Exam 2 materials Flashcards
What are the advantages to using molecular techniques for analysis of infectious agents?
The three S’s: Sensitivity, Safety and speed.
Better, faster, safer”—on a whole we don’t do a bunch of things to get bacteria because it is cumbersome and not very safe or fast; so we’ve developed “quick tests” (also, we don’t want to grow scary bacteria in our labs)
Describe how PCR works for identifying bacteria?
a copy machine for DNA—you can do PCR because of heat stable enzymes from BACTERIA (use an enzyme called tack)
- DNA fingerprinting:
- the enzymes we use to cut DNA are “restriction enzymes” which also come from bacteria
- but this can be dangerous to bacteria, the fact that it can be so flexible with genome
- bacteria have a primitive immune system which consist of “restriction enzymes”—if you inject DNA into bacteria, they have molecular scissors that cut things up at different points—can order the enzymes based on what things they cut
How does RFLP work for identifying bacteria?
RFLP – restriction fragment length polymorphism “fingerprinting”
-can detect bacteria out on STRAIN level; can tell them apart;
-“lane” 1 and 12 are what we call “markers”—can buy DNA and they give us a standard size
-lanes 2 and 11 are two unrelated strings of bug in
(also had 500kb and arrow pointing to middle of left side)
-common source is lane 10—the bug in question that was isolated from hospital with contaminated AIR FILTER; so “common source” fingerprint
-the rest-restriction fragment polyphorism—the when you cut DNA, the fragments have different shapes
-so in some cases, will see DNA fingerprinting to see if strains are the same;
How does DNA hybridization work for identifying bacteria?
look directly at a sample to detect pathogen DNA in the sample; at a quick glance
- can the probe anneal? if yes, then you have the pathogen - so a STRAIN can be ID’ed or verified by DNA hybridization - you can also verify presence or absence of a bacteria
How does in site hybridization work for identifying bacteria?
use probes to look for pathogen DNA in fixed sample
How do do we use monoclonal antibodies in Flow cytometry, ELISA, RIA, and Western Blot?
Flow Cytometry– use antibodies to look for markers on cells/separate cells
ELISA – use antibodies to detect antigen!!!
RIA – similar to ELISA but uses radiation
Western blot – identify protein or antibodies to a protein
Define idiopathic and iatrogenic diseases.
Idiopathic – unknown cause
Iatrogenic - disease contracted from a health care setting
What is the MIC?
MIC - antimicrobial susceptibility tests (Minimum Inhibitory Concentration)
- take some test tubes; cultures of bacteria—these are bacterial cultures - and then add diluted antibiotic—looking for the minimal inhibitory concentration
Describe the most important mechanism explaining how bacteria become antibiotic resistant. Describe at least one other mechanism of antibiotic resistance.
The most important mechanism - passing R plasmids
Other mechanisms include biofilm formation, phage genes for resistance, mutation, enzymes to modify bugs, metabolic pathway changes
State where antibiotics were first isolated from and how semi-synthetic and synthetic agents improve on these antibiotics.
Antibiotics isolated from bacteria and fungi
Semi-synthetic antibiotics increase spectrum and decrease breakdown
Differentiate between chemotherapeutic agents and antiseptics, disinfectants, and sterilants.
chemotherapeutic agents can be used internally – like antibiotics
Antiseptics – used externally to prevent infections - mouthwash
Disinfectants – not usually used on patient
Sterilants – never ever on patients – remove all life including spores
Describe the MIC test. Is a higher or a lower MIC test desirable? How does this compare with an agar diffusion method? The MBC test? Differentiate between empirical and rational antibiotic therapy.
MIC (minimum inhibitory concentration) determines which drug will stop bacterial GROWTH at the LOWEST concentration
Can also test drug susceptibility using an agar diffusion/Kirby-Bauer
MBC – (minimum bactericidal concentration) determines the smallest amount to kill bacteria
Empirical antibiotic therapy - ‘best-guess’
Rational antibiotic therapy – antibiotic selected based on sensitivity
If a patient is immunosuppressed, do you want a bacteriocidal or bacteriostatic antibiotic?
Bactericidal
What do beta-lactams do and give an example of two regular beta lactase and two types that are beta lactase inhibitors.
They destroy the cell wall by stopping peptidoglycan linkage by inhibiting transpeptidases
Penicillins
Cephalosporins
Beta-lactamase inhibitors (clavulanic acid)-these stop it
Carbapenems – imipenem, meropenem
Monobactams – aztreonam- narrow spectrum (Gram -) – not widely used
What are four non-beta lactic cell wall inhibitor antibiotics?
- Isoniazid – cell wall of Mycobacteria
- Vancomycin – used if bacteria have B-lactamase
- Bacitracin –used on skin; effective against Gram positive organisms
- Cycloserine – seromycin – second line against Mycobacterium TB (drug resistant) – technically an oxazolidinone because it inhibits protein synthesis.
What are some antibiotics that interfere with cell membranes?
These are BROAD spectrum
Lipopeptides - Daptomycin- Gram positive only – drug resistant Staph, Strep, Enterococcus.
Topical only - polymyxins – detergent action – skin and eye infections
What are some antibiotics that are nucleic acid inhibitors?
Quinolones – nalidixic acid – narrow spectrum – inhibits DNA gyrase/topoisomerase
Flouroquinolone – broad spectrum - modified quinolones –ciprofloxacin- damage growing bone
Rifamycin – hepatotoxic – used for Mycobacterium tuberculosis
What are some antibiotics that are translation inhibitors?
- Aminoglycosides – bind to ribosomes - streptomycin, kanamycin, gentamicin, neomycin - ototoxic and nephrotoxic
- Macrolides
Erythromycin – binds to prokaryotic ribosomes - targets Gram positive bacteria - used when patient is penicillin allergic
Dificid – first new abx for C. diff in 30 years. Macrocyclic abx that is not absorbed so works locally in GI tract. - Lincosamides – clindamycin – binds ribosomes – pseudomembranous colitis risk
- Tetracyclines – broad spectrum - translation inhibitor
- Glycyclines – tigecycline – broad spectrum- IV for MRSA and VRE – 2010 FDA warning increased mortality with serious infection
- Oxazolidinone – Zyvox and Sivextro (2014) – Gram positive drug resistant infections – MRSA and VRE
- Streptogramins – quinupristin-dalfopristin. Gram positive bacteria, MRSA and VRE
What do metabolic inhibitors do and name an example for an antibiotic?
sulfonamides – stop folate synthesis
What’s the difference in Penicillin G and V in terms of giving it to the patient?
G is IV/intravenous and V is oral form.
What are semi-synethetic antibiotics and give some examples?
Semi-synthetic penicillins – broader spectrum and can be given orally. Not susceptible to the enzyme penicillinase
Methicillin – much narrower spectrum - IV only
Ampicillin – broad spectrum – works on Gram negative , too. Beta lactam
Amoxicillin - helps prevent of infective endocarditis
Describe the beta lactam, cephalosporin vs. penicillin.
also broader spectrum – Gram negative, too (WARNING: up to 10% of penicillin allergic patients are also allergic to cephalosporins)
Compare/contrast carbapenom an monobactem with penicillin
All are beta-lactams but carbapenom and monobactem are resistant to beta-lactamase
Carbapenem broad spectrum – but enteric bacteria becoming resistant
Monobactam – narrow spectrum – Gram negative only
Compare the Isoniazid with penicillin.
It is cell wall inhibitor of mycolic acid - acid fast Mycobacteria only –hepatotoxic
Classify the mode of action of vancomycin and contrast with bacitracin and penicillin.
Vancomycin - cell wall synthesis inhibitor, but non beta-lactam – Gram positive only
Bacitracin is used on the skin for Gram positive bacteria – cell wall synthesis inhibitor - non beta lactam
Penicillin – beta lactam cell wall synthesis inhibitor
What is the mechanism of action of polymyxin? What is the significant risk of polymyxin use? What do we use polymyxin for?
Used externally for Gram negative infection – detergent action used for skin and eye infection – neurotoxic, nephrotoxic and not stable in GI tract
What is the mechanism of action of clindamycin? What is the risk?
Clindamycin – translation inhibitor – reserved for serious anaerobic infection –
Risk pseudomembranous colitis - C. difficile superinfection
What are the risks of tetracycline use?
Tetracyclines – broad spectrum - translation inhibitor
Risks – superinfections, hepatotoxicity. May effect bone growth and stain developing teeth
What are three typical gram positive strains?
staphylococcus, streptococcus, enterococcus
What are three atypical gram positive strains?
Actinomyces
Nocardia
Streptomyces
What are spore forming gram positive bacteria?
Bacillus
Clostridium
What is a typical gram negative family?
Enterobacteriacea family
What are atypical gram negative bacteria?
Chlamydia
Rickettsiae
What are odd cell wall bacteria?
Acid Fast – waxy cell wall
Mycobacterium -stains weakly Gram positive
What has NO cell wall?
Mycoplasma
What are the oxygen needs of staphylococcus?
facultative anaerobes
What bacteria is catalase positive?
Staphylococccus
What bacteria is coagulase positive?
Staph. Aureus and Yersinia pestic
Differentiate between infections caused by exotoxin release and organ invasion.
Exotoxin can make you sick in absence of bacteria. Food “intoxication”
Invasion means the bug GOT IN to your body and is growing
How does cutaneous S. aureus differ from Staphylococcal food poisoning?
Food poisoning is caused by an enterotoxin/exotoxin
Cutaneous S. aureus is a colonization
What does S. Aureus slime layer and capsule help with?
Slime layer – helps bugs stick to catheters, valves, joints, etc.
Capsule – polysaccharide layer – stops phagocytosis
What are S. Aureus cell wall components?
Peptidoglycan
Teichoic acids – helps ID species and strain
Protein A
Coagulase
What are the cytolytic toxins that S. aureus has?
Alpha – cell lysis – tissue damage Beta – cell lysis – tissue destruction Gamma – rbc lysis Delta – acts as a detergent on rbc’s and other cells PV – leukocidin
What are some enzymes that S. aureus has?
Coagulase (S. aureus) - clot formation
Catalase-H2O2 breakdown ALL Staphylococcus– not Streptococcus
Hyaluronidase -spreading in connective tissue
Staphylokinase -(fibrinolysin) - dissolves clots
Penicillinase
What are the names of the two most prevalent species of coagulase negative Staphylococci? What infections do coagulase negative Staphylococci commonly cause?
S. lugdunensis, S. epidermis
Both infect prosthetic valves and less common native valves
Also infect catheters and joints
What are some things R-plasmids can do to resist antibiotics?
Pump—> Pump drug out
Enzyme—> break down the drug
What are some reasons for making semi-synthetic bacteria?
1) Increase its spectrum (range)
2) to have a decreased breakdown in the body
What does the Kirby Bauer test do?
- if you don’t know what anti-biotic, take a plate with a “lawn” of bacteria
- and then disc with different antibiotics
- see different reactions
- TELLS US how susceptible our bacteria is to a given antibiotic
What are the different “generations” of cell wall inhibitors?
e.g. cephalosporin
“first generation”—> S. aureus & group A strep
“second gen”—> adds some gram negative coverage
“third gen”—> Good against gram negative
“fourth gen”—> Very good from gram negative, drug of choice
for pseudonomas (gram negative rod)
What does clindamycin do?
It is a translation inhibitor but watch out for C. Diff; so then switch to Dificid.
What does tetracycline affect?
Liver, bones, teeth.
Acronym for staph. infections
“SOFT PAINS” skin infections (LO9) osteomycitis food poisiting (LO 10) toxic shock syndrome (LO11) pneumonia acute endocarditis infective endocarditis nectrotizing fascitis sepsis
What is the main gram positive that causes the cutaneous infections?
Staph. Aureus.
Describe the three classification schemes used to classify Streptococci
A. Serological groupings – aka Lancefield groups
1) looks at carbs on cell surface
2) GAS, GBS, GCS, GDS
B. Hemolytic patterns – based on rbc breakdown
C. Location - for us the most important is VIRIDANS
1) viridans = green because alpha-hemolytic – partial hemolysis
2) NO Lancefield groupings in this system – viridans/non-viridans only
What diseases does Strep. pyogenes cause?
1) Strep throat/pharyngitis – kids/ young adults with tonsils – fall/winter
2) Scarlet fever – rash and then skin peeling
3) Rheumatic fever – AFTER effect - cross-reactive antibody
4) Necrotizing fasciitis – SUPERANTIGENS – deeper infection
5) Pyoderma/impetigo – purulent skin infection – hot climates, young kids
6) Erysipelas– acute skin infection – larger area
7) Cellulitis – deeper skin infection
8) Toxic Shock syndrome – from superantigens – usually bacteremic
9) Endocarditis – infection of a heart valve
10) Post-streptococcal glomerulonephritis (from antibodies to streptococcus clogging kidneys)
What are virulence factors of strep. pyogenes?
1) Capsule
2) Adhesins
a) Lipoteichoic acid
b) M-protein family
c) F-protein – binds epithelial cells
What are toxins of strep. pyogenes?
Lots of things to lyse our cells!
Pyrogenic exotoxins - mitogens for T-cells/inflamm – rash, fever – pus –
2) Streptolysin S – lyses wbc’s, platelets and rbc’s
3) Streptolysin O – lyses wbc’s, platelets and rbc’s
4) Streptokinase – lyses blood clots and allows spread
5) Hyaluronidase – spreading
6) DNase - streptodornase
7) C5a peptidase
