Introduction to Microbiology Flashcards
microbiology
the study of microbes, organisms too small to be seen by the unaided eye
this has now been broadened to include larger parasites
medical microbiology
a focus on those microbes that cause infections in people
infectious diseases
the medical subspecialty focused on the illnesses caused by microbes
microbiome
the microbes that make up our normal flora
outnumber our own cells 10:1
important for development of immune system, obesity, heart disease
provides defense againt infection
eukaryotes vs. prokaryotes
eukaryotes have nuclei with nucelar membrane, internal membrane networks, introns, and organelles
prokaryotes have chromosome in cytoplasm, cell wall, no internal membrane networks, no introns
bacterial morphology - shapes
cocci - round
bacilli - rods
coccbacilli - inbetween
spirochetes - corkscrew shape
bacterial morphology - structural properties
individual cells
in pairs
chains of connected cells
clusters
bacterial size
E. Coli - 2 microns to 0.5 microns
staphylococcus aureus - ~1 micron
treponema pallidum - spirochete, small diameter, length of 5-15 microns
in general, bacteria 1-2 microns
bacterial cell envelope
surrounds the cytosol
protection from environmental threats
housing for factors important in many cellular functions
consists of at least two parts - cytoplasmic membrane and cell wall
cytoplasmic membrane
permeability barrier
electron transport
export of membrane and secreted proteins
biosynthesis of cell wall components
partition of the newly replicated chromosome into daughter cells during cell division
cell wall
gives shape
protects the cell against osmotic lysis
all medically important bacteria except mycoplasmas and chlamydia have cell walls
peptidoglycan
a unique component of the bacterial cell wall, also known as murein
antibiotic target
made up of acetylglucosamine (NAG) and N-acetylmuramic acid (NAM)
peptidoglycan structure
NAG and NAM
peptide of alternating L- and D-amino acids
the third amino acid of some peptides are crosslinked to the terminal amino acids of other peptides
penicillin-binding proteins facillitate synthesis
penicillin binding proteins (PBPs)
responsible for the proper cross-linking of chains of peptidoglycans and are therefore good targets for antibiotics, such as penicillins
peptidoglycan synthesis in the precense of penicillin
blocks the PBPs and prevents cross-linking that form the sheets
mechanisms of bacterial resistance to penicillins
beta-lactamase production
alteration of PBPs
prevention of access
peptidoglycan synthesis in the presence of vancomycin
prevents cross-linking through methods other than blocking PBP function
vancomycin-resistant enterococci
changed the D-alanine-D-alanine bond to a D-alanine-D-lactate bond, which prevents vancomycin binding
lysozyme
enzyme that claves specific bonds in peptidoglycan, yielding NAGA-NAMA disaccharides
found in saliva, mucous secretions, tears, neutrophils
gram-positive bacteria
bacteria with thick cell walls, which contain teichoic acids
gram-negative bacteria
bacteria with thin cell walls
contain two lipid bilayer membranes, the cytoplasmic and oute rmembranes
the region between the two membranes is the periplasm, which is filled with elaborate glucan sturctures that help regulate the osmolarity of the cell
Describe the staining process for gram positive versus negative bacteria.
application of crystal violet, which is taken up by all cells
iodine added next, then alcohol wash
gram positive bacteria with thick walls will retain the violet and iodine
gram negative bacteria will lose the violet color and can then be counter-stained with safranin
Ziehl-Neelsen or Kinyoun staining
used for bacteria that have long-chain fatty acids
also called the acid-fast staining
ex. mycobacteria
darkfield microscopy
light strikes speciment at an angle, only deflected light enters objective
used for bacteria that are so thin that they can’t be seen with light microscopy
limitations of Gram-staining
mycobacteria needs acid-fast staining
spirochetes need dark-field microscopy
mycoplasma, chlamydia have no cell wall
rickettsias and legionella don’t stain well but the reason is unknown
teichioic acids
long polymers of either glycerol phosphate or ribitol phosphate that also contain sugars and amino acids
attached to either the cytoplasmic membrane or the cell wall
adhesins
exact structure varies from bacteria speciies to species
Lipid A
a diglucosamine molecule containing substituted fatty acids
lipid A is the component of LPS that is embedded in the outer membrane
in addition, the toxic effects of LPS are due to lipid A
lipopolysaccharide (LPS)
replaces phospholipids in gram-negative bacteria
contains three parts - lipid A, core polysaccharides, and O antigen
five to seven saturated fatty acid side-chains form tight barriers that prevents many molecules such as antibiotics from reaching the cell wall
extremely toxic to humans, induces fever
core polysaccharide
a region attached to lipid A conisting of 7-9 sugar residues (including some unusual ones such as ketodeoxyoctonate (KDO) and heptose)
O antigen (or O-specific side chain)
a polysaccharide chain consisting of repeating units of 3-5 sugar residues
O antigenic chain is not present in all Gram-negative organisms
when present, it is antigenic and allows serotyping of many bacteria
long O-side chains are protective against complement-mediated lysis and cause bacteria to be serum resistant
bacteria lacking the long O-side chains cannot be targeted by antibodies but are susceptible to complement -mediated lysis and are serum sensitive
endotoxin
another name for LPS, toxicity caused by lipid A
at low concentrations it induces fever and stimulates B cells and macrophages, activates complement and the acute pohase response
at high concentrations it causes septic shock, which is characterized by hypotension, criculatory collapse, disseminated intravascular coagulation, multiple organ failure, and death
CD14 receptors
receptors on monocytes and macrophages that interact with LPS through LPS-binding protein
activates a membrane protein called toll-like-receptor 4 (TLR-4)
TLR-4
toll-like receptor-4
a membrane protein on monocytes and macrophages that triggers the production of cytokines such as iL-1beta and TNF-alpha
