Microbes and Bacterology Flashcards
What makes an infectious organism harder to target
the more cellular structures we have in common
Why are viruses not shown on the tree of common ancestors?
they require a host to replicate
In terms of size how big is a prokaryote compared to the smallest eukaryotic cells?
it’s about half the size. 5μm. where eukaryote is 10μm
What shape are cocci?
spherical-shaped
what shape are staphylococci?
bunches like grapes
what shape are streptococci?
lines like beads on a string
what shape are bacilli?
rod shaped
What shape are vibrio
comma-shaped/slightly curved
What shape are fusiform bacilli?
long, slender rod
what shape are spirilla?
curving rod, NOT a corkscrew
What shape are spirochete?
helical/corkscrew-shaped, very slender rod
A typical bacillus is 3μm long, how small is the small pox virus?
.3x.2x.1μm. polio virus is .003μm
How can we use a bacteriaphage in the lab?
to target bacteria and to transfer genes b/w them
What are the only layers in a non-enveloped virus?
nucleic acid and capsid (made of capsomere)
Give an example of a non enveloped virus and why is it more stable than an enveloped virus?
polio, b/c it’s so simple, it is easier to transfer from person to person. FYI polio can be transmitted in water
How does a non-enveloped virus attach to cells?
structures in the capsid
why are enveloped viruses easier to sterilize/disable compared to non-enveloped viruses?
the lipid bilayer from is usually derived from the host. The lipid bilayer is sensitive to desiccation (drying out), heat, alcohol, detergents. typically must transfer from host to host.
what is found on the outside of enveloped viruses?
glycoproteins and a lipid bilayer
give an example of an enveloped virus
HIV– bodily fluid transfer
what form is a helical nucleocapsid typically found?
nonenveloped
how does a virus replicate?
inside a host cell. viral surface binds to proteins on host cell and are engulfed.. cells know they are infected and signal the immune system to kill them
what is the whole strategy for survival of enveloped proteins based around?
glycoproteins being the receptors for the host cells.
the genome components of viruses can be targeted by the immune system. What is unique to viruses along the lines of nucleic acids?
Viruses have double stranded RNA- this is a good target for the innate immune system.
What are some of the roles of “normal flora” or “microbiota”?
- Digest food
- synthesize vitamins
- compete against pathogens
- immune tolerance for normal bacteria
What is used as the gold standard to identify bacteria to the species level?
16s rRNA sequencing on the SSU
TLR 5 target:
Flagellin (outside)
TLR 4 target:
Lipid A of LPS (outside)
TLR 2 + TLR 6 targets:
lipoteichoic acid (LTA) (gram positive). Mannose-conjugated proteins in fungi (outside)
TLR 1 + TLR 2 target:
Bacterial lipoproteins (outside)
TLR 3 target:
dsRNA (vesicular target)
TLR 7, TLR 8 target:
endosomal RNA (vesicular target)
TLR 9 target:
unmethylated CpG motifs in DNA (vesicular target)
NOD 1 Target:
peptidoglycan alanine bridges (my cytoplasm)
NOD 2 target
n-acetyl-muramic acid (NAM) (my cytoplasm)
mechanism of lysozyme on peptidoglycan
cleaves the glycan backbone of the peptidoglycan. bacteria will succumb to the large osmotic pressure and lyse.
how many layers of peptidoglycan does gram-positve have?
lots! up to 30 layers
destruction of peptidoglycan would be more effective on which bacteria?
gram positive. peptidoglycan is the outermost layer
describe gram negative cell wall from the inside out
- plasma membrane (phospholipid bilayer)
- cell wall <5 layers of peptidoglycan
- Outer membrane, phospholipids on one side and LPS on the other
- Porin proteins make holes in the OM– very small not everything gets in.
what is contained in the periplasmic space?
gram- negative: transport components for iron, proteins, sugars, and other metabolites. enzymes that include proteases, phosphatases, lipases
what are the three components of the endotoxin LPS?
Lipid A, core polysaccharide (rough core), and O-antigen.
*the core region is the same a species of bacteria.
what do porins let in?
diffusion of hydrophilic molecules less than 700 da through the membrane
why are polymyxins primarily used externally?
they can cause serious nephrotoxicity.
Polymyxins B and Colistin
insert into bacterial membranes like detergents, by interacting with LPS and phospholipids in the OM, producing increased permeability and death. gram-negative.
why is vancomycin not useful against gram-negative bacteria?
the holes in the OM are too little for the drug to get into to access the peptidoglycan and block the two D-ala from linking to form the NAG-NAM chain. give with an IV
why would a human cell stain with safranin?
gram stain relies on the ability to bleach the purple color out. we don’t have peptidoglycan
what is the enzyme that links the two NAMs forming a bridge across layers?
transpeptidase
how do beta-lactam antibiotics work?
the ring is so similar to the D-alanine-alanine motif that is cross-linked in the peptidoglycan cell wall. the enzyme that crosslinks the alanines can bind to beta lactam ring instead, disabling it.
what is the difference b/w 1st & 2nd generation beta-lactams?
1st: destroyed by beta-lactamases
2nd: resistant to beta-lactamases
what is the benefit of mycolic acid?
on mycobacterium spp. b/c of its waxiness it protects bacteria from drying out, phagocytosis, and to some extent antiseptics
what drugs are acid-fast bacterial susceptible to?
isoniazid and pyrazinamide- they inhibit mycolic acid synthesis
what is the stain used in acid-fast staining?
carbol fuchsin and methylene blue
why could you have vaccine for a bacterial capsule type and still become infected from it?
bacteria can make more than one capsule type.
where is capsule?
on both gram negative and gram positive. deposited on the otherwise outermost layer. produced by individual bacteria
advantages of capsule:
- avoid phagocytosis
- prevent drying out- sugar layer pull h2o from environment
- inhibit effective adaptive immune response
- carbohydrates are poorly antigenic
- capsule type switching (serotype)
During which phase of the growth curve are sporulation genes expressed at the highest levels?
Stationary phase
Metronidazole can be used against…
obligate anaerobes (regardless of gram-stain status) or even if they’re not bacteria.
When is metronidazole contraindicated?
when taking with alcohol –> flushing, nausea, high pulse
How does metronidazole work?
reduced by ferredoxin (an iron storage molecule) in cells (bacteria and eukaryotes). RNS that anaerobes can’t deal with.
bacteria that can Sort of break down RBCs on blood agar
alpha hemolytic– green color– also why stool is sometimes this color
bacteria that lack hemolysis on blood agar
gamma hemolytic- maybe a very light brown color
bacteria that completely break down RBCs on blood agar
beta hemolytic- would show underlying media color
What do pin prick colonies around beta hemolysis on a blood agar indicate?
these are colonies that need components of RBCs but are unable to break them down on their own
What is chocolate agar
agar with lysed blood cells, used to grow bacteria that need blood cell component but can’t break down RBCs
What do the antibiotic sulfonamides inhibit?
folate synthesis
How does the antibiotic trimethoprim work?
stops reduction of dihydrofolate to tetrahydrofolate
