Laboratory Methods Flashcards
What is direct diagnosis
direct diagnosis? when it provides the diagnosis of the disease or condition by itself or when it provides decisive information for the diagnosis.
What is the importance of laboratory diagnosis of infectious diseases
- It is needed in the treatment of infection
- It improves the effectiveness of treatment ( monitoring patients reactions the the treatment)
- Early diagnosis helots to stop or prevent th spread of the infection . Example: if you’re sick and instead of going to the hospital for the doctor to diagnose the disease , you stay home and treat your disease it may get out of hand and worsen. Also if the disease you have is contagious and other people contract that disease, the disease will keep spreading.
What are the main organisms that cause infection
Bacteria- Cholera( Vibrio Cholerae, Tuberculosis (mycobacterium tuberculosis),syphilis( Treponema pallidum )
Fungi- candidiasis(candida albicans ), athlete’s foot, ringworm
Virus- AIDS(HIV), common cold(rhinovirus),influenza(influenza virus, H1N1)
Helminths(worms)- hookworm infection, schistosomiasis
Protozoa -malaria(plasmodium parasite),trypanosomiasis (trypanosoma brucei), amoebic dysentery ( entamoeba histolytica
What re the Methods of lab diagnosis
Direct method: detects the pathogen or the structural components of the pathogen (example DNA or RNA)
Examples: microscopy, culture,molecular test
Indirect: it shows a reaction that has occurred due to the infection or due to the presence of the pathogen in you body. It only shows positive or negative. ExMple: serological method,imaging, X-ray, CT scan, Ultrasound
Microscopy can detect all the five groups of pathogens. True or false
True
Name four Types of microscope , how they work and three merits and demerits of each.
Brightfield or light microscope: Examines stained and unstained specimen. Specimen appears dark in a white or bright background.
Merits: easy to use, not expensive to buy and maintain, Very specific( helps you see a specific pathogen), portable
Demerits: Time consuming, low resolution, low sensitivity especially when the pathogen load is low( sensitivity is the ability of a test to correctly identify all the true positive patients). If it’s high then the test will identify all the positive patients if it’s low test will be able to identify few of the positive patients.
Dark field microscope: Observes specimen that are unstained. It views live pathogen if present in the sample. Pathogens appear bright in a dark background.
Merits:
Demerits:
Fluorescent microscope: Intensity of the light source is high. This excites the molecules of the fluorescent dye used to stain the specimen, emitting light from the pathogen of it is present. Mainly used in research labs.
Merits
Demerits
Electron microscope: Uses beam of electron to create an image. It has high resolution to detect extremely small sized pathogens. It’s mainly used to examine viruses because of this.
Merits
Demerits
Types of preparation
Stained- uses dye
Unstained - doesn’t ( examples, urine is put on slide and covered, shit is put on slide and normal saline is added to it then it is covered
Types of stains
Simple stains: one color is used. Examples- iodine, methylene blue
Differential stains: two or more stains in staining procedure. ExMple, Gram staining
fluorescent stains( best used for mycobacterium species)
When are concentration methods used
When parasitic infection is suspected
Types of concentration methods
A.Sedimentation - example( if urine is centrifuged,the sediment is observed)
- Simple sedimentation-only
- Formalin ethyl centrifugation- formalin preserves pathogen there , then ethyl is added.
Microscopy observes how specimen looks. It’s collie and all
B.Floatation- NaCl or zinc sulphate are the reagents used. When centrifuged, pathogens appear at the upper portion. Upper portion is taken and lower portion is discarded
Types of substrate for culture
- Culture media(artificial media)(contains all necessary nutrients needed for pathogen to grow and is created in the laboratory )(viruses can’t grow in this media)
- Living eukaryotic cell examples viruses, some bacteria need living cells to grow (intracellular pathogens), some Protozoa example toxoplasma
Types of culture
- Blood culture
- Urine culture
- Stool culture
Sputum culture
Merits and demerits of culture
Very good sensitivity
Demerit- requires longer time to get results
Explain molecular method and the principle it works on and it’s merits and demerits
Detects nucleic acid of the pathogen. Works on the method of PCR- polymerase chain reaction ( makes many copies of the DNA or RNA using different temperatures or temperature cycles)
Demerits- expensive and requires training
Merits- useful for fastidious pathogens ( pathogens that are difficult to culture in the lab), doesn’t need many samples, even one sample is okay
Serology detects what and what
Antigen in the body and the antibodies induced by the antigen
What is sterilization
It is the complete removal of viable pathogenic microbes using physical or chemical methods
Merits and demerits of serological methods
Easy to use
Not expensive
Demerits: can produce a negative result if the time the body takes to develop antibodies in response to the antigen is long
ELISA stands for
Enzyme linked immunoassay
What is disinfection
Process of killing microbes with the exception of spore forming bacteria on inanimate surfaces. Biocides or disinfectants are used
If disinfectant is effective against spores it’s called- spirocides
If it’s effective against bacteria it’s called biocide
Define antiseptics and the term aseptic
Biocide used to destroy microbes on or in living tissues.
Aseptic means the absence of pathogens in or on living tissues
Methods of sterilization are groups into two, name them
Physical and chemical methods
Physical method of sterilization is divided into three name them
Heat method ( dry heat method( hot air oven( forceps , scissors, glassware, slides,test tubes) are put in there is used and is heated to 180degrees Celsius for two hours. Bunsen burner and incineration is also used ) and moist heat method(boiling the instruments 100 degrees for 10 mins or more)
Radiation method( non ionizing and ionizing method)
Filtration
What is tyndallization
It targets spore forming pathogens or pathogens that were not killed by simple boiling. Items are boiled for three consecutive days
Boil and cool and boil and cool and boil and cool.
What is pasteurization
Mild heat is applied to
Most food and beverages. 62 degrees Celsius for thirty minutes
What is the principle auto claving is founded on
Steam under pressure for 121 degrees , 15 mins, 151bs
For surgical instruments, culture media
How to be sure if sterilizing successful
Bowie and Dick tape is used. If sterilization was successful, there’ll be a color change
What is non ionizing radiation
Example- UV light.
Low energy is used so more time is taken to break the bonds
What is ionizing radiation
Energy is so high
ExMple X ray
What is filtration
Removal of microbes from liquids. Polyester can be used as well as candles in filter containers
What is used in Chemical sterilization
Alcohol can be used as a disinfectant and an antiseptic
It exhibits rapid and broad spectrum anti microbial activity
Example ethanol
Optimum results are achieved when the 70 percent is used
Aldehyde is used as
Disinfectant
Formaldehyde function
storing tissues
Halogen releasing agents examples
Iodine, household bleach, chlorine for water treatment
Hydrogen peroxide is used as only antiseptic. True or false
False. It’s used as both disinfectant and antiseptic.
It inhibits bacterial fatty acid synthesis.
Name some
Modes of action of disinfectants and antiseptic
Disrupt cells membrane or cell wall
Damage DNA
Denature proteins
Factors that affect the effectiveness of a chemical agent
- The concentration of the disinfectant and antiseptic:High or low concentrations of these chemicals affect it’s ability to produce the desired result which is destroying the microbes it comes into contact with. For a chemical agent to be effective, the concentration must be high enough to kill the microbes it comes into contact with. If the concentration is low, the chemical agent will not be able to kill the microbes thus rendering it ineffective.
- Temperature at which the disinfectant and antiseptic is used:High or low temperatures affect the way chemical agents work. The chemical agents have optimal temperatures at which their activity increases thereby making them effective. When the temperature of the disinfectant and antiseptic increase too much it weakens its activity. When the temperature is decreased, the chemical agent’s activity decreases
- Number of microorganisms present on the material : When the number of microorganisms is large, more time and more of the chemical agent is needed to remove all the microorganisms. When the number of microorganisms is large and the concentration of the agent is low , the effectiveness of the disinfectant and antiseptic reduces.
- Nature of the material bearing the microorganisms: The material should be free of dirt and anything that can interfere with the activity of the disinfectant and antiseptic. If the material has dirt on it and the dirt interferes with the activity of the chemical agent, the chemical agent’s effectiveness reduces.
- The kind of microorganisms present:Disinfectants destroy microbes with the exception of spore forming microorganisms. These spore forming microorganisms are difficult to handle. If the kind of microorganisms on the material are spore forming microorganisms and a disinfectant or antiseptic comes into contact with it, it may not be able to remove the spore forming microorganisms thus rendering the chemical agents ineffective .
Why is 70percent alcohol used and not 100 percent
70% percent of alcohol is ideal to a stronger solution. Pure alcohol coagulates protein in contact. Suppose the pure alcohol is poured over a single celled organism. The alcohol will go through the cell wall of the organism in all direction, coagulating the protein just inside the cell wall. The ring of the coagulated protein would then stop the alcohol from penetrating farther from the cell, and no more coagulation would take place. At this time the cell would become inactive but not dead. Under the favorable conditions the cell would then begin to function. If 70 percent of alcohol is poured to a single celled organism, the diluted alcohol also coagulates the protein, but at a slower rate, so that it penetrates all the way through the cell before coagulation can block it. Then the entire cell is coagulated and the organism dies.
Merits and demerits of dark field microscope
Easy to use or simple and effective techniques
Quality of images obtained are very high
Well suited for uses involving live and instained biological samples
Demerits
Dark field needs an intense amount of light to work. This intense light can create glare and distortion. Therefore, dark field does not create reliable specimen measurements.
- Dark field is sensitive to contaminants.
The sample must be very strongly illuminated, which can cause damage to the sample
- Specimens which are not thin enough are prone to degradation and distortion
Merits and demerits of electron microscopy
High cost High maintenance Not portable due to its large size Needs high level of expertise Can’t analyze live specimen
Merits
High resolution
High quality images
Merits and demerits of fluorescent microscope
Very specific
High sensitivity
Different molecules can now be stained with different colors, allowing multiple types of the molecule to be tracked simultaneously.
Demerits
Photo bleaching
Cells are susceptible to phototoxicity, particularly with short-wavelength light.
Explanation of tyndallization
substance to boiling point (or just a little below boiling point) and holding it there for 15 minutes, three days in succession. After each heating, the resting period will allow spores that have survived to germinate into bacterial cells; these cells will be killed by the next day’s heating. During the resting periods the substance being sterilized is kept in a moist environment at a warm room temperature, conducive to germination of the spores. When the environment is favourable for bacteria, it is conducive to the germination of cells from spores, and spores do not form from cells in th
Importance of the aura mine phenol stain
Auramine phenol stain is a stain used in clinical microbiology and histology to identify tuberculosis mycobacteria
Surgical instruments and culture media are usually sterilized by
Steam under pressure or autoclaving
Glassware such as Petri dishes etc are sterilized using what method
Hot air oven method
Inoculating needles or loops are sterilized using
Naked flame
If there is fluid in the lung
There will be a change in colour in the x ray
MRI doesn’t use radiation. It uses magnetic field and for soft tissues
CT scan uses ionizing radiation. Usually for bones or bony tissues and for seeing things in segments
