neuropathy, subacute combined degeneration of the spinal cord
Vitamin B12 deficiency can lead to severe neurological and hematological issues.
What causes Vitamin B12 deficiency?
Pernicious anemia (autoimmune gastritis), malabsorption, strict vegan diet
Pernicious anemia results from an inability to absorb Vitamin B12 due to a lack of intrinsic factor.
