MDR orgs like MRSA, susceptibilities, antibiotics, drug resistance, drug mechanisms

To screen for Vancomyin-Resistant Enterococci, which of the following culture sites is most appropriate to swab? A. Nasal B. Rectal C. Groin D. Throat

B

Which of the following is used to standardize the bacterial inoculum used in a disk diffusion test (Kirby-Bauer method)? A. 0.1 McFarland standard B. 0.5 McFarland standard C. 1.0 McFarland standard D. 2.0 McFarland standard

B

_______________ is predominantly associated with skin and soft tissue infections (SSTIs), such as abscesses, cellulitis, folliculitis and impetigo. A. Healthcare-associated MRSA B. Community-acquired MRSA C. Escerichia coli

B

An alpha hemolytic slightly concave isolate from a respiratory specimen gave a zone of inhibition of 18 mm around the optochin A. Report the isolate as optochin sensitive. B. Report this organism as Streptococcus pneumoniae. C. Report this organism as Viridans streptococci. D. Repeat the optochin susceptibility test.

B (>16 susc, only alpha strep that is S)

Which two antibiotics are used to confirm the presence of carbapenemase production in Enterobacteriaceae? A. Cefotaxime and Cefotaxime-clavulanate B. Ertapenem and Meropenem C. Cefoxitin and Oxacillin D. Clindamycin and Erythromycin

B (A is for ESBL, C is for mecA gene MRSA, D is for erm gene Staph and Strep)

Enterococcus spp. are commonly resistant to all of the following antimicrobial drug types EXCEPT: A. Aminoglycosides B. Phenicols C. Beta-lactams D. Glycopeptides

B (Chloramphenicol given if VRE)

For an isolate of Escherichia coli, Klebsiella, or Proteus species testing positive for ESBL (Extended Spectrum Beta Lactamases), all of the following antibiotics should be reported as resistant except: A. Aztreonam B. Cefazolin C. Cefoxitin D. Ceftriaxone

C (Cephalosporin and penicillin R including aztreonam. Cephamycins (cefoxitin and cefotetan) not reported as R)

A D-test is performed on gram positive cocci to determine inducible resistance to clindamycin when the isolate is sensitive to clindamycin and resistant to which antibiotic? A. Methicillin B. Vancomycin C. Cefoxitin D. Erythromycin

D

Illustrated in the top photograph are alpha-hemolytic, entire, gray-white convex colonies that are of a bacterial species that was found to be susceptible to vancomycin. In the lower photomicrograph, gram-positive cocci arranged in chains and in loose clusters that are not species distinctive are seen. Select the bacterial species that are uncommonly vancomycin resistant. A. Staphylococcus species B. Leuconostoc species C. Pediococcus species D. Streptococcus species

D

The area of suppressed growth surrounding a disk impregnated with an antimicrobial on a sensitivity plate is referred to as the zone of: A. Resistance B. Breakpoint C. MIC D. Inhibition

D

While many isolates of this organism remain susceptible to penicillin, resistance is increasing in some areas due to the organism's altered penicillin binding proteins. In such cases, the recommended treatment is erythromycin or chloramphenicol. Which of the following organisms does this describe? A. Enterococcus faecium B. Staphylococcus aureus C. Klebsiella pneumoniae D. Streptococcus pneumoniae

D (MRSA penicillin-R, Kleb ESBL includes penicillins and carbapenem R too, Entero concerned with vancomycin)

Each of the following organisms may possess extended-spectrum beta-lactamase (ESBL) activity except: A. Escherichia coli B. Klebsiella oxytoca C. Proteus mirabilis D. Pseudomonas aeruginosa

D (aztreonam often used to treat)

The use of molecular testing to identify the presence of Methicillin-Resistant Staphylococcus aureus (MRSA) is not always the best method because false-positive results can occur. However, the main purpose for performing molecular testing on surveillance cultures for MRSA is all of the following, EXCEPT? A. Shorter turnaround time B. High sensitivity C. Reduction of patient isolation days D. Does not require culture confirmation

D (high sens leads to FPs that do req confirmation)

A tech receives a call from the floor regarding antimicrobial therapy. The patient culture yielded an aerobic Gram-negative bacillus and the physician would like to use an antibiotic that inhibits cell wall synthesis. Which of the following antibiotics would be the best choice? A. Gentamycin B. Tetracycline C. Ciprofloxacin D. Cefazolin

D (part of cephalosporins in beta lactamases family with penicillins, gentamicin is a aminoglycoside targeting proteins, -cyclines also target proteins, -floxacins are FQs targeting DNA)

The ____ beta-lactamse (not an ESBL) found in Klebsiella _______, is primarily a penicillinase that also hydroloyzes aztreonam, cefuroxime, and ceftriaxone.

K-1, oxytoca

An 87-year old patient had a foot wound that grew gram-negative rods on McConkey agar as pink to dark pink oxidase-negative colonies along with the following results: TSI: A/AIndole: neg.MR: neg.VP: pos.Citrate: pos.H2S: neg.Urea: pos.Motility: neg.Ornithine: neg.Antibiotic susceptibility: Carboxicillin and ampicillin resistant, all others sensitive.

K. pneumo

The susceptibility of a bacterium to each drug on a sensitivity plate using antibiotic disks is demonstrated by the diameter of the zone of: A. Inhibition B. Resistance

A

A patient was screened for possible methicillin resistant staphylococcus aureus (MRSA) by culturing the nares of the patient. All of the following media can be used to screen for MRSA EXCEPT? A. Columbia agar B. Oxacillin screen agar C. MRSA CHROMagar D. MRSA screen agar

A

Bacitracin susceptibility testing is useful for: A. Distinguishing staphylococci from micrococci B. Presumptive identification of Group B streptococci C. Identification of Haemophilus spp. D. Identification of Neisseria spp.

A

Cultures from a post-abdominal cellulitis specimen grew Gram negative pleomorphic rods with the following characteristics: Grows on KV agar but does not show fluorescence Produces black colonies BBE agar Resistant to penicillin Which of the following is the MOST likely identification? A. Bacteroides fragilis B. Fusobacterium nucleatum C. Prevotella species D. Veillonella species

A (BBE selective for it)

Unknown species inoculated with NB, FX, A disks. It has a large zone of inhibition around NB and small one around A. It is furazolidone-R. A. Micrococcus luteus B. Staphylococcus saprophyticus C. Streptococcus pyogenes D. Staphylococcus epidermidis

A (Staph like epi S to FX, Micrococcus R)

A tech receives a request for MRSA/MSSA colonization testing on a patient in the hospital. Which of the following is an appropriate area of the body for culture for screening? A. Anterior nares B. Stool C. Urine D. Sputum

A (carriers have in groin, axilla and ear as well)

Enterococcus faecium is: A. Often vancomycin resistant B. Susceptible to the aminoglycosides C. Arabinose negative D. Motile

A (faecium tends to be amp and vanco R more frequently than faecalis)

A tech receives a call from the floor regarding antimicrobial therapy. The patient culture yielded an aerobic Gram-negative bacillus and the physician would like to use an antibiotic that inhibits DNA synthesis. Which of the following antibiotics would be the best choice? A. Ciprofloxacin B. Cefazolin (Cephalosporin) C. Tetracycline D. Gentamycin (Aminoglycoside)

A (fluoroquinolone, tetra=30S protein translation, same for amino genta)

A patient is being treated with gentamicin for a Gram negative bacterial infection. The chemistry department has repeating peak and trough orders on the patient. Which of the following antibiotic classes does gentamicin belong? A. Aminoglycosides B. Beta-lactams C. Fluoroquinolones D. Polymyxins

A (inhibits protein 30s, also includes tobramycin, amikacin, streptomycin, and kanamycin, FQs DNA synth inhibited, ciprofloxacin, levofloxacin, and ofloxacin. PM=CM disrupted, GN only)

Many organisms have developed resistance to antibiotics. What mode of resistance has MRSA acquired? A. Acquisition of new targets B. Enzymatic inactivation of antibiotics C. Efflux D. Target site modification

A (new genes reduces affinity for b-lactams allowing for new targets, resisting methicillin.)

A small, microaerophilic, curved, gram-negative rod which was isolated from a diarrhea stool specimen gave the following results: Grew best at 42 ºC Oxidase positive Resistant to cephalosporin Susceptible to nalidixic acid Hippurate hydrolysis positive What is the MOST probable identification of this organism? A. Campylobacter jejuni B. Campylobacter coli C. Salmonella species D. Vibrio cholera

A (only jejuni HIP+)

Sulfonamides, such as sulfamethoxazole (SMZ), and trimethoprim (TMP), work by targeting: A. Penicillin-binding proteins; disrupting bacterial cell wall synthesis B. Tetrahydrofolate synthesis; preventing bacterial DNA synthesis C. 30S ribosomal subunits; inhibiting bacterial protein translation D. 50S ribosomal subunits; inhibiting bacterial protein translation

B (DNA synthesis inhibitors which disrupt the folic acid pathway)

E. coli and K. pneumo mode of resistance A. Acquisition of new targets B. Enzymatic inactivation of antibiotics C. Efflux D. Target site modification

B (b-lactamase)

Penicillin, ampicillin, carbenicillin, and methicillin are antimicrobial agents whose MAIN biological function is to: A. Induce abnormal protein synthesis by targeting ribosomal subunits B. Inhibit cell wall synthesis C. Deteriorate the cell membrane D. Inhibit DNA synthesis

B (bind to PBPs in CWS, A is macrolides aminoglycosides tetracyclines, C is lipopeptides polymyxin B, D is fluorquinolones sulfonamides)

Carbapenemases are produced by various organisms such as Enterobacteriaceae, Pseudomonas aeruginosa, and Acinetobacter species. Detecting the presence of carbapenemase activity in these organisms is important to prevent spreading of the resistant organisms. Which of the following methods is used to detect the presence of carbapenemase producing organisms? A. D test B. Modified Hodge Test C. ESBL Test D. Beta-lactamase test

B (clover leaf test)

Which of the following antibiotics inhibits protein synthesis by binding to the 30S ribosomal subunits and provides coverage against Gram positive and Gram negative aerobes? A. Beta-lactams B. Aminoglycosides C. Fluoroquinolones D. Polymyxins

B (gentamicin, tobramycin, amikacin, streptomycin, and kanamycin. FQs = DNA binds to gyrase, PM=CM GN only)

VRE screening culture media

BEA w/ vancomycin

A D-test is performed to determine if Staphylococcus aureus or Streptococcus agalactiae has an inducible resistance to clindamycin. This inducible resistance is due to which of the following mechanisms? A. vanC gene B. msrA gene C. erm gene D. mecA gen

C

A methicillin-resistant Staphylococcus aureus was recovered from a wound infection. Which antibiotic would be used for treatment? A. Methicillin B. Nafcillin C. Vancomycin D. Oxacillin

C

Assume you perform microbiology for an institution submitting surveillance cultures for MRSA. Which isolate should receive further workup to rule out methicillin (oxacillin) resistance? A. On Baird Parker agar, a gray brownish colony with no clear zone. Gram-positive cocci in clusters, catalase positive. B. Black colonies on Chromagar. Catalase-positive, Gram-positive cocci in clusters. C. Yellow colonies on Mannitol Salt agar; catalase-positive, coagulase-positive. D. Clear colonies on Mannitol Salt agar; catalase-positive, coagulase-negative.

C

The following statement is true regarding hospital-associated methicillin-resistant Staphylococcus aureus (HA-MRSA) and community-associated MRSA (CA-MRSA)? A. Resistance is conferred by the mecA gene for only the HA strains. B. CA strains tend to demonstrate resistance to more drug classes than HA strains. C. CA strains tend to be associated with the PVL gene and skin and soft tissue infections. D. HA Strains are typically more susceptible to the non-beta-lactam antibiotics.

C

The organisms Klebsiella pneumonia, Enterobacter cloacae, and Escherichia coli can produce carbapenemases due to which of the following genes? A. mec A B. van A C. blaKPC D. erm

C

Which of the following scenarios represents appropriate detection of MRSA by the Kirby Bauer method? A. Mueller-Hinton agar (MHA); direct colony suspension; 37oC; cefoxitin disk; 36 hour incubation B. MHA; direct colony suspension; 35oC; oxacillin disk; 18 hour incubation C. MHA; direct colony suspension; 35oC; cefoxitin disk; 18 hour incubation D. MHA; direct colony suspension; 35oC; cefoxitin disk; 24 hour incubation

C (30 µg cefoxitin disk is recommended to detect mecA mediated resistance, better inducer than ox, must not be 37+C, Oxacillin only rec for 24 hrs with MIC not disk diffusion testing)

Fluoroquinolones, such as ciprofloxacin, work by targeting: A. Penicillin-binding proteins; disrupting bacterial cell wall synthesis B. Tetrahydrofolate synthesis; preventing bacterial DNA synthesis C. Topoisomerases, inhibiting bacterial DNA replication D. 50S ribosomal subunits, inhibiting bacterial protein translation

C (b-lactams are A, Sulfonamides disrupt folic acid pathway and DNA synthesis B, Macrolides bind to 50s D to inhibit proteins)

Streptococcus sp. may use this mechanism. S. pneumo also uses the additional mechanism of: A. Acquisition of new targets B. Enzymatic inactivation of antibiotics C. Efflux D. Target site modification

C (efflux pump moves antibiotics out of cell), D (S. pneumo modifies penicillin binding proteins so antibiotics can't bind to them)

Minimum inhibitory concentration (MIC) susceptibility tests should be performed against other beta lactam antibiotics for Streptococcus pneumoniae isolates from blood cultures and other sterile body fluids. The reason for this is due to an emerging resistance against penicillin and other beta lactam antibiotics. However, there is one antibiotic that is used to treat drug resistant Streptococcus pneumonia infections and MIC results should be questioned when a resistant susceptibility is found. Which of the following antibiotics does Streptococcus pneumonia still remain sensitive? A. Cefotaxime B. Ceftriaxone C. Vancomycin D. Tetracycline

C (last resort for S. pneumo, R to other 3 listed)

The mechanism by which certain strains of Enterococcus species have developed resistance to the synergistic combination of an aminoglycoside and beta-lactam antibiotics is considered: A. Alteration of penicillin binding proteins B. Beta lactamase activity against the beta-lactam moiety C. High level gentamicin resistance D. Efflux of antibiotics from the bacterial cell

C (normally R to aminoglyc, penicillin makes CW impermeable to help it cross. So it alters the binding sites so even IC aminoglycosides ineffective. A is S. pneumo)

Only Corynebacterium resistant to penicillin.

C. ureolyticum

Beta-lactam antibiotics act to inhibit the formation of ____. Aminoglycosides, Tetracyclines, Macrolides, Streptogramins and Phenicols inhibit _____ synthesis. Fluoroquinolones and Trimethoprim-sulfamethoxazole inhibit _____ synthesis. Rifamycins inhibit ____ synthesis.

CWs, protein, DNA, RNA

D test detects inducible _____ R due to erm gene. It makes a D with the flat side facing the ____ disk

Clindamycin, E (erythromycin)

A tech receives a call from the floor regarding antimicrobial therapy. The patient culture yielded an aerobic Gram-positive coccus and the physician would like to use an antibiotic that inhibits RNA synthesis. Which of the following antibiotics would be the best choice? A. Ciprofloxacin B. Ceftazidime C. Vancomycin D. Rifampin

D (rifamycins inhibit RNA polymerase affecting transcription and thus RNA synthesis)

A tech receives a call from the floor regarding antimicrobial therapy. The patient culture yielded an aerobic Gram-negative bacillus and the physician would like to use an antibiotic that inhibits protein translation. Which of the following antibiotics would be the best choice? A. Vancomycin B. Levofloxacin C. Daptomycin D. Tetracycline

D (the -cyclines, vanco and dapto is only GP CWs, FQs = -floxacins, target DNA)

Beta-lactam antibiotics interfere with cell wall synthesis by all of the following, EXCEPT: A. Binding with a transpeptidase enzyme B. Preventing the final stage of peptidoglycan synthesis C. Interfering with PBPs D. Targeting the 30S ribosomal subunit

D (this is aminoglycosides and tetracyclines that inhibit 30s ribosomal subunit to inhibit protein synthesis)

To screen for the Methicillin-Resistant Staphylococcus aureus, all of the following collection sites are appropriate EXCEPT? A. Nasal B. Rectal C. Groin D. Eye

D (usu on skin)

Gene is used to detect vancomycin resistant isolates of enterococci (VRE)

Van A

VISA or VRSA

Vancomycin Intermediate or Resistant Staphylococcus

This gene codes for inducible clindamycin resistance in Staphylococcus and Streptococcus species.

erm

Oxacillin resistance in clinical strains of staphylococci is confirmed by the detection of _______ gene.

mecA

______ gene offers resistance to macrolides in Streptococcus pneumonia and other viridans streptococi.

mefA

Strep pneumo oxacillin disk >20 mm, report as

oxacillin-S