HHD - Microbiology Flashcards - All Micro Videos
What is the bacterial cell wall material?
Peptidoglycan
What is the source and effect of cholera toxin?
Cholera toxin disrupts chloride channels such that chloride rushes out of the cell, followed by Na+ and water, which causes severe diarrhea
What is the organization of the Baltimore classification scheme (and the no. of classes)?
Viruses are organized by their genome (e.g. ssDNA, dsDNA, ssRNA (+), ssRNA (-), etc.), which tells us how they produce mRNA and protein. There are 7 classes.
Define immune escape.
Antigenic variation, or mutation of the antigens that would allow the immune system to recognize the virus, allows the virus to escape detection
Where does VZV hide from the immune system?
In the dorsal root ganglion, before traveling down the sensory nerves to the skin to cause a rash, known as shingles
Define virulence.
Virulence is the relative capacity to cause damage to the host
What factor of the virus does attenuation decrease?
Virulence
Why can most fungi not cause disease in humans?
Their optimal growth temperature is much lower than 37°C
Name three components of the fungal cell wall (innermost to outermost).
Chitin, β-glucans, galactomannans
What is the major fungal membrane molecule that differentiates fungi from animals?
Ergosterol
What are the three main types of pathogenic fungi?
Yeasts, molds, and thermally dimorphic fungi
What is the difference between environmental and colonizing fungi?
Their “natural” habitat outside of humans; Coccidioides is a soil fungus and Candida is a mucosal colonizer
What are the two main categories of parasites?
(1) Protozoa, eukaryotic, single-celled organisms and (2) multicellular eukaryotes such as helminths and ectoparasites
Name four groups disproportionately affected by parasitic infections
Agriculture workers, women during pregnancy, children, and poor people living in wealthy countries
What are three different kinds of hosts in a parasitic life cycle?
Definitive host: hosts the parasite during reproduction stage; intermediate host: hosts the parasite during larval development; dead-end host: parasite enters the wrong host and dies
What are four bactericidal compounds secreted by epithelial cells?
Acid in stomach, bile detergents in intestine (microbes could change LPS to withstand detergents), antimicrobial peptides and enzymes (microbes could change the cell wall to resist lysozymes), IgA (microbes could produce IgA proteases)
What is the biggest clinical concern about bacterial biofilms?
Biofilms (interbacterial mucoid adhesions) can act as a barriers, allowing bacteria to avoid the immune system! They allow bacteria to infect catheters. Catheter-related bloodstream infections often require removal of the device
What are the four common mechanisms of antibiotic resistance?
(1) Decrease entry by mutating the porin proteins in the cell membrane (gram-negative bacteria specifically), (2) degrade the antibiotic wtih an enzyme (e.g. B-lactamases), (3) remove the antibiotic by producing efflux pumps, (4) alter the target by mutating the ribosome
What percentage of the population is infected by influenza yearly?
15-20% of the world’s population
Name influenza’s viral family and its characteristics.
Orthomyxovirus; spherical, enveloped, ssRNA, (-) sense, segmented genome that replicates in the nucleus
What are the two key influenza surface molecules and their function? Are antibodies against each neutralizing?
Hemagglutinin and neuraminidase; HA binds sialic acid receptors for entry and can clump RBCs; NA degrades mucin (entry) and cleaves sialic acid (exit); antibodies against HA are neutralizing, while antibodies against NA are non-neutralizing
What are the influenza subgroups and who can they infect?
A, B, and C. Only A can infect both humans and animals and is responsible for pandemics. B and C infect humans only.
What is the difference between antigenic shift and drift?
Drift is small antigenic changes; shift is caused by a major mutation, usually from a zoonotic recombination and causes a pandemic
How is influenza transmitted?
Large respiratory droplet transmission over short distances
What is the incubation period for influenza?
1-4 days from exposure
What is the illness period of influenza and when are patients infectious?
Adults shed virus from 1 day before symptoms to 5-10 days after symptom onset. By 3 to 5 days their infectious ability is greatly decreased; children may be infectious for 10 days or more; immunocompromised people may shed virus for several weeks
Name symptoms of influenza infection.
Abrupt onset of fever, myalgias (sore muscles), headache, pharyngitis, rhinorrhea, cough, and fatigue
What is the difference between primary and secondary influenza pneumonia?
Primary pneumonia is caused by direct infection of lungs by influenza virus with the resulting immune system-mediated tissue damage; secondary is caused by a bacterial pathogen that enters right afterwards (usually after a period of improvement); S. pneumonia, S. aureus, H. influenza, nosocomial gram (-) rods
What is Reye’s syndrome?
Unknown cause, though aspirin is implicated; rare, life-threatening syndrome in children following viral infection with influenza or varicella virus; fever, rash, encephalopathy, liver failure
What are four diagnostic tests for the flu and which is the current gold standard?
Viral culture (10 days); immunofluorescence (1-4 hours); PCR (1-6 hours, gold standard); rapid antigen detection (<30 min)
What are the the two common groups of antivirals for flu treatment? Give examples of each.
Adamantanes (Ex: amantadine, rimantadine) and NA inhibitors (Ex: oseltamivir, zanamavir)
Name the mechanism, adverse effects, and usage of adamantanes.
They block the M2 ion channel to prevent uncoating; have CNS effect, anticholinergic effects, and are teratogenic; used against Influenza A; most viruses are resistant so this is NOT used in clinical practice.
Name the mechanism, adverse effects, and usage of NA inhibitors.
(Ex: oseltamivir, zanamivir) Inhibits NA cleavage of sialic acid; well-tolerated; used on Influenza A and B within 48 hours of onset, but effectiveness is debated
Who is at the highest risk for flu infection?
Elderly, infants, chronic disease patients, obese patients, pregnant women
What are the two kinds of flu vaccines?
Inactivated IM vaccine; LAIV intranasal (best for children 2-8)
Who should be vaccinated against influenza?
All those over 6 months of age
What is the morphological difference between Strep and Staph?
Streptococci form chains; staphylococci form “grape clusters”
What is the catalase test difference between Strep and Staph?
Streptococci are catalase negative (they will NOT bubble); staphylococcus are catalase positive
What is the species of Group A Strep?
S. pyogenes
What are the two β-hemolytic Strep species and how do you distinguish them?
β-hemolytics show complete hemolysis; the two species are S. pyogenes (Group A) and S. agalactiae (Group B); GAS is bacitracin sensitive, while S. agalactiae is not.
What are the α-hemolytic Strep species and how do you distinguish them?
α-hemolytics show partial hemolysis; S. pneumoniae and Viridans, and S. pneumoniae is optochin-sensitive and has pearly colonies due to its capsule and Quellung (+); neither have Lancefield antigens.
What are the γ-hemolytic Strep species and how do you distinguish them?
γ-hemolytic means no hemolysis; Enterococcus and non-Enterococcus species (Lancfield group D); both are bile esculin (+) but only Enterococcus grows in salt media.
What does hyalorunate do in S. pyogenes?
It forms a protective capsule to help protect it from the immune system
What are the functions of the M-protein?
(1) Binds complement, (2) anti-opsonization; autoantibodies can form to M-proteins
What are the two invasion factors of Strep?
Hyaluronidase breaks down ECM and Streptokinase activates plasmin, dissolving the blood clots to release bacteria
What are the two major toxins from Strep?
(1) Streptolysin O: lyse RBCs and WBCs, cause beta-hemolysis.
(2) Strep pyogenic exotoxins: agents like erythrogenic toxin cause scarlet fever; superantigens overactivate T cells, leading to Toxic Shock Syndrome.
What is a suppurative infection?
A pus-producing infection
What are some common suppurative infections caused by GAS?
Erysipelas (outermost layer, dermis); cellulitis (middle layer, dermis/sub-cu); necrotizing fasciitis; impetigo (crusty red sores around the nose)
What are some of the classic signs of scarlet fever?
Desquamating sandpaper rash, circumoral pallor, strawberry tongue, fever
What are some of the signs and causes of streptococcal toxic shock syndrome?
Hypotension, end organ damage; thought to be caused by superantigen activation
What are the organ systems usually affected by acute rheumatic fever?
Skin, joints, heart, brain