Virus Diversity & Unique Replication
The family of very large dsDNA viruses that replicate in the cytoplasm and encode virtually all their own DNA replication machinery, making them an exception to the rule for dsDNA viruses.
Poxviruses
The influenza virus uses two major spike proteins — one for host-cell attachment, and another for virion release. Name each spike protein and match it to its function.
Hemagglutinin (HA) — mediates attachment and entry
Neuraminidase (NA) — release progeny virions
This process claims “sterilization” of canned goods by targeting Clostridium botulinum spores but is not true sterilization because some microbes may survive.
Commercial Sterilization
Name two antibiotics that inhibit cell wall synthesis
Penicillins, Cephalosporins, Vancomycin
The area of the body containing the largest microbiota by ratio (anaerobe: aerobic ~1000:1) is this.
colon/intestine
This group of bacteria, small, obligate intracellular parasites, are bacteria, not viruses, yet are often mistaken as viruses because of size and dependency.
Rickettsia/Chlamydia
This antiviral-drug target for influenza inhibits the NA spike protein to prevent release of new virions.
Tamiflu
Which pathogen is an exception in food microbiology because it can grow at refrigeration temperatures (≈4 °C)?
Listeria monocytogenes
Chloramphenicol causes this syndrome in infants under 2 years old, causing an important toxicity recall.
Gray baby syndrome
When comparing coagulase-positive and coagulase-negative staphylococci, which species is coagulase-positive, and which is generally more virulent?
Staphylococcus aureus — coagulase-positive, forming a visible clot and more virulent; coagulase-negative staphylococci are less virulent
Within Group V (-ssRNA) viruses, there is one notable exception that replicates its RNA genome in an unusual location compared to the other -ssRNA viruses.
Name this virus and where replication occurs.
Influenza
Replication occurs in the nucleus
With HPV infection, over-expression of what genes leads to inactivation of this host tumor-suppressor protein, driving cervical cancer.
E6 & E7 oncogenes
A lab tests ampicillin: growth persists up to 1 µg/ml, no growth at 2 µg/ml on plate, but when plated from 2 µg/ml tube there is growth; no growth at 4 µg/ml and above. What is the MIC? What is the MBC?
MIC = 2 µg/ml; MBC = 4 µg/ml
Fungal infections are difficult to treat because fungal cells are similar to human cells. However, antifungal drugs can selectively target this unique component of fungal membranes, similar to cholesterol in humans, disrupting membrane integrity by forming pores.
Ergosterol
True or False: Lungs are a sterile organ
False, normal flora exist there.
Antigenic shift involves the creation of a _______ virus; Name the virus type and define it.
Chimeric virus — a virus formed through reassortment, when two different strains (often human and animal) co-infect the same cell and exchange genome segments, producing a new hybrid virus.
During the clinical latency stage of HIV infection, the patient may show few or no symptoms.
What happens to the viral load and CD4 T-cell count during this stage?
The viral load remains low, while the CD4 T-cell count gradually declines over years as the virus continues slow replication
In a disk-diffusion antibiotic test: If Antibiotic X has a patient zone diameter of 14 mm, and the susceptible cutoff is ≥22 mm, intermediate 15–21 mm, resistant ≤14 mm. How would you interpret the result?
Resistant
The antibiotic sulfanilamide works by blocking which metabolic pathway in bacteria? How does it block the pathway?
Folic acid synthesis by mimicking PABA and limiting DNA synthesis
Strict anaerobes survive on the skin and in the mouth because of the activity of which type of microbes, and how do they help?
Aerobes. By consuming oxygen, they create a low-oxygen environment for anaerobes.
Which viral groups use reverse transcriptase, and name the three functions of the enzyme?
Groups 6 and 7; (1) RNA-dependent DNA synthesis, (2) RNase H activity (degrades RNA), (3) DNA-dependent DNA synthesis.
Group 7 viruses have a partially double-stranded DNA genome that replicates through an RNA intermediate.
Walk through the key steps of its genome replication, transcription, and translation, starting from entry into the nucleus and ending with synthesis of new viral DNA.
After entry, the partially double-stranded DNA is delivered to the nucleus, where host enzymes convert it to covalently closed circular DNA (cccDNA).
The cccDNA serves as a template for host RNA polymerase to pre-genomic RNA (pgRNA).
The pgRNA is then reverse transcribed by the viral reverse transcriptase into partially double-stranded DNA, completing the new genome.
Translation of mRNAs by the host ribosomes produces capsid and envelope proteins, which assemble into new virions.
If the D-value is 30 min for a microbial population of 10⁵ cells, how long until the population will be considered sterile?
150 minutes
Define the chemotherapeutic index and state what value indicates greater drug safety.
Chemotherapeutic index = toxic dose ÷ therapeutic dose
A higher ratio means the drug is safer (the larger the ratio, the safer the drug)
Compare and contrast normal and transient microbiota, including their potential to cause disease.
Normal microbiota are permanently present and usually do not cause disease under normal conditions but can become opportunistic pathogens if given the opportunity.
Transient microbiota are temporary, often removed by hygiene like handwashing, and can be especially dangerous to immunocompromised patients.