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137 Cards in this Set
- Front
- Back
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antimicrobial concentration test
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measure the amount of antimicrobial agent in serum or body fluid
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minimum bactericidal concentration (MBC) test
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measure of the lowest concentration of antimicrobial agent that kills a bacterial isolate
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serum bactericidal test (SBT)
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measure of the highest dilution or titer that is bactericidal
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synergy test
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measure of the susceptibility of a bacterial isolate to a combination of two or more antimicrobial agents
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time-kill assay
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measure of the rate of killing of bacteria by an antimicrobial agent as determined by examining the number of viable bacteria remaining at various intervals after exposure to an agent
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MBC endpoint
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the lowest concentration of antimicrobial agent that kills 99.9% of the test bacteria
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The decreased bactericidal activity at higher concentration is referred to as a ____.
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paradoxic (eagle) effect
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In MBC test, when small numbers (but slightly greater than 0.1% of the test inoculum) of bacteria grow on several subculture plates
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persisters
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An interpretive problem of MBC testing. demonstrated when the numbers of colonies growing on subculture plates exceed the 0.1 cutoff for several successive drug concentrations above the MIC
b. asociated with a defect in bacterial cellular autolytic enzymes |
Tolerance
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the activity of the antimicrobial combination less than than (and MICs are greater than) that of the single agents
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antagonism
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activity of the combination of antimicrobials is equal to that of the single agents
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indifference
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bacteria have acquired elaborate mechanisms to mobilize and dissimenate toxic effects of resistance mechanisms via:
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-plasmid
-transposons -insertion sequences -integrons |
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acquired resistance
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-present in only certain isolates of species
-distinct from parental strain -arises as result of chromosomal mutations or by horizontal transfer of preexisting resistance genes |
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intrinsic mechanism of resistance are innate characteristics of microorganisms and are transmitted to progeny _____.
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vertically
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acquired mechanisms of resistance are those that result from:
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the acquisition of DNA by transformation and recombination
or by acquisition of extrachromosomal DNA and is transmitted horizontally |
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mechanisms of action of antimicrobials
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1. target cell wall biosynthesis
2. folate synthesis 3. DNA replication 4. RNA transcription 5. mRNA translation |
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resistance that is natural to species, results from biochemical makeup of wild-type organism and is passed vertically to progeny cells. limits the spectrum of antimicrobial activity
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intrinsic resistance
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Some Gram negative bacteria are resistant to activity of macrolides because these agents are either too large to traverse the cell wall or are pumped out via efflux. this is an example of what form of resistance
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intrinsic resistance
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Agents with activity only in the urinary tract should be reported only on isolates from urine. why?
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because these drugs are clinically ineffective in treating other infections
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When would you report and test for group C antimicrobials agents as recommended by CLSI?
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if particular institution encounters large number of isolates resistant to group A and group B agents
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According to the suggested groupings of antimicrobial agents for routine testing, when should secondary agents be reported:
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1. polymicrobial infection and secondary but not primary agent is more likely to be effective against all pathogens present
2. diseminated infection where sencondary agent would be more effective than primary agent |
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For several organism groups, CLSI categorizes antimicrobial agents into four groups. As a general guideline, how should reporting be executed within a certain antimicrobial class ?
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primary (group A) reported first , secondary (group B) agents be reported only if the following conditions exists:
-isolate resistant to 1st agent -patient cant tolerate 1st agent infection not responding to 1st agents -2ndary agents are better clinical choice for infection -patient has organism isolated from another site, and secondary might be useful in treating both. |
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which aminoglycosides are preferred for treating infections caused by gentamicin-resistant pseudomonas aureginosa?
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tobramycin or amikacin
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Why are 3rd generation cephalosporins better for treatment of meningitis caused by susceptible E.coli?
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can cross blood-brain barrier more effectively than 1st generation cephalosporins
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which Factors should be considered when determining whether susceptibility testing is warranted ?
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1. organisms (potential resistance)
2. site of infection 3. host status - allergy, immunosuppressed patient 4.quality of specimen collected - contaminants present? 5. spectrum of activity |
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susceptibility tests are NOT performed on bacteria that are:
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predictably susceptible to the antimicrobial agents commonly used to treat infection caused by these bacteria
example : group A Beta hemolytic Strep not tested for penicillin since it is universally susceptible |
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two ways to perform susceptibility testing in the clinical lab are:
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1. disk difusion/dilution method
2. minimum inhibitory concentration (MIC) |
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Glycopeptides:
A. include which antibiotics B. mode of action C. spectrum |
A.- vancomycin
- dalbavancin -telcoplanin -ortivancin -televancin B.MOA- inhibits cell wall synthesis by complexing the non-cross linked strands preventing incorporation into peptidoglycan layer C. limited to gram positives- staph, strep, enterococcus in USA |
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Sulfa drugs:
A. include which antibiotics B. mode of action C. spectrum |
A. sulfamethoxazole, trimethoprin
B. (bacteriostaitc drugs) MOA- inhibits folate synthesis; interferes with nucleic acid synthesis. C. spectrum: combo works best. broad spectrum against Enterobacteriaceae that cause UTIs |
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Quinolones:
A. include which antibiotics B. mode of action C. spectrum |
A. ciprofloxacin, norfloxacin
B. interference with DNA replication; targets DNA gyrase and topoisomerase IV |
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B-lactam drugs:
A. include which antibiotics B. mode of action C. spectrum |
A. -carbapenems
-penicillins -monobactams -cephalosporins B. inhibit cell wall biosynthesis by binding to enzymes PBP that crosslink peptidoglycan C. spectrum: narrow spectrum - gram positives |
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Rifamycin
A. include which antibiotics B. mode of action C. spectrum |
A. Rifampin (orange)
B MOA- interferes with DNA transcription by blocking RNA polymerase and interferes with RNA chain elongation |
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Which of the following drugs belong to the amynoglycoside family of antibiotics?
a. rifampin b. tobramycin c. norfloxacin d. Tetracycline |
b. Tobramycin
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Aminoglycisides
A. include which antibiotics B. mode of action C. spectrum |
A. gentamicin
streptomycin amikacin tobramycin B. MOA- interferes with mRNA translation into protein by targeting the 30S ribosomal subunit; prevents docking of tRNA |
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Macrolide antibiotics impact an organisms ability to grow by
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interfering with the protein synthesis by targeting the 50S ribosomal subunit
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The MIC is:
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a. the lowest concentration of antibiotic that inhibits growth of an organism
b, the first well or tube that shows no visible growth |
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Beta-lactam antimicrobial drugs include all of the following except:
a. cabapenems b.monobactams c. fluroquinolones d. cephalosporins |
c. fluroquinolones are not beta-lactams
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Which of the following drug pairs are prescribed together because they exhibit synergy?
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1. dalfopristin/quinupristin
2. trimethoprim/sulfamethoxazole |
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Polyketides
A. include which antibiotics B. mode of action C. spectrum |
A. doxycycline
tetracycline minocycline B. MOA- target the 30S subunit; inhibits protein synthesis by binding to 16S rRNA near A site --> inhibits rotation of bound tRNA into A site during translation |
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Tetracycline inhibits protein synthesis by
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inhibiting amynoacyl-tRNA binding to the A site on ribosome
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Macrolides
A. include which antibiotics B. mode of action |
A. Erythromycin
Clarithromycin Azithromycin B. MOA- targets 50S subunit interferes with mRNA translation |
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Erythromycin inhibits mRNA translation by
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blocking translocation step of protein synthesis (mRNA translation)
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chloramphenicol is known to inhibit ____ in prokaryotes
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peptidyl transferase
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oxazolidinone class
A. include which antibiotics B. mode of action |
A. linezolid
B. targets protein synthesis; binds to 50S subunit of proks prevents formation of preinitiation complex with 30S specific target on 50S --> P site |
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Linezolid differs from other protein synthesis inhibitors in that:
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it blocks the initiation step. other protein synthesis inhibitors such as macrolides and tetracyclines block peptide chain elongation therefore allow mRNA translation to start
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Streptogramin class
A. include which antibiotics B. mode of action |
A. composed- mix of streptogramin A and B
A2. Dalfopristin-quinupristin B.MOA- disrupt translation of mRNA by binding to peptidyltransferase domain of bacterial ribosome dalfoprstin- streptogramin A - interfere with peptide chain elongation - prevents binding of aminoacyl-tRNA to ribosome quinupristin- stimulates dissaociation of peptidyl-tRNA and may interfere with release of peptide chain by blocking exit tunnel |
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Glycylcycline
A. include which antibiotics B. mode of action |
A. tigecycline
B. inhibits mRNA translation by binding to 30S subunit and blocking entry of Aminoacyl-tRNA into A site on ribosome. |
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Organisms that acquire drug resistance using plasmids can use which of the following drug resistance mechanisms?
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-destruction/inactivation of drugs using enzymes
-prevent penetration of drug by altering cell wall composition -alter drug target sites by making capsule |
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which factor is most important in choosing an antibiotic?
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patient allergy
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Antimicrobial drugs which exert their action on DNA gyrase include:
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fluroquinolones
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An _____ disk can be used to screen for penicillin susceptibility in S.pneumoniae from specimens other than sputum
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oxacillin
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Which of the following organisms would require some sort of antimicrobial susceptibility testing?
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Streptococcus pneumoniae
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D zone tests is used to detect:
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inducible clindamycin resistance in staphylococci and B-streptococci
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What does the mecA gene code for in staphylococci?
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penicillin binding protein 2a and oxacillin
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The ______ disk performs better than the oxacillin disk in detecting oxacillin resistant staphylococi.
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cefoxitin disk
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which test is recommended to detect VRSA or VISA
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vancomycin-broth microdilution
or vancomycin agar screen |
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ESBL producing isolates should be considered resistant to which of the following agents?
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cephalosporins, penicillins, and aztreonam
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which antimicrobial should be considered for susceptibility testing when an entercocci is shown to have high levels of amynoglycoside resistance?
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streptomycin
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the turbidity of a 0.5 macfarland standard corresponds to approximately _____ bacteria per mL
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1.5x 10^8
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B-lactamase testing is performed on _______ to determine whether isolate is resistant to ampicillin and amoxicillin
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H.influenzae
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Microorganisms can exhibit antibiotic resistance due to which of the following?
a.intrinsic b.acquired c. both d. neither |
both
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which mechanisms of antibiotic resistance are intrinsic and acquired?
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efflux
enzymatic |
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Plasmids can contain which of the following ?
a. transposons b. insertion sequences c. integron cassettes d. all of the above e. a and c |
all of the above
a. transposons b. insertion sequences c. integron cassettes |
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transposons do not contain:
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cytoplasmic membranes
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which of the following characteristics apply to efflux pumps?
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a. they are found in gram-pos and gram-neg bacteria
b.they are transporter proteins c. they have single or multiple substrates (all of the above) |
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which apply for antibiotic resistance due to target site modification?
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a. chromosomal mutation of target site
b. quinolone resistance determining region d. erythromycin resistance methylase |
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enzymatic modificationb of aminoglycosides is due to which of the following?
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N-methylation
O-phosphorylation O-adenylation |
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Which is characteristic of integrons?
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genetic elements capable of integrating resistance genes (cassettes) by recombinase
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Staphylococcus epidermidis is recovered from which of sources?
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prosthetic heart valves
intravenous catheters |
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which staph species, in addition to S. aureus also produces clumping factor?
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S. lugdenesis
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toxic shock syndrome is attributed to infection with:
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s. aureus
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which enzymes contribute to the virulence of S.aureus?
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hyalorinidase and b-lactamase
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staph saprophyticus is best differentiated by using which test?
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novobiocin (its resistant)
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A staph sp. recovered from a wound specimen from a patient with cellulitis was negative for the slide coagulase test, and negative for novobiocin resistance. what is the next test needed for identification?
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tube coagulase
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which of the following will differentiate micrococci from staphylococci?
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modified oxidase
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A gram positive coccus recovered from a wound ulcer from a 31 yo diabetic patient showed school bus yellow, creamy colonies on blood agar. The following test results were noted: catalase positive; mannitol salt negative; slide and tube coagulase negative; the most likely id for this organisms is:
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micrococcus luteus
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Risk factors for bacterial endocarditis include:
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tooth extraction
mitral valve proplapse |
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Vancomycin, a drug that interferes with assembly of peptidoglycan polymers, is most likely to inhibit which of the following organisms?
a. h.influenzae b.kingella kingae c.s.aureus d. capnocytiphaga spp |
staph aureus
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Gram positive cocci arranged in clusters belongs to the genus
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staphylococci
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A gram positive cocci that is catalase positive, coagulase negative and resistant to novobiocin is:
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s. saprophyticus
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the recommended treatment for family members of patients with meningococcal meningitis is:
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rifampin
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alcohol is a standard antiseptic used to cleanse venipuncture sites, but for blood culture collection:
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the site should be cleansed three times using alcohol and iodine or chlorhexidine
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factors that affect succesful detection of organisms in the blood include
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a. collecting 10-20ml of blood per culture
b. collect 2+ blood cultures c. use anticoagulant SPS in the broth |
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The zone of inhibition in Kirby-Baurer testing:
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depends on the size of the drug molecule and its ability to diffuse
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contamination of the blood cluture by skin commensals is called:
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pseudobacteremia
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the oorganisms most frequently recovered from blood cultures is:
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coagulase negative staphylococci
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when bacteremia is not associated with signs or symptoms, it is called:
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occult
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This species of staph is associated mainly with urinary tract infections predominantly in female adolescents and young women (very sexually active women)
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S. saprophyticus
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How does protein A contribute to the virulence of S. aureus
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it binds the Fc portion of the immunoglobulin G (IgG) therefore neutralizing the Ab and blocking phagocytosis
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primary reservoir for staphylococci is which part of the human body:
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nares
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Staph
round,smooth, white, creamy colonies on SBA after 18 to 24 hours of incubation at 35-37C exhibiting hemolytic zones and yellow pigment production |
staphylococci aureus
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Staph
small to medium sized colonies, nonhemolytic, white to gray colonies. some may be weakly hemolytic. round,smooth, white, creamy colonies on SBA after 18 to 24 hours of incubation at 35-37C |
s. epidermidis
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Staph
forms slightly larger colonies with about 50% of strains producing yellow pigment. round,smooth, white, creamy colonies on SBA after 18 to 24 hours of incubation at 35-37C |
s.saprophyticus
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Staph
medium sized colonies with moderate or weak hemoysis and variable pigment production round,smooth, white, creamy colonies on SBA after 18 to 24 hours of incubation at 35-37C |
S. haemolyticus
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Staph
often hemolytic, medium sized although small sized variants can occur. round,smooth, white, creamy colonies on SBA after 18 to 24 hours of incubation at 35-37C |
S.lugdunesis
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Staph is differentiated from micrococci by which test?
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modified oxidase test
staph is neg micrococci - positive |
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Staph aureus is differentiated from S.lugdunesis, S. intermedius, S.schleiferi by which test?
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pyrrolidonyl arylamidase (PYR)
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In what populations does S. aureus cause infection?
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associated with hospitals, nursing home patients, community populations such as pediatrics
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How does protein A contribute to the virulence of S. aureus?
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blocks phagocytosis via binding of Fc portion of IgG
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What toxin causes toxic shock syndrome?
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TSST-1
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what type of toxin is associated with scalded skin syndrome?
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exfoliative toxin
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what toxins are involved in staph food poisoning?
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enterotoxins
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in what clinical condition would CoNS be significant?
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CoNS recovered from sterile sites and indwelling devices and from immunocompromised patients
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which coagulase-neg staph is considered more significant and might need to be identified to the species level?
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s.saprophyticus is important cause of UTIS in young women. id should be made if found in urine specimens
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what are the two types of coagulase produced by S. aureus and how is each type detected in the lab?
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staphylcoagulase (free coagulase) detected by tube method
clumping factor (cell bound coagulase) detected by slide coag test or latex slide |
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How is s.aureus differentiated from other similar isolates?
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frequently separated from less pathogenic species by being coagulase positive
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what test is used to identify s. saprophyticus?
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novobiocin susceptibility test
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Yeast typically reproduce by ____ whereas molds often reproduce by _______.
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yeast- budding
mold-forming spores |
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dematiaceous fungi produce
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dark pigments
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dematophytoses are caused by
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trichophyton, microsporum, and epidermophyton species
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which fungi are often associated with systemic mycoses?
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thermally dimorphic fungi
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where are saprobic fungi most problematic
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in immunocompromised host
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the most commonly isolated yeast
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c. albicans
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important fungal pathogen of patients with AIDS
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pneumocystis sp
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infection of the cuticle surrounding the nail bed
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paronychia
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inflammatory cutaneous condition that infects skin folds, usually seen in obese or newborns. caused by Candida and often S. aureus
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Intertrigo
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scalded skin syndrome causative agent?
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s. aureus
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Erysipelas causative agent?
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s.pyogenes
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Bullous Impetigo causative agent
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S. aureus
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Non-bullous impetigo causative agent?
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S. pyogenes
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Infection of the muscle, myonecrosis such as gas gangrene is often caused by which organisms
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C.perfringens
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Caused by Erysipelothrix rhusiopathiae, occupational handling of animals. superficial soft tissue infection. Penicillin G is preferred treatment
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Erysipeloid
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caused by corynebacterium minustissimum. lesion tends to be finely scalded and wrinkled usually seen on groin, toe web and axilla.
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Erythrasma
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inflammation of hair follicle usually occurs at points of friction
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folliculitis
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skin abscess or boil that involves hair follicle and surrounding tissue.
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Furuncles
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larger than a boil, multiple drainage points
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carbuncles
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The zone of inhibition in Kirby-Bauer Testing
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a. would be smaller if depth of agar was too thin
b. would be bigger if incubation time was shorter c. depends on size of drug molecule and its ability to diffuse |
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Selective media that can be used to isolate Staphylococci include:
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mannitol salt
CNA agar PEA agar |
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About erysipeloid
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-common occupational hazard of animal handlers
-drug of choice is Penicillin G -difficult to see on gram stain but may be isolated in culture -introduced by trauma fingers and dorsum of hand are most frequent sites of infection |
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Presence of viable organism in blood determined by positive blood culture
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bacteremia
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bacteremia plus physiological signs and symptoms of bacterial invasion and toxin production
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septicemia
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contamination of blood culture from skin commensals
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pseudobacteremia
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unsuspected bacteremia associated with s. pneumo in children younger than 2 yo
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occult
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primary bacteremia
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endovascular source
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secondary bacteremia
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infected extravascular source
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systemic response to microbial infection
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sepsis
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sepsis with severe hypotension
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septic shock
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