Microbiology Final Exam Study Guide
The β-lactams consist of all the following antibiotics EXCEPT: Vancomycin Penicillins Cephalosporins Carbapenems
Vancomycin
The tendency for the mycobacterial cells of M. tuberculosis to assemble in linear aggregates as seen in this photomicrograph of an acid-fast stained preparation is caused by production of: A. Lysozyme B. Niacin C. Cording factor D. Oleic acid
C. Cording factor
The Chinese transcription shown here is most consistent with the cell morphology of: A. Bacillus cereus B. Rothia dentocariosa C. Corynebacterium diphtheriae D. Actinomyces meyeri
C. Corynebacterium diphtheriae
This type of resistance mechanism modifies the antibiotic targets and results in reduced affinity of antibiotics for their microbial targets. Cell-wall inhibition Protein synthesis modification Enzyme alteration Frameshift mutation
Enzyme alteration
Efflux pumps: Allow nutrients into the cells through specialized channels in the bacteria's outer membrane Allow electrolytes into the cells through specialized channels in the bacteria's outer membrane Act as a semipermeable membrane and maintain the cell's osmotic pressure Function as transporter proteins involved in the removal of toxic substances from the interior of the cell to the external environment
Function as transporter proteins involved in the removal of toxic substances from the interior of the cell to the external environment
The outer membrane of gram-negative bacteria is composed of: Lipopolysaccharides, phospholipids, and porin proteins Peptidoglycan, phospholipids, and proteins Enzymes, cholesterol, and carbohydrates Carbohydrates, peptidoglycan, and proteins
Lipopolysaccharides, phospholipids, and porin proteins
Biofilms are groups of bacteria that are irreversibly attached to a solid and embedded in a matrix of extracellular polymeric substances. They are commonly found on: Organic heart valves Dialysis shunts Indwelling medical devices Patient beds
Indwelling medical devices
Intrinsic mechanisms of resistance are: Those that inhibit protein synthesis and RNA transcription Those that a bacterium acquires through plasmids Also called inducible enzymes Innate characteristics of the bacterium and transmitted to progeny vertically
Innate characteristics of the bacterium and transmitted to progeny vertically
Streptococcus pneumoniae and Streptococcus pyogenes use efflux as an effective mechanism for acquired resistance to: Macrolides Peptidoglycans Aminoglycosides Quinolones
Macrolides
These two classes of antibiotics allow initiation and mRNA translation to begin, but they act by inhibiting peptide elongation. Aminoglycosides and glycopeptidians Aminoglycosides and quinolones Macrolides and tetracyclines Macrolides and quinolones
Macrolides and tetracyclines
Integrons are: Circular structures present in bacteria that contain genes encoding proteins and RNA and have the capacity to self-replicate and portion into daughter cells during cellular division DNA elements that encode transposition and excision function and can transpose from one place on the chromosome to another. Genetic elements capable of integrating resistance genes (cassettes) by an integron-encoded, site-specific recombinase DNA elements found in bacteria that carry genes only for the enzymes needed to promote their own transposition
Genetic elements capable of integrating resistance genes (cassettes) by an integron-encoded, site-specific recombinase
All of the following are recently approved classes of antibiotics that target protein synthesis EXCEPT: Sixth generation cephalosporins Oxazolidinones Streptogramin Glycylcycline
Sixth generation cephalosporins
A young, healthy patient goes into the hospital for reconstructive knee surgery and spikes a fever the day after surgery. The doctor finds the patient has a nosocomial infection with methicillin-resistant Staphylococcus aureus (MRSA). What antibiotic should the doctor use to treat this patient? Penicillin Aminoglycosides Macrolides Vancomycin
Vancomycin
The anaerobe shown in this photograph growing on the surface of the blood agar plate, the toxins of which cause a form of necrotizing enteritis known as Darmbrand ("fire bowels") in Germany or "Pig bel" in New Guinea, is: A. Bacillus cereus B. Fusobacterium mortiferum C. Clostridium perfringens D. Bacteroides distasonis
C. Clostridium perfringens
The tube to the left is a slant of esculin medium, the tube to the right contains heart infusion broth with 6.5% sodium chloride. The bacterial species characteristically producing the positive reactions seen in each of these tubes is most likely: A. Staphylococcus aureus B. Streptococcus bovis C. Enterococcus faecalis D. Listeria monocytogenes
C. Enterococcus faecalis
The colonies growing on blood agar (upper image) were recovered from a sinus aspirate from a patient with acute sinusitis. The large, Staphylococcus colonies are obvious; however, note the satellite growth of small colonies. Small, gram-negative coccobacilli are observed in gram stains. The pattern of bacterial growth around the X and V filter paper strips in the image confirms these satellite colonies are Factor X and V dependent. From the list of multiple choices, select the name of this isolate. A. Pasteurella multocida B. Haemophilus parainfluenzae C. Haemophilus inluenzae D. Aggregabacterium (Haemophilus) aphrophilus
C. Haemophilus inluenzae
My home is in the stomach coat, Urea serves as my anecdote. A. Bordetella parapertussis B. Campylobacter jejuni C. Helicobacter pylori D. Staphylococcus intermedius
C. Helicobacter pylori
The tiny, gray-white, non-hemolytic colonies growing on blood agar are non-descript. The gram-stain reveals elongated, rectangular gram-positive bacilli in short chains. Key to the identification would be the lack of biochemical activity as seen on an inoculated API strip or other identification assays. This bacterium is usually recovered as a genital tract commensal, but has also been found to provide protection against other infective bacteria. With these observations, select from the multiple choices the identification of this isolate. A. Bacillus cereus B. Oerskovia xanthineolytica C. Lactobacillus species D. Actinomyces neuii
C. Lactobacillus species
Buffered charcoal yeast extract agar (BCYE) is the nonselective solid culture medium used for the primary recovery of: A. Treponema pallidum B. Mycoplasma pneumoniae C. Legionella pneumophila D. Spirillum minor
C. Legionella pneumophila
A human spirochetal disease associated with contact with rats is: A. Lyme disease B. Relapsing fever C. Leptospirosis D. Syphilis
C. Leptospirosis
Each of the following tests is helpful in the species identification of Staphylococcus aureus, EXCEPT: A. Thermostable endonuclease B. Deoxyribonuclease C. Modified dimethyl sulfoxide (DMSO) test D. Tube coagulase test
C. Modified dimethyl sulfoxide (DMSO) test
The 48-hour growth of small pinpoint gray-white, smooth colonies on chocolate agar (right plate) are commonly recovered as normal upper respiratory flora but may cause otitis media and sinusitis. There was no growth on Thayer Martin media (left plate). Growth on MacConkey agar is poor or absent. Short, plump, gram negative cocci lying singly and in loose clusters are seen in Gram stain, as illustrated in the lower photomicrograph. This non-fermenter is non-motile, oxidase positive, and does not utilize carbohydrates (assacharolytic). Nitrates are reduced and DNAse is positive. From these observations, select from the multiple choices the presumptive identification of this isolate. A. Burkholderia cepacia B. Alcaligenes faecalis C. Moraxella lacunata D. Acinetobacter baumannii
C. Moraxella lacunata
Small, gray-white colonies, as observed growing on 7-H10 agar to the left in the upper composite photograph, were recovered from on upper respiratory specimen after 7 days incubation. This Mycobacterium species in the past was uncommonly recovered from human infections until the advent of AIDS when it became an agent of pulmonary and other infections. Notably, colony isolates from patients with AIDS have developed a pale-yellow pigmentation that does not intensify with light exposure (right image in upper composite photograph). The acid-fast bacilli as observed in the lower photomicrograph are short and lie singly or in loose clusters. From these observations select from the multiple choices the presumptive identification of this isolate. A. Mycobacterium marinum B. Mycobacterium tuberculosis C. Mycobacterium avium/intracellulare D. Mycobacterium kansasii
C. Mycobacterium avium/intracellulare
The small beta hemolytic bacterial colonies growing on blood agar as shown in the upper photograph were recovered from an induced sputum specimen from a young child with pneumonia. The colonies were slow growing, small, entire and show soft beta hemolysis. Short pump, gram-negative coccobacilli, lying singly, in pairs and short chains, are seen on gram stain as illustrated in the lower photomicrograph. Most strains are chemically non-reactive except for a positive oxidase reaction and acid produced from dextrose and maltose. From these observations, select from the multiple choices the name at the isolate as presented in this exercise. A. Capnocytophaga species B. Cardiobacterium hominis C. Eikenella corrodens D. Kingella kingae
D. Kingella kingae
The distinctly large, spreading mucoid colonies seen on blood agar in the upper left image, and the display of lactose fermentation on MacConkey agar in the upper right image provide for a presumptive identification. This species is most commonly recovered from respiratory specimens of patients with pneumonia. Observing a weak reaction for urea, and strong reactions for citrate and Voges Proskauer confirm the presumptive identification. From the multiple choices, select the name of the isolate presented in this exercise. A. Proteus mirabilis B. Edwadsiella tarda C. Citrobacter freundii D. Klebsiella pneumoniae
D. Klebsiella pneumoniae
Insertion sequences are: Circular structures present in bacteria that contain genes encoding proteins and RNA and the capacity to self-replicate and portion into daughter cells during cellular division DNA elements that encode transposition and excision function and can transpose from one place on the chromosome to another Genetic elements capable of integrating resistance genes (cassettes) by an integron-encoded, site-specific recombinase DNA elements found in bacteria that carry genes only for the enzymes needed to promote their own transposition
DNA elements found in bacteria that carry genes only for the enzymes needed to promote their own transposition
Transposons are: Circular structures present in bacteria that contain genes encoding proteins and RNA and have the capacity to self-replicate and portion into daughter cells during cellular division DNA elements that encode transposition and excision function and can transpose from one place on the chromosome to another Genetic elements capable of integrating resistance genes (cassettes) by an integron-encoded, site-specific recombinase DNA elements found in bacteria that carry genes only for the enzymes needed to promote their own transposition
DNA elements that encode transposition and excision function and can transpose from one place on the chromosome to another
In gram-positive bacteria, this is substantially thicker and more multilayered than in gram-negative bacteria. Lipopolysaccharide Phospholipid Peptidoglycan Cholesterol
Peptidoglycan
Penicillins, cephalosporins, monobactams, and carbapenems all have this ring in their structure that is responsible for inhibiting the transpeptidation reaction, resulting in bacterial lysis and cell death. Benzene β-Lactam α-Lactam Δ-cephems
β-Lactam
β-Lactamases hydrolyze β-lactam antibiotics using two distinct mechanisms: those having a metallo-based mechanism of action and those with: Ring-specific enzymes A serine-based mechanism of action A chromosomal mechanism of action A transporter mechanism of action
A serine-based mechanism of action
Which of the following is a presumptive test for the identification of Lancefield group A Streptococcus: A. Bacitracin susceptibility B. Positive coagulase C. Hippurate hydrolysis D. Gram stain
A. Bacitracin susceptibility
An eleven-year old boy developed signs and symptoms of acute appendicitis. At surgery, the appendix was found to be ruptured and encased in a 3 cm in diameter abscess. Aspiration material was inoculated to an anaerobic blood agar plate. Small, gray, nonhemolytic, semi-opaque colonies grew anaerobically in 36 hours. The upper photograph illustrates the gram stain features of the organism; the lower photograph is a Presumpto plate indicating the biochemical reactions (reading clockwise from the 12 o'clock quadrant): growth in 20% bile agar, indole negative, esculin hydrolysis positive and lecithinase negative. The bacterial species most likely associated with the abscess is: A. Bacteroides fragilis B. Fusobacterium nucleatum C. Porphyromonas asaccharolytica D. Prevotella intermedia
A. Bacteroides fragilis
Although an uncommon isolate in most microbiology laboratories, this bacterial species is included in the microbiota of the mouth and intestinal tract. The colonies on blood agar are irregular in size, smooth, non-hemolytic, entire, convex, ranging from gray-white to light yellow. Distinctive is the "dog bone" appearance of branching gram-positive bacilli as illustrated in this photomicrograph of a gram stain. Biochemical activity is limited to fermentation of glucose and lactose. With these observations, select from the multiple choices the presumptive identification A. Bifidobacterium species B. Propionibacterium acnes C. Actinomyces israelii D. Clostridium septicum
A. Bifidobacterium species
In the gold rush days of yore, Rice water stools at death's door. A. Cholera B. Typhoid fever C. Shigellosis D. Campylobacterosis
A. Cholera
Observed growing on the surface of a blood and MacConkey agar as shown in the upper photograph are large, smooth, entire colonies after 24 hours incubation. The colonies growing on blood agar are yellow-white; those on MacConkey agar are light pink to red, with reddish pigment extending into the agar, better seen in the lower close-in image. A positive acid/acid reaction with gas on Kligler Iron Agar (not shown) and the detection of indole identify this isolate as the most common member of the Enterobacteriaceae recovered in clinical microbiology laboratories. From the multiple choices, select the name of this isolate. A. Escherichia coli B. Shigella sonnei C. Edwardsiella tarda D. Klebsiella pneumoniae
A. Escherichia coli
Which one of the following organisms is sensitive to bacitracin: A. Group A Streptococcus B. Group B Streptococcus C. Group D Streptococcus D. Staphylococci
A. Group A Streptococcus
Which organism is a cell wall deficient bacterium that commonly causes atypical or "walking pneumonia?" A. Mycoplasma pneumoniae B. Pneumocystis carinii C. Mycobacterium xenopi D. Bifidobacterium dentium
A. Mycoplasma pneumoniae
Acquired antibiotic resistance mechanisms include: Efflux Acquisition of new targets Modification of existing antibiotic targets All of the above
All of the above
Resistance to aminoglycosides is mediated by: Efflux Changes in the target site Impermeability or by enzymatic modification of amino and hydroxy moieties appended to the cyclitol rings All of the above
All of the above
These antibiotics are cationic carbohydrate-containing molecules, and their positive charge provides the basis for their interaction with the 30S ribosomal subunit. What class of antibiotic are these? Sulfamethoxazole Trimethoprim Aminoglycosides Peptidoglycans
Aminoglycosides
How does Staphylococcus aureus acquire resistance to methicillin? An enzyme alteration Mobile DNA element Frameshift mutation RNA porin
An enzyme alteration
Which of the following public health issues is uniting scientists from across the world to develop strategies to address it? Reclassifying bacteria according to their genomes The shortage of low toxicity antifungal drugs Antibiotic resistance Emerging pathogens
Antibiotic resistance
What is the genome of a virus composed of? Single-stranded DNA RNA Double-stranded DNA Any of the above
Any of the above
If a blood agar plate and on EMB plate are both inoculated with 0.001 ml of urine, and 90 colonies of Staphylococcus aureus grew on the blood agar plate, what should be reported? A. 90 colony forming units/ml of Staphylococcus aureus B. 90,000 colony forming units/ml of Staphylococcus aureus C. 9,000 colony forming units/ml of Staphylococcus aureus D. 9 colony forming units/ml of Staphylococcus aureus
B. 90,000 colony forming units/ml of Staphylococcus aureus
Which of the following organisms display the characteristic "Medusa head" on sheep blood agar (SBA) after 18 hours of incubation at 35oC? A. Yersinia pestis B. Bacillus anthracis C. Francisella tularensis D. Bacillus subtilis
B. Bacillus anthracis
In the upper bi-plate image are shown colonies growing on MacConkey, and on blood agar (right). Relatively large confluent gray white colonies are observed growing on blood agar, while smaller smooth convex colonies with a deep red pigmentation are growing on MacConkey agar. Note that the pigment is confined to the colonies growing on MacConkey agar that does not diffuse into the adjacent agar. In follow up to making a presumptive identification, observe that the colonies growing on the DNAse agar in the lower image show a positive reaction with clearing of the adjacent agar, compared to the growth at a negative control growing in the streak lines to the left. From these observations, select from the multiple choices the presumptive identification of this isolate. A. Proteus vulgaris B. Serratia marcescens C. Providencia stuartii D. Citrobacter koseri
B. Serratia marcescens
Antibiotics work by targeting all of the following EXCEPT: DNA replication Bacterial plasmid DNA Bacterial cell wall RNA transcription
Bacterial plasmid DNA
The mechanisms of action of antibiotics include all the following EXCEPT: Blocking the Embden-Meyerhof pathway Bacterial cell wall synthesis DNA replication RNA transcription
Blocking the Embden-Meyerhof pathway
How do the β-lactamase inhibitors work? By structurally rearranging the β-lactamase molecule so that it loses specificity for the β-lactam antibiotic By competing with the antibiotic for porin sites on the outer membrane By acting as substrates for the β-lactamase and reducing their effect on the antibiotic By acting as transport molecules to transport the antibiotic into the bacterial cell
By acting as substrates for the β-lactamase and reducing their effect on the antibiotic
Illustrated in the photograph is a citrate tube in which sodium citrate that is converted into alkaline products by bacteria that can utilize citrate as the sole source of carbon giving a blue color from the conversion of the bromthymol blue indicator. Select from the multiple choices the species of Enterobacteriaceae that produces this reaction. A. Echerichia coli B. Yersinia enterocolitica C. Citrobacter freundii D. Shigella sonnei
C. Citrobacter freundii
The growth on a blood agar plate as illustrated in the photograph was prepared from the surface drainage of a subcutaneous abscess of a 50-year old man following a deep penetrating splinter wound. The colonies on this young culture are small, rough, gray-white, and non-hemolytic. Older larger colonies become sunken centrally having a "molar tooth" appearance. The Gram stain reveals gram-positive branching filaments. Key biochemical reactions include hydrolysis of esculin, nitrate reduction and negative catalase. From these observations, select from the multiple choices the identification of this isolate A. Bifidobacterium species B. Propionibacterium species C. Actinomyces israelii D. Clostridium septicum
C. Actinomyces israelii
From the choices listed below, select the biochemical reaction that exclude a bacterial isolate from the family of Enterobacteriaceae. A. Positive nitrate reduction B. Positive cytochrome oxidase C. Alk/Alk reaction on Kligler's Iron Agar D. H2S production
C. Alk/Alk reaction on Kligler's Iron Agar
Illustrated in the top photograph is a relatively rapidly growing 4-day old colony on Sabouraud's dextrose agar incubated at 30° C. This colony was recovered as part of an environmental study. The colony has a wooly surface with distinctive block pigmentation both centrally and at the periphery, also visible when observed on the reverse of the Petri dish. Based on the microscopic presentation as illustrated in the bottom photomicrograph, select from the multiple choices the identification of this rapidly growing dematiaceous fungus. A. Curvularia species B. Ulocladium species C. Alternaria species D. Stemphylium species
C. Alternaria species
Illustrated on the photograph is a close in view of immature gray-white colonies growing on Xylose-lysine-decarboxylase (XLD) agar recovered from a stool specimen of a middle-aged patient with fever and diarrhea. Note that more mature colonies have a distinctive black pigmented center surrounded by a pink halo. With these observations, select from the multiple choices the presumptive identification of this isolate. A. Proteus mirabilis B. Proteus vulgaris C. Salmonella species D. Citrobacter freundii
C. Salmonella species
Plasmids are: Circular structures present in bacteria that contain genes encoding proteins and RNA and have the capacity to self-replicate and portion into daughter cells during cellular division DNA elements that encode transposition and excision function and can transpose from one place on the chromosome to another Genetic elements capable of integrating resistance genes (cassettes) by an integron-encoded, site-specific recombinase DNA elements found in bacteria that carry genes only for the enzymes needed to promote their own transposition
Circular structures present in bacteria that contain genes encoding proteins and RNA and have the capacity to self-replicate and portion into daughter cells during cellular division
The colonies illustrated in the top photograph are 48 hour old colonies growing on the surface of blood agar that had been incubated anaerobically. The colonies are small, gray-white and convex with irregular borders and internal flecking. Long, slender fusiform gram-negative bacilli with tapered ends are seen in the gram stain as observed in the bottom photomicrograph. The indole reaction is strongly positive and glucose fermentation is variable; other biochemical reactions are negative except for H2S production by some strains. This isolate is commensal in the upper respiratory tract and has been associated with hospital acquired aspiration pneumonia, lung abscesses, and empyema in hospitalized patients. Based on these observations, select from the multiple choices the name of this isolate. A. Veillonella parvula B. Prevotella melaninogenica C. Bacteroides fragilis D. Fusobacterium nucleatum
D. Fusobacterium nucleatum
Extended β-lactamases target all the following antibiotics EXCEPT: Penicillins Cephalosporins Monobactams Macrolides
Macrolides
Antibiotics that demonstrate a narrow spectrum of activity: Kill a wide variety of bacteria. Kill only a few specific types of bacteria. Kill bacteria by using only one specific mechanism. Kill bacteria by using a narrow spectrum of mechanisms.
Kill only a few specific types of bacteria.
All of the following are β-lactam antibiotics EXCEPT: Penems Monobactams Carbapenems Monoterpenes
Monoterpenes
This type of pathogen, showing decreases or loss of porin synthesis, is observed in combination with other resistance mechanisms, resulting in multidrug-resistant pathogens. Nosocomial Community-acquired Emerging Gram negative
Nosocomial
What is a porin? An inner membrane pore that allows proteins out into the cytoplasm Outer membrane pores that allow the membrane to "breathe" Substrates for enzymes that enable protein synthesis Outer membrane channels that permit the inflow of nutrients and the outflow of wastes
Outer membrane channels that permit the inflow of nutrients and the outflow of wastes
The members of the polypeptide class of antibiotics include all the following EXCEPT: Tetracycline Doxycycline Minocycline Oxycycline
Oxycycline
Acquired mechanisms of resistance are those that: Are passed on from one bacteria to the next using pili Are the result of a frameshift mutation in chromosomal DNA Result from acquisition of DNA by acquisition of extrachromosomal DNA Passed on from generation to generation.
Passed on from generation to generation.
Both gram-positive and gram-negative bacteria have an inner cytoplasmic membrane that is composed of: Nucleotides Phospholipids and proteins Cholesterol and carbohydrates Lipopolysaccharides
Phospholipids and proteins
This antibiotic interferes with DNA transcription by blocking of RNA chain elongation. Rifampin Quinolone Trimethoprim Glycopeptide
Rifampin
The members of the macrolide class of antibiotics include all the following EXCEPT: Rifamycin Erythromycin Clarithromycin Azithromycin
Rifamycin
All of the following antibiotics target the 50S ribosomal subunit to prevent mRNA translation in the bacteria EXCEPT: Macrolides Quinolones Oxazolidinones Streptogramins
Streptogramins
This antibiotic inhibits folate synthesis, which provides the essential precursor molecule, pyridine thymidylate, needed in DNA synthesis. Vancomycin Quinolones Aminoglycosides Sulfamethoxazole
Sulfamethoxazole
A patient undergoes a colon resection. Because of the amount of bacteria present in the colon, the physician put the patient on broad-spectrum antibiotics after surgery. The patient develops a fever 2 days after surgery. He developed an infection with vancomycin-resistant enterococci (VRE). What antibiotics can be used to treat this organism? Synercid Quinolones Aminoglycosides Erythromycin
Synercid
What is the mechanism of action of the glycopeptides (vancomycin and teicoplanin)? The glycopeptides inhibit folate synthesis and prevent the bacteria from using this as an energy source. The glycopeptides interfere with DNA replication and disrupt the protein synthesis operation. The glycopeptides bind to the substrate of the transpeptidation enzyme and disrupt the cell membrane construction. The glycopeptides interfere with transfer RNA production and disrupt the protein synthesis operation.
The glycopeptides bind to the substrate of the transpeptidation enzyme and disrupt the cell membrane construction.
Observed in the top photographs ore colonies growing on blood agar after 24-hour incubation, obtained from a positive blood culture. The colonies are tiny and surrounded by narrow zones of beta hemolysis. The initial presumptive identification was that of a Streptococcus and a CAMP test was set up. A follow up gram stain (middle image) revealed Gram positive bacilli in loose clusters rather than cocci. The lower image demonstrates a rectangular zone of hemolysis compared to the arrow-head shape of a control Streptococcus. From these observations. select the most likely presumptive identification of this isolate. A. Listeria monocytogenes B. Erysipelothrix rhusiopathiae C. Arcanobacterium haemolyticum D. Lactobacillus species
A. Listeria monocytogenes
The entire, smooth, convex Mycobacterium species colonies growing on 7H10 agar were observed to be dark yellow pigmented early in culture even before having been exposed to light. This isolate was found to be Tween-80 positive as seen in the reaction tubes in the bottom photograph. Select from the multiple choices the presumptive identification of this isolate A. Mycobacterium gordonae B. Mycobacterium fortuitum C. Mycobacterium kansasii D. Mycobacterium marinum
A. Mycobacterium gordonae
An infective agent of skin wound infections and an agent of toxic shock syndrome, the large, entire, golden-yellow, smooth convex colonies on blood agar were recovered from a swab specimen after 48-hour incubation at 37° C. In the photomicrograph, clusters of gram-positive cocci were observed microscopically in a gram stain prepared from one of the colonies. The coagulase reactions are pictured in the lower images. With these observations, select the name of this isolate from the multiple choices as listed. A. Staphylococcus aureus B. Staphylococcus saprophyticus C. Micrococcus luteus D. Staphylococcus epidermidis
A. Staphylococcus aureus
Illustrated in the upper photograph are large, mucoid appearing colonies on blood agar after 36-hour growth on blood agar incubated at 37°C, as recovered from an induced sputum specimen. Narrow zones of alpha hemolysis may be observed. In the lower photograph are observed more mature colonies after 48-hour incubation, with sunken centers. Gram stains reveal lancet-shaped gram positive cocci in pairs ("diplococci"). Select from the multiple choices the presumptive identification of this isolate. A. Streptococcus pneumoniae B. Enterococcus species C. Streptococcus anginosus D. Streptococcus bovis
A. Streptococcus pneumoniae
The small, transparent, gray-yellow 48 hour colonies incubated at 37 degrees C as illustrated in the upper photograph, are surrounded by wide zones of beta hemolysis. This culture was obtained from a throat swab of a patient with pharyngitis. The lower photograph demonstrates susceptibility of this isolate to the "A" disc. With these observations, select from the multiple choices the presumptive identification of this isolate. A. Streptococcus pyogenes (Group A) B. Streptococcus agalactiae (Group B) C. Streptococcus bovis (Group D) D. Streptococcus (milleri) anginosus (Group F)
A. Streptococcus pyogenes (Group A)
A culture from a sputum specimen grew a mucoid, lactose fermenting organism. Biochemical testing on this isolate gave the following key reactions: VP: positive, Urea: 1+, Motility: nonmotile, citrate: positive. These reactions are helpful in separating Klebsiella from Escherichia coli. A. True B. False
A. True
Growing on the surface of the anaerobic blood agar plate illustrated in the upper image are indistinct small, gray, convex, translucent colonies free of beta hemolysis. Gram negative cocci lying singly and in clusters are seen on Gram stain, as illustrated in the lower photomicrograph. Nitrates are reduced, indole is negative, and carbohydrates are not utilized (asaccharolytic). This isolate being part of the microbiota of the mouth, upper respiratory tract and intestine, may be part of a mixed culture with other bacterial species. Colonies may be recovered in blood cultures from hospitalized patients with bacteremia and endocarditis. From these observations, select from the multiple choices the presumptive identification of this isolate. A. Veillonella parvula B. Prevotella melaninogenica C. Bacteroides fragilis D. Fusobacterium nucleatum
A. Veillonella parvula
The urease reaction seen in the Christensen's urea agar slant on the far right indicates: A. Weak activity B. Strong activity C. Slant only inoculated D. Use of outdated medium
A. Weak Activity
This is one of the first resistance mechanisms identified and is a strategy that bacteria use successfully to survive the action of many classes of antibiotics. Frameshift mutation Plasmid DNA acquisition Acquisition of inactivating enzymes Impermeability to the cell wall
Acquisition of inactivating enzymes
Mechanisms that mediate intrinsic antibiotic resistance include all the following EXCEPT: Cell-wall impermeability Biofilm formation Expression of genes mediating inactivating enzymes Alternate biosynthetic pathways
Alternate biosynthetic pathways
The recovery if this bacterial species from diarrhea stool specimens require the use of selective culture media such as Butzler selective media, Blaser medium, or Skirrow blood agar incubated at 42oC in an atmosphere of 5% oxygen, 10% CO2, and 85% nitrogen. Growth on Skirrow blood agar as illustrated in the upper image are confluent smooth non-hemolytic colonies growing along the streak line with lateral extensions (arrows). Slender, long branching S-shaped gram-negative rods are observed on Gram stain, as observed in the lower photomicrograph. Positive reactions for indoxyl and hippurate provide for a more definitive identification. With these observations, select from the multiple choices the name of this isolate. A. Campylobacter coli B. Campylobacter jejuni C. Helicobacter cinaedi D. Cardiobacterium hominis
B. Campylobacter jejuni
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? A. KPC - Klebsiella pneumoniae Carbapenemase B. Chromosomal AmpC plus Porin Mutation C. Extended Spectrum Beta Lactamase D. None of the above
B. Chromosomal AmpC plus Porin Mutation
The irregular-sized, gray-white colonies. with irregular margins as shown in the image were recovered from a stool specimen in a case of antibiotic associated colitis. The colonies are flat, gray-white and spreading with irregular margins. Some patients with this infection develop pseudo-membranous colitis that can be life threatening. Growth is enhanced when Cycloserine-cefoxitin-fructose agar (CCFA) is used. The observation of elongated, gram positive bacilli with distinctive sub-terminal and central spores in gram-stain mounts provides for a presumptive identification. An additional key identifying biochemical reaction is the hydrolysis of esculin and gelatin. With these observations, select from the multiple choices the presumptive identification of this isolate. A. Propionibacterium acnes B. Clostridium difficile C. Actinomyces israeli D. Bacteroides fragilis
B. Clostridium difficile
The infective stage for the majority of all intestinal amoebae is the: A. Trophozoite B. Cyst C. Larva D. Egg
B. Cyst
The colonies illustrated on the blood and chocolate agar plates represent a slow-growing bacterial species that is endogenous in the oral cavity and upper respiratory tract, but may be recovered from human bite skin infections incurred during fist fights. Note the pitting of the agar surrounding the colonies growing in the chocolate agar plate. The Alk/Alk non-fermentative reaction seen in the Kligler Iron Agar tube to the left in the lower photograph indicates the non-fermentation of glucose, also indicated by the lack of carbohydrate assimilation in the individual carbohydrate reaction tubes to the right of the KIA tube. A reduction of nitrate demonstrated and decarboxylation of ornithine are the positive reactions included in this exercise. From these observations, select from the multiple choices identification of this bacterial isolate A. Brucella species B. Eikenella corrodens C. Francisella tularensis D. Haemophilus influenza
B. Eikenella corrodens
The satellite phenomenon on culture plates is most often associated with: A. Neisseria meningitidis B. Haemophilus influenza C. Klebsiella pneumoniae D. Bordetella pertussis E. Pasteurella tularensis
B. Haemophilus influenza
Illustrated in the upper photograph are small, gray-white to light yellow colonies surrounded by zones of beta hemolysis. Short, gram-positive bacilli with rounded ends that lie singly or in loose clusters are observed in gram stains. Two key identifying features as illustrated in the lower photograph are a narrow bond of "umbrella" motility observed beneath the surface of semi-solid motility medium and the deep black slant of positive esculin activity. This species may be recovered during influenza-like infections during 2nd and 3rd trimester of pregnancy. With these observations, select from the multiple choices the identification of this isolate. A. Rothia dentocariosa B. Listeria monocytogenes C. Arcanobacterium haemolyticum D. Erysipelothrix rhusiopathiae
B. Listeria monocytogenes
Illustrated in the upper photograph are smooth, entire, convex gray-yellow pigmented 48-hour old colonies growing on the surface of Thayer Martin medium. These isolates may be observed in cultures of specimens received from a physician's office obtained from patients with endocarditis in females or urethral epididymitis in males. Illustrated in the lower photomicrograph is a gram stain prepared from the sediment of the specimen. These observations are sufficient to make a presumptive identification of Neisseria species. Further testing revealed the characteristic selective carbohydrate utilization of glucose with maltose utilization being negative. From the multiple choices, select the identification of this isolate. A. Neisseria meningitidis B. Neisseria gonorrhoeae C. Aeromonas species D. Kingella kingae
B. Neisseria gonorrhoeae
Small intracellular gram-negative cocci were observed in a centrifuged spinal fluid sediment as presented in the upper photomicrograph. A clinical diagnosis of meningitis was suspected. Yellow-gray colonies after 24-hour incubation had been observed on blood agar. Based on the carbohydrate utilization tube reactions observed in the lower photograph, select from the multiple choices the presumptive identification of this isolate. A. Neisseria gonorrhoeae B. Neisseria meningitidis C. Aeromonas species D. Kingella kingae
B. Neisseria meningitidis
The capsular material used to identify capsular subtypes of Pneumococci consists of: A. Proteins B. Polysaccharides C. Lipids D. Lipoproteins
B. Polysaccharides
Illustrated in the photograph of the blood agar plate are slow-growing colonies after 72-hour incubation that are pink-white and appear dry and heaped in areas of confluent growth (arrows). They were recovered from a tooth abscess of a 14-year old boy. Gram stain reveals short gram positive bacilli that characteristically are in a diphtheroidal arrangement. Key characteristics to provide a definitive identification include positive reactions for catalase, nitrate reduction, esculin and pyrazinamidase. Based on these observations, select from the multiple choices the presumptive identification of this isolate. A. Corynebacterium striatum B. Rothia dentocariosa C. Bacillus cereus D. Lactobacillus species
B. Rothia dentocariosa
Observed on the surface of blood agar are smooth, white 48-hour-old colonies incubated at 37°C, demonstrating a negative coagulase reaction. The sample was taken from an intravenous catheter. In the photomicrograph are illustrated gram positive cocci distinctly arranged in loose clusters and in tetrad formation. From these observations, select from the multiple choices the identification of this isolate. A. Staphylococcus aureus B. Staphylococcus epidermidis C. Micrococcus luteus D. Rothia mucilaginosis
B. Staphylococcus epidermidis
The entire, smooth, transparent colonies surrounded by distinct zones of beta hemolysis, as illustrated in the photograph to the upper left, were recovered after 24-hour incubation from a vaginal canal swab culture from a 26-year old mother with signs of premature lobar during her 35th week of gestation. Observed in a gram stain prepared from one of the colonies were gram-positive cocci arranged in chains of ranging between 4 and 15 cells (upper right). More characteristic is the arrow-head zone of beta hemolysis observed in the agar CAMP test shown in the lower right image. From these observations, select from the multiple choices the presumptive identification of this isolate. A. Streptococcus pyogenes B. Streptococcus agalactiae C. Streptococcus bovis D. Streptococcus pneumoniae
B. Streptococcus agalactiae
Antimicrobial agents include all of the following EXCEPT: Plant extracts Antibiotics Preservatives Antiseptics
Plant extracts
This antibiotic affects the DNA replication by targeting topoisomerases II and IV, enzymes considered important in controlling DNA replication. Glycopeptide Sulfamethoxazole Trimethoprim Quinolone
Quinolone
The primary mechanism of resistance to this antimicrobial class is modification by mutations encoding single amino acid changes in these targets. What antibiotic class is this? Macrolides Quinolones Peptidoglycans Aminoglycosides
Quinolones