Principles Of Infectious Disease I (Foundations Exam 1)

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virus

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- microorganism, smaller than bacterium
- cannot grow or reproduce apart from a living cell
- invades living cells and uses their chemical machinery to keep itself alive and to replicate itself

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prokaryotic cells

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(bacteria)
- do not maintain a nucleus or cell organelles
- cytoplasm contains genetic material in the form of a single chromosome
- full metabolic machinery to synthesize proteins and secrete substances
- chromosome is circular molecule organized into loops
- 70S ribosomes (30S and 50S)
- asexual binary fission

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eukaryotic cells

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(fungi and parasites)
- contain a nucleaus and cytoplasmic organelles
- maintain full metabolic machinery
- chromosomes are linear DNA condensed with histones
- 80S ribosome (40S and 60S)
- free living
- sexual and asexual reproduction --> mitosis and meiosis

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virus features

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- smallest replicating life form
- set of genes surrounded by protein coat (capsid)

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classification of viruses

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- nucleic acid type (DNA or RNA)
- shape of capsid (icosahedral or helical)
- presence/absence of envelope
--> no envelope = naked virus
--> lipid envelope = sometimes from host cell
- mode of replication
- preferred host type
- disease pathology they cause

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obligate intracellular organisms

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viruses
- cannot grow outside of cell
- replication requires host cell metabolism

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replication sequence

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- commandeer host's machinery
- adsorption
- entry
- uncoating
- transcription, translation
- genome assembly
- release

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infections by viruses

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- largest % of human infections
- acute or transient
- persistent
- latent with re-activation
- some can transform cells to cancer
- one species --> different symptoms (CMV)
- several species --> similar symptoms (resp. viruses)

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diagnosis of viruses

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- microscopy
--> electron microscope to visualize
--> light microscope can visualize viral inclusions
- antigen detection
- culture in cell culture
- polymerase chain (PCR) or reverse-transcription PCR

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bacteria features

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- smallest free-living life form 2-8microns
- single cell bounded by a rigid wall
--> peptidoglycan (sugar, aa)
--> cell wall composition affects stain
- single circular chromosome
- no nucleus or organelles
- full metabolic machinery

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facultative intracellular organism

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bacteria
- can replicate extracellular or intracellular
- also gain nutrition from host

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gram-positive bacteria

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(cell wall)
- thick, rigid peptidoglycan outer cell wall
- stains purple

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gram-negative bacteria

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(outer membrane)
-inner wall consisting of a thin peptidoglycan layer
- outer lipopolysaccharide membrane containing lipid A
- stains pink

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shape

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- spherical = cocci
- rod-shaped = bacilli (rods)

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respiration of bacteria

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- aerobic: most pathogens identified in lab
- anaerobic: 99.9% of bacteria

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appendages of bacteria

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- pili allow attachment to host cell
- flagella permit movement

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reproduction of bacteria

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binary fission

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infections by bacteria

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- common cause of disease, but can also be normal flora

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diagnosis of bacterial infections

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- stains
- antigen testing
- antibody testing (serology)
- culture (agar or broth)
- molecular testing

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fungi features

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- size: 2 microns to visible
- single cell bounded by a rigid cell wall
- cell extended by budding
- cell wall
- cytoplasmic membrane

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yeast cell

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- asexual budding to create simple conidia

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mold hyphae

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(mycelium)
- slender and filamentous
- septate (cell walls separate individual cells) or aseptate (imp. for clinical considerations)
- spores from asexual reproduction or sexual

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infections by fungi

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- superficial/taenia (skin hair, nails), dermatophytes
- subcutaneous (abscesses and granulomas)
- deep/systemic infections
- dimorphic
- opportunistic fungi attach immunocompromised patients
--> characterized by tissue necrosis, hemorrhage, and vascular occlusion

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diagnosis of fungal infections

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same methods as bacteria but different culture media

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protozoa features

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- eukaryotic cell, 2micron to visible
- single celled
- eggs and trophozoites
- specialized organelles (pseudopods and cilia)
- can replicate intracellularly in hosts or extracellularly in urogenital system, intestine, or blood

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reproduction of protozoa

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binary fission

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infections by protozoa

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- common in developing countries
- blood-borne protozoa: replicate within insect vectors before transmission to new human host

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diagnosis of protozoan infection

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- direct smear
- concentrated smear
- antigen
- antibody
- molecular

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helminths-worms

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3 classes: roundworms, flatworms, flukes
- highly differentiated
- worms 1mm - >10m with suckers, hooks, teeth, digestive tracts, circulatory

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reproduction of helminths-worms

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- excrete eggs or birth live young
- eggs 8-100 microns
- alternate between sexual reproduction in host and asexual reproduction in intermediary host or vector

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pathology of helminths-worms

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- usually due to inflammatory responses to the eggs or larvae rather than to the adult forms

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roundworms

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- collagenous tegument and non-segmented structure

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flatworms

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gutless worms whose head sprouts a ribbon of flat segments covered by an absorptive tegument

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flukes

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- primitive, leaf-like worms with a syncytial integument

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ectoparasites

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- arthropods (insects, arachnids)
- direct tissue damage
- may cause disease indirectly by serving as vectors for transmission
- some induce itching and excoriations at site of bite

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mycoplasma/ureaplasma

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- smallest bacteria but lack any cell wall (M pneumonia)

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chlamydia

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- bacteria-like, intracellular and extracellular forms
- sexually transmitted disease
- replicate in membrane bound intracellular vacuole in epithelial cells

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rickettsia sp.

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- arthropod vectors
- depends on host ATP
- causes rocky moutain spotted fever
- replicate in cytoplasm of infected cell
- cannot self-replicate

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prions

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- found in high levels in neurons
- accumulation of abnormal PrP leads to neuronal damage and distinctive foamy "spongiform" changes in brain and cause transmissible encephalopathies

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bacteriophages, plasmids, and transposons

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- mobile genetic elements that infect bacteria
- indirectly promulgate human disease encoding bacterial virulence factors
-exchange of these elements between bacteria often gives the recipient a survival advantage

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antigen detection methods

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- fluorescent antibody tags
- enzymatic tag: enzyme linked immunosorbent assay (ELISA)

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structure of gram-negative cell wall

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- relatively thin
- little peptidoglycan
- no teichoic acids
- outer membrane that is attached to peptidoglycan sheet by unique group of lipoprotein molecules
- outer membrane outside of peptidoglycan layer

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structure of gram-positive cell walls

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- relatively thick
- many layers of peptidoglycan interspersed with teichoic acids
- acids run perpendicular to peptidoglycan sheets