ANTIMICROBIAL

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.

Klebsiella pneumonia

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?

Rifampin

The upper photomicrograph illustrates a Gram stain of sputum obtained from a 55-year-old man with symptoms of bacterial pneumonia. The lower photograph represents the growth of an inoculum from the specimen on 5% sheep blood agar, on which had been placed an optochin ("P") and a 1 µg oxacillin disk. After 18 hours incubation at 37°C in 5% CO2, the zone around the optochin disk is 18 mm and around the OX disk is 8 mm. The interpretation is that the organism is most likely:

A pneumococcus, penicillin resistant

With regards to identifying resistance in Enterococcus species, all of the statements below are true, EXCEPT:

All antibiotics on a gram-positive panel should be reported.

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?

Aminoglycosides

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?

Aminoglycosides

Most infections caused by Streptococcus anginosus can be treated with any of the following antibiotics, EXCEPT:

Aztreonam

Group A beta-hemolytic streptococci are best characterized by which of the following:

Bacitracin sensitivity

Cultures from a post-abdominal cellulitis specimen grew Gram negative pleomorphic rods with the following characteristics: Grows on KV agar but does not show fluorescenceProduces black colonies BBE agarResistant to penicillin Which of the following is the MOST likely identification?

Bacteroides fragilis

An abdominal wound culture grows E. coli on the aerobic culture. The anaerobic culture has growth of two, gram- negative rods, one of which is aerobic. The other gram negative rod has 2+ growth on BBE plate and is resistant to kanamycin, colistin, and vancomycin disc. What is this organism's identification?

Bacteroides fragilis group

Which of the following enzymes, produced by Staphylococcus aureus is responsible for preventing penicillin antibiotics from being effective?

Beta-lactamase

A small, microaerophilic, curved, gram-negative rod which was isolated from a diarrhea stool specimen gave the following results: Grew best at 42 ºCOxidase positiveResistant to cephalosporinSusceptible to nalidixic acidHippurate hydrolysis positive What is the MOST probable identification of this organism?

Campylobacter jejuni

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?

Cefazolin

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:

Cefoxitin

This isolate, identified as an Enterobacter cloacae, was recovered from the urine and blood cultures of a patient who had recently returned from India where he had received a total hip replacement. He presented to the ED with multiple decubiti, sinusitis and a urinary tract infection. The Hodge Test that was performed on this organism was negative. What resistance mechanism may be identified from the KB plate and the susceptibility interpretations?

Chromosomal AmpC plus Porin Mutation

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?

Ciprofloxacin

The disease most commonly associated with the novobiocin-resistant staphylococcus illustrated in this photograph is:

Community-acquired urinary tract infection

The image shows an antimicrobial susceptibility result for a Corynebacterium species on a 5% sheep blood agar plate. The zone around the 10 µg penicillin disk rules out:

Corynebacterium ureolyticum

Which one of the following organisms is sensitive to bacitracin:

Group A Streptococcus

Illustrated in this photograph is the surface of a MacConkey agar plate growing colonies of a non-fermentative Gram negative bacillus recovered from a wound specimen. The iridescent light pink colonies suggest Acinetobacter species. Each of the following characteristics are helpful in supporting this identification EXCEPT:

Denitrification of nitrates

Bacitracin susceptibility testing is useful for:

Distinguishing staphylococci from micrococci

The Carba NP confirmatory test is used to detect all of the following carbapenemases EXCEPT?

ESBL (Extended Spectrum Beta-Lactamase)

Enterobacter cloacae colonies were isolated from a blood culture taken from a 45-year-old woman undergoing chemotherapy for breast cancer. Observe this Kirby-Bauer susceptibility plate and the result report form for this organism. From the multiple choices, identify the resistance mechanism (if any) that this organism demonstrates.

ESBL- Extended-Spectrum Beta Lactamase with Amp C expression

Which two antibiotics are used to confirm the presence of carbapenemase production in Enterobacteriaceae?

Ertapenem and Meropenem

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?

Erythromycin

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:

High level gentamicin resistance

Penicillin G, ampicillin, carbenicillin, and methicillin are antimicrobial agents whose MAIN biological function is to:

Inhibit cell wall synthesis

Illustrated in this photograph is an agar plate on which an unknown species has been inoculated. A 5 µg novobiocin disk (NB), a 100 µg furazolidone disk (FX), and a 0.04 µg bacitracin (A) disk had been applied immediately after inoculation of the plate. Based on the pattern of the zones of inhibition to these three antibiotics, the most likely identification is

Micrococcus luteus

MIC is an acronym for:

Minimum inhibitory concentration

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?

Modified Hodge Test

Enterococcus spp. are commonly resistant to all of the following antimicrobial drug types EXCEPT:

Phenicols

Which of the following media is commonly used when performing the Kirby-Bauer disk diffusion?

Mueller-Hinton agar

An 85-year-old female nursing home patient was treated empirically with a cephalosporin for a urinary tract infection, but later failed therapy. The physician then requested a culture and sensitivity on a new urine specimen which grew >100,000 CFU/mL of Escherichia coli. After reviewing the Kirby-Bauer disc susceptibility plate and susceptibility interpretations, what is the resistance mechanism (if any) for this organism?

Plasmid-mediated AmpC

The following is true of the disk diffusion method of measuring antimicrobial sensitivity:

Provides only an interpretation value of sensitive, intermediate, or resistant correlated to MIC values

Enterococcus faecium is:

Often vancomycin resistant

Oxacillin resistance of MRSA is due to production of which of the following penicillin binding proteins (PBPs)?

PBP2a

Each of the following organisms may possess extended-spectrum beta-lactamase (ESBL) activity except:

Pseudomonas aeruginosa

On a plate growing Streptococcus pneumoniae, the zone of inhibition around the disk shown in the image has been measured at 23 mm. Based on this result, you should:

Report oxacillin-susceptible

Examine the following test results and identify what action you would take. CAMP: Arrowhead appearance Bacitracin disk: 6mm zone of inhibition PYR: Negative Bile Esculin: Tan appearance, no darkening

Report the isolate as Streptococcus agalactiae

This Gram-positive coccus is catalase positive. The tests shown are a tube coagulase test inoculated with the isolate, and a MRSA screen plate containing 4% NaCl and 6 µg/mL of oxacillin. A 0.5 McFarland standardized inoculum of the isolate is inoculated to the plate. What step should you take next?

Report the isolate as methicillin resistant Staphylococcus aureus

An alpha hemolytic slightly concave isolate from a respiratory specimen gave a zone of inhibition of 18 mm around the optochin disk. What should the next step be?

Report this organism as Streptococcus pneumoniae.

All of the following organisms are known to be resistant to vancomycin EXCEPT?

Rhodococcus equii

The McFarland Comparison Card shown in the illustration is used to:

Standardize concentrations of organisms

Based on the results below, what is the most likely organism? Gram stain: Positive cocci Catalase: Positive Coagulase: Negative Bacitracin susceptibility: Resistant Novobiocin susceptibility: Resistant

Staphylococcus saprophyticus

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

Streptococcus species

Beta-lactam antibiotics interfere with cell wall synthesis by all of the following, EXCEPT:

Targeting the 30S ribosomal subunit

Fluoroquinolones, such as ciprofloxacin, work by targeting:

Topoisomerases, inhibiting bacterial DNA replication

A methicillin-resistant Staphylococcus aureus was recovered from a wound infection. Which antibiotic would be used for treatment?

Vancomycin

The photograph on the right illustrates the Rosco Diagnostica IMI/EDTA disk test and the bioMerieux MBL E test. Both tests are used to detect metallo beta-lactamse production. After viewing the results of these tests, does this organism produce metallo-beta-lactamase?

Yes

The organisms Klebsiella pneumonia, Enterobacter cloacae, and Escherichia coli can produce carbapenemases due to which of the following genes?

blaKPC

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?

erm gene

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

mecA

Isolates of nonmotile and nonpigmented enterococci that are resistant to vancomycin can be assumed to have an acquired resistance by the transfer of which of the following genes?

van A and van B genes

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 desribe?

Streptococcus pneumoniae

Which of the following is used to standardize the bacterial inoculum used in a disk diffusion test (Kirby-Bauer method)?

0.5 McFarland standard

Which of the following statements is true about the emergence of penicillin-resistant strains of Streptococcus pneumoniae?

A zone size of = 20 mm with the oxacillin disk screen must be confirmed with an MIC method to determine if Penicillin is susceptible or resistant.

The area of suppressed growth surrounding a disk impregnated with an antimicrobial on a sensitivity plate is referred to as the zone of:

Inhibition

Which of these describes the mode of action of the beta-lactam class of antibiotics?

Inhibits cell wall synthesis

In this image is a quadrant plate containing brain heart infusion agar supplemented with 6 µg/mL of vancomycin. The right upper quadrant was inoculated with the test strain of Enterococcus faecium. The presence of growth in the inoculated quadrant indicates ___________?

The organism is resistant to vancomycin

Which of the following statements concerning vancomycin resistance in Enterococci is TRUE?

Both ampicillin and vancomycin resistance are found more frequently in E. faecium than in E. faecalis.

A patient grew out a Staphylococcus lugdunensis and after susceptibility testing, the isolate gave results indicating probable resistance to oxacillin. Which of the following is the best method to detect the mec-A gene to determine if the organism has true oxacillin resistance?

Cefoxitin disk diffusion

Which one of these Gram-positive species has a high incidence of vancomycin-resistance?

Enterococcus faecium

The images represent a gram-positive, catalase-negative, non-motile coccus inoculated to bile esculin agar as seen in the top image. The organism grows in 6.5% NaCl broth and the reaction on 6 µg/mL of vancomycin in Mueller Hinton agar is shown in the bottom image. The organism should be reported as:

Enterococcus spp., Resistant to vancomycin

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

Inhibition

This organism, identified as a Klebsiella oxytoca, was recovered from the blood of an elderly patient with an infected anal fissure . The Vitek identified this organism as an ESBL. After reviewing the Kirby-Bauer plate and susceptibility interpretations, what is the resistance mechanism demonstrated by this organism?

K-1 beta-lactamase

A 65 y/o male with type 2 diabetes presented to ED complaining of febrile episodes following his last dialysis treatment. The microscopic examination of his urine showed numerous white blood cells and bacteria. His urine was sent to the laboratory for culture and sensitivity. Urine colony count was >100,000 CFU/mL for a single organism that was identified as Klebsiella pneumoniae. Observe the reactions of this organism on the Kirby Bauer antibiotic susceptibility plate and review the susceptibility results on the AST report form. The Hodge Test was positive. Which resistance mechanism is this organism demonstrating?

KPC - Klebsiella pneumoniae Carbapenemase

The top image shows a MacConkey agar plate on which mucoid, lactose fermenting colonies are present. The bottom image is the bacterial isolate streaked on the surface of a Mueller-Hinton agar plate. The disk to the left is ceftazadime, and the disk to the right is a combination of ceftazadime + clavulanic acid. Note the larger zone of inhibition around the combination disk on the right, an indicator for extended spectrum beta lactamase (ESBL) activity. Which of the following organisms fits this situation?

Klebsiella pneumoniae

Based on the results of in-vitro susceptibility testing, patients with septicemia from each of the bacterial species listed below can potentially be treated with vancomycin EXCEPT:

Leuconostoc species

This is a catalase-positive, coagulase-negative, gram-positive coccus isolated from a urine specimen from a 20-year-old female college student. The image shown is a Mueller Hinton plate streaked with a 0.5 MacFarland standardized inoculum and a 5 microgram disk of novobiocin after overnight incubation. What is the identification of the isolate?

Staphylococcus saprophyticus

The optochin (ethylhydrocupreine hydrochloride) disk is most often used for the identification of which organism?

Streptococcus pneumoniae

This isolate is a catalase negative, gram positive coccus on sheep blood agar. The P disk has 5µg of optochin and the zone around it is 16 mm. It has been streaked perpendicular to a beta-lysin producting strain of Staphylococcus aureus. The presumptive identification is:

Streptococcus pneumoniae

This image shows a gram-positive, catalase negative coccus on sheep blood agar (beta-hemolytic). Please note the reactions with bacitracin (A) and trimethoprim sulfamethoxazole (SXT) disks seen on the right side of the agar plate. On the left side of the agar, a beta lysin-producing Staphylococcus aureus is streaked perpendicular to the unknown organism. What is the presumptive identification of this organism?

Streptococcus pyogenes

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?

Tetracycline

Sulfonamides, such as sulfamethoxazole (SMZ), and trimethoprim (TMP), work by targeting:

Tetrahydrofolate synthesis; preventing bacterial DNA synthesis

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?

Vancomycin