Midterm #1 Flashcards
1
Q
Antibiotic Impact on Healthcare
A
- Make up a substantial amount of prescriptions
- Places where use is most intense leads to greatest resistance (Ex: ICU)
- Frequently prescribed unnecessarily
2
Q
Antimicrobial vs. Antibiotics
A
- Antimicrobial:
- Microbial secondary metabolites or synthetic compounds that is small doses inhibit the growth and survival of microorganisms without serious toxicity to the host
- Antibiotics:
- Natural subset of antimicrobials
3
Q
What percent of us is bacterial?
A
- >90%
- Targeting pathogenic bacteria with antibacterials will impact our normal flora
4
Q
Impact of antibiotics on our microbial flora
A
- Not specific enough to only target the primary pathogen
- Potentially act against other species of our flora
- Can compromise the balanced bacterial ecology, especially of the gut
- e.g. leading to diarrhea (antibiotic associated diarrhea AAD) and C. difficile overgrowth
- The flora can be reservoirs for transferrable resistance factors (R-factors)
- R-factors can be detected even during the course of therapy, and persist for years after antibiotic therapy
- plasmids
5
Q
Ways commesal bacteria impact our health
A
- Organs and internal tissues are normally sterile
- Commensal bacteria do colonize “exterior” including skin, gut, respiratory tract, mouth, eyes, urogenital tract, etc.
- Provide:
- Aid in digestion of food and production of vitamins, link to obesity
- Processing of nutrients and drugs in our guts
- Overall metabolite profile (metabolome) of host with natural bacterial flora is significantly different from those that are germ-free
- Prevent establishment of pathogenic competitors
- Immunity
- Imbalance can impact asthma
- Affect can persist and lead to long-term health consequences
6
Q
Enterotypes
A
- Microbiome of gut can be categorized into 3 different “enterotypes” each dominated by a main genus
- Bacteroides
- Prevotella
- Ruminococcus
- Not related to nation, gender, age, or ethnicity
- May be linked to long-term diet
- There may be a link between the enterotype found in an individual and susceptibility to disorders/disease
7
Q
Sources of pathogenic bacterial infections
A
- organs and internal tissues are normally sterile. Commensal bacteria do colonize “exterior”.
- Opportunistic pathogens: when commensal bacteria gain acess to interior
- Compromised immune systems
- Some pathogens are extrinsic and are not related to our commensal flora
8
Q
Sinusitus
A
- S. pneumoniae
- H. influenza
- M. catarrhalis
9
Q
Acute otitis media
A
- M. catarrhalis; 90-95% produce beta-lactamases
- S. pneumonia
- H. influenza
10
Q
Community acquired pnumonia
A
- S. pneumoniae
- H. influenzae
- S. aureus
- anaerobes
- other Gram -
11
Q
Hospital acquired pnumonia
A
- Pseudomonas auerginosa
- Staph. aureus
- Klebsiella pneumoniae
- Enterobacteriaceae
12
Q
Urinary Tract Infections
A
- E. coli
- Staphlococcus saprophyticus
13
Q
Nosocomial UTI
A
- Klebsiella
- Proteus
- Enterobacter
- Pseudomonas
14
Q
S. pneumoniae
A
- Respiratory, sinus and ear infections
- Streptococcus
- Gram +
- Cause of pneumonia
- 28% resistant to at least one antibiotic
- 11% resistant to 3 or more antibiotics
- 40,000 cases/yr
- Sinusitis and otitis media (7 M cases/yr)
- Sepsis (55,000 cases/yr)
- Meningitis (6,000 cases/yr)
- Penicillans are front line drug, but not 30% have resistance (PRSP); multi-drug resistance is also seen
- Vaccine available to help reduce antibiotic resistance
15
Q
H. influenzae
A
- Respiratory, sinus and ear infections
- Gram -
- aerobe/facultative anaerobe
- Opportunistic comensal bacteria
- Pneumonia
- Sinusitus
- Otitis media
- Vaccine (HiB) is available and has reduced frequency of invasive infections relating to encapsulated serotype B
- 30% beta lactamase producing
- Some show modified PBPs conferring penicillin resistance, but cepholosporins may be effective, as well as macrolides, fluoroquinolones
16
Q
M. catarrhalis
A
- Respiratory, sinus and ear infections
- Moraxella catarrhalis
- Gram -, aerobic
- 75% in children, more prevalent in fall and winter
- Emerged as a pathogen for children, adults with COPD, immune compromised
- Otitis media
- Pneumonia
- Bronchitis
- Sinusitus
- Meningitis, sepsis is rare
- Lower respiratory tract infections
- COPD
- Pneumonia in elderly
- Hospital outbreaks
17
Q
Strep. pyogenes
A
- Gram +, group A beta-hemolytic streptococcus (GAS)
- Sometimes part of flora, nonpathogenic, asymptomatic
- Skin and wound infections
- 10 M cases/yr: cellusitus and impetigo
- 4500 cases/yr: necrotizing facitis
- Strep throat
- Scarlet fever
- Streptococcal toxic shock: reaction to toxin
- Acute rhematic fever; autoimmune reaction triggered by strep. pyogenes
- Penicillin is the drug of choice, very little resistance has emerged; for those penicillin allergic, clindamycin, macrolides
18
Q
Penicillin, the drug of choice for necrotizing facitis, has little drug resistance. Why then is necrotizing facitis so hard to treat?
A
There is tissue damage that causes poor circulation, so it is hard for the drug to reach the site
19
Q
Staphylococcus aureus
A
- Gram +, faculatative anerobe
- Often found on skin and respiratory tract without causing illness
- Typical infections:
- Wound
- Cellusitis
- Sinusitus
- Pneumonia
- Food poisining
- Bacteremia (sepsis)
- Bone (osteomyelitis)
- Meningitis
- Endocartitis
- Toxic shock syndrome (TSS; immune response to protein)
20
Q
Types of nosocomial infections
A
- UTI
- pneumonia and respiratory infections
- surgery-related
- skin and mucosa
- bacteremia
21
Q
Nosocomial infection: Example: P. aeruginosa
A
- Gram -, faculatative anerobe/aeobic, opportunist
- Minimal nutrient requirements
- Frequent colonizer of medical equipment
- Burn and wound infections
- UTI
- Gastrointestinal
- Bone and joint
- Bacteremia (blood infection)
- Respiratory infections, cystic fibrosis
- 10% of hospital-acquired infections
-
Significant antimicrobial infections
- biofilm formation
- low cellular permeability to antibiotics
- efflux pumps, multi-drug efflux pumps transports across BOTH membranes
22
Q
Clostridium difficile
A
- Gram + anaerobe, spore (infective state) forming
- while some normally carry the bacteria, most are exposed to it in health care settings; ingested from contaminated surfaces, contact
- Spores are resistant to antimicrobial therapy, can lead to relapse
- Gain foothold when gut microbes wiped out or imbalanced
- Produces enterotoxin (toxin A) and cytotoxin (toxin B) that damage host cells
- 14,000 deaths/yr in US
- AAD, fever, abdominal pain
- Pseudomembranous colitis; a severe infection on the colon
23
Q
Antibacterials: Drugs
A
- Sulfa drugs (sulfonamides)
- Quinolones
- Linezolid (zyvox)
- Synthetic products from chemical screens
24
Q
Bacteriostatic
A
- Some antimicrobials do not necessarily kill the bacteria
- Break the logarithmic growth phase, allowing the immune system to deal with the infection. Tend to involve inhibition of protein synthesis
- Ex: tetracyclines, suflonamides, Chloramphenicols, Macrolides, Licosamides
25
Q
Bacteriacidal:
A
- Kill the bacterium
- Ex: Beta-lactams, Glycopeptides (vanco), Aminoglycosides, Fluorquinolones, Metronizadole
- Weaken the cell wall, leading to lysis (ex: penicillins)
- Disrupt DNA replications (Quinolones)
- Disrupt RNA synthesis (rifampin)
- Some drugs that are bacteriostatic at lower concentrations can be -cidal at higher concentrations
26
Q
MIC and MBC
A
- Minimum inhibitory concentration
- Not necessarily kill all the bacteria
- Lowest concentration of drug that gives no visible growth after 24h incubation
- Minimum bacterialcidal concentration
- Concentration of drug that gives no visible growth even in absense of drug
27
Q
Bioavailability
A
- Before the anti-microbials such as penicillins, arsenicals, and sulfa drugs, topical antiseptics, disinfectants were the only tools available for treating infection
- Penicillin in particular provided low host toxicity, high potency that could get to the site of infection and permeate it
- The drug must get to its target
- Tissue penetration
- Penetrate biofilms
- Bacterialcidal cell penetration to bind to the target
- Attain adequate concentrations to occupy a sufficient number of target active sites to produce desired effect, but without toxicity to host
- Must remain bound for sufficient time to inhibit the biological/metabolic process that will lead to bacterial cell death
28
Q
Narrow vs. Broad Spectrum
A
- Would like narrow spectrum to save normal flora
- reduce risk of antibiotic associated diarrhea
- reduce risk of C. diff overgrowth
- Often don’t know the target or have a superinfection with multiple species
- **Empiric therapy **with broad spectrum
- Identify pathogen
- Switch to narrower spectrum
29
Q
Targets for Antibacterial Drugs
A
- Ribosomes
- Metabolism
- Peptidoglycan cell wall
- DNA replication machienary
- RNA synthesis
- unique to bacteria and not found in humans
30
Q
Natural Products Antibiotics and their derivatives
A
- Beta-Lactams
- Vancomycin
- Cycloserine
- Bacitracin
- Polymixin
- Daptomycin
- Rifampin
- Rifabutin
- Chloramphenicol
- Macrolids
- Clindamycin
- Aminoglycosides
- Tetracyclines
- Tigecyclines
- Quinupristindalfoprisitin
- Telithromycin
31
Q
Synthetic Antimicrobial Agents
A
- Isoniazid
- Ethambutol
- Quinolones
- Metronidazole
- Clofazimine
- Linezolid
- Sulfonamides
- Dapsone
- Trimethoprim
- Para-aminosalicylic-acid
32
Q
MOA: Broad Array of Drug Classes
A
Diversity of chemical structures
33
Q
Details in Choosing Antibiotic
A
- Differences among bacterial species mean a drug will only be active against certain types of bugs
- Narrow vs. Broad spectrum
- Gram + vs. Gram -
- Target expressed?
- Details of target enzyme structure
- Differences in resistance mechanisms
34
Q
Gram Positive Bacteria Cell Wall
A
- Relatively simple cell wall
- Single membrane
- Thick peptidoglycan layer
- High internal osmolality
- Less developed biosynthetic capability
- Lysozyme, a protein in our innate immune defense, digests peptidoglycan; found in mucus, tears and saliva
35
Q
Gram Negative Bacteria
A
- complex cell wall
- Outer and inner membranes
- Thin peptidoglycan, one 1 or 2 layers
- Periplasmic space separating the membranes
- Porin channels in outer membrane can restrict uptake of drug
- Low internal osmololity
- Highly developed synthetic capabillty
- Highly adaptive
36
Q
Gram Positive Bacteria: Close up of cell wall
A
- PBP: Penicillin Binding Protein (transpeptidases)
37
Q
Gram Negative Bacteria: Close up of cell wall
A
- More complex
- Outermembrane adding additional protection
- Beta-lactamases concentrated in the periplasmic space
38
Q
Porins
A
- Large, bulky drugs (e.g. vancomycin), >700 Da exculded
- Apolar compounds are excluded
- Smaller, polar compounds may cross outer membrane via porins
- Drastically limit the uptake of drugs
39
Q
Example of drugs and crossing porins
A
- PenG is apolar and can’t cross through the porins
- Ampicillin is made polar with the amino group, can cross through the porin channel
40
Q
Which is harder to treat, Gram + or Gram -?
A
- Gram -
- Because they have an outermembrane they are intrinsically resistant to some drugs
41
Q
How cell wall synthesis inhibitors work?
A
- Target peptidoglycan cell wall
- It’s biosynthesis and maintenance
- Generally bacterialcidal
42
Q
Stages of biosynthesis in which drugs can affect cell walls
A
- Intracellular
- Transport
- Extracellular
43
Q
How protein syntheis inhibitors work?
A
- target the bacterial ribosomes
- Shut down protein translation and elongation
- Generally bacteriostatic
44
Q
Drugs that attack bacterial ribosome
A
- Tetracyclines
- Macrolides
- Aminoglycosides
- Chloramphenicol
- Lincosamides
45
Q
How drugs attack the ribosome
A
- 70s (30+50) ribosome is very different than eukaryotic 80s (40+60) ribosome
- Antibacterials can bind to many different targets in the ribsome
- 30s
- tetracyclines
- Aminoglycosides
- 50s
- chloramphenical
- macrolides
- lincosamides
- streptogramins
- linezolid
46
Q
How Macrolides Work
A
- Bind 50s
- Induce premature dissociation of peptidyl-tRNA from ribsome, hence premature termination
- Prevent addition of residues onto nacsent polypeptide by blocking A to P translocation
47
Q
How Tetracyclines works
A
- Bind to 30s
- Prevent aminoacyl-tRNA binding, hence peptide elongation
48
Q
How Aminoglycosides Work
A
- Bind to 30s subunit
- Prevent tRNA movement from A to P site
- Induce errors into “proofreading” and induce premature release of nonsense peptides
49
Q
How Quinolones/Fluroquinolones work
A
- Helicases during DNA replication induce supercoiling and gyrase (a topoisomerase) uncoils
- Block topo II and IV (-, +) inhibits gene reguatlion
- The nuclease domain still functions properly
- DNA gets fragmented and ends up killing the bacterium
- Pass through porins
- Bacterialcidal
- Ciprofloxicin, levofloxicin
50
Q
How rifamycins works
A
- From Actinobacteria Amycolaptis mediteranie
- Binds to bacterial RNA polymerase, inhibit RNA synthesis by blocking chain elongation, blocks mRNA transcription
- Bacterialcidal
- Treatment of mycobacterial infection, some grm +
- Some activity against HIVs reverse transcriptase (not clinically tested)
51
Q
Folic Acid Synthesis Inhibitors
A
- Inhibiton of folate synthesis in bacteria
- Sulfa drugs (sulfonamides); an “antimetabolite” that inhibits dihydropteroate synthase by competitive binding with p-aminobenzoic acid (PABA)
- Folate is crucial for DNA synthesis
- Bacteria make their own folate, we do not synthesize our own
- Prontosil, the original sulfonamide drug (actually a prodrug)
- Trimethoprim/Sulfamethoxazole (TMP-SMX) synergistic
52
Q
The nightmare of CRE
A
- Carbapenem-resistance enterobacteriacea
- Resistant to all or nearly all drugs
- High mortality rates
- Spread their resistance to other bacteria
53
Q
Resistance: Definition?
A
- The continued growth of microorganisms in the precense of cytotoxic concentrations of antimicrobial therapeutics
54
Q
Mutant Selections Window
A
Apply antimicrobial and the strong survive
55
Q
Vertical Transfer of Antibiotic Resistance
A
- Mutation that allow bacteria to be resistance, then it transfers that to its prodigy
56
Q
MPC
A
- Mutant Prevention Concentration
- The inhibitory concentration (MIC) for the most resistant mutant in the population
- If [drug]>MPC, resistance does not emerge
- If MIC<[drug]<mpc>
</mpc><li>Serum drug concentration should remain above MPC</li><li>Combination therapies?</li>
</mpc>
57
Q
Acquisition of Resistance: Mutation + Vertical Transfer
A
- Spontaneous mutation
- Single mutation rarely leads to complete resistance
- Infection contain >1010 cells, infection in 1 of 106-8
- Selective pressure leads to selection of mutant with more resistance to drug,
- descendants will posses resistance too (vertical transfer)
- Example: MRSA
58
Q
Acquisition of Resistance: Horizontal Transfer
A
- Transformation:
- Uptake of genetic material from a cell’s surroundings; e.g resistance-encoding DNA from a lysed neighboor; often involves the same species
- Transduction:
- Bacteriophage transfer genetic pieces from one bacterium to another
- Important in Staph. aureus
- Bacteriophages infect specific species, more likely to get transfered between like species
- Conjugation:
- A plasmid may be transferred from one bacterium to another
- Can be between different species, even between gram+/-
59
Q
Conjugation: plasmids
A
- Multi-drug resistance can be encoded on a single plasmid
- Can be between bacteria of different genera
- Transposons: gene with insertion sequences at both ends, which can jump from plasmid to chromosome to plasmid
- Gut bacteria serve as reservoirs for plasmids encoding resistance genes
60
Q
Resistance and Fitness
A
- Costly to maintain plasmids when antibiotic not present; less-fit will be outcompeted by more fit when antibiotic withdrawn; resistance fades
- Can take advantage of this by cycling antimicrobials to control resistance
- BUT:
- Comepentasory mutations can restore fitness
- Some resistance mutation don’t have a cost
- Resistance mutation may improve fitness even in abcense of antimicrobial
- These can causes resistance to persist indefinently (even with antibio is removed)
61
Q
Molecular Mechanisms of Antimicrobial Resistance
A
-
Destroy the drug
- Beta-lactmases
- Aminoglycoside kinases
-
Modify the drugs target
- PBP modified to prevent methicillin binding in MRSA
- PBP mutated in penicillin resistant strep pneumo
- Efflux pumps
-
Modify porin selectivity
- Aminoglycoside resistance in Pseudomonas
-
Thicken the cell wall
- VISA
-
Other ways to counter drug’s action on their targets: Rescue proteins
- R-factor encoded proteins (QNR gene) can bind the DNA gyrase and protect it from a fluroquinolones action
- Proteins bind to ribosomes and rescue function in prescence of drug (tetracyclin)
62
Q
Beta-Lactam Drug Structure/Function
A
- Ring in penicillin and cephlasporins
- Beta-lactamases hydrolyze the beta-lactam ring
- Enzymatic turn-over of drug inactivation
- Beta-lactam normally binds transpeptidase and prevents it from crosslinking the cell wall
- beta-lactamases fuck up the beta lactam so it can’t bind to the transpeptidase
63
Q
Gram + bacteria beta lactamases
A
- Primarily in staphlococci
- SA makes a narrow activity penicillinase
- Many gram + do not make beta lactamases
- Usually plamid mediated
- Constitutive “always on” expression generally
- Excreted to surrounding environment, thus lowers extracellular antibiotic concentration
64
Q
Gram - bacteria beta lactamases
A
- Constitutive or inducible beta lactamases
- Concentrated in periplasmic space, lowers intra but not extracellular levels of drug
- Plasmid encoded beta-lactamases (constitutive)
- Hflu, gonohorrea, salmonella, shigella, e coli, klebsiella
- Inhibited by beta-lactamase inhibitor like clauvuanic acid
- Chromosomollay encouded beta-lactamases (inducible)
- Enterobacter, Citrobacter, Psuedomonas, Serratia, Morganelli, Providencia
- Noto inhibited by beta-lactamse inhibitors
- Hundred of known beta-lactamase enzymes with different beta-lactam targets
- Some have broad specifity
