mimg 100L final

O-F test purpose

distinguish glucose oxidation/fermentation

What color does Only oxidative metabolism look like

slight yellow in the unsealed tube

What color does No oxidation/fermentation?

Green/Blue

What color does E. Coli turn in O/F test?

yellow in both tubes

Phenol Red test purpose

tests for fermentation + gas production of sugars

Phenol red: pink result

degradation of peptone alkaline end products

key ingredient in phenol red

peptone to determine deamination

MR test purpose

tests for mixed acid fermentation

VP test purpose

tests for 2,3 butanediol fermentation (neutral end products)

VP test: red

+ for 2,3 butanediol fermentation

+ Control for MR

E. Coli

+ Control for VP

K. pneumoniae

Culture density formula

CFU/mL= # of colonies/(dilution x volume plated)

Vertical gene transfer

transfer of genes from an organism to its offspring

Horizontal Gene Transfer

transfer of genes btwn organisms via transformation, conjugation, transduction

benefit of HGT for bacteria

gain new virulence factors + acquire antimicrobial resistance

Transformation

uptake of DNA from environment

transduction

transfer of DNA from one bacteria to another using bacteriophage

conjugation

temporary joining of 2 bacterial cells to copy DNA from donor to recipient cell

Which type of HGT requires cell-cell contact?

conjugation

bactericidal antibiotics

kill bacteria

bacteriostatic antibiotics

inhibit bacterial growth/reproduction

synergism

some bacteriostatic drugs are bactericidal when administered together

3 reasons why bactericidal abx are used

patients with immunodeficiency, severe infection, site of infection is poorly accessible to phagocytic cells

3 reasons why bacteriostatic abx are used

to target specific bacteria, when its used for synergistic effects, when its the only drug available due to ab resistance

Broad abx

act against wide range of bacteria

narrow abx

act against specific types of bacteria

selective toxicity

using drugs to kill pathogen without harming host cells by targeting unique pathogen features (bacterial ribosomes/cell wall)

Con of using broad spectrum abx

they kill non-resistant cells while resistant cells survive and proliferate causing superinfections

Abx Cell wall inhibitors

penicillin, vancomycin, bacitracin

Abx cell membrane inhibitors

polymyxins, daptomycin

Abx Metabolic inhibitors

Sulfonamides+ trimethoprim

Abx DNA replication inhibitors

Quinolones

RNA pol inhibitors

Rifampin

Protein Synth inhibitors

Macrolides, aminoglycosides, tetracyclines

How do B-lactams work?

binds transpeptidase enzyme which prevents crosslinking of peptide chains

Target of B-lactams

mostly G+ some G-

B-lactam ex

penicillins

Glycopeptide ex

Vancomycin

Glycopeptide mechanism of action

binds to and physically blocks peptidoglycan subunits from cross linking with enzyme

Vancomycin target

Gram +

Bacitracin mechansim

inhibits peptidoglycan precursors from being transported across CM

Bacitracin targets

Gram +

B-lactam resistance

aquisition of B-lactamase which breaks the B-lactam ring of penicillin

How does polymyxin work

dissolves membranes like detergent

How does daptomycin work?

inserts into cell membrane + induces depolarization of electrostatic potential

Which drugs have low selective toxicity

daptomycin + polymyxins

Sulfonamides + Trimethoprim mechanism of action

inhibit folic acid biosynthesis (which is required for DNA/RNA synth)

how are metabolic inhibitors selectively toxic to bacteria and not humans?

Humans can obtain folic acid elsewhere but bacteria's only source is when they synthesize it

Vancoymycin resistance

bacteria mutate/acquire cluster of genes to synthesize D-ala-D-lactate instead of D-ala-D-ala

why are both sulfonamides and trimethoprim prescribed together?

Bc you must block 2 sequential steps in the biosynthesis rxn to inhibit it

Quinolones ex

ciprofloxacin

Quinolones mechanism of action

interact with DNA gyrase preventing supercoiling/chromosome compaction

What abx is completely synthetic

ciprofloxacin

Rifampin mechanism of action

binds to and inhibits bacterial RNA pol activity which prevents DNA transcription

What infections is rifampin used for

myobacterial infections

why is protein biosynthesis a good selective target for antibacterial drugs?

Bc ribosomes in animal cells (80S) are structurally distinct from those found in bacterial cells (70S)

Macrolides mechanism of action

prevent peptde bond formation by binding to 50S

When are macrolides used?

when patient is allergic to penicillin

What spectrum is macrolides

broad spectrum

Aminoglycosides MOA

impair proofreading resulting in faulty proteins that insert into cyto membrane + are bacteriacidal

Which protein synth inhbitors bind to 30S ribosomal subunit

aminoglycosides + tetracycline

What spectrum does tetracyline act on

broadest spectrum

Tetracycline MOA

blocks binding of tRNAs

Which protein synthesis abx are bacteriostatic/bacteriacidal?

bacteriostatic: tetracycline, macrolides bacteriacidal: aminoglycosides

Genes for drug resistance are naturally found in bacteria. T/F

T

What 2 methods allow acquired abx resistance?

spontaneous mutations + HGT

What are intrinsic abx resistance methods?

ab inactivation, target modification, changes in permeability

Which drug resistance mechanisms do tetracyclines use?

efflux pump + blocked penetration

Which drug-resistance mechanism do B-lactams use?

all 4

Which drug resistance mechanism do aminoglycosides use?

efflux pump, enzyme inactivation, target mods

Which drug resistance mechannism do quinolones use

efflux pupm, target mods

which drug resistance mechanism do macrolides use?

efflux pump, enzyme inactivation, target mods

which drug resistance mechanism do rifamycins use

target mods, enzyme inactivation

How do target mods work

enzymes alter drug structure via acetylation/phosphorylation not allowing drug to bind

how does enzyme inactivation work

enzymes degrade drugs inactivating it

Resistance to Quinolones

point mutation in gyrase gene

Minimum inhibitory concentration (MIC)

minimum concentration to slow down microbe so immune system can eliminate pathogen

Minimum bactericidal concentration (MBC)

minimum concentration to kill the bacteria

why might we not want to use MBC

to limit endotoxin release

What is the therapeutic index? What is high index

Quantifies side effects/High= low side effects

What 2 factors affect MIC

how well drug penetrates a cell + affinity of drug for intracellular target

Pathogenicity

harm causing potential of pathogen

what does pathogenicity depend on

host genetics and physiology, pathogen virulence factors

Virulence

level of harm caused by pathogen following infection

Virulence is determined by pathogen virulence factors including

invasion, invasiveness, toxins

steps of pathogenesis

1)entry into host
2)adhere to host tissues
3)avoid/overcome host defense
4)damage host tissues
5)exit host

primary pathogens

cause disease in healthy hosts

Shigella flexneri is example of _______ pathogen

primary

opportunistic pathogens

less likely to cause disease in a healthy host, low virulence

What are the portals of entry?

mucous membranes, skin, parenteral route

why do pathogens adhere to tissues

to prevent pathogen removal

How to pathogens adhere to host cells

microbial adhesin interacts with host cell receptor

How do pathogens avoid host defenses?

evade, alter pathogen antigens, damage immune system

How do pathogens damage host tissues

Direct damage, immunopathy, indirect damage

why is antimicrobial resistance higher in a biofilm than free-floating cells

Cells are metabolically inactive at the base of biofilm

How do pathogens avoid immune system

1)Capsules to prevent phagocytes form binding
2)Alter their antigens to avoid ab binding
3)quorum sensing to express virulence factors at high cell density

facultative intracellular pathogens

can invade host cells but can also survive outside the host cell

obligate intracellular pathogens

invade and reproduce inside of a host cell only

immunopathy

pathogen stimulates immune response that causes disease