IAHI Block 2 Flashcards
Most species of bacteria use _____ for growth. Which ones don’t?
-glucose -clostridia, Legionella (amino acids) -leptospira (fatty acids)
What are 7 important differences between prokaryotes and eukaryotes? Why does this make prokaryotes better at adapting to the environment?
- 30s/50s ribosomal subunits 2. extra-chromosomal DNA (plasmids) 3. single circular chromosome, non-membrane bound 4. Many genes can be encoded within a single operon (translation/transcription are coupled and translation of different proteins can happen at same time on single mRNA) 5. No mitotic apparatus/nuclear envelope 6. NO introns/exons 7. Only one type of RNA polymerase (as opposed to 3 for eukaryotes)
- easy to replicate and can horizontally share DNA
Name 5 characteristics specific to gram positive bacteria.
- Thick, peptidoglycan outer layer, high amount of cross-linking 2. Can have flagellum (NO PILLI) 3. Teichoic acids in outer peptidoglycan layer (capsule) 4. Produces primarily exotoxins 5. More susceptible to antibiotics
Describe the Gram Stain process:
(a) crystal violet; both purple (b) gram’s iodine; both purple (c) Decolorizer (alcohol/acetone); gram– will be transparent, gram+ will stay purple (d) Safranin Red; gram– will be pink, gram+ will stay purple
Name 6 characteristics specific to gram negative bacteria.
- Thin, peptidoglycan middle layer, cross-liked to outer layer (little cross linking; more permeable); in periplasmic space 2. Can have flagellum or PILLI 3. Liposaccharides in capsule 4. Produces primarily endotoxins 5. Less susceptible to antibiotics 6. Double membrane layer (outer membrane is not very permeable due to porins/etc.)
What is the basic unit of a peptidoglycan? What are the 5 amino acids, starting from the amino saccharide bond, that are on the subunit? Between which two amino acids does ___ cut for crosslinking?
- NAG-(ß1-4)-NAM
- penicillin binding protein (PBP)
- L-alanine, D-glutamine, L-lysine, D-alanine, D-alanine -Between D-ala-D-ala
What does a lipopolysaccharide consist of (3 parts)? Which part elicits an immune response/used for diagnostics (due to its variability)? Which LPS is fever inducing?
(1) lipid (at outer membrane) (2) sugar with sugar core (polysaccharide) (3) O-antigen (polysaccharide) -O-antigen -Lipid A (binds TLR on immune cells; known as endotoxin; ex. P. aeruginosa)
What structure stimulates innate immune response in gram+ bacteria?
lipoteichoic acid (PAMP)
Pili and Fimbriae are polymers of ________, specific to the pathogen, and their function is to _____. They are found in gram _____ bacteria.
-proteins -adhere to eukaryotic cells and between bacteria (important for virulence) -negative
Flagella are polymers of proteins and their function is to _____. They are found in gram _____ bacteria. Name 2 types of flagella.
-provide motility -G+ and G- (1) Pseudomonads = single polar flagellum (2) enteric bacteria - flagella over entire surface of cell
Name the three types of secretion mechanisms. How do these virulence factors evolve?
(1) Type II = secrete protein across inner membrane (toxins out) (2) Type III = deliver toxins directly into host cells (3) Type IV = deliver DNA into host cells -gene duplication of flagellum genes
What does a capsule consist of and what is its function? How can the virulent function of a capsule be used in medicine?
-polysaccharide (very virulent) or protein -function = to prevent host cell phagocytosis/opsonization by increasing size -to produce vaccines!!
Before the vaccine was developed, what bacteria caused meningitis in the younger demographic? What does the vaccine consist of?
-Haemophilus serotype B (HiB); type of influenza -capsular polyribosylribose phosphate
Haemophilus: (a) What is its reservoir? (b) Pathogenesis (c) What causes virulence? (d) Can you have asymptomatic carriers?
(a) humans only (b) nasopharynx = uncomplicated; only bad when gets into blood stream to cause meningitis (c) Type B polysaccharide capsule (ribose and ribitol); 5 other serotypes don’t cause infections (d) YES!
Why can’t a child under 3 months contract HiB? When is HiB most invasive? Why?
-Still has maternal Ab’s = protective -Between 3 months and 3 years because humoral immune system hasn’t matured yet to produce Ab’s
Why was the 1st generation Hib vaccine not effective for children under 18 months? What did the 2nd generation vaccine do differently?
-used purified polysaccharide (PRP) capsule which were poor immunogens, stimulated T-independent antibodies and had poor immunologic memory (humoral immune system not developed) -PRP protein conjugates (diphtheria toxoid) as an adjuvent for T-dependent immune response for sustained Ab production
Name the bacterial shape of each.
A = cocci
B = diplococci
C = streptococci
D = staphylococci
E = micrococci (tetrad)
F = baccili (coccobaccili)
G = diplobaccili
H = streptobaccili
I = vibrio
J = spirochete
Name some targets for antimicrobial agents. Why are these targets?
- ribosomes
- cell wall (peptidoglycan)
- gene products
- selective toxicity for prokaryotes
How do you classify the species of a prokaryote? What 2 methods can you use to identify a species?
- by genetic relatedness and possession of similar physiological functions (because horizontal gene transfer)
1. molecular identification (look at hybridization/amplification of DNA); rapid, high accuracy, decreased selectivity
2. conventional diagnostics based on morphology and biochemistry; rapid diagnostics (sometimes)
What are two types of Molecular Diagnostics for bacteria? Describe a real-life application of each.
- PCR; for organism difficiult to grow and isolate/one that produces toxin, like Clostridium difficile (amplify toxin)
- RFLP (restriction fragment length polymorphisms); use to see whether bacterial is nosocomial (isolates identical between patient and personnel) or community based (isolates different between patient and personnel); use gel electrophoresis
Suppose Lane 1 is the isolated RFLP from the doctor and Lanes 2-4 are those of various patients with similar clinical symptoms. Is this bacterial nosocomial or community-aquired? How do you know?
All the isolates have different ID markers, meaning that they are community-aquired. If they were nosocomial, the doctor would have the same ID pattern as at least one of the patients.
Name the 3 morphological determinants in order to ID a bacteria. Name the 3 biochemical determinants.
Morphological:
- colony morphology
- cell shape/Gram stain/Motility
- Presence of a capsule
Biochemical:
- ability to metabolize specific substrates
- production of specific end products (aerobic = CO2, H2O and energy efficient [ATP, NADH2] ; anaerobic = reduce NO3 to organic end products [NO2+, N2], little energy production, unique to microbes)
- antibiotic sensitivity
Define the following terms and give an example of each:
(a) Aerobes
(b) Microaerophiles
(c) Facultative anaerobes
(d) Aerotolerant
(e) Anaerobes
(a) metabolizes O2; only grows in O2 conditions; ex) Mycobacterium tuberculosis, Pseudomonas aeruginosa
(b) metabolizes O2; only grows in low O2 conditions; ex) Helicobacter pilori
(c) metabolizes O2 when available, otherwise undergoes fermentation; ex) Escherichia coli
(d) ferments/grows in presence/absence of O2; ex) Lactobacillus
(e) ferments/grows only in abscence of O2; ex) Clostridium difficile, C. perfringens, C. tetani, C. botulinum
How would you tell the difference between an aerobic bacterium vs facultative anaerobic bacterium?
Aerobic bacteria use cytochrome C as terminal oxidase wherease facultative anaerobic bacteria use cytochrome D; the difference in redox potential allows bacteria with cytochrome C to turn BLUE with an OXIDASE TEST
What is the NITRATE TEST? List the steps.
Diagnostic of whether a bacteria is anaerobic
- add nitrite reagent = anaerobe will be BROWN and aerobe will be red
- add zinc to brown tube = anaerobe will remain BROWN (+) and aerobe will remain red (-)
Most pathogens undergo fermentation. Why is this? Which pathogens make these final fermentation products as follows: (a) Lactate (b) propionate + CO2 & Butanol/Iso-propanol (c) Formate (pH low)–> CO2 (g) + H2 (g)
- Gives them a selective advantage in environment; when make pyruvate from glucose there’s only a net +2 ATP to go to fermentation product, but these bacteria don’t need much energy to replicate (a lot of potential energy stored in lactate)
(a) Streptococcus
(b) Clostridium
(c) Enterobacteriaceae
How would you tell the difference between E. coli/Salmonella and Shigella/S. typhi?
CARBOHYDRATE FERMENTATION TEST aka ACID/GAS TEST = Grow each in sugar and test for acid and gas due to production of formate dehydrogenase (E. coli/Salmonella); (+) test will show yellow bacteria and gas at bottom of test tube (see right tube)
NOTE: E. coli uses formate DH to decrease pH in stomach (Formate –>CO2 + H2)
Define psychrophilic, mesophilic and thermophilic. Which class has the most human pathogens?
Psychrophilic = grows -5-10 degrees C
Mesophilic = grows 10-45 degrees C (MOST PATHOGENS)
Thermophilic = grows 25-80 degrees C
Most bacteria tolerate only _______ salt conditions. Wherease ______ bacteria require up to ______ salt for growth. For selective media, use ______ to select for G+ bacteria. Name a G- bacteria that needs high salt to grow.
- moderate
- halophilic
- 30% (5 NaCl M equivalent)
- Mannitol salt media (ex: G+ = Staphylococcus aureus)
- Vibrio cholerae
Sporulation is a unique property of ______ bacteria, such as [give examples and types of spores]. Spores will form in the absence of ____, and sporulation is an example of ____ differentiation.
- G+
- Bacillus (aerobe) = subterminal spore [endospore], Clostridium (anaerobe) = terminal spore
- C, N or P
- unicellular (due to asymmetric cell division)
How do you inactivate a spore?
Wet heat, 120 degrees C, 20 min (AUTOCLAVE)
What are disinfectants? Antiseptics? How are antibiotics different?
Disinfectants = toxic to humans AND bacteria (bleach); nonspecific; used for inanimate objects
Antiseptics = toxic to bacteria, but too toxic for systemic use in humans (peroxides, alcohols); nonspecific; OK for topical use
Antibiotics = selective toxicity and not toxic to humans
Define bacteriostatic and bactericidal. Which graph represents which term? List antibiotics that belong in each class.
Bacteriostatic = inhibit growth of bacteria by targeting protein synthesis (must rely on immune system to eradicate bacteria); left graph
ex) Sulfonamides, tetracyclines, chloramphenicol, erythromycin, ethambutol, clindamycin, linezolid
Bactericidal = kill bacteria directly by targeting replication, DNA synthesis and cell lysis; right graph
ex) penicilin, aminoglycosides, polypeptides, rifampicin, isoniazid, cephalosporins, ciprofloxacin, metronidazole
What factors must you consider when choosing an antibiotic? (Name 3)
- pharmacology/bioavailability; antibiotic needs to get site of infection
- Spectrum of activity = (a) narrow spectrum is effective against small group of bacteria {i.e. aerobic G+}; important for GI because we have lots of natural flora (b) broad spectrum is effective against wide range of bacteria {i.e. G+ and G-}; important because if don’t know infection, can treat to cover all bases (but be careful with GI side effects)
- Antibiotic resistance (lack of susceptibility); all isolates of given bacterial species are NOT susceptible to the same antibiotics (therefore must know straintype and ANTIBIOTIC SUSCEPTIBILITY PROFILE)
In the context of antibiotic resistance, define Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) and when each is used. Additionally, name a type of antibiotic susceptibility test.
MIC = defines lowest concentration of antibiotic that inhibits growth (ask: Did it grow?)
MBC = defines lowest concentration of antibiotic that kills a defined proportion of bacterial population after specified time; antibiotic must exceed MBC (ask: Did they die?)
DISK DIFFUSION TEST = qualitative measure of susceptibility due to zone of inhibition; use discs of different antibiotics on plate of bacterial strain
To which discs is the bacteria resistant? To which discs is the bacteria susceptible? What 2 factors can cause antibiotic resistance?
Resistant = 2/4
Susceptible 1/3
- Horizontal gene transfer (MDR strains!)
- Spontaneous mutations (strong selection for growth with rare resistant mutants)
What are some adverse effects of antibicrobials. List the drug associated with the effect if there is one.
- Toxicity = discoloration of teeth in children (tetracycline), auditory damage (streptomycin), anemia (chloramphenicol)
- hypersensitivity = anaphylaxis (penicilin)
- Alteration of normal microflora = antibiotic-associated diarrhea (endogenous C. difficile [G+] grows and produces exotoxins A and B/Pseudomembraneous enterocolitis)
- Selection for Ab-resistance = renders antibiotics useless
Name the 3 ways bacteria overcome inhibition by antibiotics and name examples.
- Modification (inactivation) of antibiotic itself; ex) ß-lactamases; modification of aminoglycosides/chloramphenicol
- Modification (reporgramming) of antibiotic target; ex) point mutation in gyrA, rpoB, ribosomes, PBPs; alternative peptioglycan structure for vancomycin resistance
- Reduction of antibiotic concentration/prevent access to target; ex) efflux pumps [tetracycline, macrolides], some with broad substrate specificity; altered cell envelope permeability via mutations in porins
What are the 4 peptidoglycan synthesis-targeting antibiotics. What does each do? Which kind of bacteria do these target? When are these Ab most effective?
- ß-lactams (penicilin, cephalosporin) = bind penicilin binding proteins (PBPs) at D-ala-D-ala active site to inhibit cross-linking; have ß-lactam ring that mimics D-ala-D-ala; different R groups change bioavailability but not mechanism of action
- Vancomycin = binds D-ala-Dala on peptidoglycan subunit chains to prevent PBPs from binding
- Bacitracin = inhibits flipping of lipid carriers, carrying peptidoglycan subunits outside the PM
-
Cycloserine = inhibits peptidoglycan crosslinking by inhibiting precursors to D-ala-Dala –> D-ala-Cycloserine (competitive inhibition)
- G+ because G- has permeability barrier (OM) with porins
- during bacterial growth (making new cell walls); high bacterial specificity and low host toxicity
Primarily _____ bacteria have primary resistance to ß-lactam antibiotics with an enzyme called ______. Describe the mechanism of the enzyme. Some bacteria, like ______ code this enzyme in their chromosome and other code it on their plasmids.
- G-
- ß-lactamase
- Mechanism = cleaves ß-lactam ring; allows PBPs to work
- Pseudomonas aeruginosa
Define ESBLs. Where are they found, mostly?
extended spectrum ß-lactamases can cleave a wide range of different ß-lactam antibiotics
-G- bacteria
NOTE: porin mutation can also prevent ß-lactam entri in some G- bacteria by decreasing pore size/chemical composition
Primarily ______ bacteria can resist ß-lactam antibiotics due to mutations in their ______. How does this mechanism confer resistance and which common organism uses this type of ß-lactam resistance?
- G+
- Penicilin binding proteins (PBPs)
- ß lactams cannot mimic PBP binding sites anymore and so they will not bind to inhibit PBP activity
- methicillin-resistant Staphylococcus aureus (MRSA)
What would you give to a patient with a G- infection in addition to a ß-lactam antibiotic to help cure her infection? What is the mechanism behind this decision?
- ß-lactamase inhibitor (clavulanic acid, sulbactam, tazobactam)
- share structural features with ß-lactams so that ß-lactamases bind these and are inactivated, allowing ß-lactam antibiotics to bind PBPs more readily
Glycopeptides, like _______ tend to be most effective on _____ bacteria. Describe why. When would this medication be prescribed?
- vancomycin (HUGE!!)
- G+
- too big to get through porins of OM of G- bacteria
- for ß-lactam-resistant infections like MRSA or ß-lactam hypersensitivity
What is the mechanism behind vancomycin resistance? Where is this resistance found? Which bacterial strain specifically is associated with vancomycin resistance? Why is VRSA incredibly dangerous and how does it occur?
- change peptioglycan structure from D-ala-D-ala to D-ala-D-lactate so that vancomycin will not recognize binding site (loss of H-bonding!! and thus low affinity)
- plasminds or transposons (easily transferred)
- Enterococci in hospitals (VRE)
- because vancomycin is the choice antibiotic for MRSA and VRSA is MRSA + vancomycin resistance, which is incredibly difficult to treat; happened due to catheter with VRE horizontally transferring VR gene to MRSA
Bacitracin must be administered ______ because it is _________. Describe bacitracin’s mechanism. Which bacteria are particularly susceptible to bacitracin?
- topically
- too toxic for systemic use (cause killing of GI flora)
- binds pyrophosphate on lipid carrier to block recycling of lipid carrier for peptidoglycan precursors (bactoprenol-P)
- Group A Streptococci (GAS)
Which 2 antibiotics target the cell membrane? Which type of bacteria is each specific for and what is the mechanism of each?
- Daptomycin = lipopeptide, bacteriocidal; binds to and disrupts PM by poking holes in it and losing Vm; targets G+
- Polymyxins (polymyxin B, colistin) = lipopetide, bactericidal; binds LPS in OM of G- bacteria, leading to disruption of both OM and cytoplamsic membrane by poking holes; high host toxicity –> topical use only
Name 5 antibiotics that inhibit protein synthesis. What are their mechanisms and which type of bacteria do they work best on?
- Tetracyclines = inhibit 30s ribosomal subunit to block the initiation of protein synthesis (binding of aminoacyl tRNA to ribosome); bacteriostatic, broad spectrum; G+/G-
- Aminoglycosides = irreversibly binds 30s ribosomal subunit via enzymatic modification to cause misreading (incorporation of incorrect aa into growing polypeptide) and premature release of ribosome from mRNA; bactericidal, G- mostly (because can’t go through G+ wall); ototoxic and nephrotoxic
- Macrolides (erythromycin, azithromycin, chloramphenicol) = binds 50s ribosomal subunit to block protein elongation; G+ mostly; bacteriostatic often used in patient allergic to ß-lactams
- Clindamycin = binds 50s ribosomal subunit to block elongation of proteins; G+ mostly (not effective against G- aerobes); useful for community-aquired MRSA Tx; to treat toxin-producing bacteria, like S. aureus
- Oxazolidinone (Linezolid) = new class of antibiotic; binds 23S rRNA on 50s subunit (unique) to prevent 70s initiation complex; bacteriostatic; G+; oral availability but high $
Describe the 2 mechnaisms of resistance to tetracycline.
- tetracycline effux pump to reduce [tetracycline] in bacteria; most common
- mutation on ribosome; less common
Describe the resistance mechanism of bacteria to aminoglycosides.
emzymatic modification of antibiotic (aceyl, phosphoryl, etc. group) to prevent binding to 30s structure of ribosome; genes on plasmids/transposons
Describe the mechanism for macrolide resistance in bacteria.
- enzyme modification (methylation) of 50s rRNA on ribosome; erm methylase gene; erythromycin/clindamycin can’t bind (cross-resistance of different macrolides!!)
- efflux pumps expel macrolides from cells
Describe the mechanism of resistance to chloramphenicol (macrolide).
Addition of acetyl group (via chloramphenicol acetyltransferase) to antibiotic in order to prevent ribosome binding
Describe the mechanism of linezolid resistance.
Point mutation in ribosomal components to prevent linezolid binding; no cross-resistance because binds different sit than either erythramycin or clindamycin
Which (above/below) is Bacteriodes fragilis and which is Clostridia perfringens in this catalase test? How do you know?
Bacteriodes fragilis = above because G-, catalase +
Clostridia perfringens = below because Clostridia are G+, catalase -
What kind of selective medium is this that the bacterium can produce a black precipitate (medium contains bile and gentamicin)?
Bacteroides bile-esculin agar
(hydrolyzes esculin to produce black precipitate)
An immunocompromised patient on antibiotics is complaining of perfuse diarrhea and general GI pain. The endoscopy reveals this and PCR tests positive for Toxin A and Toxin B. Which bacteria is this?
Clostridia difficile
A small kid stepped on a sharp stick and punctured his heal. Not thinking it was a big deal, he put a bandaid on it and went about his way. A couple hours later, the kid comes to the ER with the following (see picture). Which pathogen is this? What is the toxin causing this clinical showing?
Clostridia perfringens
∂ toxin
A 6 yo female comes into the ER complaining of headache, neck stiffness and previously tiny red dots on her legs. Upon examination, she has hyperreflexia and purpura on her legs (petechiae that have coalesced–see picture). What caused the purpura? What is your diagnosis and treatment?
- Sloughing off of LOS (lipooligosaccharide) caused inflammatory reaction
- Meningitis due to N. meningitidis
- Tx with penicillin (broad range antibiotic)
A young caucasian male (IMPORTANT) comes into the orthopedist’s office complaining of polyarthritis. After asking some questions, the orthopedist realized the patient had unprotected sex recently and has been complaining of “discharge” coming out of his penis. You diagnose him with Reiter’s Syndrome. What is the bacterial pathogen?
Chlamydia trachomatis
What is the disease name of the clinical presentation (picture) caused by Chlamydia trachomatis?
Lymphogranuloma venereum (LGV) = swollen inguinal lymph nodes
What is the name of this test? What does this test show?
Antibiogram = analysis of antibiotic sensitivity locally
A 20 yo patients comes into the ER with a poitive Nikolsky sign (picture shown), severe pain due to large bullae and erythroderma. Patient says she just began a new medication (allopurinol) 3 days ago. Why would you diagnose this patient with TEN (toxic epidermal necrolysis)? If the patient had not been taking new meds, but instead had fallen and scraped her knee, how would your diagnosis change?
The two diagnoses in the Dxx would be TEN and Staphylococcal scalded skin syndrome (caused by exofolatin proteins ETA/ETB = degrade desmoglein-1 in kaeratinocyte-epidermis layer); TEN does not need an epidermal insult because it is an allergic reaction (1st scenario); However, if patient fell and scraped her knee AND was not on new meds, it is most likely due to Staphylococcus aureus, which would produce ETA/ETB (2nd scenario)
A pregnant lady eats a canteloupe that she cut and stuck in your refrigerator 4 days ago. She develops gastroenteritis, which she thinks is just an awful bout of morning sickness at first, but she deveops a fever and flu-like symptoms. What bacterial strain was she infected with and how many months pregnant is she?
- Listeria monocytogenes*
- in her 3rd trimester (cellular immunity impaired)
There once was a cook named Mary, Typhoid Mary. She carried with her Salmonella typhi and gave it to anyone she served food to. Upon autopsy (after a lengthy excommunication/isolation/prison scenario), where was the S. typhi located and how did this cause chronic infection w/o antibiotic treatment?
Typhoid Mary had a chronic infection in her gall bladder, causing her to shed S. typhi in her feces. Clearly she wasn’t hygenic because she passed on the bacteria to those she served food to. She wouldn’t necessarily have “typhoid fever” symptoms if bacteria was isolated in gall bladder
A 58 yo male comes into clinic complaining of bloody diarrhea about 3 days after eating BBQ chicken during a 4th of July celebration. A colonoscopy reveals the following picture of flat mucosal ulcers and stool sample showed S-shaped bacteria and RBCs/WBCs. (The bacteria was difficult to culture due to its higher incubation temperatures.) Which bacterial strain is this and what toxin does it produce? As a physician, what autoimmune disorders would you be on the lookout for following this infection?
- Campylobacter jejuni*
- toxin = cytolethal distending toxin (Cdt), which stops cell division in host cells
- -*Guillain-Barre syndrome and reactive arthritis
The earthquake in Haiti caused the destruction of infrastructure in Port au Prince. Devasting, many people became violently ill with an osmotic diarrhea, excreting over 20L of fluid per day about 2-3 days after eating food containing fecal matter. This rice-stool diarrhea is indicative of which strain of V. cholerae? Be specific. Also, describe the mechanism of the toxin causing this terrible disease. If you were to culture this bacteria, what type of plate would you grow it on?
- Serotype O1–El Tor biotype
- Cholera toxin = A:5B toxin that ADP-ribosylates GCPR to constiuitively activate AC–>the increase in cAMP causes excretion of Cl- from the CFTR channel in the GI tract and thus massive water efflux
- Mannitol agar because it needs NaCl to grow!
The following are pictures of acid-fast staining procedures. Identify the three types of staining for Mycobacterium tuberculosis. Why do you need to use this procedure instead of a Gram stain?
(a) Carbol Fuschin
(b) Ziehl-Neelsen
(c) Auramine Rhodamine (immunofluorescene)
- Because lots of mycolic acids (long FA chains) make it difficult to Gram stain; must visualize with another technique
The bacteria being identified is Legionella pneumophilia. What are the two methods of identification (be sure to describe the TYPE of media on the right).
(LEFT) DFA = differential fluorescent antibody
(RIGHT) agar with buffered charcoal yeast extract; selective culture plate
