Cloned from: Microbiology



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Define \"microbe\"
microscopic living thing
Define \"pathogen\"
a microbe that can cause disease
What is virulence?
a measure of how pathogenic an organism is; how capable of causing disease
What is a virulence factor?
a molecule that gives a microbe its virulence (can be lipid, carbohydrate, protein)
What is an avirulent organism?
one that does not cause disease
What types of infections do low virulence microbes generally cause?
opportunistic infections in immuno-compromised hosts
What does \"normal flora\" mean?
bacteria on skin and mucosal surfaces
What is a commensal relationship?
when bacteria live on the host but don\'t cause harm (normal flora), in fact normal flora have a beneficial relationship with the host
What is a nosocomial infection?
one acquired in the hospital
What defines \"infection\"?
A step beyond colonization; an organism crosses anatomical barriers, crosses cell surface, or host develops an immune response to the organism
What defines \"colonization\"?
an organism establishes and multiplies on the body surface
What is the difference between infection and disease?
infection can be asymptomatic
What are the common steps of microbial pathogenesis?
colonization or attachment, invasion (common but not obligatory), evasion of host defenses, host damage (several mechanisms exist)
Name some areas of the body that have little normal flora?
stomach and small intestine
Name some areas of the body that have no normal flora?
lower respiratory tract, sterile fluids (CSF, blood, urine, bile) pleural and peritoneal spaces
What are a few examples of when normal flora cause infections?
perforate into abdomen and cause abdominal infection; obligated anaerobes break off of gingival crevae and are aspirated, cause lung abscesses
What are Koch\'s postulates for micobial role in disease?
1. Pathogenic organism should always be present, 2. it should be specific for the disease in questions, 3. it should be able to induce disease (hard to show)
Why is the microbial surface important?
it is critical for attachment, it is the first thing seen by the host, it evokes innate immunity, many surface molecules are virulence factors, and it is a target for adaptive immunity
What is a serotype?
a strain of microbe recognized by a particular serum
What is a nucleoid?
single circular double-stranded DNA chromosome of bacteria
Why is a nucleoid not called a nucleus?
it is not membrane bound
What is important about prokaryotic ribosomes as compared to eukaryotic ribosomes?
prokaryotes have 70s; eukaryotes have 80s
What chemical motif is found in the membranes of eukaryotes but not prokaryotes?
sterols
What is a cell envelope?
all the layers that encircle and retain the cytoplasmic contents-- includes the peptidoglycan and cytoplasmic membrane
What is the murein layer?
a rigid cell wall composed of peptidoglycan
What is the structure of the peptidoglycan backbone?
N-acetylglucosamine and N-acetylmuramic acid (≤(1!í4) linkage); tetrapeptide side chains composed of alternating D and L amino acids are attached at the N-acetylmuramic acids and parallel chains of PDG are crosslinked at these side chains by transpeptidase
How does lysozyme affect the peptidoglycan backbone?
it breaks ≤(1!í4) linkages
How do ≤-lactam antibiotics affect the peptidoglycan backbone?
they disrupt transpeptidase, which links parallel PDG chains
What are the functions of the peptidoglycan wall?
shape+rigidity, prevents lysis, acts as polar barrier to block entry of hydrophobic compounds
What are the functions of the prokaryotic cytoplasmic membrane?
osmotic barrier, active transport of nutrients via permeases, DNA attachment site for nucleoid and plasmids (allows for segregation during division), mediates iron uptake and protein export, site of electron transport chain, site of PDG synthesis
What is a mesosome?
an invagination of cytoplasmic membrane; thought to promote cell division and chromosomal separation. More common in gram+ bacteria
Who has more mesosomes, gram- or gram+?
gram+
What is important to know about bacterial protein synthesis?
transcription is coupled to translation, and polygenic mRNAs are produced
What is the \"capsule\"?
layer of acidic polysaccharides that surrounds some organisms; usually composed of 2-3 sugars characteristic of organism; main function is defense against phagocytosis
What is the main function of a capsule in bacteria?
protect against phagocytosis
What is the Quellung reaction?
used to type bacteria (esp. S. pneumoniae) by its capsule; mix microbe with Ab against a known capsule, if capsule swells the antibody is reactive and the microbe is typed
What are flagella made of?
single proteinaceous helical filament of the globular protein flagellin
What are the two main types of flagella described in this course?
polar (e.g. Pseudomonas) and peritrichous (e.g. Enterobacteriaceae)
What is glycocalyx?
an adhesive polymer film that contains polysaccharides; helps inhibit phagocytosis of the organism, can help organism stick to surfaces
What are some common storage granules?
poly-≤-hydroxybutyrate (storage form for lipids), glycogen or starch (storage form for sugar), polymetaphosphate AKA volutin (a storage form for phosphate)
How can volutin be visualized?
metachromatic stai-- turns red in the presence of methylene blue
What is a spore?
a cryptobiotic form of an organism, resistant to heat, desiccation and freezing; genera include Bacillus and Clostridium
What does the cross-section of a spore look like?
coat-layers of keratin-like proteins with many disulfide bonds; cortex-2 layers of PDG (inner for stability, outer for autolysis); germ cell membrane; core (contains high concentrations of dipicolinic acid and calcium as well as materials for resuming growth).
Lecture 2
Bacterial Structure and Classification
What is lipoteichoic acid?
polymers of ribitol or glycerol. Also a virulence factor for Gram+ bacteria and major antigen of both Strep and Staph
What is beta hemolysis?
complete RBC hemolysis-- plate becomes clear
What is alpha hemolysis?
does not lyse RBCs-- plate has green zones that surround the colonies
How can one differentiate between strep A, B and C and Pneumococci?
using an agglutination test with different specific antisera
Which has catalase, Strep or Staph?
staph
What is the only coagulase positive Staph species?
Staph aureus
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