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EXAM 3 mlt 124
MLT 124:MEDICAL MICRO PT 1 (10-14)
| Question | Answer |
|---|---|
| What is the goal of Therapeutic Index What is done to measure selective toxicity? | - to identify antibiotics that harm the pathogen, but not the host - we use the Therapeutic Index to assess the ratio of the toxic dosage to therapeutic dosage |
| Bacteriostatic agents (blank) and rely on (blank) to clear out the infection | inhibits growth; bodily defenses |
| What type of antibiotic group would work best for immunocompromised patients? (Bacteriostatic or Bactericidal) | Bactericidal |
| Describe the differ ence between narrow, broad/wide-spectrum. | Narrow=only specific bacteria get affected, such as GI bacteria Broad=drug that can kill multiple organisms |
| Although you can utilize broad-spectrum antibiotics, why are they associated with superinfections? | they can damage normal flora |
| Describe the purpose of Pharmacokinetics? | It is a layout of different ways that antibiotics enter the tissues, activate/metabolism in the body, and how they get excreted out the body |
| True or false: In Pharmacokinetics, the peak level of antibiotic concentration should be (blank) than toxic dose | lower |
| What affect do Beta Lactam antibiotics like penicillin and cephalosporins have on Gram positives? | they inhibits the peptidoglycan synthesis, damaging the cell wall |
| Amoxicillin and Ampicillin are (blank) antibiotics that mainly target Gram negatives | Extended spectrum (ESBLs) Penicillin |
| Why would amoxicillin and clavulanic acid be considered Co-Drugs? | They are a combination of B lactam and a B lact. inhibitor to prevent the destruction of the B lactamase ring by inhibiting B lactamase |
| Which generation of Cephalosporins is the most easily inactivated? What organisms do they and do they not affect? | 1st gen; affect gram positives, but not MRSA and Enterococcus spp. |
| What is the main 2nd gen. drug that fights against gram positives and Gram negative enteric bacteria? | Cefoxitin |
| What type of Cephalosporin generation can be used against MRSA? | 4th gen |
| List the generations of Cephalosporins that can affect gram negatives | 2nd gen onwards |
| When would Carbapenems be used? | For highly-resistant bacteria that get sent to the state |
| What type of antibiotics would Vancomycin be? How does it work? | Glycopeptides; they inhibit the cross-linking of peptidoglycan chains, causing cell leakage when the phospholipids get damaged |
| What antibiotics would be used to target the 30S subunits? | Aminoglycosides, Tetracyclines |
| Which 30S-inhibiting antibiotic has a narrow therapeutic index and is bactericidal for Gram negatives? | Aminoglycosides (tobramycin) |
| Describe Tetrycyclines | they are 30S subunit-inhibiting wide-spectrum antibiotics that can suppress normal flora |
| What 50S subunit is a broad spectrum antibiotic? Which example(s) is used for gram positives? | Macrolides; erythromycin and cindamycin (used also for anaerobes) |
| Chloramphenicol are 50S subunit antibiotics used for | serious G. negatives |
| What bacteriostatic is used to treat UTIs by inhibiting folic acid synthesis? | Sulfonamides like Trimethoprim/Sulfamethoxazole |
| Bacteriostatic agents are antagonistic to Bactericidal, meaning that the actual killing rate of bacteria will be | decreased |
| Define an additive combination of drugs | they are two separate antibiotics that will equally kill bacteria without actively interacting with each other |
| Bactericidal agents can be synergistic drugs, making the actual killing rate | increase |
| The number of resistant bacteria is dependent on | the rate of mutation to resistance |
| Describe Intrinsic resistance | the organism lacks for targets that antibiotics can attach to |
| How can antibiotics acquire resistance? | acquiring of plasmids that incorporate genes (environment) or chromosomal mutation |
| What is the main negative effect of Antimicrobial Therapy? | Killing of normal flora |
| Define Minimum Inhibitory Concentration (MIC) | the lowest concentration of antibiotic that causes inhibition |
| What kind of Broth dilution should always show growth | Growth well |
| What kind of Broth dilution should never have microbial growth? | Sterile well |
| What is the most common disc diffusion method? How does it work? | Kirby Bauer; it tests multiple antibiotics at once on one organism |
| True or false: In the Kirby-Bauer test, the concentration of antibiotic (aka the concentration gradient) is lowest closest to the disc | false; highest |
| Which antibiotic testing method can produce a quantitative MIC result based on where the bacteria stops growing? | E test |
| Why would we do a D-test? | To test for S. aureus and S. agalactiae that are clindamycin resistant, even when in conjunction with erythromycin, which can cause double resistance if in they were to be administered to a paitent |
| How do we determine the positive result of a D-test? | The bacteria can be resistant to the Erythromycin, which will cause a harsh straight line near the Clindamycin's inhibition zone. This would be a POSITIVE D test because the Clindamycin is considered resistant |
| When performing an antimicrobial susceptibility test, the organism dilution in the broth is standardized by using the | 0.5 McFarland standard |
| What are the main things that all Enterobacteriaceae have in common? | - gram negative rods - glucose fermenters - oxidase negative - reduce nitrates to nitrites - oxidase positive |
| Coliform bacilli are known to ferment which kind of surgar? | lactose |
| Coliform bacteria are made up of which species? | escherichia, klebsiella, enterobacter, serratia, citrobacter |
| "Enterics" are made up of which species? (Remember MaConKEES) | citrobacter, klebsiella, escherichia, enterobacter, serratia |
| Although most enterics or coliforms don't often cause disease, which Enterobacteriaceae species are always pathogenic? | salmonella, shigella, yersinia, some E.coli strains (eg. O157:H7) |
| What would a negative lactose fermenter look like on a MAC plate? | growth, but clear or light pink (not bright pink) |
| What are the antigenic structure classifications based on? | cell wall (somatic - O), polysaccharide capsules (K), flagellar protein antigens (H) for motility |
| What is the antigenic formula of the E. coli one we have to know? | E. coli O157:H7 |
| Why would E. coli O157:H7 not have K in the antigenic formula? | it does not have a capsule |
| Which Enterobacteriaceae is transmitted via vector? | Yersinia pestis |
| How are Salmonella, Shigella, and Yersinia contracted? | ingestion of contaminated food or water |
| What are the common characteristics among all Enterobacteriaceae? | grow on MAC, ferment glucose, oxidase negative, reduce nitrates to nitrites, gram negative rods, catalase positive |
| In the E. coli O157:H7, what does the O - Somatic Antigen stand for? | cell wall |
| In the E. coli O157:H7, why does it not contain the K antigen? | E. coli O157:H7 does not have a capsule |
| In the E. coli O157:H7, what does the H antigen stand for? | the bacteria contains a flagella |
| Which Enterobacteria would be considered overt pathogens? | salmonella, shigella, yersinia, some E. coli |
| Which species of Yersinia is transmitted via a vector? | Y. pestis |
| An elderly patient acquired Pneumonia, and a Gram negative rod was isolated. What biochemical testing can we do to confirm that they have K. pneumoniae? | VP(+) red, non-motile, indole (-) |
| True or false: Klebsiella pneumoniae is a common cause of nosocomial infections, including pneumonia and UTIs for catheterized patients | true |
| Describe the virulence factors of K. pneumoniae | heat-stable enterotoxin, intrinsic resistance to ampicillin and carbenicillin via R-plasmids, capsules |
| What would K. pneumoniae look like on a MAC plate? | growth with lactose fermentation (yellow), pink colonies with gelatinous capsule |
| To differentiate K. oxytoca from K. pneumoniae, we have to do an Indole test. What reaction would K. oxytoca have to determine its presence? | Indole (+) |
| An IV drug user is rushed into the ER for endocarditis. The bacteria is isolated from the patient, and it turns out to be a slow fermenter with red colonies on TSA plate. What other biochemical testing can we do to prove it is S. marcescens? | VP (+), motile, DNAse (+) |
| What is the principle of the VP test? | analyze whether or not the bacteria produces an acetoin end product |
| Which lactose fermenter is slightly mucoid, associated with nosocomial infections, motile, and DNase positive? | Enterobacter spp. |
| Which species of Gram negative rods are highly motile, a non-lactose fermenter, and swarms on plates? How does it affect the body? | Proteus spp. it produces kidney stones due to the urea breakdown producing ammonia, causing UTIs |
| Which Enterobacteria are PAD+? | Proteus, Providencia, Morganella |
| SPEC Enterobacteria are H2S+. What does the acronym stand for? | Salmonella, Proteus, Edwardsiella, Citrobacter |
| Which Enterobacteria is highly opportunistic for immunocompromised and neonates, and often causes sepsis in IV drug users? | Citrobacter species |
| C. freundii, the most common species of Citrobacter, is known for causing severe (blank) and (blank) nosocomial infections | respiratory; urinary tract |
| What does C. freundii look like on a MAC plate? | flat colonies, center indentation, lactose fermenter |
| What is the most common species of Edwardsiella? What is the biochemical timeline we follow to determine this isolate and differentiate it from Salmonella? | H2S(+), PAD (-), ONPG/MAC Lactose fermentation (-), Indole (+) |
| Edwardsiella tarda causes Salmonella-like (blank) | enterocolitis |
| Shigella species is known to cause shigellosis, otherwise known as (blank). Which species produces "Shiga" toxin | dysentery; S. dysenteriae |
| Which Enterobacteria is known for being H2S(+), PAD(-), ONPG/MAC lactose (-), Indole (-) | Salmonella |
| How is Salmonella is transmitted and what can it cause? | fecal contaminated food/water, typhoid fever or GI symptoms |
| Which species of Yersinia causes GI symptoms? | Y. enterocolitica |
| Aside from Proteus species, what other pathogen is most well-known for causing UTIs? What form of contamination causes this? | E. coli; fecal contamination |
| EPEC is a form of E.coli that causes | diarrhea in infants |
| ETEC is known as (blank), producing watery stools constantly | traveler's diarrhea |
| Describe EHEC | Hemorrhagic E. coli that is transmitted by undercooked ground beef or raw milk; it has increased virulence and serotypes like E.coli O157:H7, meaning it is non-motile |
| EIEC is a form of E.coli that causes | dysentery in young kids |
| Idiopathic, prolonged watery diarrhea is referred as | EAEC (enteroaggregative E. coli) |
| What population of patients can causes mental confusion post-UTI | elderly population |
| What other opportunistic infections can E. coli also cause? | meningitis, bacteremia |
| Enterobacter spp. is closely associated with what infection? | nosocomial bacteremia |
| What is the pivotal test for all gram negative rods? What is the principle and result? | Oxidase; assesses how cytochrome c oxidizes the bacteria to transfer electrons. Pos=purple/blue Neg=no color change |
| Which biochemical tests assesses a bacteria's ability to break down tryptophan and uses Kovac's reagent? What are the results? | Indole test; pos=red, negative=no color change (remains yellow) |
| The diagnostic test for E. coli, following partial hemolysis on BAP, green metallic sheen on EMB, and pink MAC plate result, is... | Indole (+) red |
| What test differentiates Proteus spp. from Salmonella and Shigella? What are their respective test results? | Urease; Proteus=pos (pink), Salmonella and Shigella (-) remains yellow |
| What is the principle of the Urease test? | assesses whether or not bacteria produces urease to break down urea into ammonia, which raises pH to change from yellow to pink |
| What is the principle of the Citrate test? What are the results? | Determines whether or not bacteria can utilize citrate as its sole carbon and energy source Pos=blue Neg=no color change(stays green) |
| What test separates Providencia from Morgenella? What are the respective results? | Citrate; Pos=Providencia, Neg=Morganella |
| The indicator dye used for Citrate is | bromothymol blue |
| Describe the Nitrate/Nitrite reaction and respective results | - assess ability to reduce nitrate to nitrite (to nitrogen gas) - if Reagent A/B are added, red leads to a positive color. - if it's still clear after added reagents, zinc dust is added. a clear is positive, and red is negative (gas was never produced) |
| What are the interpretations of Oxidation-Fermentation Tests. | carbs fermentation occurs in anaerobic bacteria that will produce acid end products, while carbs oxidation is done by aerobic bacteria that produces weaker/less acid products |
| Describe the TSI agar and its purpos | contains sucrose, lactose, and glucose to test sugar fermentation, and iron products (ferrous iron and sodium thiosulfate) to detect H2S production |
| Would an aerobic bacteria grow in the slant or the butt of the TSI agar? | slant |
| In a TSI slant agar, what would a red top/yellow butt indicate? | glucose fermenter only, no H2S |
| In a TSI slant, a A/A reaction means (blank) | the bacteria ferments not just glucose, but also sucrose and/or lactose |
| What is the principle of the ONPG test? What are the possible results? | determines whether or not a bacteria is a slow lactose fermenter or a true non-lactose fermenter via hydrolysis; yellow=positive |
| Which test(s) analyze the end products of glucose fermentation? Out of the two, which one produces acetoin? | MR/VP; VP produces acetoin, while MR produces acid end products |
| Describe PAD testing principle and possible results | Phenylalanine Deamination assesses a bacteria's ability to reduce the amine group in the presence of oxygen. It uses 10% ferric chloride, which produces a green color for positive results |
| What is the purpose does the LIA test serve? | analyze the bacteria's ability to decarboxylate via glucose metabolism, which would lower the pH to 5.5, turning it yellow |
| If the bacteria carboxylates the media, what color do you expect to see? | purple; the amines are released and bring the pH back to alkaline |
| What substance is used in LIA and TSI to visualize H2S production? | Ferrous iron |
| How can you prove a bacteria is motile in a broth agar? | there is growth past the stab line |
| Which selective agar is used to cultivate Salmonella and Shigella? | Hektoen/SS/XLD |
| What agar is used to cultivate Yersinia enterocolitica? | CIN agar |
| Hektoen agar is selective of Salmonella and Shigella, and is differential for (blank) and (blank) | lactose fermentation and H2S production |
| What would Salmonella look like on a Hektoen (HE) plate? | green (non-lactose fermenter) with black center dots in their colonies |
| XLD is differential for lactose and H2S. What wiil non-lactose ferment look like on the plate? | pink (colonies) |
| Which bacteria is XLD positive with lactose fermentation? | E.coli |
| Which enteric bacteria responds negatively to all our testing? | Shigella |
| What reaction will lactose fermenters have on SS agar? | pink/red |
| What storage requirements does CIN agar have in order to grow Y. enterocolitica? How does Y. enterocolitica present on the agar? | room temp for 48hrs; red bulls-eye on colonies due to mannitol fermentation |
| What selective agar is used to prove EHEC presence? How will E.coli O157:H7 respond to the agar? | Sorbitol MAC; clear colonies |
| If a bacteria is H2S positive and PAD positive, what is it? | Proteus spp |
| Which group of bacteria are VP positive? | KES: Klebsiella, Enterobacter, Serratia |
| Describe Klebsiella genus and its confirmatory tests | mucoid on MAC, lactose fermenter that is non-motile; VP positive, urease positive -> indole + = K. oxytoca, Indole - = K. pneumoniae |
| Describe Enterobacter genus and its confirmatory tests | motile, quasi-mucoid, lactose fermenter, VP+, DNase negative |
| Describe Serratia genus and its confirmatory tests | VP+, motile, DNase positive, [OMPG pos] slow lactose fermenter, red pigment on MAC, |
| Which group of bacteria are PAD +, and what is the second test used to differentiate them? | Proteus, Providencia, Morganella; H2S (only Proteus is positive) |
| Describe Proteus genus and its confirmatory tests | PAD+, H2S+, Urease positive, highly motile swarming on plate Indole + = vulgaris, Indole - = mirabillis |
| Describe Providencia genus and its confirmatory tests | PAD+, H2S-, citrate positive, Urease neg motile |
| Describe Morganella genus and its confirmatory tests | PAD+, H2S-, Citrate negative, Urease pos, motile |
| Which enteric bacteria are non motile | Shigella, Klebsiella, Yersinia |
| SPEC enterics= | H2S producers (Salmonella, Proteus, Edwardsiella, Citrobacter) |
| Describe Salmonella genus and its confirmatory tests | H2S+, PAD-, ONPG-/non-lactose fermenter, indole negative |
| What separates Salmonella from Edwardsiella? | Indole (pos=Edwardsiella, neg=Salmonella) |
| Describe Citrobacter genus and its confirmatory tests | pink on MAC (lactose fermenter), H2S+, PAD-, ONPG+, Citrate positive |
| Describe E. coli genus and its confirmatory tests | sometimes beta hemolytic, lactose fermenter (pink on MAC), motile, Indole+, green metallic sheen on EMB, H2S-, MR+, PAD- |
| What will EHEC/E. coli O157:H7 look like on a Sorbitol MAC/XLD/Hektoen? | clear on sorbitol |
| Which E. coli test utilizes fluorogenic compound to identify E. coli presence? What would a positive result look like? | MUG Test; blue=positive |
| Which antibiotics are often resisted by gram negative enterics like Proteus, Klebsiella, and E. coli? | ESBL (Ceftazidime, Cefepime, Ceftriaxone, Aztreonam) |
| Carbapenems are antibiotics used for | ESBL resistant gram negative rods |
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