Using the Gram Stain to Help Diagnose Meningitis (Labster Lab Manual | P) Flashcards
What is meningitis and what happens if a pt has meningitis?
It is a medical condition where the protective membranes (meninges) that surround the brain and spinal cord become inflamed and compresses the nervous tissues of the central nervous system
How to diagnose meningitis (method of sx collection)?
A lumbar puncture is performed to collect cerebrospinal fluid (CSF) from the spinal canal
What should be done to CSF after being collected from the pt?
CSF should be sent for biochemical and microbiological testing, including Gram stain
What are the causes of meningitis?
1) Bacterial infections [variety of Gram (+) and Gram (-)]
2) Viral infections
3) Fungal infections
4) Parasitic infections
5) Autoimmune disorders
What is bacterial meningitis?
It is considered a medical emergency and requires prompt antibiotic treatment
What are the examples of bacteria that can cause meningitis?
1) Streptococcus pneumoniae [Gram (+)]
2) Neisseria meningitidis [Gram (-)]
3) Haemophilus influenzae [Gram (-)]
What are the types of meningitis that are less severe (compared to bacterial meningitis)?
1) Viral
2) Fungal
3) Parasitic
4) Autoimmune
What is required for viral, fungal, parasitic, and autoimmune types of meningitis?
Less intense or sometimes no treatment
What is Gram stain (Gram staining)?
It is a differential technique that differentiates nearly all bacterial species into 2 large groups
What is the basis of differentiation in Gram staining?
Based on structural differences in the cell wall of bacteria
What is the significance of cell wall (of bacteria)?
1) It is significant because it protects and shapes the bacteria
2) It is involved in including disease in the infected host
3) It can also be a target for certain antibiotics
What are the characteristics of Gram (+) bacteria?
1) They have a thick peptidoglycan layer
2) They retain the primary stain
3) They stain (or appear) purple
What is the function of peptidoglycan layer for Gram (+) bacteria?
It remains the primary stain used in Gram staining
What is the primary stain used in Gram staining?
Crystal violet
What are the characteristics of Gram (-) bacteria?
1) They have a thin peptidoglycan layer
2) They have an outer membrane
3) They don’t retain the primary stain
4) They stain (or appear) pink
Can Gram staining be used to identify specific bacteria?
No, hence, additional microbiologic tests are needed
What are the purposes of Gram staining?
1) The presence of bacteria can be diagnosed or detected
2) The characteristic [either Gram (+) or Gram (-)] of the bacteria can be determined
What is the purpose of knowing the Gram type and morphology of the bacteria present in the sx?
By this, it aids in selecting an initial antibiotic needed to treat the pt
What is the color of Gram (+) bacteria?
Purple
What is the color of Gram (-) bacteria?
Pink
Can light microscope be used to examine a Gram stained slide?
Yes
How many are the reagents (or stains) used in Gram staining?
4
What are the reagents (or stains) used in Gram staining?
1) Crystal Violet (CV)
2) Iodine (I)
3) 95% Ethyl Alcohol (Ethanol)
4) Safranin
What is (and its function) CV?
1) It is the primary stain
2) It is used to color both Gram (+) and Gram (-) bacteria purple
What is the purpose of iodine?
It acts as a dye-fixator (mordant) that fixes the purple stain in both Gram (+) and Gram (-) bacteria
How is the principle of iodine executed?
The Iodine molecules bind to CV molecules via electrostatic forces, forming a large, insoluble Crystal Violet - Iodine complex (CV-I complex)
What is the purpose of ethanol and what is the principle of action brought by ethanol?
1) It is used to decolorize the Gram (-) bacteria
2) It dissolves the outer membrane and disrupts the thin peptidoglycan, allowing the purple CV-I complexes to escape the Gram (-) cell wall
Do Gram (+) bacteria remain purple after alcohol wash? Why or why not?
Yes, because of the presence of their thick and robust peptidoglycan which withstand the alcohol and retain the CV-I complexes
What is safranin (including its purposes and its working principle)?
1) It is used as a counterstain
2) It stains Gram (-) bacteria pink
3) It is a positively charged molecule (like CV) that binds to negative bacterial cell wall structures
What happens to Gram (+) bacteria after the application of all stains?
Gram (+) bacteria are already colored purple by the darker CV and remain purple despite the addition of the pink safranin. Hence, it stains purple
What should be done after addition of each chemical compounds (or stains)?
It is essential to wash the slide with water (after each step)
What is the time duration needed for staining using CV?
60 secs
What is the time duration needed for staining using Iodine?
60 secs
What is the time duration needed for staining using 95% Ethyl Alcohol?
5 - 10 secs