<< Chapter < Page Chapter >> Page >
This chart has three columns labeled components, interactions and mictotiter results. In row A the components are the red blood cells which do not interact with anything and show no reaction in a microtiter result. The lack of reaction is seen as a small red dot in the center of the well. In row B the components are viruses and red blood cells. The viruses and red blood cells clump together and this is seen in a microtiter result as redness throughout the well. This is called hemagglutination. In row C, the components are viruses, red blood cells and antibodies. The viruses and antibodies clump together but the red blood cells do not clump with anything. This is again seen as no reaction; this is called hemagglutination inhibition.
This chart shows the possible outcomes of a hemagglutination test. Row A: Erythrocytes do not bind together and will sink to the bottom of the well plate; this becomes visible as a red dot in the center of the well. Row B: Many viruses have hemagglutinins that causes agglutination of erythrocytes; the resulting hemagglutination forms a lattice structure that results in red color throughout the well. Row C: Virus-specific antibody, the viruses, and the erythrocytes are added to the well plate. The virus-specific antibodies inhibit agglutination, as can be seen as a red dot in the bottom of the well. (credit: modification of work by Centers for Disease Control and Prevention)
  • What is the outcome of a positive HIA test?

Nucleic acid amplification test

Nucleic acid amplification tests (NAAT) are used in molecular biology to detect unique nucleic acid sequences of viruses in patient samples. Polymerase chain reaction (PCR) is an NAAT used to detect the presence of viral DNA in a patient’s tissue or body fluid sample. PCR is a technique that amplifies (i.e., synthesizes many copies) of a viral DNA segment of interest. Using PCR, short nucleotide sequences called primers bind to specific sequences of viral DNA, enabling identification of the virus.

Reverse transcriptase-PCR (RT-PCR) is an NAAT used to detect the presence of RNA viruses. RT-PCR differs from PCR in that the enzyme reverse transcriptase (RT) is used to make a cDNA from the small amount of viral RNA in the specimen. The cDNA can then be amplified by PCR. Both PCR and RT-PCR are used to detect and confirm the presence of the viral nucleic acid in patient specimens.

Hpv scare

Michelle, a 21-year-old nursing student, came to the university clinic worried that she might have been exposed to a sexually transmitted disease (STD). Her sexual partner had recently developed several bumps on the base of his penis. He had put off going to the doctor, but Michelle suspects they are genital warts caused by HPV. She is especially concerned because she knows that HPV not only causes warts but is a prominent cause of cervical cancer. She and her partner always use condoms for contraception, but she is not confident that this precaution will protect her from HPV.

Michelle’s physician finds no physical signs of genital warts or any other STDs, but recommends that Michelle get a Pap smear along with an HPV test. The Pap smear will screen for abnormal cervical cells and the CPEs associated with HPV; the HPV test will test for the presence of the virus. If both tests are negative, Michelle can be more assured that she most likely has not become infected with HPV. However, her doctor suggests it might be wise for Michelle to get vaccinated against HPV to protect herself from possible future exposure.

  • Why does Michelle’s physician order two different tests instead of relying on one or the other?

Enzyme immunoassay

Enzyme immunoassays (EIAs) rely on the ability of antibodies to detect and attach to specific biomolecules called antigens. The detecting antibody attaches to the target antigen with a high degree of specificity in what might be a complex mixture of biomolecules. Also included in this type of assay is a colorless enzyme attached to the detecting antibody. The enzyme acts as a tag on the detecting antibody and can interact with a colorless substrate, leading to the production of a colored end product. EIAs often rely on layers of antibodies to capture and react with antigens, all of which are attached to a membrane filter (see [link] ). EIAs for viral antigens are often used as preliminary screening tests. If the results are positive, further confirmation will require tests with even greater sensitivity, such as a western blot or an NAAT . EIAs are discussed in more detail in EIAs and ELISAs .

The explanation of EIA is separated to show what occurs in a positive sample and what occurs in a negative sample. First patient sample is applied to a membrane filter. If the sample contains viruses they are trapped by the filter. Next, antibody with enzyme conjugate is added. Antibody will attach to antigen if present. Next is a wash step. If the virus is present the enzyme binds to the virus, otherwise the enzyme washes away. Finally substrate is added. If the antibody is present (because it is bound to the virus) the attached enzyme causes a color change. If no enzyme linked antibody is present, no color change occurs.
Similar to rapid, over-the-counter pregnancy tests, EIAs for viral antigens require a few drops of diluted patient serum or plasma applied to a membrane filter. The membrane filter has been previously modified and embedded with antibody to viral antigen and internal controls. Antibody conjugate is added to the filter, with the targeted antibody attached to the antigen (in the case of a positive test). Excess conjugate is washed off the filter. Substrate is added to activate the enzyme-mediated reaction to reveal the color change of a positive test. (credit: modification of work by “Cavitri”/Wikimedia Commons)
  • What typically indicates a positive EIA test?

Part 3

Along with the RT/PCR analysis, David’s saliva was also collected for viral cultivation. In general, no single diagnostic test is sufficient for antemortem diagnosis, since the results will depend on the sensitivity of the assay, the quantity of virions present at the time of testing, and the timing of the assay, since release of virions in the saliva can vary. As it turns out, the result was negative for viral cultivation from the saliva. This is not surprising to David’s doctor, because one negative result is not an absolute indication of the absence of infection. It may be that the number of virions in the saliva is low at the time of sampling. It is not unusual to repeat the test at intervals to enhance the chance of detecting higher virus loads.

  • Should David’s doctor modify his course of treatment based on these test results?

Jump to the next Clinical Focus box. Go back to the previous Clinical Focus box.

Key concepts and summary

  • Viral cultivation requires the presence of some form of host cell (whole organism, embryo, or cell culture).
  • Viruses can be isolated from samples by filtration.
  • Viral filtrate is a rich source of released virions.
  • Bacteriophages are detected by presence of clear plaques on bacterial lawn.
  • Animal and plant viruses are detected by cytopathic effects , molecular techniques (PCR, RT-PCR), enzyme immunoassays, and serological assays (hemagglutination assay, hemagglutination inhibition assay).

Fill in the blank

Viruses can be diagnosed and observed using a(n) _____________ microscope.

Electron

Got questions? Get instant answers now!

Cell abnormalities resulting from a viral infection are called ____________ _____________.

cytopathic effects

Got questions? Get instant answers now!

Short answer

Briefly explain the various methods of culturing viruses.

Got questions? Get instant answers now!

Questions & Answers

differences between acid fast and non acid fast bacilli
ANTHONY Reply
acid fast have cell wall that holds to carbol fuschin stain while non acid fast doesn't have. it readily releases out the primary stain the carbol fuschin.
LAFIA
where do I post a question that isn't related to that topic
eklectc
hi everyone
kennedy
hello
Olivia
for sure, this question is not related to the topic.
LAFIA
can someone explain the process of glycolysis and the electron transport chain? I'm so freakin lost. it loses carbons, gains hydroxyls, gains, loses Hydrogens....ugh it's like a foreign language to me! or direct me to a youTube video or something that will make this seem easier to concept?
eklectc
it's a loaded question, sorry!
eklectc
why is DNA a genetic material
Mcbeth Reply
DNA is genetic material because it contains chromosome contains the traits which includes characters and behavioral characteristics
chima
why is it difficulty to classfy protista
Tanaka
Good
Eddy
what is infection prevention
Muhammed Reply
good hygiene
Dhaqan
way of preventing disease causing germs
henry
maintenance of sterilization
Pooja
h
Faustina
describe the components of the epidemiology triangle
Muhammed Reply
Hai
Nantongo
hii
Md
where from you
Md
i am Indian
Md
you
Md
Hello friend
effiong
How are you people doing
effiong
أ‌) Host factor ب) pathogen ج) environment
Widad
Hello
Kofi
Hi
Widad
hey hi
kalai
The epidemiologic triangle is made up of three parts: agent, host and environment
Princess
what are the fluids used in biochemistry Lab used to diagnose diseases
Jb Reply
fadumo qule a gemil3
fadumo Reply
Faadum mahamud disease micro biology
fadumo
makuway diinkaraan suaalo
fadumo
history of microbiology
Balqees Reply
Penicillin is caused by what microorganism
Balqees
Penicillin is caused by what microorganism
Balqees
penicillium notatum
Pooja
M sorry I mean penicillin is caused by what Fungi
Balqees
penicillium fungi
Pooja
mention 5 characteristics of prokaryotic cell and also 5 characteristics of euryotic cell
Grace Reply
PROKARYOTES _ does not have nucleus _does not have membrane bound organels like eukaryotes -does not have endoplasmic reticulum _does not have a mitchochondrion _it have plasmid instead of chromosome EUKARYOTE S _have true nucleus _have all membrane bound organels _have mitochondria have
Pooja
continuation _have endoplasmic reticulum _have chromosomes does not have plasmid
Pooja
antigenisity define
kalai
explanation of spores
nahida Reply
what specific types of biological macromolecules do living things require?
Jonathan Reply
define spores its classification
nahida
define spores its structure and classification
nahida
what is a complement
Alecia Reply
something which completes or combine with something else to make it complete.
Kosi
hello
Kosi
medical microbiology
Kosi
you?
Kosi
hi
Amina
Guys who's doing nursing in here
Mumba
I have a question
Mumba
what's the importance of microbiology in nursing
Mumba
yah
Mumba
wow..nice meeting you
Kosi
thanks
Mumba
for
Mumba
anytime
Mumba
microbiology also important for understanding the communicable or non-communicable disease in our hospitals...which is very important for patients and healthy people.
Kiran
what is a microbial flora
Chetan
normal microbial flora
Chetan
Definition of microbiology?
Mohamed Reply
study of microorganisms is known as microbiology
Pooja
no
Mumba
microbiology is the study of small or minute organisms that cannot be seen with our naked eyes but with the aid of a microscope
Mumba
write and explain the infection chain of 6 common disease infections
Adjowa Reply
diphtheria. dysentery. bubonic plague. pneumonia. tuberculosis. typhoid. typhus. Aug 22, 2017
shamim
good afternoon
Dasaah
OK
Dasaah
Good night
fine
Dasaah
which bacteria can be isolated from abattoirs ( slaughter houses).
Omoja
bacteria that csn be isolated from abattoirs are- Clostridium Bacteroides Desulfobulbus Desulfomicrobium Desulfovibrio
Yashkin
what is a microscope
Louise Reply
Is an instrument used to magnify object which can not be seen with our naked eyes.
Mohamed
are virus host specific?
koguriyem Reply
are viruses effective in small dose?
koguriyem

Get the best Microbiology course in your pocket!





Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Microbiology' conversation and receive update notifications?

Ask