Microbiology Flashcards
micro objectives
Infection
Organism present and multiplying in host tissues usually leading to immune response. May or may not cause symptoms.
Colonization
Presence of bacteria on a host without producing disease. Comes and goes, asymptomatic.
Infectivity
Ability of a microbe to cause infection in a susceptible host. May or may not cause symptoms.
Pathogenicity
Ability of a microbe to cause disease. Disease is defined by signs and symptoms.
Virulence
Degree of pathogenicity within a specified group which depends on both bacterial and host factors. Some diseases more virulent in an immunocompromised host, or neonates, pregnant women, etc.
Example of High infectivity, low virulence?
Rhinovirus
Example of high infectivity, high virulence?
Ebola
Example of low infectivity, low virulence?
Certain HPV (non cancer causing)
Example of low infectivity, high virulence?
Tuberculosis
Characteristics of prokaryotes?
- E.g. Algae/fungi/plants/animals
- Cell wall: Absent or chitin/cellulose
- Nuclear structure: present
- Cytoplasm: Mitochondria/chloroplasts
- Motility: Flagella complex/others
- Energy: Mitochondria
- Sexual reproduction: present
- Recombination: Diploid formed by haploids, meiosis with recombination
Characteristics of prokaryotes?
- Bacteria/algae
- Cell wall: peptidoglycan/lipids
- Nuclear structure: absent
- Cytoplasm: No organelles
- Motility: Flagella
- Energy: Membrane associated
- Sexual reproduction: Absent
Recombination: Chromosomal/plasmid transformation, transduction, conjugation
Gram positive characteristics?
- Only cone cell membrane
- Thick layer of peptidoglycan making 90% of cell wall.
- Stains dark purple
Gram negative characteristics?
- Outer and inner membrane
- Lipopolysaccharides (LPS) anchored in outer membrane
- Stains pink
Gram stain?
Determine presence of outer membrane.
Positive purple. Negative pink.
Acid-fast stain?
Acid-fast organisms characterized by wax-like, nearly impermeable cell walls. Contain mycolic acids and large amounts of fatty acids, waxes, and complex lipids
Coagulase test?
Different staph. aureus (positive) from coagulase negative Staph (CONS). Coagulase is an enzyme produced by S. aureus that converts soluble fibrinogen in plasma to insoluble fibrin.
Indole test?
Determine ability of organism to convert tryptophan to indole.
Hemolysis on blood agar?
Determine hemolytic capabilities of an organism. Some bacteria produce exoenzymes that lyse RBCs and degrade hemoglobin (hemolysins)
Kirby-Bauer?
Disk diffusion antibiotic sensitivity. Antibiotic containing disks to test for susceptibility (how far can bacteria travel?)
Adherence?
Bacteria produce adhesins to stick to cell surfaces
Surface modifications?
Bacteria can modify their surfaces to avoid the immune system or resist antibiotics
Invasion?
Bacteria may invade cells to avoid extracellular immune factors (antibodies, complement, etc.) They must be adapted to intracellular antibacterial strategies (reactive oxygen species, antimicrobial peptides, etc.)
Modify-the-host?
Bacteria modify the host to favor colonization and transmission (e.g. abscess formation to create a “home” where they can grow)
What are endotoxins?
Substances that come from within the bacteria that promotes inflammatory cascade.
E.g. lipopolysaccharide
What are exotoxins?
Substances, usually proteins, expressed externally to the bacteria that causes immune response.
E.g. tetanus, botulism, diptheria, anthrax. Cholera example.
What are normal flora?
Bacteria are common colonizers in “normal” hosts. Can protect from pathogens and are part of innate immunity. If normal flora is disrupted pathogens can establish infection.
What are sterile body sites?
Urine, blood, CSF
What are the major means of bacterial transmission?
a. Contact: direct contact via sexual, fomites, blood, fluid.
b. Food or water: Contamination
c. Airborne: Droplets
d. Vector-borne: Dependent on biology of vector (mosquito, tick, snail) and bacteria
e. Perinatal: contact in utero or during delivery
f. Nosocomial: from health care facilities (high level of resistance)
How can bacteria transfer genes?
- Transformation: uptake of DNA from environment.
- Transduction: Bacteriophage (viruses) that affect bacteria can transfer genes
- Conjugation: Sex pili connect two bacteria transferring DNA between them ;)
What is obligate intracellular parasite?
Contains DNA or RNA, requires living cells for replication (uses host energy sources, ribosomes, enzymes for replication), small infectious agents
What is virion?
Infectious unit, composed of nucleic acid core covered by capsid, the protein coat
What are capsomeres?
Capsomeres are small subunits that create the capsid of a virus
8 steps of viral replication
- Attachment (tropism)
- Penetration by translocation, endocytosis, or fusion
- Disassembly
- Transcription
- Translation
- Replication
- Assembly
- Release to infect other cells
5 ways Viruses get to mRNA?
I. +/- DNA strand to mRNA II. +DNA to +/-DNA to mRNA III. +/- RNA to mRNA IV. +RNA to -RNA to mRNA V. -RNA to mRNA
5 different types of viral infections?
- Asymptomatic “Subclinical” (Pt carrier for disease but no symptoms, slow infection, years to emerge. Think HSV, VZV)
- Acute infection (short duration. Think influenza, norovirus)
- Persistent “Subacute” (Virus infected cells continually present in body and not cleared by innate immune system. Generally fatal. Think subacute sclerosing panencephalitis SSPE, brain disorder caused by measles)
- Chronic (Virus present at all times and disease is present and absent for extended periods. Think Hep B and C)
- Latent (pt recovers from initial infection, then viral production stops and reactivates later. Think measles, HIV)
Difference between direct and indirect viral damage?
Direct= diversion of cell energy, competition of viral mRNA for cellular ribosomes, competition of viral promoters for RNA polymerase.
2. Indirect= Immune response to viral infection leads to cell death, integration of viral genome alters cellular phenotype, induction of mutations in host genome
7 stages of virus-host interaction:
- Entry into host
- Primary replication
- Spread
- Cell/tissue tropism
- Secondary replication
- Cell injury and persistence
- Host immune response
Types of interferon:
- Type 1: alpha (produced by viral infected leukocytes) and beta (produced by viral infected fibroblasts or epithelial cells)
- Type 2: gamma (produced infected T and NK cells)
Describe lab procedures to diagnose viral infections:
- Histology (poor sensitivity, specificity variable, requires tissue/invasive, diagnose more advanced disease)
- Culture (Cells observed for cytopathic effect, not all clinically relevant viruses can be isolated, sensitivity affected by transport and previous treatment)
Mechanisms of CD4 depletion in HIV infection:
- Disruption of cell membrane by budding
- Interference/competition with cellular function
- Apoptosis
- Immune attack on infected CD4 cells
- HIV inhibited hematopoiesis
Difference btwn antigenic drift and shift
- Drift: point mutations in surface proteins that alter antigen structure
- Shift: genetic reassortment between different strains, causes pandemics
Identify members of the herpes family of viruses
- HSV-1: herpes labialis, keratoconjunctivitis (site of latency: neurons)
- HSV-2: genital herpes (site of latency: neurons)
