Block A - Microbial Identification Flashcards
Define a virus? (2 marks)
-genetic elements which replicate inside a host
-distinct from plasmids; have extracellular form
What are the 4 stages of the viral replication cycle (4 marks)
-attachment - the virus binds to a specific receptor on the surface of a susceptible host cell. This interaction determines host specificity. for example the Influenza virus uses hemagglutinin (HA) to bind to sialic acid receptors on epithelial cells
-entry - the virus enters the cell via endocytosis (not-enveloped) or membrane fusion (if enveloped). the viral capsid breaks down, releasing the viral genome into the host cell. this can occur in the cytoplasm or nucleus, depending on the virus
-replication - the viral genome is replicated, and viral proteins are synthesized using host machinery. new viral genomes and proteins are assembled into complete virions. some viruses self-assemble, while others require molecular chaperones.
-release - new virions exit the host cell via budding (for enveloped viruses) or lysis (for non-enveloped viruses). some viruses remain latent before causing symptoms.
In the one-step growth curve, what is the eclipse stage and what does it look like on graph?
-eclipse phase is when no infectious particles are detected
-it looks like a plateau of 0 infectious virions
In the one-step growth curve, what is the latent stage and what does it look like on graph?
-is when the virus replicates inside the host
-place where there is no detectable increase in the number of virus particles
TRUE/FALSE: the maturation phase is not part of the latent phase
false, it is part of the latent phase
Describe the lytic consequences of viral infection
host cell lysis, virions are released
Describe the latent consequences of viral infection
viral DNA does not replicate, host cell is unharmed
Describe the persistent consequences of viral infection
slow release of viral particles without host cell death, some enveloped viruses ‘bud’ from host cell without lysis.
Describe the transformation consequences of viral infection
-transformation of host cell into tumor cells through the expression of oncogenes
Approximately how many bacterial species are currently known to infect humans?
A) 150
B) 1,500
C) 15,000
D) 150,000
B
Which two bacterial classes contain nearly half of all known human pathogens?
A) Alphaproteobacteria & Firmicutes
B) Gammaproteobacteria & Actinomycetes
C) Spirochaetes & Bacteroidetes
D) Mycobacteria & Cyanobacteria
B
Why is bacterial classification important in clinical microbiology?
A) It ensures all bacteria are named according to their habitat.
B) It helps in diagnosing infections and determining treatment.
C) It prevents the discovery of new bacterial species.
D) It is only useful for research, not medicine.
B
What is the main difference between taxonomy and phylogeny?
A) Taxonomy classifies organisms based on appearance, while phylogeny classifies based on evolutionary relationships.
B) Taxonomy is always correct, while phylogeny is theoretical.
C) Phylogeny follows Linnaean classification, while taxonomy does not.
D) They are two names for the same concept.
A
What is the role of the International Code of Nomenclature of Prokaryotes (ICNP)?
establishes rules and guidelines for the naming and classification of prokaryotic organisms (Bacteria and Archaea)
The Genome Taxonomy Database (GTDB) is primarily based on:
A) Morphological features
B) 16S rRNA gene sequencing
C) Whole-genome similarity
D) Bergey’s Manual classifications
C
Which of the following best defines a bacterial species?
A) A group of bacteria that share at least 95% 16S rRNA gene similarity.
B) Bacteria that always cause disease in humans.
C) A set of bacteria that can sexually reproduce.
D) Any bacteria found in the same ecological niche.
A
Why is the concept of a bacterial species still controversial?
A) Bacteria can exchange genetic material horizontally.
B) Bacteria do not have cell nuclei.
C) All bacteria belong to the same species.
D) Bacterial species are defined purely by morphology.
A
What is the first step in the classical polyphasic approach for bacterial identification?
A) Whole-genome sequencing
B) 16S rRNA gene sequencing
C) Isolation & microscopy
D) MALDI-TOF analysis
C
Which of the following is an example of a differential but not selective medium?
A) Mannitol Salt Agar
B) MacConkey Agar
C) Eosin Methylene Blue (EMB) Agar
D) Blood Agar
D
MALDI-TOF mass spectrometry identifies bacteria based on:
A) Ribosomal protein mass fingerprints
B) DNA sequence similarity
C) Colony color on agar plates
D) Cell wall structure
A
What is a major limitation of MALDI-TOF mass spectrometry?
A) It cannot be used on cultured bacteria.
B) It requires sequencing the entire genome.
C) It cannot distinguish between some closely related species.
D) It is slower than traditional biochemical tests.
C
What makes 16S rRNA sequencing useful for bacterial classification?
A) It accumulates mutations at a constant rate, allowing phylogenetic comparison.
B) It is unique to each bacterial cell.
C) It mutates rapidly, allowing fine-scale discrimination.
D) It is present only in Gram-negative bacteria.
A
Why is Multi-Locus Sequence Typing (MLST) more accurate than 16S sequencing?
A) It analyzes multiple genes, increasing resolution.
B) It is faster and cheaper than 16S sequencing.
C) It uses mass spectrometry instead of DNA sequencing.
D) It does not require a reference database.
A
Metagenomics (shotgun sequencing) is superior to traditional culture methods because:
A) It can identify unculturable bacteria in a sample.
B) It always provides species-level resolution.
C) It does not require DNA extraction.
D) It is the standard method for bacterial identification.
A
