micro test 2

mutations

heritable change in DNA sequence that can lead to a change in phenotype

wild-type allele

refers to reference strain or gene isolated from nature

mutant

cell or virus derived from wild type that carries a nucleotide sequence change

isolation of mutants: selection

under certain conditions, the mutant generation can thrive while the wild type generation dies

Isolation of mutants: Screening

all or most cells can grow. Isolation through phenotypic change

replica plating

screens for nutritionally defective mutants. Colony is transferred from an original plate. If it does not grow, it is lacking nutrients

auxotroph

requires added nutrients for growth

prototroph

has all required nutrients to grow

transitions

change from purine to purine or pyrimidine to pyrimidine

transversion

purine to pyrimidine or pyrimidine to purines

reversion

point mutations that are typically reversible to wild type genotype

revertant

individual organism or strain in which original phenotype is restored

same-site revertant

a second mutation is at the same site as original mutation that can restore original function or original gene sequence

true revertant

restores original genotypic sequence

second site revertant

mutation at a different site in the DNA that restore function or replaces the non functional one

mutation rate

errors that escape repair. depends on frequency of DNA changes and efficiency of proofreading and DNA repair processes. 10^-6 to 10^-7 per cell

virus mutation rate

100-1000x greater error rate because their polymerases often have less proofreading capacity

mutagens

chemical, physical, or biological agents that increase mutation rate

nucleotide base analogs

resemble nucleotides but faulty base-pairing leads to higher frequency of replication errors

chemical modifications

chemically modify bases and can alter pairing behavior or destabilize DNA

frameshift mutations

intercalating agents push 2 base pairs apart, triggering insertion or deletion

nonionizing radiation

bases absorb UV, pyrimidine dimers on the same strand cross link.

ionizing radiation

x-ray, cosmic rays, gamma rays. ionize water, forming free radicals that damage DNA.

translesion synthesis

DNA repair without template and random addition of dNTPs. Error prone, but needed for survival

SOS DNA response

repairs DNA using LexA and RecA. RecA causes LexA to self-cleave and allows for repair to occur.

homologous recombination

“crossing over”. genetic exchange between homologous DNA from 2 different sources

strand invasion

base pairing displaces other strand of recipient DNA

competent cell

a cell that can take up DNA and be transformed

chemical transformation

treatment of e.coli with high Calcium and chilling to make competent cells

electroporation

using electricity to transfer DNA into bacteria

generalized transduction

DNA from any portion of the host genome is packaged inside the virion

specialized transduction

DNA from a specific region of the host chromosome is integrated directly into the virus genome

horizontal gene transfer

required physical contact between donor cell and recipient cell

F (fertility) plasmid

~99 kbp circular DNA molecule that could integrate into the host chromosome

tra genes

encode transfer functions such as synthesis of pili

F’ (F-prime) plasmid

contain some chromosomal regions

episome

can exist independently or integrate into the bacterial chromosome

F+

cells that possess a non-integrated F plasmid

Hfr (high frequency of integration)

cell possessing integrated F plasmids

chromosomal mobilization

Transfer from Hfr chromosome to F- cell through a pilus

transposable elements

discrete segment of DNA that move as a unit from one location to another within other DNA molecules

Insertion sequences

relatively simple transposable elements in bacteria. have inverted repeats and only gene is for transposase

transposons

larger, carry accessory genes such as antibiotic-resistance determinants

transposase

recognizes, cuts, ligates DNA

conservative transposition

“cut and paste”

replicative transposition

“copy and paste”

CRISPR (clustered regularly interspaced short palindromic repeats

a prokaryotic “immune system” that destroys foreign DNA and maintains genome stability

antibiotic

kills bacteria or inhibits bacterial growth

bactericidal

reduces viable bacterial numbers

bacteriostatic

halts growth, host defenses and help clear infections

MIC (minimum inhibitory concentration)

lowest concentration preventing visible growth in vitro

broth dilution

directly measures MIC

disk diffusion

inhibition-zone diameter interpreted with breakpoints

gradient trips

MIC where growth ellipse intersects the scale

breakpoints

predefined MIC cutoffs for a specific organism-drug pair

targets cell wall

beta-lactams, vancomycin

targets ribosomes

aminoglycosides, tetracyclines, macrolides

targets DNA/RNA

fluoroquinolones, rifampin, metronidazole

target folates

sulfonamides and trimethoprim

targets cell membrane

polymyxins

beta-lactams

block peptidoglycan cross-linking during cell-wall synthesis

beta-lactamase

hydrolyses beta-lactam ring and inactivates the drug

vancomycin

binds the D-ala-D-ala terminus of peptidoglycan.

vancomycin resistance

D-ala-D-ala is replaced with D-ala-D-lac gene. much weaker binding

aminoglycosides

target 30s ribosomal subunits. energy-dependent uptake linked with aerobic metabolism. usually bactericidal

tetracyclines

bock aminoacyl-tRNA entry into site A. target 30s ribosomal subunits. usually bacteriostatic, broad activity

aminoglycoside resistance

enzymatically modifies the drug or modifies the binding site to reduce binding.

tetracyclines

efflux pumps the drug out of the cell or alter the ribosome so translation can continue

fluoroquinolones

DNA gyrase/topoisomerase IV. blocks DNA replication

rifampin

bacterial RNA polymerase. blocks transcription

metronidazole

reduced in anaerobes. damages DNA

sulfonamides

dihydropteroate synthase. blocks folate synthesis

trimethoprim

dihydrofolate reductase. blocks folate synthesis

trimethoprim + sulfonamides

sulfonamides compete with PABA earlier in folate synthesis, trimethoprim inhibits dihydrofolate reductase later in the pathway

staphilococci

gram positive, catalase positive, form grape-like clusters

staphylococcus aureus

“golden grape-cluster berry”. most common species to cause staph infections

staphyloxanthin

golden pigment of staph aureus. also a virulence factor

coagnulase

an enzyme that causes citrate plasma to clot. S. aureus

features of S. aureus

toxic shock syndrome, food poisoning, skin infection, impetigo surgical would infections, sepsis, endocarditis.

S. aureus enterotoxins

A-E. ingestion can cause food poisoning

Staphylococcal scaled skin syndrome

young child with blister-like lesions widely disseminated over the body

bullous impetigo

a localized form of staphylococcal scaled skin syndrome

pustular impetigo

pus-filled vesicles on an erythematous base and dry, crusted lesions

superantigens

cause non-specific activation of T cells resulting in polyclonal T cell activation and massive cytokine release

pyoderma in dogs

staphylococcus pseudintermedius

greasy pig disease

staphylococcus hyicus

mastitis in cattle

staphylococcus aureus

Staphylococcus epidermidis

infection of intravenous catheter sites and prosthetic devices. failure to follow aseptic procedure

Staphylococcus saprophyticus

urinary tract infection. sexual activity

streptococcus

gram positive, catalase negative, spherical or football-shaped cocci in pairs or chains

Strep. pyogenes

group A strep in humans. strep throat, scarlet fever, rheumatic fever, rheumatic heart disease

tissue tropism

preference for a particular site of infection

acute pharyngitis/ pharyngotonsillitis

most common S. pyogenes infection. severe, purulent inflammation of the posterior oropharynx

scarlet fever

caused by exotoxins released by pyogenes. sore throat, fever, bright red strewberry toungue

necrotizing fasciitis

flesh eating bacteria

rheumatic fever

autoimmune disease. fever, rash, carditis, arthritis

Streptococcus agalactiae

group B strep. Mastitis in cattle. Meningitis and septicemia in neonates

streptococcus pneumoniae

arranged in pairs or short chains. most trains have an outer capsule. obligate parasite of humans. pneumonia, meningitis, bacteremia

strangles

respiratory infection of young horses, donkeys, and ponies caused by streptococcus equi.

enterococcus

opportunistic pathogens that cause nosocomial infections. Has antibiotic resistance. E. Faecalis and E. Faecium are common commensal organisms in the intestine.