Microbiology Flashcards
Obligate intracellular parasites
virus
*Rely on host cell for replication
What are the various omponents making a viral capsid?
DNA or RNA + structural proteins + enzymes and nucleic acid binding proteins (nucleocapsid)
Virus morphology is divided into 2. We have ______and _____viruses
- Enveloped
- Non-enveloped (have a capsid component only, no envelope part)-NAKED VIRUSES. (Polio)
These virus types have lipoproteins lining their envelope
- The enveloped viruses
Features of a viral envelope
-Glycoproteins (gp 120 n 41 with HIV)
- Lipoprotein
*Glycoproteins are also known as viral antigens
Where does the nuclear envelope of a virus comes from?
- It is derived from the nuclear membrane of the host cell
Protein subunits that make up the capsid of a virus
Capsomers
Three forms of capsid symmetry, resulting from arrangement of capsomers
- Icosahedral (triangular arrangement of capsomers around the viral nucleic acid)
- helical (capsomer subunits arranged in a helical fashion around the viral nucleic acid)—ON RNA VIRUSES ONLY
- Complex (Found on DNA viruses only)
Viral genome/ nucleic acid is either_________
-DNA or RNA never both
- Single or double stranded
- Continuous or segmented
These viruses are all double stranded except parvo viruses
DNA viruses
These viruses are all single stranded, except reoviruses
RNA viruses
A sense strand that can be directly translated into proteins. It has the same sequence as RNA. It functions like mRNA. Needs no further processing to code proteins.
positive sense strand
*+sense mRNA is found on SARS COV2 virus
A sense strand that acts as a temple for a + sense strand or mRNA. Cannot be directly transcribed into proteins. It needs a medium strand to convey it info of what proteins to be encoded
Negative sense strand
A classification of viruses based on their genome type and replication strategy (whether they produce mRNA)
Baltimore classification
Modes of viral transmission
- Inhalation
- Ingestion
- Direct contact with skin or mucous membranes
- Indirect contact (fomites)
- Transplacental
- Organ transplant of blood transfusion
What viruses cause chronic viral infections
- HBV, HCV, HTLV1, HIV
- They ‘‘flare up’’ (sudden and significant increase in viral replication)
- May or may not be symptomatic
-Shedding continues and therefore are infectious in varying degrees
What are latent viral infections?
- Does not cause disease in latency periods with little or no replication
- Remains relatively undetectable diagnostically and immunologically
- '’Flare up’’ disease may occur if the virus reactivates (eg: Herpesviridae (eg. zoster)
How does Hepers Simplex Type-1 Virus (HSV-1) spread?
-Through close contact with infected person e.g kissing
- Sharing utensils,
- or Touching the affected area
- And through oral sex, causing genital herpes
Pathogenesis of HSV-1?
HSV-1 can remain dormant in nerve cells near the site of the initial infection (typically the trigeminal ganglia) and reactivate periodically.
*Latency and reactivation are its features
*Triggers of reactivation: illness, fever, sun exposure, hormonal changes, menstruation, stresss
Two types of HSV
- HSV-1: facial herpes (above the waist; gingivostomatitis, fluid-filled blisters or sores around the mouth or on the lips, herpetic whitlow-skin infection, HSV keratitis-infctn of cornea,
encephalitis, pneumonitis) - HSV-2: associates with genital infections (below the waist – genital herpes, encephalitis,
meningitis)
HSV infection of newborn within 28 days of birth
*results from transmission of virus during delivery through infected genital secretions from
mother
Neonatal herpes
Diagnoses of type 1 HSV
- Clinical presentation (gingivostomatitis-fluid filled blisters around the mouth/on lips)
- (LAB)
-Viral culture
-Immunofluorescence staining
-Serology
-Polymerase chain reaction (PCR)
Is there possible cure for HSV?
No,
There is no cure for HSV-1, but antiviral medications such as acyclovir, valacyclovir, and famciclovir can help reduce the severity and duration of outbreaks and decrease the frequency of recurrence.
Episodic Topical creams to reduce frequency of HSV
- Acyclovir cream
- Docosanol cream
- Penciclovir cream
Different types of HIV diagnostic tests?
- Rapid point-of-care: measures antigens and antibodies
- At-home tests: measures antibodies
- Standard point-of-care: measures anitbodies
- Nucleic acid test: measures HIV RNA
How is adenovirus transmitted from one person to the next?
- Usually enter host by inhalation of droplet
- Or by oral route
Direct inoculation of _______virus onto nasal or conjunctival mucosa by hands, contaminated towels, or ophthalmic medications may occur
Adenovirus
A virus that replicates in epithelial cells, producing cell necrosis and inflammation
Adenovirus
Large number of patients are asymptomatic, but mostly presents with features of URTI.
Which virus cud they be infected with?
Adenovirus
*Affects multiple organs
Diagnostic methods of adenovirus
- PCR routinely done
- High specificity and sensitivity
- Respiratory sample – swab or aspirate
Adenovirus has no treatment, just a drug helping with symptom management. What drug is this?
Cidofovir
Infection with this virus is prevented with live-viral vaccine (enclosed-enteric capsules), where viruses are administered orally into your small intestine
Adenovirus
Diagnostic techniques of adeno-virus
- Serology
- Molecular
- Culture
What are the 3 analytic stages of microbe diagnostic cycle
- Post-analyticstage
-Final Reports
-Doctor interprets report and treats appropriately
-Record keeping - Pre-analytic stage
-Patient consultation and clinical diagnosis
-Appropriate specimen collection
-Transport to lab
-Registration in the laboratory - Analytic stage
-Direct examination and specimen processing
-Presumptive Reports
The Triumphant Trio
Three essential components or approaches that are crucial for effectively identifying microbes and their possible inhibitors:
- microscopy
- Culture
- Susceptibility test
What can a doctor learn from microscopy results?
The gram stain result will tell her/him whether his choice of antibiotic covers that group
of organisms empirically (fairly broad)
What can a doctor learn from culture results?
name of the microbe
What a doctor can learn from susceptibility testing?
the results will tell him if his choice of antibiotics will work on this exact strain of the
organism
Normative ways of diagnosing viruses
Molecular methods
How to possible isolate bacteria and fungi in a single patient sample?
Grow them on the surface of solid nutrient media, to get a pure culture of each organism
*Such a medium normally consists of a mixture of protein digests (peptone, tryptone) & inorganic salts,
hardened by the addition of 1.5% agar
Culture media used for antibiotic susceptibility testing
Mueller Hinton agar plate
What is the basic quantitative measure of in vitro activity of antibiotics?
MIC
- The lowest concentration of the antibiotic that results in inhibition of visible growth
MIC
What are the methods used to carry out antimicrobial susceptibility testing?
- Disk diffusion: (Kirby-Bauer)
- Antibiotic gradient strips: (Etest®)
-Broth microdilution - AUTOMATED- Vitek
Remains the gold standard
Culture based diagnostic
What makes non-culture based samples favorable over culture based samples?
- Non-culture based does not need sample from sites of infection, it uses blood samples.
What 3 diagnostic tests are considered non-culture based?
- Molecular tests
- Antigen detection
- Immunoassays- antibody tests (serology)
Examination of blood serum regarding the response of your immune system to the pathogen
Serology test
*We looking at antibodies produced
1st antibody to be produced with every pathogen infection, but has a shorter half-life.
*clears sooner
IgM
*Produced in 7-10 days after infection, and lasts for 1-3 months
An antibody produced with persistent, chronic infections and has a longer half life
*doesn’t clear up for a very long time
IgG
How many genes does HIV genome have?
9 genes
What are the 3 structural genes of HIV?
- Gag – encodes group antigen and structure of capsid
- Env – making of the envelope gene
- Pol – codes for the polymerase
What are the 3 common modes of HIV transmissions?
- Sexual
-Main mode of transmission
-Accounts for 70−80% of all HIV infections - Parenteral
-Blood transfusions (estimated risk from a single unit of HIV-infected whole blood is > 90%)
-Contaminated needle pricks
-Needle sharing among HIV-infected drug users - Vertical (perinatal)
-In utero, during labour and delivery, and through breastfeeding
What cells does HIV targets
And how does it bind to them?
-HIV targets CD4 T cells. Binds to their receptor, as well as their co-receptor.
-It also targets macrophages, binding their receptor and core receptor
What’s a core receptor of CD4 T cell to which HIV binds?
CXCR4
What’s a core receptor of macrophage to which HIV binds?
CCR-5
What’s the HIV entry pathway into the host cell?
Endocytosis
What’s the host DNA called after it has been integrated with tht of HIV (HIV) by intergrase?
proviral DNA
What’s the process by which HIV exits the host cell called?
Budding
Who can have immunity against HIV 1?
- Individual without a CCR5 receptors
- Homozygous persons: those with two deleted CCR5 gene segments are homozygous for the CCR5Δ32 mutation
A cell surface receptor primarily found on immune cells, including T cells, macrophages, and dendritic cells; utilized by the majority of HIV strains during the initial stages of infection
CCR-5
Which 2 groups of Individuals, may not be on ART treatment (may be excused)?
- Elite Controller: someone who can keep nearly undetectable levels of virus, without antiretroviral therapy
- Long Term Non-Progressor: someone who maintains a normal count of CD4 and CD8 T-cells for a minimum of 10 years without the aid of antiretroviral therapy
What are the 2 main approaches to testing for HIV?
- Antibody based e.g HIV ELISA (Ag/Ab combo), HIV Rapid Test
- Nucleic Acid Testing e.g HIV DNA PCR
*These 2 are impacted by age of a patient (which one to use depend on patient age)
What’s a preferred HIV diagnostic strategy for children <18 months?
HIV nucleic acid test
*We cannot use HIV ELISA test coz it tests HIV antibodies. And martenal antibodies take over affecting credibility of the results
What’s a preferred HIV diagnostic strategy for individuals > 18 months?
-HIV ELISA test
*Detects antibodies to HIV
What is the goal of ART?
ART must result to viral load below the limit of detection in 3-4 months following initiation
*CD4 count expected to increase by 50 -100 cells/mm3 in the first month and thereafter increase much slower
HIV can be measured in blood products. Or, u can measure viral load in patient’s blood. What assay test is best used for this?
Quantitative molecular assay/Viral Load Assays
*Predict disease progression
-Assist with deciding when to initiate anti-retroviral therapy
-Monitors response to antiretrovirals
What’s the enzyme responsible for reverse transcription of HIV?
Reverse transcriptase
What are the 2 forms of viral infections?
- Inapparent infections
-Asymptomatic - Apparent infections
-Acute
-Chronic (persistent, latent)
The process by which viruses are released from infected cells and spread to infect other cells or individuals.
Shedding
What’s the NUCLEIC ACID TEST used in early neonate diagnoses of HIV, mapping out marternal antibodies?
HIV qualitative PCR (HIV 1 DNA PCR)
*Detects virus b4 the viral load is present
What are characteristics of ‘slow growing virus’ and its exaple?
- Longer incubation period for like years
- Virus replicates without causing disease
- Cause disease years later, at the end of the infectious period
example JC virus
