Micro: Bacterial Structure & Classification Flashcards
What are the two major shapes of bacteria?
rods (bacilli) and spheres (cocci)
What is streptococci?
chains of cocci bacteria
What are comma-shaped bacteria called?
vibrio
Describe the bacterial genome.
single circular ring of DNA, no introns, no histones
What composes bacterial cell walls?
peptidoglycan
Bacterial cell membranes are notable for lacking what?
sterols
Components of bacteria that differ enough from animal cells to be used as antibiotic targets include:
cell wall, ribosome, RNA polymerase, topoisomerase
What is the major gross difference between gram positive and gram negative bacteria?
gram negative has an additional outer membrane
What is the major role of pili in pathogenesis?
to attach bacteria to host cell surfaces
What is the composition and role of the bacteria’s capsule?
composed of either polysaccharides or polypeptides; serves to protect against phagocytosis; visualized by its ability to exclude dye from its immediate surroundings; all organisms causing meningitis characteristically have a capsule
What is a spore or endospore?
dehydrated, dormant forms that allow potential pathogens (certain Gram positive rods) to survive in harsh conditions for a long time; typically formed in response to stress or nutrient limitation
Up to 50% of the Gram positive cell wall is composed of ____ acid or ____ acid.
teichoic acid; lipoteichoic acid
Describe the differences between peptidoglycan walls of Gram positive and negative cells in terms of layers thick, amount of cross-linking, and location.
Gram+: >40 layers thick, heavily cross-linked, lies between cytoplasmic membrane and capsule
Gram-: 2 layers thick, lightly cross-linked, lies between the cytoplasmic membrane and the outer membrane in region called periplasmic space
What is the role of the outer membrane in Gram negative bacteria?
additional permeability layer, is negatively charged thereby helping avoid phagocytosis, hinder antibiotic uptake, and avoid action of complement
What structure allows the import of nutrients into the Gram-negative cell?
porins in the outer membrane
What is lipopolysaccharide (LPS)?
component unique to Gram-negative bacteria outer membrane that contain 3 components: lipid A (aka endotoxin), a core polysaccharide, and O antigen polysaccharide (major surface antigen of Gram-neg bacteria)
What is the role of Lipid A in sepsis?
lipid A is recognized by the innate immune system to elicit a cytokine storm which leads to septic shock
Describe the Type I secretion system for Gram-negative bacteria.
ATP binding cassette transporters connected to a channel-tunnel via adaptor proteins secrete proteins; through this system antimicrobial drugs can be expelled, promoting resistance
Describe the Type II secretion system for Gram-negative bacteria.
two-step secretion system for delivering proteins first to the periplasm and then EC space
Describe the Type III secretion system for Gram-negative bacteria.
hydrophobic segments extend through cytoplasmic and outer membranes, as well as the membrane of the targeted animal cell, allowing direct injection of toxins and virulence factors into the target cell
Describe the staining difference between Gram negative and positive bacteria.
extensive cell wall (thick heavily cross-linked peptidoglycan layers) in Gram positive cells retain the stain
What is peptidoglycan composed of?
backbone of repeating disaccharides, NAM and NAG; the NAM residue of each disaccharide also has a pentapeptide attached
What is transglycosylase?
an enzyme that links disaccharides to form long chains of peptidoglycan
What are the targets of penicillin?
transpeptidases, also known as penicillin-binding proteins
What do the enzymes transpeptidase and carboxypeptidase catalyze?
cross-linking of pentapeptides between peptidoglycan chains
Cross-linking is a simple bond in Gram ____ bacteria peptidoglycan.
negative
A pentaglycine interpeptide cross-links the polypeptides in Gram _____ bacteria peptidoglycan.
positive
Cell wall assembly begins in what part of the cell?
cytoplasm; lipid carrier
Describe the location and function of lipid carriers.
localized in the cytoplasmic membrane; used to transport individual disaccharide pentapeptide subunits across the membrane to the external face of the cytoplasmic membrane for incorporation into the growing cell wall
What is the major regulatory step of the lipid carrier that can serve as the target of antimicrobials such as bacitracin?
dephosphorylation of the carrier, to allow for recycling and reloading with new cargo
What is lysozyme?
a naturally occurring glycosidase that hydrolyzes the NAM-NAG bond, thereby defending against microbes; present in tears, saliva, lysosomes of phagocytes, and is particularly effective against Gram-positive bacteria
What is the action of vancomycin?
it directly binds the D-alanine D-alanine pair while the cell wall is subunit is still attached to the carrier, thereby preventing cell wall growth (aka peptidoglycan chain elongation)
What is the action of beta-lactams?
because the beta-lactam ring is structurally similar to D-alanine D-alanine terminal pair of pentapeptide side chains, they get bound by the transpeptidases and cross-linking is prevented; requires cell growth to have an effect because it must interfere with cross-linking of new subunits
What two genera of bacteria fail to stain using the Gram method?
mycoplasma and chlamydia
True or false: aerobic bacteria use fermentation for growth, and anaerobic bacteria use respiration.
False (it’s actually the other way around)
What process(es) do facultative anaerobes use for growth?
respiration in the presence of oxygen; fermentation in the absence of oxygen
Microaerophillic bacteria can grow in the absence of oxygen, but grow optimally in what concentrations of oxygen?
low, i.e. 5-10%
Serotyping classifies bacteria of one genus based on what?
the expression versus the lack of a specific antigen
The E. coli strain O157:H7 causes severe diarrhea. The O and H refer to antigens located where, respectively?
O antigen found on the lipopolysaccharide (LPS), and H antigen found on the flagellum
What is the utility of serotyping a bacterial infection?
to identify the specific strain; for food-borne illnesses to identify the origin or source of the infection
What portion of LPS leads to sepsis?
Lipid A, aka endotoxin
“A polysaccharide polymer joined by peptide chains” describes what component of bacterial cell walls?
peptidoglycan
Which bacterial secretion system is often termed “the molecular syringe”?
Type III
